Terrestrial Ecosystem

into soils. The fraction of 202 Hg bound to vegetation was much higher than seen for native Hg (<5% vegetation), suggesting that atmospherically derived mercury enters the soil pool with a time delay, after plants senesce and decompose. The initial mobility of mercury received through small rain events or dry deposition decreased markedly in a relatively short time period, suggesting that mercury levels in terrestrial runoff may respond slowly to changes in mercury deposition rates.

Silicophytoliths were produced in the plant communities of the Pampean Plain during the Quaternary. The biogeochemistry of silicon is scarcely known in continental environments of Argentina. The aim of this work is to present a synthesis of: the plant production and the presence of silicophytoliths in soils with grasses, and its relationship with silica content in soil solution, soil matrix and groundwaters in temperate ecosystems of the Pampean Plain, Argentina. We quantified the content of silicophytoliths in representative grasses and soils of the area. Mineralochemical determinations of the soils' matrix were made. The concentration of silica was determined in soil solution and groundwaters. The silicophytoliths assemblages in plants let to differenciate subfamilies within Poaceae. In soils, silicophytoliths represent 40e5% of the total components, conforming a stock of 59e72 Â 10 3 kg/ha in A horizons. The concentration of SiO 2 in soil solution increases with depth (453e1243 mmol/L) in relation with plant communities, their nutritional requirements and root development. The average concentration of silica in groundwaters is 840 umol/L. In the studied soils, inorganic minerals and volcanic shards show no features of weathering. About 10e40% of silicophytoliths were taxonomically unidentified because of their weathering degrees. The matrix of the aggregates is made up by microaggregates composed of carbon and silicon. The weathering of silicophytoliths is a process that contributes to the formation of amorphous silica-rich matrix of the aggregates. So, silicophytoliths could play an important role in the silica cycle being a sink and source of Si in soils and enriching soil solutions and groundwaters.

The hyporheic invertebrate community from the pre-alpine river (W Slovenia) was studied in order to analyze the impacts of high discharge and in-stream gravel extraction. Two distinct river reaches were sampled from June 2004 to May 2005. At impacted site, where gravel extraction was carried out, the response of hyporheic community to the anthropogenic disturbance was studied. Physical and chemical parameters, together with the amounts organic matter and activity of the biofilm were measured. Invertebrates were sampled by Bou-Rouch pumping method. Discharge of the Baca River varied from 108 m3s-1 in October 2004 to 1.6 m3s-1 in March 2005. Streambed sediments at both sites were composed of heterogeneous mixture of boulders, cobbles, pebbles, gravel, sand and silt. Oxygen saturation was close to 100 %, indicating good sediment permeability. A total of 75 invertebrate taxa were identified, 40 of which belonged to the occasional hyporheos, 26 to the permanent hyporheos and 9 were stygo...

A new generation of an Earth System Model now includes a number of land surface processes directly relevant to analyzing potential impacts of climate change. This model, HadGEM2-ES, allows us to assess the impacts of climate change, multiple interactions, and feedbacks as the model is run. This paper discusses the results of BGD

The photosynthetic pathway composition (C 3 :C 4 mixture) of an ecosystem is an important controller of carbon exchanges and surface energy flux partitioning, and therefore represents a fundamental ecophysiological distinction. To assess photosynthetic mixtures at a tallgrass prairie pasture in Oklahoma, we collected nighttime above-canopy air samples along concentration and isotopic gradients throughout the 1999 and 2000 growing seasons. We analyzed these samples for their CO 2 concentration and carbon isotopic composition and calculated C 3 :C 4 proportions with a twosource mixing model. In 1999, the C 4 percentage increased from 38% in spring (late April) to 86% in early fall (mid-September). The C 4 percentages inferred from ecosystem respiration measurements in 2000 indicate a smaller shift, from 67% in spring (early May) to 77% in mid-summer (late July). We also sampled daytime CO 2 concentration and carbon isotope gradients above the canopy to determine ecosystem discrimination against 13 CO 2 during net uptake. These discrimination values were always lower than corresponding nighttime ecosystem respiration isotopic signatures would suggest. After accounting for the isotopic disequilibria between respiration and photosynthesis resulting from seasonal variations in the C 3 :C 4 mixture, we estimated canopy photosynthetic discrimination. The C 4 percentage calculated from this approach agrees with the percentage determined from nighttime respiration for sampling periods in both growing seasons. Isotopic imbalances between photosynthesis and respiration are likely to be common in mixed C 3 :C 4 ecosystems and must be considered when using daytime isotopic measurements to constrain ecosystem physiology. Given the global extent of such ecosystems, isotopic imbalances likely contribute to global variations in the carbon isotopic composition of atmospheric CO 2 .

Understanding terrestrial carbon metabolism is critical because terrestrial ecosystems play a major role in the global carbon cycle. Furthermore, humans have severely disrupted the carbon cycle in ways that will alter the climate system and directly affect terrestrial metabolism. Changes in terrestrial metabolism may well be as important an indicator of global change as the changing temperature signal. Improving our understanding of the carbon cycle at various spatial and temporal scales will require the integration of multiple, complementary and independent methods that are used by different research communities. Tools such as air sampling networks, inverse numerical methods, and satellite data (top-down approaches) allow us to study the strength and location of the global-and continental-scale carbon sources and sinks. Bottom-up studies provide estimates of carbon fluxes at finer spatial scales and examine the mechanisms that control fluxes at the ecosystem, landscape, and regional scales. Bottom-up approaches include comparative and process studies (for example, ecosystem manipulative experiments) that provide the necessary mechanistic information to develop and validate terrestrial biospheric models. An iteration and reiteration of top-down and bottom-up approaches will be necessary to help constrain measurements at various scales. We propose a major international effort to coordinate and lead research programs of global scope of the carbon cycle.

E missions of greenhouse gases are expected to raise global mean temperature over the next century by 1.0-3.5 °C . Ecologists from around the world have begun experiments to investigate the effects of global warming on terrestrial ecosystems, the aspect of global climate change that attracts the most public attention McKenzie 1995, Walker and Steffen 1999). The effort to understand response to warming builds on a history of investigations of the effects of elevated CO 2 on plants and ecosystems Mooney 1996, Schulze et al. 1999). There are important differences, however, between increases in atmospheric CO 2 and temperature change, both in the temporal and spatial patterns of change and in how they affect ecosystems. The scientists involved in temperature change research have had to face new technical and conceptual challenges in designing and interpreting their experiments . In this paper we describe these challenges and present a conceptual framework for interpreting experimental results and predicting effects of warming on ecosystems.

The molecular hydrogen isotope composition (dD) of leaf waxes from terrestrial plants is increasingly used to infer hydrological characteristics of ancient high latitude climates. Analysis of the hydrogen isotope composition of n-alkanes (dD n-alkane ) from a global dataset of individual plants growing at low and middle latitudes indicates that plant ecological life form is an important factor in determining the hydrogen isotope fractionation. However, environmental and biological controls of high latitudinal leaf wax dD values are poorly understood because of a lack of dD records from modern flora in these regions. We previously noticed smaller apparent hydrogen isotope fractionations between n-alkanes and environmental water (e alk-water ) in deciduous trees growing at high latitudes (>59°N; Liu, W.-G., Yang, H., 2008. Multiple controls for the variability of hydrogen isotopic compositions in higher plant n-alkanes from modern ecosystems. Global Change Biology 14, 2166-2177.) To further examine these issues, we measured dD n-alkane from a variety of plants that inhabit high latitude environments and added critically needed leaf wax dD data from grass and herbs to the existing global dD n-alkane database. Inclusion of these new data with the existing global dataset (n = 408) confirms plant ecological life form as an important control for leaf wax dD variation for terrestrial plants living at high latitudes. Our results suggest that, while precipitation dD is captured in these high latitude plants, physiological characters such as leaf area, venation pattern and hydraulic system, that enhance transpiration rate during summer growth, may impart dD n-alkane differences among plants with different ecological life forms.

Key messageWe demonstrate that, beyond leaf phenology, the phenological cycles of wood and fine roots present clear responses to environmental drivers in temperate and boreal trees. These drivers should be included in terrestrial ecosystem models.ContextIn temperate and boreal trees, a dormancy period prevents organ development during adverse climatic conditions. Whereas the phenology of leaves and flowers has received considerable attention, to date, little is known regarding the phenology of other tree organs such as wood, fine roots, fruits, and reserve compounds.AimsHere, we review both the role of environmental drivers in determining the phenology of tree organs and the models used to predict the phenology of tree organs in temperate and boreal forest trees.ResultsTemperature is a key driver of the resumption of tree activity in spring, although its specific effects vary among organs. There is no such clear dominant environmental cue involved in the cessation of tree activity i...

Increasing global atmospheric CO2 concentration has led to concerns regarding its potential effects on the terrestrial environment. Attempts to balance the atmospheric carbon (C) budget have met with a large shortfall in C accounting (≈1.4 × 1015 g C y–1) and this has led to the hypothesis that C is being stored in the soil of terrestrial ecosystems. This study examined the effects of CO2 enrichment on soil C storage in C3 soybean (Glycine max L.) Merr. and C4 grain sorghum (Sorghum bicolor L.) Moench. agro‐ecosystems established on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). The study was a split‐plot design replicated three times with two crop species (soybean and grain sorghum) as the main plots and two CO2 concentration (ambient and twice ambient) as subplots using open top field chambers. Carbon isotopic techniques using δ13C were used to track the input of new C into the soil system. At the end of two years, shifts in δ13C content of soil organic m...

E missions of greenhouse gases are expected to raise global mean temperature over the next century by 1.0-3.5 °C . Ecologists from around the world have begun experiments to investigate the effects of global warming on terrestrial ecosystems, the aspect of global climate change that attracts the most public attention McKenzie 1995, Walker and Steffen 1999). The effort to understand response to warming builds on a history of investigations of the effects of elevated CO 2 on plants and ecosystems Mooney 1996, Schulze et al. 1999). There are important differences, however, between increases in atmospheric CO 2 and temperature change, both in the temporal and spatial patterns of change and in how they affect ecosystems. The scientists involved in temperature change research have had to face new technical and conceptual challenges in designing and interpreting their experiments . In this paper we describe these challenges and present a conceptual framework for interpreting experimental results and predicting effects of warming on ecosystems.

Shrubland expansion is a globally occurring phenomenon under global change and has caused a wide range of ecological consequences. However, due to the visual similarity between shrubland and grassland, the accuracy of shrubland interpretation and its spatial distribution varies across different products, making shrub encroachment on the Tibetan Plateau (TP) uncertain. To address these challenges, we developed a phenology-based and pixelwise method utilizing the Landsat, Sentinel-1, and Sentinel-2 image archives to map shrubland distribution from 1990 to 2022 across the TP. We also investigated the factors affecting shrubland distribution. Using the Random Forest (RF) model, we achieved moderate to high accuracies (Kappa = 0.70-0.81) in predicting shrubland distributions, and we found that shrubland primarily occupies transitional zones between forest and grassland. In the southeast TP, solar radiation intensity is the dominant factor explaining the spatial distribution of shrubland, whereas in arid regions, water availability is the most important. From 1990 to 2022, the shrubland area slightly increased from 3.40% to 4.71%, with expansion showing a clustered pattern, mainly in the shaded aspects of arid regions. The shrubland identification method proposed here shows potential applicability in other areas with similar environmental conditions, such as arid landscapes or high-altitude ecosystems with pronounced seasonal vegetation dynamics. It also plays a crucial role in evaluating vegetation responses to climatic changes.

Increases in the concentration of carbon dioxide, as well as of other so-called greenhouse gases, in the Earth’s atmosphere will lead to climate change. So far, policy responses to limit the effects of climate change have focused on the reduction of emissions of greenhouse gases at source. Another possibility would be to enhance the capacity of ecosystems to act as carbon sinks, such as by increased afforestation, in order to reduce carbon dioxide (CO2) concentrations in the atmosphere. Many countries, especially in the Third World, lack sufficient information on the actual ground cover of different types of (agro) ecosystems, i.e. on carbon pools in the form of terrestrial ecosystems. Without such land cover data, it is almost impossible to analyze properly the non-fossil cycles of these countries. However, such data can be obtained with remotely sensed data from satellite images. To obtain insight into the effects of changes in land cover and the time-scales over which they occur, a dynamic simulation model on carbon cycling of terrestrial ecosystems has been converted into a GIS environment. The results of our case study show a significant correlation between field data on the amount of biomass/carbon of different natural forests and NDVI values from a satellite image of the study area. The results on field data and on NDVI data in combination with production and decomposition rates from literature have been used to calibrate the simulation model. After a sensitivity test, the model has been applied to study the effects of fragmentation on the carbon cycle of the Iztaccihuatl — Popocatepetl National Park and its surrounding buffer areas.

Accurate assessment of anthropogenic carbon dioxide (CO 2 ) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize datasets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO 2 emissions (E FOS ) are based on energy statistics and cement production data, while emissions from land-use change (E LUC ), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO 2 concentration is measured directly, and its growth rate (G ATM ) is computed from the annual changes in concentration. The ocean CO 2 sink (S OCEAN ) is estimated with global ocean biogeochemistry models and observation-based data products. The terrestrial CO 2 sink (S LAND ) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (B IM ), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ . For the first time, an approach is shown to reconcile the difference in our E LUC estimate with the one from national greenhouse gas inventories, supporting the assessment of collective countries' climate progress. For the year 2020, E FOS declined by 5.4 % relative to 2019, with fossil emissions at 9.5 ± 0.5 GtC yr -1 (9.3 ± 0.5 GtC yr -1 when the cement carbonation sink is included), and E LUC was 0.9 ± 0.7 GtC yr -1 , for a total anthropogenic CO 2 emission of 10.2 ± 0.8 GtC yr -1 (37.4 ± 2.9 GtCO 2 ). Also, for 2020, G ATM was 5.0 ± 0.2 GtC yr -1 (2.4 ± 0.1 ppm yr -1 ), S OCEAN was 3.0 ± 0.4 GtC yr -1 , and S LAND was 2.9 ± 1 GtC yr -1 , with a B IM of -0.8 GtC yr -1 . The global atmospheric CO 2 concentration averaged over 2020 reached 412.45 ± 0.1 ppm. Preliminary data for 2021 suggest a rebound in E FOS relative to 2020 of +4.8 % (4.2 % to 5.4 %) globally. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959-2020, but discrepancies of up to 1 GtC yr -1 persist for the representation of annual to semidecadal variability in CO 2 fluxes. Comparison of estimates from multiple approaches and observations shows (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO 2 flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and datasets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this dataset (Friedlingstein et al.

The maximum rate of Rubisco carboxylation (Vcmax) determines leaf photosynthetic capacity and is a key 20 parameter for estimating the terrestrial carbon cycle, but its spatial information is lacking, hindering global ecological research. Here, we convert leaf chlorophyll content (LCC) retrieved from satellite data to Vcmax, based on plants' optimal distribution of nitrogen between light harvesting and carboxylation pathways. We also derive Vcmax from satellite observations of sun-induced chlorophyll fluorescence (SIF) as a proxy of leaf photosynthesis. These two independent global Vcmax products agree well (r 2 =0.79, RMSE=15.46 μ mol m -2 s -1 , P<0.001) and compare well with 3672 ground-based 25 measurements (r 2 =0.68, RMSE=13.55 μmol m -2 s -1 and P<0.001 for SIF; r 2 =0.55, RMSE=17.55 μmol m -2 s -1 and P<0.001 for LCC). Through a data assimilation technique, these two types of Vcmax products from remote sensing are combined to provide an optimized Vcmax product. The global distributions of these products are compatible with Vcmax computed from an ecological optimality theory using meteorological variables, but importantly reveal additional information on the influence of land cover, irrigation, soil pH and leaf nitrogen on leaf photosynthetic capacity. These satellite-based approaches and 30 spatial Vcmax products are primed to play a major role in global ecosystem research. The three remote sensing Vcmax products are available at

Tables Figures Full Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | basin, and southeastern Yangtze river basin. Decreases of annual ET mainly occurred in parts of northeast, north, northwest, south China, especially in eastern Qinghai-Tibet plateau, the south part of Yunnan province, and Hainan province. Vast regions in China, especially the regions south of Yangtze river, experienced significant decreases in water yield caused by the reduction of precipitation and increase of ET while some areas sporadically distributed in northeast, east, northwest, central, and south China experienced increases in water yield. This study shows that recent climatic variability and human activity induced vegetations changes have intensified the terrestrial water cycles in China's terrestrial ecosystems, which is worthy of further thorough investigation.

Terrestrial carbon and water cycles are interactively linked at various spatial and temporal scales. Evapotranspiration (ET) plays a key role in the terrestrial water cycle, altering carbon sequestration of terrestrial ecosystems. The study of ET and its response to climate and vegetation changes is critical in China because water availability is a limiting factor for the functioning of terrestrial ecosystems in vast arid and semiarid regions. To constrain uncertainties in ET estimation, the process-based Boreal Ecosystem Productivity Simulator (BEPS) model was employed in conjunction with a newly developed leaf area index (LAI) data set, MODIS land cover, meteorological, and soil data to simulate daily ET and water yield at a spatial resolution of 500 m over China for the period from 2000 to 2010. The spatial and temporal variations of ET and water yield were analyzed. The influences of climatic factors (temperature and precipitation) and vegetation (land cover types and LAI) on these variations were assessed. Validations against ET measured at five ChinaFLUX sites showed that the BEPS model was able to simulate daily and annual ET well at site scales. Simulated annual ET exhibited a distinguishable southeast to northwest decreasing gradient, corresponding to climate conditions and vegetation types. It increased with the increase of LAI in 74 % of China's landmass and was positively correlated with temperature in most areas of southwest, south, east, and central China. The correlation between annual ET and precipitation was positive in the arid and semiarid areas of northwest and north China, but negative in the Tibetan Plateau and humid southeast China. The national annual ET varied from 345.5 mm in 2001 to 387.8 mm in 2005, with an average of 369.8 mm during the study period. The overall rate of increase, 1.7 mm yr -1 (R 2 = 0.18, p = 0.19), was mainly driven by the increase of total ET in forests. During 2006-2009, precipitation and LAI decreased widely and consequently caused a detectable decrease in national total ET. Annual ET increased over 62.2 % of China's landmass, especially in the cropland areas of the southern Haihe River basin, most of the Huaihe River basin, and the southeastern Yangtze River basin. It decreased in parts of northeast, north, northwest, south China, especially in eastern Qinghai-Tibetan Plateau, the south of Yunnan Province, and Hainan Province. Reduction in precipitation and increase in ET caused vast regions in China, especially the regions south of Yangtze River, to experience significant decreases in water yield, while some sporadically distributed areas experienced increases in water yield. This study shows that the terrestrial water cycles in China's terrestrial ecosystems appear to have been intensified by recent climatic variability and human induced vegetation changes.

The maximum rate of Rubisco carboxylation (V cmax ) determines leaf photosynthetic capacity and is a key parameter for estimating the terrestrial carbon cycle, but its spatial information is lacking, hindering global ecological research. Here, we convert leaf chlorophyll content (LCC) retrieved from satellite data to V cmax , based on plants' optimal distribution of nitrogen between light harvesting and carboxylation pathways. We also derive V cmax from satellite (GOME-2) observations of sun-induced chlorophyll fluorescence (SIF) as a proxy of leaf photosynthesis using a data assimilation technique. These two independent global V cmax products agree well (r 2 = 0.79, RMSE = 15.46 µmol m -2 s -1 , P <0.001) and compare well with 3672 ground-based measurements (r 2 = 0.69, RMSE = 13.8 µmol m -2 s -1 and P <0.001 for SIF; r 2 = 0.55, RMSE = 18.28µmol m -2 s -1 and P <0.001 for LCC). The LCC-derived V cmax product is also used to constrain the retrieval of V cmax from TROPical Ozone Mission (TROPOMI) SIF data to produce an optimized V cmax product using both SIF and LCC information. The global distributions of these products are compatible with V cmax computed from an ecological optimality theory using meteorological variables, but importantly reveal additional information on the influence of land cover, irrigation, soil pH, and leaf nitrogen on leaf photosynthetic capacity. These satellite-based approaches and spatial V cmax products are primed to play a major role in global ecosystem research. The three remote sensing V cmax products based on SIF,

Satellite-based models have been widely used to simulate vegetation gross primary production (GPP) at site, regional, or global scales in recent years. However, accurately reproducing the interannual variations in GPP remains a major challenge, and the long-term changes in GPP remain highly uncertain. In this study, we generated a long-term global GPP dataset at 0.05° latitude by 0.05° longitude at 8-day interval by revising a light use efficiency model (i.e. EC-LUE). In the revised EC-LUE model, we integrated the regulations of several major environmental variables: atmospheric CO2 concentration, radiation components, and atmospheric vapor pressure deficit (VPD). These environmental variables showed substantial long-term changes, which could greatly impact the global vegetation productivity. Eddy covariance (EC) measurements at 84 towers from the FLUXNET2015 dataset, covering nine major ecosystem types of the globe, were used to calibrate and validate the model. The revised EC-LUE model could explain 83% and 68% of the spatial variations in the annual GPP at 42 calibration and 43 validation sites, respectively. In particular, the revised EC-LUE model could very well reproduce (~74% sites R 2 >0.5; averaged R 2 = 0.65) the interannual variations in GPP at 51 sites with observations greater than 5-years. At global scale, sensitivity analysis indicated that the long-term changes of environmental variables could be well reflected in the global GPP dataset. The CO2 fertilization effect on the global GPP (0.14 ± 0.001 Pg C yr -1 ) could be offset by the increased VPD (-0.16 ± 0.02 Pg C yr -1 ). The global GPP derived from different datasets exist substantial uncertainty in magnitude and interannual variations. The magnitude of global summed GPP simulated by the revised EC-LUE model was comparable to other global models. While the revised EC-LUE model has a unique superiority in simulating the interannual variations in GPP at both site level and global scales. The revised EC-LUE model provides a reliable long-

There have been no significant changes to the national critical loads data sets since February 2004. Consequently part of Task 1 which supports the UK Critical Load National Focal Centre at CEH Monks Wood has been mainly concerned with providing advice on the existing data sets in relation to the development of dynamic models to link soil biogeochemistry to above-ground biodiversity. A key highlight regarding revision of critical loads has followed the results from the Whim experiment which were central to the setting of a new Critical Level for ammonia of 1 µg m -3 (cf. previous value of 8 µg m -3 ) for ecosystems containing lichens and bryophytes. A more objective approach to assessing empirical critical loads of nitrogen, using differentiated values within the range recommended for application within UNECE, based on ecosystem characteristics. With respect to climate change, an assessment of changes required for forests has been undertaken and methodology developed. Experimental results suggest the increased supply of N to plants may require increased removal of N though management or a decrease in the N critical load. However, a more complete analysis for a wider range of habitats together with application of models under development is required. Results from the new field surveys are not inconsistent with current critical load ranges. The manipulation experiments also continue to be broadly consistent with these ranges although new evidence from our bog experiment and monitoring work suggests there are still uncertainties and issues concerning the importance of concentration and N form.

Fixed nitrogen is a limiting nutrient in most terrestrial ecosystems and has been assumed to be supplied almost entirely by freeliving bacteria as well as by bacteria living in association with plants. The survival and growth of many arthropods on diets with extremely high carbon to nitrogen (C:N) ratios suggest that these arthropods are not obtaining sufficient nitrogen from their diets but must be obtaining additional nitrogen from some other source(s). Estimates of N 2 fixation have suggested that symbiotic microbes of some arthropod hindguts could be obtaining this additional nitrogen as a result of nitrogen fixation. With the recent availability of antibody and nucleic acid probes, the presence of the enzyme that reduces dinitrogen gas to ammonia (nitrogenase) as well as the presence of its transcripts can be detected and localized with great sensitivity. A preliminary survey of a few detritivores indicates that nitrogen-fixing microbes of diverse forms are widespread in arthropod hindguts. In calculating nitrogen budgets, the possible contributions of nitrogen fixation by symbionts in arthropod guts, however, has been largely ignored. N 2 fixation in arthropod guts, with rates as high as 10-40 kg/ha/year being possible, may represent a significant contribution both to the growth of arthropods and to their ecosystem functions of processing carbon and nitrogen.

ABSTRACTAim  The Tibetan Plateau accounts for about a quarter of the total land area of China and has a variety of ecosystems ranging from alpine tundra to evergreen tropics. Its soils are dominated by permafrost and are rich in organic carbon. Its climate is unique due to the influence of the Asian monsoon and its complex topography. To date, the carbon dynamics of the Tibetan Plateau have not been well quantified under changes of climate and permafrost conditions. Here we use a process‐based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), which was incorporated with a soil thermal model, to examine the permafrost dynamics and their effects on carbon dynamics on the plateau during the past century.Location  The Tibetan Plateau.Methods  We parameterize and verify the TEM using the existing data for soil temperature, permafrost distribution and carbon and nitrogen from the region. We then extrapolate the model and parameters to the whole plateau.Results  During the 20th...

This European Red List highlights that almost half (44%) of the freshwater species and one out of five (20%) of the selected terrestrial molluscs are threatened. This compares with 37% of freshwater fishes, 23% of amphibians, 19% of reptiles, 15% of mammals and dragonflies, 13% of birds, 9% of butterflies and 7% of the aquatic plants, the other groups that have been comprehensively assessed in Europe. Additional European Red Lists assessing a selection from species groups indicate that 12% of the crop wild relatives and 11% of the saproxylic beetles are also threatened. Furthermore, there are declining populations in 11% of Europe’s freshwater molluscs and 6% of selected terrestrial species, but for 82% of freshwater and 53% of terrestrial species the population trend is still unknown and could also be declining. The main reason for these declines include pollution, dams and water extraction (mainly for agriculture and drinking purposes) for the freshwater mollusc species and urbani...

In this Perspective, we put forward an integrative framework to improve estimates of land-atmosphere carbon exchange based on the accumulation of carbon in the landscape as constrained by its lateral export through rivers. The framework uses the watershed as the fundamental spatial unit and integrates all terrestrial and aquatic ecosystems as well as their hydrologic carbon exchanges. Application of the framework should help bridge the existing gap between land and atmosphere-based approaches and offers a platform to increase communication and synergy among the terrestrial, aquatic, and atmospheric research communities that is paramount to advance landscape carbon budget assessments.

Land use change can affect terrestrial C stocks, resulting in increased CO 2 flux from soil to the atmosphere. In Africa, conversion of natural ecosystems to agricultural lands is the most common land use change. This study investigated the effects of six land use types occurring in Mt. Kilimanjaro ecosystems i.e. (1) lower montane forest (2) grassland and (3) savannah (natural ecosystems) (4) Chagga homegardens (semi-natural ecosystem) and ( ) maize fields and (6) coffee plantation (agroecosystems) on microbial biomass carbon (MBC) and dynamics of 14 C labelled glucose added into soil. Decomposition of 14 C labelled glucose and its incorporation into microbial biomass in surface soils (0e10 and 10e20 cm) were determined. MBC decreased significantly with increased intensity of land use. Mineralization of the 14 C labelled glucose occurred in two phases with contrasting rates: 0e10 days (6e18% of 14 C d À1 ) and 15 e65 days (<0.1% of 14 C d À1 ). Land use intensification in agroecosystems led to an average increase of glucose decomposition of 14%. The decay rates of the labile C pool in intensively used agricultural lands were up to three times higher compared to natural ecosystems. The incorporation of 14 C glucose into microorganisms ranged between 1 and 7% of 14 C input in all soils, and was highest in savannah. Agricultural intensification decreased C content in soil through increased mineralization of organic substances and negatively impacted the upper soil layer more compared to the lower one. Based on these results we conclude that semi-natural ecosystems (e.g. Chagga homegardens) are more sustainable in Mt. Kilimanjaro ecosystems compared to intensive agroecosystems.

Terrestrial gamma radiation is one of the important radiation exposures on the earth's surface that results from the three primordial radionuclides 226 Ra, 232 Th and 40 K. The elemental concentration of these elements in the earth's crust could result in the anomalous variation of the terrestrial gamma radiation in the environment. The geology of the local area plays an important role in distribution of these radioactive elements. Environmental terrestrial gamma radiation dose rates were measured around the eastern coastal area of Odisha with the objective of establishing baseline data on the background radiation level. The values of the terrestrial gamma radiation dose rate vary significantly at different locations in the study area. The values of the terrestrial gamma dose rate ranged from 77 to 1651 nGy h 21 , with an average of 230 nGy h 21 . During the measurement of the terrestrial gamma dose rate, sand and soil samples were also collected for the assessment of natural radionuclides. The activities of 226 Ra, 232 Th and 40 K from these samples were measured using a gamma-ray spectrometry with a NaI(Tl) detector.

During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO2) exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO2seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO2gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO2cycles from 48 European stations were available for 2017 and 2018. Earlier data w...

The current paper presents the first effort to organize a comprehensive review of the Invasive Alien Species (IAS) of Greece. For this purpose, a database was developed with fields of information on the taxonomy, origin, ecology and pathways of introduction of terrestrial, freshwater and marine species. Our database includes a) taxa in the Union’s list that are present in Greece, b) taxa already present in Greece and considered to be invasive, and c) taxa highly likely to enter Greece in the next 10 years and become invasive. The Database served as the starting point for the compilation of the National List of Alien Invasive Species (HELLAS-ALIENS) in compliance with the EU Regulation 1143/2014. Overall, the HELLAS-ALIENS comprises 126 species, i.e. 32 terrestrial and freshwater plant species, 14 terrestrial invertebrates, 28 terrestrial vertebrates, 30 freshwater fishes and invertebrates and 22 marine species. Terrestrial invertebrates, birds and mammals are mainly of Asiatic origi...

Improvement of terrestrial submodels in Earth system models (ESMs) is important to reduce uncertainties in future projections of global carbon cycle and climate. Since these submodels lack detailed validation, evaluation of terrestrial submodels using networks of field observations is necessary. The purpose of this study is to improve an ESM by refining a terrestrial submodel using eddy covariance observations. We evaluated the terrestrial submodel (MOSES2/TRIFFID) included in the UVic Earth System Climate Model (UVic-ESCM) and tested the effects of terrestrial submodel improvements on future projection of carbon cycle and climate. First, we evaluated the terrestrial submodel as an off-line mode at point scales using 48 eddy covariance observation data, and improved it through fixing model parameters and structures. The terrestrial submodel was improved with the reduction of the root mean square error and the closer simulation of the seasonal carbon fluxes. Second, using the UVic-ESCM with the improved terrestrial submodel, we confirmed model improvement at most observation sites. The terrestrial submodel refinement also affected future projections; the UVic-ESCM with the improved terrestrial submodel simulated 100 ppmv lower atmospheric CO 2 concentration in 2100 compared with the default UVic-ESCM. Our study underscores the importance of refinement of terrestrial submodels in ESM simulations.

Grasslands, accounting for one third of the world terrestrial land surface, are important in determining phosphorus (P) cycle at a global scale. Understanding the impacts of management on P inputs and outputs in grassland ecosystem is crucial in environmental management since a large amount of P is transported through rivers and groundwater and detained by sea reservoir every year. To better understand the P cycle in global grasslands, we mapped the distribution of different grassland types around the world and calculated the corresponding P inputs and outputs for each grassland type using data from the literature. The distribution map of P input and output revealed a nonequilibrium condition in many grassland ecosystems, with: (i) a greater extent of inputs than outputs in most managed grasslands, but (ii) a more similar inputs and outputs in the majority of natural grasslands. Based on the mass balance between P input and output, we developed a framework to achieve sustainable P management in grasslands and discussed the measures targeting a more balanced P budget. Greater challenge is usually found in heavily-managed than natural grasslands to establish the optimum amount of P for grass and livestock production while minimizing the adverse impacts on surface waters. This study provided a comprehensive assessment of P budget in global grasslands and such information will be critical in determining the appropriate P management measures for various grassland types across the globe.

Quantifying the interannual variability (IAV) of the terrestrial ecosystem productivity and its sensitivity to climate is crucial for improving carbon budget predictions. In this context it is necessary to disentangle the influence of climate from impacts of other mechanisms underlying the spatiotemporal patterns of IAV of the ecosystem productivity. In this study we investigated the spatiotemporal patterns of IAV of historical observations of European crop yields in tandem with a set of climate variables. We further evaluated if relevant remote-sensing retrievals of NDVI (normalized difference vegetation index) and FAPAR (fraction of absorbed photosynthetically active radiation) depict a similar behaviour. Our results reveal distinct spatial patterns in the IAV of the analysed proxies linked to terrestrial productivity. In particular, we find higher IAV in water-limited regions of Europe (Mediterranean and temperate continental Europe) compared to other regions in both crop yield and remotesensing observations. Our results further indicate that variations in the water balance during the active growing season exert a more pronounced and direct effect than variations of temperature on explaining the spatial patterns in IAV of productivity-related variables in temperate Europe. Overall, we observe a temporally increasing trend in the IAV of terrestrial productivity and an increasing sensitivity of productivity to water availability in dry regions of Europe during the 1975-2009 period. In the same regions, a simultaneous increase in the IAV of water availability was detected. These findings suggest intricate responses of carbon fluxes to climate variability in Europe and that the IAV of terrestrial productivity has become potentially more sensitive to changes in water availability in the dry regions in Europe. The changing sensitivity of terrestrial productivity accompanied by the changing IAV of climate is expected to impact carbon stocks and the net carbon balance of European ecosystems.

Evidence that enhanced reactive nitrogen deposition is affecting semi‐natural terrestrial ecosystems comes from historic increases in plant tissue N concentrations, correlations between tissue N concentrations and present‐day total atmospheric N deposition, changes in plant amino‐acid composition and effects on N assimilation. The ecological significance of such changes in biomarkers is uncertain. This paper explores the ecological significance of reactive atmospheric N deposition through a review of previous experimental findings and new experimental evidence from an acidic and a calcareous grassland, both showing phosphorus limitation, and a N‐limited Calluna vulgaris (L.) Hull heathland in upland Britain. Nitrogen addition in the range 0–20 g N m−2 yr−1 initially (years 0–4) increased the growth of Calluna and a decline in some subordinate species. In subsequent years, shoot extension was not stimulated, but winter injury was observed from 1993 onwards, suggesting a strong intera...

Knowledge of soil SO 4 adsorption characteristics is required for predicting the fate of atmospheric S depositions on terrestrial ecosystems. This study developed two models for predicting the SO 4 sorption characteristics of field moist soils from routinely measured soil physical and chemical properties. Sixty-two soil samples from the U.S. Northeastern (NE) and Southern Blue Ridge Province (SBRP) regions were used in model development. The first modeling approach used stepwise multiple regression to identify which combinations of soil properties best predicted each Langmuir constant. The Langmuir constant regression equations were then substituted back into the Langmuir model and used to predict SO 4 sorption for each equilibrium SO 4 concentration. This approach described SO 4 sorption reasonably well for both regions (R 2 of 0.57-0.89). In the second approach, a better fit of SO 4 sorption was achieved (R 1 of 0.81-0.92) using fewer soil properties by expressing the Langmuir constants as linear functions of selected soil properties and directly estimating the soil property coefficients by nonlinear regression. Soil properties used in the second model included: dithionite-citrate-extractable A1 (Al d ), total organic C (TOC), and extractable SO 4 for the NE region; and Al d , TOC, clay content, pH, and CEC for the SBRP region. These results indicated that regional soil SO 4 sorption characteristics could be predicted for field moist soils with the knowledge of only a few routinely measured soil properties.

Svalbard is an archipelago at the north-western edge of the Barents Sea. Despite its extreme northerly position, the climate is relatively mild in the western part of the archipelago. This is due to the warm North Atlantic Current reaching Spitsbergen, the largest island, causing temperatures there to frequently fluctuate around freezing, even in winter. Svalbard ecosystems share some attributes typical of islands. However, in spite of the limited land area there is large heterogeneity among ecosystems on different spatial scales: three out of five Arctic bioclimatic subzones occur in the archipelago, stretching from extremely low productive polar deserts to relatively productive tundra. Plant community data presented in this paper demonstrate that plant communities in mesic (zonal) habitats are well differentiated among the different bioclimatic subzones. Within a subzone, strong community differentiation occurs between mesic and ridge habitats in the two warmest zones, but not in the coldest, the polar desert. Relative to 'mainlands', species diversity is low on Svalbard and terrestrial food webs are simple, with strong links to marine food webs. However, fully accounting for the invertebrate components of the food webs reveals a considerable complexity that may contribute to ecosystem robustness. Fragility of the terrestrial ecosystems on Svalbard is discussed in terms of island characteristics. It is concluded that these ecosystems are robust in terms of temporal variation in herbivore populations and climate, but are fragile in terms of human disturbance. Their fragility in terms of climate change is still an open question that needs more thorough evaluation.

Svalbard is an archipelago at the north-western edge of the Barents Sea. Despite its extreme northerly position, the climate is relatively mild in the western part of the archipelago. This is due to the warm North Atlantic Current reaching Spitsbergen, the largest island, causing temperatures there to frequently fluctuate around freezing, even in winter. Svalbard ecosystems share some attributes typical of islands. However, in spite of the limited land area there is large heterogeneity among ecosystems on different spatial scales: three out of five Arctic bioclimatic subzones occur in the archipelago, stretching from extremely low productive polar deserts to relatively productive tundra. Plant community data presented in this paper demonstrate that plant communities in mesic (zonal) habitats are well differentiated among the different bioclimatic subzones. Within a subzone, strong community differentiation occurs between mesic and ridge habitats in the two warmest zones, but not in the coldest, the polar desert. Relative to 'mainlands', species diversity is low on Svalbard and terrestrial food webs are simple, with strong links to marine food webs. However, fully accounting for the invertebrate components of the food webs reveals a considerable complexity that may contribute to ecosystem robustness. Fragility of the terrestrial ecosystems on Svalbard is discussed in terms of island characteristics. It is concluded that these ecosystems are robust in terms of temporal variation in herbivore populations and climate, but are fragile in terms of human disturbance. Their fragility in terms of climate change is still an open question that needs more thorough evaluation.

Emerging aquatic insects play a key role in transporting aquatic contaminants into terrestrial ecosystems. Tree swallows are frequently the focus of studies examining this movement because they are thought to forage heavily on emerging aquatic insects when breeding in riparian areas. We examined the tree swallow diet to determine if trace elements from a recently remediated coal fly ash spill were moving into the terrestrial ecosystem. We collected bolus samples from adult tree swallows as they entered the nest box to feed their young. Despite strategically locating boxes in riparian areas, we found that the consumption of insects with an aquatic larval stage ranged from 28 to 75 % of insects among colonies. We also found significant differences among colonies in the taxa found in bolus samples. Chironomidae (midges) were the primary emerging aquatic insects consumed by tree swallows, whereas Ephemeroptera were brought to nestlings infrequently. The consumption of insects with an aquatic larval stage, Chironomidae in particular, was positively correlated with exposure to trace elements from the spill. Bolus samples from the spill site contained greater concentrations of many trace elements compared with reference locations, but concentrations of most elements were lower than levels thought to cause reproductive impairment. These results support the hypothesis that emerging aquatic insects transport trace elements to terrestrial consumers and that Chironomidae play an important role in this movement. Our results also indicate that it is important to assess the composition of the diet and to not infer exposure to trace elements based on nesting location. The movement of environmental contaminants through ecosystems and their potential effects on wildlife populations is of great conservation concern. Aquatic ecosystems often become concentrated sources of contaminants due to run-off from terrestrial habitats or industrial disposal practices that use water to dilute or hold contaminated materials (Rowe et al. 2002; United States Environmental Protection Agency 2002). Thus, much contaminant research focuses on aquatic or piscivorous species and the movement of contaminants through primarily aquatic ecosystems . However, freshwater streams produce an incredible biomass of emerging aquatic insects, which can average between 10,000 and 20,000 individuals/m 2 /year (Jackson and Fisher 1986), and lakes typically produce even greater biomass . As a result, emerging aquatic insects provide important nutrient and energy subsidies to terrestrial consumers, including birds, bats, spiders, and amphibians (Sabo and Power 2002;. Emerging aquatic insects also export contaminants from aquatic systems and introduce contaminants into terrestrial food webs (Vander Zanden and Sanzone 2004;. Terrestrial animals that eat emerging aquatic insects can be at considerable risk of contaminant exposure and resulting toxicity (

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• For the State of Hawaiʻi, total carbon storage was projected to increase by about 6 percent (14.7 TgC) to 267.6 TgC in 2061. • Carbon stored in living biomass was projected to decrease by approximately 1.3 percent by 2061, from 52.0 TgC to 51.3 TgC; soil organic carbon was projected to increase from 183.6 TgC to 198.0 TgC. • Net ecosystem production (NEP) for the State of Hawaiʻi was estimated at an average annual rate of 0.799 TgC/yr (mean annual NEP carbon flux density of 49 gC/m 2 /yr). When land-use change and disturbances were considered, statewide net ecosystem carbon balance (NECB) was estimated at an average annual rate of 0.595 TgC/yr (mean annual NECB carbon flux density of 36 gC/m 2 /yr). Both NEP and NECB were projected to decrease during the 50-year projection period, indicating a reduction in statewide carbon-sink strength. Developed lands were projected to more than double (increasing by ~1,100 km 2 ) by 2061 and account for 12.2 to 13.7 percent of the State's land area. Conversion to development would account for an average net annual loss of 0.1 TgC/yr. • Agricultural lands were projected to decrease sharply in the "business as usual" projection, with contraction rates (~45 km 2 /yr) more than double the rate of expansion (20 km 2 /yr). Agricultural expansion accounted for an average annual loss of 0.078 TgC/yr. • Wildfire was projected to impact 41 km 2 /yr and burn 2,047 km 2 by 2061. Grasslands accounted for 41 percent of all fire, shrublands accounted for 42 percent, and forests accounted for 17 percent. Fire was most common in the dry moisture zone (average of 31 km 2 /yr), accounting for 76 percent of the annual burned area. • Changes involving land-use transitions had the largest impact on total ecosystem carbon storage. Urbanization had the largest negative impact on total ecosystem carbon storage (from 4.0 to 7.4 TgC) and losses of agriculture had the strongest positive impact (from 7.4 to 10.4 TgC). By comparison, wildfire had a relatively small influence. The LUCAS model was used to understand how changes in land use and land cover-in particular urbanization, agricultural expansion and contraction, wildfire, and vegetation dynamicsaffect carbon storage and fluxes for the State of Hawaiʻi. The LUCAS model is an integrated state-and-transition simulation

The c o n c e n t r a t i o n of a m m o n i u m and nitrate in p r e c i p i t a t i o n has increased during this century. The d e p o s i t i o n of N compounds (wet + dry) is reaching 30 to 40 kg h a -l y r -l in many areas in Central Europe and above 20 kg in the southern parts of Scandinavia. In extreme situations throughfall data indicate d e p o s i t i o n s above 60 kg h a -l y r -I in Central Europe and above 40 kg ha-lyr -I in south Sweden. Very high d e p o s i t i o n s are observed on slopes at forest edges and adjacent to areas with animal farms and manure spreading. In areas with low N d e p o s i t i o n almost all deposited N (>95%) will be absorbed in the tree canopies or in the soil. In areas with high d e p o s i t i o n an increased o u t f l o w is observed which in some cases reach i0 to 15 kg ha-lyr -I. The increased output is an indication of N s a t u r a t i o n of the e c o s y s t e m and it leads to a c i d i f i c a t i o n effects in soils, soilwater, g r o u n d w a t e r and surface waters. i. I n t r o d u c t i o n The c o n c e n t r a t i o n of N compounds in the p r e c i p i t a t i o n over North A m e r i c a and Europe has s u c c e s s i v e l y increased (N.A.S., 1983; G a l l o w a y and Dillon, 1983; G a l l o w a y and Likens . Data from the European Air C h e m i s t r y N e t w o r k (EACN) show a significant upward trend in ammonia and nitrate d e p o s i t i o n during the last decades . A doubling in nitrate c o n c e n t r a t i o n s from the end of the 50's to the b e g i n n i n g of the 70's has been shown . The upward trend for nitrate, however, is not observed after 1975 . The ratio of nitrate to sulphate in p r e c i p i t a t i o n has also changed during the last decades. In south S c a n d i n a v i a NO3-/SO42was 0.27 (on an equivalent basis) for the period 1955-59 and 0.47 for the period 1975 -79 (Persson, 1982)). The upward trend in nitrate c o n c e n t r a t i o n s in p r e c i p i t a t i o n c o r r e s p o n d s well w i t h the trend in NO emissions (W.S.L., 1983; J e r n e l ~v and L~vblad, 1985). No similar study of the changes in ammonia emissions during this century has been made. since the wet d e p o s i t i o n of nitrate and ammonium has increased b o t h in absolute terms as well as in relation to sulphate it is important to evaluate the m a g n i t u d e of this deposition, its interactions with the e c o s y s t e m and its possible effects. In this paper we will discuss these terms with respect to a coniferous forest ecosystem.

Significance How terrestrial plants use N and respond to soil N loading is central to evaluating and predicting changing ecosystem structure and function with climate warming and N pollution. Here, evidence from NO 3 − in plant tissues has uncovered the uptake and assimilation of soil NO 3 − by Arctic tundra plants, which has long been assumed negligible. Soil NO 3 − contributed about one-third of the bulk N used by tundra plants of northern Alaska. Accordingly, the importance of soil NO 3 − for tundra plants should be considered in future studies on N and C cycling in Arctic ecosystems where C sequestration is strongly determined by N availability.