Skip to main content

Joe Berry

Followers

7

Following

6

Co-authors

6

Public Views

I am an emeritus faculty member of the Carnegie Institution for Science’s Department of Global Ecology. My research is mostly focused on photosynthesis and related processes and on measurement and modeling approaches for linking laboratory based knowledge to regional and global scales and ultimately to the flow of metabolic energy in the Biosphere.

less

Interests

Uploads

Papers by Joe Berry

Regional-scale estimates of forest CO2 and isotope flux based on monthly CO2 budgets of the atmospheric boundary layer

The Carbon Balance of Forest Biomes, 2004

Photosynthetic Fractionation of the Stable Isotopes of Oxygen and Carbon

Plant Physiology, 1993

lsotope discrimination during photosynthetic exchange of O2 and COz was measured using enzyme, th... more lsotope discrimination during photosynthetic exchange of O2 and COz was measured using enzyme, thylakoid, and whole cell preparations. Evolved oxygen from isolated spinach thylakoids was isotopically identical (within analytical error) to its source water. Similar results were obtained with Anacystis nidulans Richter and Phaeodactylum tricornutum Bohlin cultures purged with helium. For consumptive reactions, discrimination (A, where 1 + A/1000 equals the isotope effect, k16/k'" or kl2/kl3) was determined by analysis of residual substrate (Oz or COz). The A for the Mehler reaction, mediated by ferredoxin or methylviologen, was 15.3%0. Oxygen isotope discrimination during oxygenation of ribulose-1,5bisphosphate (RuBP) catalyzed by RuBP carboxylase/oxygenase (Rubisco) was 21.3%0 and independent of enzyme source, unlike carbon isotope discrimination: 30.3%0 for spinach enzyme and 19.6 to 23%0 for Rhodospirillum rubrum and A. nidulans enzymes, depending on reaction conditions. The A for Oz consumption catalyzed by glycolate oxidase was 22.7%0. The expected overall A for photorespiration is about 21.7%0. Consistent with this, when Asparagus sprengeri Rege1 mesophyll cells approached the compensation point within a sealed vessel, the 6'"O of dissolved Oz came to a steady-state value of about 21.5%0 relative to the source water. The results provide improved estimates of discrimination factors in several reactions prominent in the global O cycle and indicate that photorespiration plays a significant part in determining the isotopic composition of atmospheric oxygen. ~ ~ ~ ~ ~ On a global scale, photosynthetic O2 is added to the atmosphere at a rate equal to its consumption. That is, the

Isotope Fractionation during Oxygen Production and Consumption by Plants

Progress in Photosynthesis Research, 1987

Knowledge of isotope discrimination factors related to oxygen production and consumption by plant... more Knowledge of isotope discrimination factors related to oxygen production and consumption by plants is important to an improved understanding of the global oxygen cycle. This information is also needed for the application of stable oxygen isotope methods, at natural abundance levels, to plant physiology and ecology.

A coupled model of the global cycles of carbonyl sulfide and CO2: A possible new window on the carbon cycle

Journal of Geophysical Research: Biogeosciences, 2013

Carbonyl sulfide (COS) is an atmospheric trace gas that participates in some key reactions of the... more Carbonyl sulfide (COS) is an atmospheric trace gas that participates in some key reactions of the carbon cycle and thus holds great promise for studies of carbon cycle processes. Global monitoring networks and atmospheric sampling programs provide concurrent data on COS and CO2 concentrations in the free troposphere and atmospheric boundary layer over vegetated areas. Here we present a modeling framework for interpreting these data and illustrate what COS measurements might tell us about carbon cycle processes. We implemented mechanistic and empirical descriptions of leaf and soil COS uptake into a global carbon cycle model (SiB 3) to obtain new estimates of the COS land flux. We then introduced these revised boundary conditions to an atmospheric transport model (Parameterized Chemical Transport Model) to simulate the variations in the concentration of COS and CO2 in the global atmosphere. To balance the threefold increase in the global vegetation sink relative to the previous basel...

Nocturnal stomatal conductance effects on the 18O signatures of foliage gas exchange observed in two forest ecosystems

Tree Physiology, 2007

We report field observations of oxygen isotope ( 18 O) discrimination during nocturnal foliage re... more We report field observations of oxygen isotope ( 18 O) discrimination during nocturnal foliage respiration ( 18 ∆ R ) in branch chambers in two forest ecosystems: a Sitka spruce (Picea sitchensis (Bong.) Carr.) plantation in Scotland; and a beech (Fagus sylvatica L.) forest in Germany. We used observations and modeling to examine the impact of nocturnal stomatal conductance on the 18 O/ 16 O (δ 18 O) signatures of foliage gas exchange at night. We found that nocturnal stomatal conductance can influence the δ 18 O signature by affecting: (1) the bidirectional diffusion of CO 2 into and out of the leaf (with isotopic equilibration); and (2) the 18 O enrichment of the foliage water with which the CO 2 equilibrates. Both effects were manifest in high apparent 18 ∆ R values and enriched δ 18 O signatures of foliage water at night. The effects were more pronounced for Sitka spruce because of its higher nocturnal stomatal conductance and higher specific leaf water content compared to beech. We found that taking the effects of nocturnal stomatal conductance into account may change the sign of the δ 18 O signature of nocturnal foliage respiration, generally thought to decrease the δ 18 O of atmospheric CO 2 . We conclude that nocturnal stomatal exchange can have a profound effect on isotopic exchange depending on species and environmental conditions. These effects can be important when using δ 18 O signatures of canopy CO 2 to distinguish foliage and soil respiration, and when modeling the δ 18 O signature of CO 2 exchanged between ecosystems and the atmosphere.

$Research paper thumbnail of Differential fractionation of oxygen isotopes by cyanide-resistant and cyanide-sensitive respiration in plants$

Differential fractionation of oxygen isotopes by cyanide-resistant and cyanide-sensitive respiration in plants

Planta, 1989

Stable-isotope discrimination factors (D) for the uptake of oxygen during respiration by a variet... more Stable-isotope discrimination factors (D) for the uptake of oxygen during respiration by a variety of plant materials were determined by measuring (18)O enrichment in a closed system. Baker&#39;s yeast (Saccharomyces cerevisiae Meyer) and mitochondrial preparations from baker&#39;s yeast and from castor bean (Ricinus communis L.) endosperm, all of which are fully sensitive to cyanide, discriminated againt (18)O by about 16-18‰. Whole Medicago sativa L. seedlings, isolated intact Asparagus sprengeri Regel mesophyll cells, and spadix mitochondria of Eastern skunk cabbage (Symplocarpus foetidus L.) had higher Ds of about 20-22‰. These materials all had some capacity for the cyanide-resistant alternative respiration pathway and in the presence of cyanide discriminated by about 24-26‰. When treated with salicylhydroxamic acid or tetraethylthiuram disulfide, which inhibit the alternative pathway, discrimination was about 17-19‰. Where respiration was limited by oxygen diffusion (slices of thermogenic tissues from S. foetidus and Sauromatum gutfatum Schott), fractionation was much reduced and the difference between the two respiratory pathways was masked. Isotope discrimination by soybean lipoxygenase (EC 1.13.11.12) supplied with linoleic acid was much lower than by respiration. Where diffusion is not a problem, the D value obtained in the absence of inhibitor can be used to estimate the partitioning of electron transport between the two pathways at steady-state by linear interpolation between the Ds characteristic of cyanide-resistant and cyanide-sensitive respiration.

Non‐steady state effects in diurnal 18O discrimination by Picea sitchensis branches in the field

Plant, Cell & Environment, 2006

ABSTRACTWe report diurnal variations in 18O discrimination (18Δ) during photosynthesis (18ΔA) and... more ABSTRACTWe report diurnal variations in 18O discrimination (18Δ) during photosynthesis (18ΔA) and respiration (18ΔR) of Picea sitchensis branches measured in branch chambers in the field. These observations were compared with predicted 18Δ (18Δpred) based on concurrent measurements of branch gas exchange to evaluate steady state and non‐steady state (NSS) models of foliage water 18O enrichment for predicting the impact of this ecosystem on the δ18O of atmospheric CO2. The non‐steady state approach substantially improved the agreement between 18Δpred and observed 18Δ (18Δobs) compared with the assumption of isotopic steady state (ISS) for the δ18O signature of foliage water. In addition, we found direct observational evidence for NSS effects: extremely high apparent 18Δ values at dusk, dawn and during nocturnal respiration. Our experiments also show the importance of bidirectional foliage gas exchange at night (isotopic equilibration in addition to the net flux). Taken together, negl...

Association between Carbonyl Sulfide Uptake and 18Δ during Gas Exchange in C3 and C4 Leaves

Plant Physiology, 2011

Carbonyl sulfide (COS) and C 18 OO exchange by leaves provide potentially powerful tracers of bio... more Carbonyl sulfide (COS) and C 18 OO exchange by leaves provide potentially powerful tracers of biosphere-atmosphere CO 2 exchange, and both are assumed to depend on carbonic anhydrase (CA) activity and conductance along the diffusive pathway in leaves. We investigated these links using C 3 and C 4 plants, hypothesizing that the rates of COS and C 18 OO exchange by leaves respond in parallel to environmental and biological drivers. Using CA-deficient antisense lines of C 4 and C 3 plants, COS uptake was essentially eliminated and discrimination against C 18 OO exchange ( 18 D) greatly reduced, demonstrating CA's key role in both processes. 18 D showed a positive linear correlation with leaf relative uptake (LRU; ratio of COS to CO 2 assimilation rates, A s /A c , normalized to their respective ambient concentrations), which reflected the effects of stomatal conductance on both COS and C 18 OO exchange. Unexpectedly, a decoupling between A s and 18 D was observed in comparing C 4 and C 3 plants, with a large decrease in 18 D but no parallel reduction in A s in the former. This could be explained by C 4 plants having higher COS concentrations at the CA site (maintaining high A s with reduced CA) and a high phosphoenolpyruvate carboxylase/CA activity ratio (reducing 18 O exchange efficiency between CO 2 and water, but not A s ). Similar A s but higher A c in C 4 versus C 3 plants resulted in lower LRU values in the former (1.16 6 0.20 and 1.82 6 0.18 for C 4 and C 3 , respectively). LRU was, however, relatively constant in both plant types across a wide range of conditions, except low light (,191 mmol photon m 22 s 21 ).

The contribution of C 3 and C 4 plants to the carbon cycle of a tallgrass prairie: an isotopic approach

Oecologia, 2003

The photosynthetic pathway composition (C 3 :C 4 mixture) of an ecosystem is an important control... more 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 .

Effects of climate and atmospheric CO 2 partial pressure on the global distribution of C 4 grasses: present, past, and future

Oecologia, 1998

Photosynthesis á C 4 á Climate change á CO 2 á Grassland Oecologia (1998) 114:441±454

Life form-specific variations in leaf water oxygen-18 enrichment in Amazonian vegetation

Oecologia, 2008

Leaf water 18 O enrichment (D o ) influences the isotopic composition of both gas exchange and or... more Leaf water 18 O enrichment (D o ) influences the isotopic composition of both gas exchange and organic matter, with D o values responding to changes in atmospheric parameters. In order to examine possible influences of plant parameters on D o dynamics, we measured oxygen isotope ratios (d 18 O) of leaf and stem water on plant species representing different life forms in Amazonia forest and pasture ecosystems. We conducted two field experiments: one in March (wet season) and another in September (dry season) 2004. In each experiment, leaf and stem samples were collected at 2-h intervals at night and hourly during the day for 50 h from eight species including upper-canopy forest trees, upper-canopy forest lianas, and lower-canopy forest trees, a C 4 pasture grass and a C 3 pasture shrub. Significant life form-related differences were detected in 18 O leaf water values. Initial modeling efforts to explain these observations over-predicted nighttime D o values by as much as 10%. Across all species, errors associated with measured values of the d 18 O of atmospheric water vapor (d v ) appeared to be largely responsible for the over-predictions of nighttime D o observations. We could not eliminate collection or storage of water vapor samples as a possible error and therefore developed an alternative, plant-based method for estimating the daily average d v value in the absence of direct (reliable) measurements. This approach differs from the common assumption that isotopic equilibrium exists between water vapor and precipitation water, by including transpiration-based contributions from local vegetation through 18 O measurements of bulk leaf water. Inclusion of both modified d v and non-steady state features resulted in model predictions that more reliably predicted both the magnitude and temporal patterns observed in the data. The influence of life form-specific patterns of D o was incorporated through changes in the effective path length, an important but little known parameter associated with the Pe ´clet effect.

Relationships between carbonyl sulfide (COS) and CO2 during leaf gas exchange

New Phytologist, 2010

Carbonyl sulfide (COS) exchange in C 3 leaves is linked to that of CO 2 , providing a basis for t... more Carbonyl sulfide (COS) exchange in C 3 leaves is linked to that of CO 2 , providing a basis for the use of COS as a powerful tracer of gross CO 2 fluxes between plants and the atmosphere, a critical element in understanding the response of the land biosphere to global change. • Here, we carried out controlled leaf-scale gas-exchange measurements of COS and CO 2 in representative C 3 plants under a range of light intensities, relative humidities and temperatures, CO 2 and COS concentrations, and following abscisic acid treatments. • No 'respiration-like' emission of COS or detectable compensation point, and no cross-inhibition effects between COS and CO 2 were observed. The mean ratio of COS to CO 2 assimilation flux rates, A s ⁄ A c , was c. 1.4 pmol lmol )1 and the leaf relative uptake (assimilation normalized to ambient concentrations, (A s ⁄ A c ) (C a c ⁄ C a s )) was 1.6-1.7 across species and conditions, with significant deviations under certain conditions. Stomatal conductance was enhanced by increasing COS, which was possibly mediated by hydrogen sulfide (H 2 S) produced from COS hydrolysis, and a correlation was observed between A s and leaf discrimination against C 18 OO. • The results provide systematic and quantitative information necessary for the use of COS in photosynthesis and carbon-cycle research on the physiological to global scales.

Influence of clouds and diffuse radiation on ecosystem‐atmosphere CO2 and CO18O exchanges

Journal of Geophysical Research: Biogeosciences, 2009

This study evaluates the potential impact of clouds on ecosystem CO2 and CO2 isotope fluxes (“iso... more This study evaluates the potential impact of clouds on ecosystem CO2 and CO2 isotope fluxes (“isofluxes”) in two contrasting ecosystems (a broadleaf deciduous forest and a C4 grassland) in a region for which cloud cover, meteorological, and isotope data are available for driving the isotope‐enabled land surface model (ISOLSM). Our model results indicate a large impact of clouds on ecosystem CO2 fluxes and isofluxes. Despite lower irradiance on partly cloudy and cloudy days, predicted forest canopy photosynthesis was substantially higher than on clear, sunny days, and the highest carbon uptake was achieved on the cloudiest day. This effect was driven by a large increase in light‐limited shade leaf photosynthesis following an increase in the diffuse fraction of irradiance. Photosynthetic isofluxes, by contrast, were largest on partly cloudy days, as leaf water isotopic composition was only slightly depleted and photosynthesis was enhanced, as compared to adjacent clear‐sky days. On th...

Interannual variability of photosynthesis across Africa and its attribution

Journal of Geophysical Research: Biogeosciences, 2008

Africa is thought to be a large source of interannual variability in the global carbon cycle, onl... more Africa is thought to be a large source of interannual variability in the global carbon cycle, only vaguely attributed to climate fluctuations. This study uses a biophysical model, Simple Biosphere, to examine in detail what specific factors, physiological (acute stress from low soil water, temperature, or low humidity) and biophysical (low vegetation radiation use), are responsible for spatiotemporal patterns of photosynthesis across the African continent during the period 1982–2003. Acute soil water stress emerges as the primary factor driving interannual variability of photosynthesis for most of Africa. Southern savannas and woodlands are a particular hot spot of interannual variability in photosynthesis, owing to high rainfall variability and photosynthetic potential but intermediate annual rainfall. Surprisingly low interannual variability of photosynthesis in much of the Sudano‐Sahelian zone derives from relatively low vegetation cover, pronounced humidity stress, and somewhat ...

A three‐dimensional synthesis study of δ18O in atmospheric CO2: 1. Surface fluxes

Journal of Geophysical Research: Atmospheres, 1997

The isotope 18O in CO2 is of particular interest in studying the global carbon cycle because it i... more The isotope 18O in CO2 is of particular interest in studying the global carbon cycle because it is sensitive to the processes by which the global land biosphere absorbs and respires CO2. Carbon dioxide and water exchange isotopically both in leaves and in soils, and the 18O character of atmospheric CO2 is strongly influenced by the land biota, which should constrain the gross primary productivity and total respiration of land ecosystems. In this study we calculate the global surface fluxes of 18O for vegetation and soils using the SiB2 biosphere model coupled with the Colorado State University general circulation model. This approach makes it possible to use physiological variables that are consistently weighted by the carbon assimilation rate and integrated through the vegetation canopy. We also calculate the air‐sea exchange of 18O and the isotopic character of fossil emissions and biomass burning. Global mean values of the isotopic exchange with each reservoir are used to close t...

Analysis of leakage in IRGA's leaf chambers of open gas exchange systems: quantification and its effects in photosynthesis parameterization

Journal of Experimental Botany, 2007

The measurement of the response of net photosynthesis to leaf internal CO 2 (i.e. A-C i curves) i... more The measurement of the response of net photosynthesis to leaf internal CO 2 (i.e. A-C i curves) is widely used for ecophysiological studies. Most studies did not consider CO 2 exchange between the chamber and the surrounding air, especially at the two extremes of A-C i curves, where large CO 2 gradients are created, leading to erroneous estimations of A and C i . A quantitative analysis of CO 2 leakage in the chamber of a portable open gas exchange system (Li-6400, LI-COR Inc., NE, USA) was performed. In an empty chamber, the measured CO 2 leakage was similar to that calculated using the manufacturer's equations. However, in the presence of a photosynthetically inactive leaf, the magnitude of leakage was substantially decreased, although still significant. These results, together with the analysis of the effects of chamber size, tightness, flow rate, and gasket material, suggest that the leakage is larger at the interface between the gaskets than through the gaskets. This differential leakage rate affects the parameterization by photosynthesis models. The magnitude of these errors was assessed in tobacco plants. The results showed that leakage results in a 10% overestimation of the leaf maximum capacity for carboxylation (V c,max ) and a 40% overestimation of day respiration (R l ). Using the manufac-turer's equations resulted in larger, non-realistic corrections of the true values. The photosynthetic response to CO 2 concentrations at the chloroplast (i.e. A-C c curves) was significantly less affected by leakage than A-C i curves. Therefore, photosynthetic parameterization can be improved by: (i) correcting A and C i values for chamber leakage estimated using a photosynthetically inactive leaf; and (ii) using A-C c instead of A-C i curves.

18 O composition of CO2 and H2 O ecosystem pools and fluxes in a tallgrass prairie: Simulations and comparisons to measurements

Global Change Biology, 2003

In this paper we describe measurements and modeling of 18 O in CO 2 and H 2 O pools and fluxes at... more In this paper we describe measurements and modeling of 18 O in CO 2 and H 2 O pools and fluxes at a tallgrass prairie site in Oklahoma. We present measurements of the d 18 O value of leaf water, depth-resolved soil water, atmospheric water vapor, and Keeling plot d 18 O intercepts for net soil-surface CO 2 and ecosystem CO 2 and H 2 O fluxes during three periods of the 2000 growing season. Daytime discrimination against C 18 OO, as calculated from measured above-canopy CO 2 and d 18 O gradients, is also presented. To interpret the isotope measurements, we applied an integrated land-surface and isotope model (ISOLSM) that simulates ecosystem H 2 18 O and C 18 OO stocks and fluxes. ISOLSM accurately predicted the measured isotopic composition of ecosystem water pools and the d 18 O value of net ecosystem CO 2 and H 2 O fluxes. Simulations indicate that incomplete equilibration between CO 2 and H 2 O within C 4 plant leaves can have a substantial impact on ecosystem discrimination. Diurnal variations in the d 18 O value of above-canopy vapor had a small impact on the predicted d 18 O value of ecosystem water pools, although sustained differences had a large impact. Diurnal variations in the d 18 O value of above-canopy CO 2 substantially affected the predicted ecosystem discrimination. Leaves dominate the ecosystem 18 O-isoflux in CO 2 during the growing season, while the soil contribution is relatively small and less variable. However, interpreting daytime measurements of ecosystem C 18 OO fluxes requires accurate predictions of both soil and leaf 18 O-isofluxes. Nomenclature at the high and low sampling points (mmol m À 3 ) F al , F la ¼ CO 2 fluxes into and out of the leaf (mmol m À 2 s À 1 ) F g , F sm , F s ¼ growth, stem, and net soil-surface CO 2 fluxes (mmol m À 2 s À 1 ) R eq ¼ CO 2 18 O isotopic ratios in the atmosphere, chloroplast, net ecosystem flux, and in equilibrium with leaf water z 0 ¼ e-folding depth for soil CO 2 source (m) d a , d e , d l , d H , d L , d nl , d sw , d s ¼ d 18 O values of atmospheric CO 2 , net ecosystem CO 2 flux, leaf water; CO 2 at the high sampling point, CO 2 at the low sampling point, net leaf CO 2 flux, stem respiration CO 2 flux, and soil CO 2 flux (%) D c ¼ difference in d 18 O values of chloroplast and atmospheric CO 2 (%) D eq ¼ difference in d 18 O values of equilibrium chloroplast and atmospheric CO 2 (%)

Combining meteorology, eddy fluxes, isotope measurements, and modeling to understand environmental controls of carbon isotope discrimination at the canopy scale

Global Change Biology, 2006

Estimates of terrestrial carbon isotope discrimination are useful to quantify the terrestrial car... more Estimates of terrestrial carbon isotope discrimination are useful to quantify the terrestrial carbon sink. Carbon isotope discrimination by terrestrial ecosystems may vary on seasonal and interannual time frames, because it is affected by processes (e.g. photosynthesis, stomatal conductance, and respiration) that respond to variable environmental conditions (e.g. air humidity, temperature, light). In this study, we report simulations of the temporal variability of canopy‐scale C3 photosynthetic carbon isotope discrimination obtained with an ecophysiologically based model (ISOLSM) designed for inclusion in global models. ISOLSM was driven by half‐hourly meteorology, and parameterized with eddy covariance measurements of carbon and energy fluxes and foliar carbon isotope ratios from a pine forest in Metolius (OR). Comparing simulated carbon and energy fluxes with observations provided a range of parameter values that optimized the simulated fluxes. We found that the sensitivity of pho...

A mechanistic model of H218O and C18OO fluxes between ecosystems and the atmosphere: Model description and sensitivity analyses

Global Biogeochemical Cycles, 2002

The concentration of 18O in atmospheric CO2 and H2O is a potentially powerful tracer of ecosystem... more The concentration of 18O in atmospheric CO2 and H2O is a potentially powerful tracer of ecosystem carbon and water fluxes. In this paper we describe the development of an isotope model (ISOLSM) that simulates the 18O content of canopy water vapor, leaf water, and vertically resolved soil water; leaf photosynthetic 18OC16O (hereinafter C18OO) fluxes; CO2 oxygen isotope exchanges with soil and leaf water; soil CO2 and C18OO diffusive fluxes (including abiotic soil exchange); and ecosystem exchange of H218O and C18OO with the atmosphere. The isotope model is integrated into the land surface model LSM, but coupling with other models should be straightforward. We describe ISOLSM and apply it to evaluate (1) simplified methods of predicting the C18OO soil‐surface flux; (2) the impacts on the C18OO soil‐surface flux of the soil‐gas diffusion coefficient formulation, soil CO2 source distribution, and rooting distribution; (3) the impacts on the C18OO fluxes of carbonic anhydrase (CA) activi...

The application and interpretation of Keeling plots in terrestrial carbon cycle research

Global Biogeochemical Cycles, 2003

Photosynthesis and respiration impart distinct isotopic signatures to the atmosphere that are use... more Photosynthesis and respiration impart distinct isotopic signatures to the atmosphere that are used to constrain global carbon source/sink estimates and partition ecosystem fluxes. Increasingly, the “Keeling plot” method is being used to determine the carbon isotope composition of ecosystem respiration (δ13CR) in order to better understand the processes controlling ecosystem isotope discrimination. In this paper we synthesize emergent patterns in δ13CR by analyzing 146 Keeling plots constructed at 33 sites across North and South America. In order to interpret results from disparate studies, we discuss the assumptions underlying the Keeling plot method and recommend standardized methods for determining δ13CR. These include the use of regression calculations that account for error in the x variable, and constraining estimates of δ13CR to nighttime periods. We then recalculate δ13CR uniformly for all sites. We found a high degree of temporal and spatial variability in C3 ecosystems, wit...