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Carbon dioxide is the main greenhouse gas inducing climate change. Increased global CO2 emissions, estimated at 8.4 Pg C yr(-1) at present, have accelerated from 1% yr(-1) during 1990-1999 to 2.5% yr(-1) during 2000-2009 (ref. 1). The carbon balance of terrestrial ecosystems is the greatest unknown in the global C budget because the actual magnitude, location and causes of terrestrial sinks are uncertain(2); estimates of terrestrial C uptake, therefore, are often based on the residuals between direct measurements of the atmospheric sink and well-constrained models of ocean uptake of CO2 (ref. 3). Here we report significant terrestrial C accumulation caused by CO2 enhancement to net ecosystem productivity in an intact, undisturbed arid ecosystem(4-8) following ten years of exposure to elevated atmospheric CO2. Results provide direct evidence that CO2 fertilization substantially increases ecosystem C storage and that arid ecosystems are significant, previously unrecognized, sinks for atmospheric CO2 that must be accounted for in efforts to constrain terrestrial and global C cycles.
Greater ecosystem carbon in the Mojave Desert
after ten years exposure to elevated CO2
R. D. Evans1*, A. Koyama1,2, D. L. Sonderegger1,3, T. N. Charlet4, B. A. Newingham4,5,
L. F. Fenstermaker6, B. Harlow1, V. L. Jin1,7, K. Ogle8, S. D. Smith4and R. S. Nowak9
Carbon dioxide is the main greenhouse gas inducing climate
change. Increased global CO2emissions, estimated at
8.4 Pg C yr1at present, have accelerated from 1% yr1during
1990–1999 to 2.5% yr1during 2000–2009 (ref. 1). The carbon
balance of terrestrial ecosystems is the greatest unknown in
the global C budget because the actual magnitude, location
and causes of terrestrial sinks are uncertain2; estimates of
terrestrial C uptake, therefore, are often based on the residuals
between direct measurements of the atmospheric sink and
well-constrained models of ocean uptake of CO2(ref. 3). Here
we report significant terrestrial C accumulation caused by
CO2enhancement to net ecosystem productivity in an intact,
undisturbed arid ecosystem4–8 following ten years of exposure
to elevated atmospheric CO2. Results provide direct evidence
that CO2fertilization substantially increases ecosystem C
storage and that arid ecosystems are significant, previously un-
recognized, sinks for atmospheric CO2that must be accounted
for in eorts to constrain terrestrial and global C cycles.
Arid and semiarid ecosystems are significant components of
the terrestrial C budget; they cover 47% of the terrestrial surface9,
represent the fifth largest pool of soil organic C (208–241 Pg;
ref. 10) and exhibit large increases in net primary productivity
(NPP) in response to small changes in water availability11. The
Nevada Desert Free-Air CO2Enrichment Facility (NDFF) was
established in 1997 to better understand the sensitivity of arid
ecosystems to increasing atmospheric CO2([CO2]). Soil organic C
and nitrogen are concentrated in the top 0.1 m and no significant
differences in soil C and N were observed between CO2treatments
in 1999 (ref. 4). Above- and belowground biomass and soils
to 1 m were harvested by plant-cover type after ten years of
continuous treatment. Soils were the dominant pool of C and
N and contents were significantly greater under elevated [CO2]
across all cover types (Fig. 1 and Supplementary Tables 1–5). Mean
total ecosystem organic C under elevated CO2was 1,170 g C m2
with a 90% credible interval of 1,062–1,285 g C m2, compared
with 1,030 g C m2(credible interval of 937–1,130 g C m2)under
ambient conditions. Differences were owing solely to soil organic
C; no differences were observed in plant pools. This contrasts
with more mesic grassland and forested ecosystems that observed
increases in plant biomass after two to nine years of exposure
to elevated [CO2] (ref. 12). Mass balance analysis of the carbon
isotope composition (δ13C) of C entering the soil after a change
in CO2sources in 2003 was 26.2h(Fig. 2), indicating ~70%
of accrued soil organic C originated from aboveground (27.1h)
compared with belowground (24.0h) sources. Comparisons of
the relative contribution of different C sources to accrued soil
organic C between elevated and ambient [CO2] treatments are not
possible, however, as the δ13 C of CO2for ambient CO2treatments
remained constant throughout the experiment.
Flux estimates of net ecosystem productivity (NEP) are problem-
atic in aridlands13, thus our harvest provides the first direct measure
of long-term enhancements to NEP stimulated by elevated [CO2].
Estimates of the spatial extent of aridlands range from 2.65×109ha
(ref. 10) to 4.89×109ha (ref. 9) and plant cover in arid biomes has
increased 11% as atmospheric CO2increased from 1982 to 2010
(ref. 14). Assuming that responses observed over this ten-year study
are representative of other arid ecosystems, then enhancements to
NEP in arid and semiarid lands caused by elevated CO2could
range from 0.37 to 0.68 Pg C yr1. This enhancement of NEP is
equivalent to 4–8% of current global CO2emissions of 8.4 Pg C yr1
and 15–28% of current terrestrial uptake estimates of 2.4 PgC yr1
(ref. 1). The recent generation of representative concentration path-
ways (RCPs) for climate simulations predict that atmospheric [CO2]
will reach levels used in this experiment (513 µmol mol1)between
2045 (RCP8.5) and 2063 (RCP4.5; ref. 15) and CO2enhance-
ment of NEP reported here could account for 4–8% and 2–4% of
predicted total emissions for RCP4.5 (9.0Pg C yr1)and RCP8.5
(19.0 Pg C yr1), respectively, at that time. Although extrapolations
such as this can be problematic, as evidenced by the range in
atmospheric [CO2] trajectories proposed in the RCPs and possible
interactions between elevated [CO2] and other global change factors
beyond the goals of this experiment, such as increased atmospheric
N deposition, changes in precipitation regimes and warming, they
do point out the potential for CO2stimulation of NEP in arid regions
to impact global [CO2].
Increases in total ecosystem C at the NDFF under elevated [CO2]
are the direct result of CO2fertilization effects on photosynthesis.
Plants grown under elevated [CO2] had photosynthetic rates 1.3–2.0
times greater than those grown under ambient [CO2] (ref. 5).
Further, integrated leaf-level C gain for the dominant shrub Larrea
tridentata was 170 g C m2yr1and 118 g C m2yr1greater in
wet and dry years under elevated [CO2], respectively5. Increased
1School of Biological Sciences and WSU Stable Isotope Core Facility, Washington State University, Pullman, Washington 99164, USA, 2Natural Resource
Ecology Laboratory and Department of Biology, Colorado State University, Fort Collins, Colorado 80523, USA, 3Department of Mathematics and Statistics,
Northern Arizona University, Flagsta, Arizona 86011, USA, 4School of Life Sciences, University of Nevada, Las Vegas, Nevada 89154, USA, 5College of
Natural Resources, University of Idaho, Moscow, Idaho 83844, USA, 6Division of Earth and Ecosystem Sciences, Desert Research Institute, Las Vegas,
Nevada 89119, USA, 7USDA-Agricultural Research Service, Lincoln, Nebraska 68583, USA, 8School of Life Sciences, Arizona State University, Tempe,
Arizona 85287, USA, 9Department of Natural Resources and Environmental Science, University of Nevada, Reno, Nevada 89557, USA.
Amb. Elev. Amb. Elev.
Carbon (g C m−2)
Nitrogen (g N m−2)
Figure 1 | Ecosystem C and N under ambient and elevated CO2.
a,b, Posterior means and 90% credible intervals (error bars) for
aboveground (filled uptriangle, open uptriangle) and belowground (filled
downtriangle, open downtriangle) plant biomass, soils (filled square, open
square) and total (filled circle, open circle) ecosystem C (a) and N (b)
under ambient (Amb.) and elevated [CO2] (Elev.). Estimates are derived by
summing cover-weighted values for individual cover types (Supplementary
Information). Mean soil (Bayesian p-value = 0.002, 0.002) and total
ecosystem (p=0.021,0.004) were significantly dierent between CO2
treatments for C and N, respectively.
photosynthesis and leaf-level C gain in all years, however, translated
to increases in aboveground NPP in only wet, but not dry, years11,13.
The absence of [CO2] treatment differences in plant C and N
pools at final harvest seems to contradict the measured increases
in photosynthesis and NPP under elevated [CO2]. This observation,
in fact, highlights a primary mechanism for the observed increase
in soil organic C, as well as a fundamental difference in the
response between arid and more mesic ecosystems. Arid ecosystems
are characterized by rapid increases in NPP and biomass in
response to stochastic increases in water availability11. The greatest
enhancement in NPP and growth of plants under elevated [CO2]
at the NDFF occurred when moisture was most available. The
final harvest at NDFF occurred during a dry year, indicating
that peaks in production that occur under elevated [CO2] when
moisture is readily available cannot be sustained during intervening
drought. Hence, additional biomass senesced, increasing C inputs
into soil as litter. High rates of above- and belowground plant
biomass turn-over are common in arid ecosystems; turnover of
aboveground biomass at NDFF may occur every two to six years
based on measurements of aboveground NPP of 10–30 g C m2s1
at a nearby site13 and total aboveground biomass can turn over
every 1.5 yr based on NPP and standing biomass estimates in the
Chihuahuan Desert16.
The 118–170 g C m2yr1increase in leaf-level C gain observed
here under elevated [CO2] without consistent, concurrent increases
in aboveground NPP suggests a second mechanism for the observed
increases in soil organic C; significant increases in belowground
allocation of C. Belowground biological activity beneath shrubs, as
estimated by soil respiration, can be 60% greater under elevated
compared with ambient [CO2], but this increase is occurring
without significant differences in fine-root standing crop, turnover
rates6, or root respiration17 . Thus, this increase in belowground
biological activity is probably due to increases in soil microbial
activity or population size, and that increased rhizodeposition and
Amb. Elev. Amb. Elev.
δ13C (% )
δ15N (% )
Figure 2 | Ecosystem C and N isotope composition under ambient and
elevated CO2.a,b, Posterior means and 90% credible intervals (error bars)
for aboveground (filled uptriangle, open uptriangle) and belowground
(filled downtriangle, open downtriangle) plant biomass, soils (filled square,
open square) and total (filled circle, open circle) ecosystem δ13C (a) and
δ15N (b) under ambient (Amb.) and elevated [CO2] (Elev.). Estimates are
derived by summing cover-weighted values for individual cover types
(Supplementary Information). Mean δ13C was significantly dierent
between treatments for above- and belowground biomass (Bayesian
p-value <0.0001) and total carbon (p=0.066). No significant dierences
were observed between treatments for δ15N.
subsequent assimilation and stabilization by the soil microbial
community is a significant mechanism for increased C inputs to
the soil under elevated [CO2]. Rates of rhizosphere C deposition
have been shown to increase 56–74% under elevated [CO2] in
diverse ecosystems18,19 and labile compounds immobilized into
microbial residues can be a major source of stable C and N in
soils20. A previous study8demonstrated that plant photosynthates
are assimilated by rhizosphere microbial communities within
1 h of exposing L. tridentata to 13 C-labelled CO2, highlighting
the tight linkage between plants, rhizodeposition and microbes
in this arid ecosystem as well as the ability of C to rapidly
transfer from the site of photosynthesis to the soil without
increases in plant biomass or turnover rates. The C:N ratio of
accumulated C and N observed here (5.5, total soil C:N =7.3)
is consistent with accumulation of bacterial and fungal residues
(C:N from 4:1 to 10:1), an observation supported by increased
amounts of fungal and bacterial biomarkers under elevated [CO2]
(A.K. and R.D.E., manuscript in preparation). Thus, root exudation
and microbial stabilization may be more important determinants of
belowground C balance in arid ecosystems than the input of fine-
root litter found in more mesic ecosystems12. The patterns observed
at the NDFF are congruent with observations from the semiarid
shortgrass steppe21, where elevated [CO2] stimulated aboveground
production of only 33% over five years but caused a doubling of
rhizodeposition over the same time period.
Mean organic N was 161 g N m2(credible interval of
145–178 g N m2) under elevated [CO2] in contrast to 136 g Nm2
(credible interval of 122–150 g N m2)for controls (Fig. 1). The
N cycle in arid ecosystems is open with relatively high rates of N
input that are balanced by similar rates of loss from soil emissions,
thus small changes in either inputs or losses can significantly alter
ecosystem N storage. The observed differences in N can therefore
result from increased N2fixation or atmospheric deposition,
greater retention of N through decreased gas emissions from
volatilization, nitrification and denitrification, or transfer of N
from below our sampling zone into the top 1 m of soil. Rates of
atmospheric deposition in this region are 0.5–1.0g N m2yr1,
whereas another study22 recently determined the mean rate of N2
fixation in aridlands is 1 g N m2yr1, strongly suggesting that the
differences in accumulation rates observed here are at the lower
region of the credible interval. Increased rates of heterotrophic
N2fixation were observed under elevated [CO2] (ref. 23), but
rates are not great enough to solely account for the observed
treatment differences. Changes in rooting dynamics and plant N
acquisition below the 1 m depth examined in this experiment may
have also contributed to the observed differences. Nitrate readily
leaches in coarse soils and the greatest concentrations are often
observed at depths of 1 m or greater24 . Nutrient acquisition by
dominant shrubs can occur to 5 m (ref. 25) and seasonal patterns
and observed treatment differences in leaf δ15N of L. tridentata7
are consistent with patterns observed with plant use of nitrate at
depth26; effectively transferring N from depth to the top 1 m of soil.
Finally, elevated [CO2] may increase total ecosystem N over time
by increasing rates of N retention by plants and microbes, thereby
decreasing rates of gaseous loss27. This hypothesis is supported by
experimentation; volatilization is the primary source of N loss at
the NDFF (refs 4,28) and experimental addition of C (ref. 27) or
elevated [CO2] (ref. 28) greatly decreased gaseous N emissions,
thus facilitating retention of N in the soil. Reliable estimates of
annual N fluxes in arid ecosystems are problematic due to their
episodic occurrence. The observed differences in ecosystem N
content observed here are probably due to a combination of each of
the above factors, and separating their relative roles requires further
experimentation beyond the goals of this study.
The progressive N-limitation hypothesis predicts increased
N limitations to NPP as ecosystems accumulate C, but this has
not yet been observed at the NDFF. [CO2] enhancement and
direct C-addition studies demonstrate that microbial activity at
the NDFF is limited by available C (refs 23,27) and increased C
inputs accelerate rates of soil N transformations, thus increasing N
mineralization and inorganic N availability7,29. Soil organic matter
in arid ecosystems is largely recalcitrant7, but increased litter and
rhizodeposition under elevated [CO2] have caused an increase in
microbial biomass and diversity, especially for fungi8that are more
efficient at using recalcitrant substrates. This is accompanied by
an increase in the diversity of substrates used by the microbial
community as well as the activities of enzymes involved in N and
C cycling29.
Assessing the location and magnitude of terrestrial C sinks
is challenging because of their spatial and temporal complexity.
Previous efforts to estimate C uptake by the terrestrial surface
often focused on easily identified sinks such as forest regrowth and
typically did not consider non-forested ecosystems or physiological
enhancements to photosynthesis and growth caused by increasing
[CO2]. Despite suggestions that the strength of global C sinks has
recently declined or remained static, recent mass balance analyses
of global C indicate that uptake of CO2by oceans and the land
surface has accelerated over the past 50 yr (ref. 2), highlighting the
uncertainties present in our knowledge of the global C cycle. Results
from this ten-year experiment clearly demonstrate two critical
areas that must be considered to develop a more comprehensive
understanding of the fates of atmospheric CO2. First, non-forested
ecosystems must be accounted for in studies of terrestrial sinks;
arid and semiarid lands are the most widespread terrestrial biomes
and the enhancements in NEP in response to elevated [CO2]
observed here indicate their importance as a significant C sink.
Second, increases in C storage observed here were the result of
[CO2] enhancements to photosynthesis, subsequent increases in
plant biomass during wetyears followed by greater senescence in dry
years and increased rhizodeposition. Thus, more mechanistic detail
is necessary in models predicting plant, rhizodeposition and NEP
responses to elevated [CO2] (ref. 30). Consideration of both factors
will in turn allow us to better constrain terrestrial C dynamics and
ultimately the global C cycle.
Free-air-CO2-enrichment (FACE) experiments allow investigators to quantify
whole-ecosystem responses to elevated [CO2] in coupled plant–soil systems. The
NDFF was the only FACE experiment located in an intact arid ecosystem. The
NDFF was located 15 km north of Mercury, (36°490N, 115°550W; elevation
965–970 m) in the northern Mojave Desert. The site consisted of nine
23-m-diameter experimental plots exposed to three fumigation treatments. Three
plots were fumigated at ambient atmospheric [CO2] (~380 µmol CO2mol1)as a
blower control (ambient), three at ~550 µmolC O2mol1(elevated) and three
received no fumigation (non-blower control). Treatments began in April 1997
and continued until June 2007. Fumigations were maintained continuously
throughout the experiment except when air temperatures were below 4 °C or
when wind speeds >7 m s1for more than 5 min. Mean [CO2] concentrations
were 513 µmol mol1and 375 µmol mol1for elevated and ambient treatments,
respectively, over the life of the experiment. The δ13C of supplemental CO2was
5.4huntil 10 February 2003 when the source CO2was switched to 32.0h
for the remainder of the experiment. Dilution with ambient air resulted in δ13C of
CO2in the elevated treatment of 7.3hand 18.2hbefore and after the source
switch, respectively. The δ13 C of ambient and control treatments was 8h
throughout the experiment.
Seven cover types based on the dominant species were identified in each plot.
The final harvested area for each ring was calculated from aerial photographs
using image-processing software (ENVI, Exelis Visual Information Solutions).
Vegetation and soils to 1 m depth were destructively harvested from two-thirds of
each plot at the end of the 2007 growing season. Aboveground biomass was
determined by cutting all plants at ground level and summing biomass for all
individuals of each species. Belowground biomass was measured for each cover
type using two approaches. First, root biomass was determined from excavated
soil collected in association with specific cover types. Second, roots were collected
from transects through the plot. Fine-root data were obtained from
minirhizotron tubes6. Soils were collected under the canopies of the five most
abundant plant-cover types and in plant interspaces to 1 m in depth at 0.2m
increments. Soils were collected from two microsites, centre and edge of
aboveground vegetation canopies, under all cover types except Pleuraphis rigida
(a C4bunchgrass). Rock and soil volumes and soil bulk densities were measured
by excavation. Two square pits (0.5 ×0.5 m projected area) in each plot were
excavated to 1 m in 0.2 m increments. Samples were passed through 2 mm mesh
screens to separate rocks (>2 mm) from soils (2 mm). Rock volume was
quantified by measuring the amount of water displaced in a 20l plastic container.
Bulk densities were used to scale soil content measurements to an aerial basis.
The mean rock and soil volumes for all plots by depth were used to correct for
rock content. Plant C and N contents and stable isotope compositions were
determined at the Washington State University Stable Isotope Core Facility
(Pullman) using an ECS 4010 elemental analyser (Costech Analytical, Valencia)
interfaced with an isotope ratio mass spectrometer (Delta PlusXP, Thermo
Finnigan). Soil samples for organic C content and stable isotope composition
were treated with 3NH3PO4to remove carbonates before analysis.
Final harvest data were analysed at the level of the cover type to address
merging of data from the soil, aboveground and belowground samples from each
sample location (see Supplementary Information for complete description of the
statistical analysis methods). All C and N content data were log transformed for
analysis, whereas δ13C and δ15 N data were not transformed. Data were analysed
through a linear mixed-effects model with cover type and [CO2] treatment as
fixed effects, and ring within treatment as a random effect. Separate models were
fitted to each response variable to obtain pool and isotope estimates for each
ring-cover type combination. Change in the relative proportion of the cover types
was not detected during the experiment, so landscape-level estimates were
calculated by summing values for soil, root and aboveground estimates for each
cover type, yielding cover-type pool totals and computing weighted averages of
these cover type totals to obtain the plot-level totals. All statistical models were
simultaneously implemented in a Bayesian framework that allowed us to
propagate uncertainty in the cover type ×pool type ×ring estimates, yielding
accurate estimates (posterior means and credible intervals) of the ring, cover type
by ring and treatment-level total pool estimates. The fixed effect coefficients and
standard deviation terms were assigned relative standard priors and a
semi-informative prior was used for the ring random effect standard deviations
due to the small number of rings per treatment.
Received 24 June 2013; accepted 5 March 2014;
published online 6 April 2014
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The authors gratefully acknowledge grant support from the Department of Energy’s
Terrestrial Carbon Processes Program (DE-FG02-03ER63650, DEFG02-03ER63651) and
the NSF Ecosystem Studies Program (DEB-98-14358 and 02-12819). We also
acknowledge the DOE’s National Nuclear Security Administration for providing utility
services and undisturbed land at the Nevada National Security Site (formerly Nevada
Test Site) to conduct the FACE experiment. We also thank S. Chung at WSU for advice on
current emission inventories.
Author contributions
S.S. and R.N. conceived the study. R.E., S.S., R.N., T.C., B.N. and L.F. designed the final
harvest. R.E. and A.K. collected soils data, S.S., T.C. and B.N. collected aboveground
plant data and R.N. collected belowground plant data. L.F. and T.C. determined plot area
and species composition. B.H. provided elemental and isotopic analyses, and D.S. and
K.O. analysed the data. All authors wrote the paper.
Additional information
Supplementary information is available in the online version of the paper. Reprints and
permissions information is available online at
Correspondence and requests for materials should be addressed to R.D.E.
Competing financial interests
The authors declare no competing financial interests.
... The soils we use as an example in this work are from the Nevada Desert Free-air Carbon dioxide Enrichment Facility (NDFF), a long-term wholeecosystem elevated CO 2 experiment conducted in the Mojave Desert in North America. After 10 years of elevated CO 2 treatment, SOC stocks at the NDFF were reported to have increased by as much as 20-37% (Evans et al. 2014;Koyama et al. 2019). This conclusion assumes that the increase in SOC was due to accretion of organic carbon under the elevated CO 2 treatment. ...
... The two methods used for comparison are the direct addition of a liquid inorganic acid ("acid washing") and indirect treatment with volatized acid ("fumigation"). Acid washing has been used extensively on soils from the NDFF experiment (Jin and Evans 2007;Schaeffer et al. 2007;Evans et al. 2014;Koyama et al. 2019). This method is known to cause a loss of organic C during the application and removal of acid and that the amount of C lost varies among soils from different sites (Fernandes and Krull 2008). ...
... The NDFF study was an undisturbed, wholeecosystem experiment using standard FACE ring structure to increase atmospheric CO 2 concentrations to 550 ppm (Jordan et al. 1999). During the destructive sampling of this ten-year experiment, soil samples were taken from beneath the canopy of perennial vegetation covers to a depth of 0-20 cm (Evans et al. 2014). Within each plot, soils were collected from beneath the canopy of three individuals of five different plant species (Larrea tridentata, Lycium andersonii, Lycium palldium, Ambrosia dumosa, and Pleuraphis rigida) and from unvegetated interspace for a total of six cover types. ...
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Isolating soil organic carbon (SOC) from soil inorganic carbon (SIC) is necessary to quantify SOC stocks and understanding SOC dynamics. Inorganic acids are commonly used to remove SIC and several methods have been developed to minimize the impacts these acid treatments have on the residual SOC. Negative impacts on the SOC pool, such as underestimating SOC stocks, are caused in part due to differences in the amount and composition of the organic matter pool. The effects of SIC removal on SOC are often ignored within experimental studies based on the assumption that soils from the same site do not differ enough to impact results. However, some experimental treatments, such as elevated atmospheric CO2, change SOC pools in both concentration and composition. Therefore, SIC removal can introduce different biases in control and treatment soils that may differ by method. In this work, we compare two commonly used methods of SIC removal on a set of soil samples from the same elevated CO2 experiment. We use soils from the Nevada Desert Free Air Carbon dioxide Enrichment Facility to quantify how SIC removal with either acid washing or acid fumigation affect SOC in control and elevated CO2 plots. We then use the difference in SOC (%C and δ13C) between methods to infer changes in the SOC pool driven by the elevated CO2 treatment. Our results show that acid washing underestimates SOC relative to fumigation and that this difference is larger in soils from control CO2 plots than elevated CO2 plots. This may suggest that stabilization mechanisms sensitive to acidification, such as calcium bridging, are disrupted under elevated CO2 treatment and therefore are less susceptible to SOC loss during acid washing. Our results present future research avenues for exploring the effects of acidic organic compounds, such as root exudates, on SOC stability in alkaline soils.
... Soil organic carbon (SOC) content is a crucial indicator of soil fertility (Maikhuri and Rao, 2012), and is also essential for vegetation growth (Elser et al., 2000). Slight changes in SOC pools can have a profound effect on CO 2 levels in the air, which could cause positive land-atmosphere feedback (Evans et al., 2014). Scientists have considered on whether the desert ecosystem is a 'core carbon sink' (Evans et al., 2014;Li et al., 2015). ...
... Slight changes in SOC pools can have a profound effect on CO 2 levels in the air, which could cause positive land-atmosphere feedback (Evans et al., 2014). Scientists have considered on whether the desert ecosystem is a 'core carbon sink' (Evans et al., 2014;Li et al., 2015). Previously, the scholars believed that in extreme environments with relatively poor productivity (such as saline soil, Gobi, desert, etc.) in which, there was only one soil type and vegetation distribution was sparse (Li et al., 2003), scholars believed that the contributions of abiotic processes to soil respiration led to almost zero SOC density (SOCD) in deserts, which could be negligible . ...
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Accurate quantitative estimation of soil organic carbon (SOC) and its storage is crucial for ecosystem response over desert areas, and is an important component of understanding dryland climate change, which can effectively reflect the processes and regulatory mechanisms in the carbon cycle. Nevertheless, the relationship between carbon sources and carbon sinks in sandy soils is a hotly debated subject. In particular, how plants and environmental conditions interact to affect SOC remains unclear in sandy deserts. Here, we investigated 77 sites at depths of 0–100 cm (soil depth was divided by 0–5 cm, 5–10 cm, 10–20 cm,20–30 cm, 30–50 cm, 50–70 cm and 70–100 cm intervals), collected 1617 soil samples, and obtained the climatic conditions, vegetation types, and edaphic factors associated with the sampling sites. This study aims to determine whether there are divisions in the allocation strategies of SOC by various vegetation types, and to analyze the mechanisms of environmental factors on the soil carbon pool in sandy deserts. Our results found that (1) the mean value of SOC in the sandy desert was 2.19 g·kg−1, which differed significantly among different vegetation types (P
... Al respecto, expertos de la Nature Climate Change sostienen que las tierras áridas pueden aumentar la absorción de dióxido de carbono en la medida en la que se mantenga la cobertura vegetal de la zona. Por esta razón, estas zonas son foco de atención global (Evans et al., 2014;Romanyá et al., 2000), sobre todo si se considera que, si bien se afirma que los suelos de los climas semiáridos presentan mayor resistencia a la pérdida de carbono (Rovira y Vallejo, 2007), su resiliencia es menor, al ser vulnerables a los cambios climáticos. ...
... Si tenemos en cuenta que la principal característica de las tierras semiáridas es la alta temperatura con escasez de agua, unida a pH elevado, y que así se limita la productividad de las especies vegetales de forma drástica y se acelera la mineralización de la materia orgánica Evans et al., 2014), es de esperar que la acumulación de carbono en estos casos sea mínima y que cualquier ganancia de COS resulte significativa. Esto se ha constituido en foco de atención para fijar carbono en áreas que hasta la fecha eran despreciadas, un propósito para el cual, según los valores reportados en esta investigación, podría ser significativa la incorporación abono verde, así como mantener la cobertura vegetal (prados ornamentales). ...
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Suelo y cambio climático es un enfoque sistémico resultado de investigaciones en el área de edafología, orientado a contribuir a la comprensión y apropiación del recurso como base del sistema ecológico. Este texto contiene experiencias contextualizadas que permiten repensar el uso del suelo y hacer aportes en la transformación de las relaciones socioculturales que sustentan los saberes, a fin de orientar un mejor manejo del recurso, prioridad indispensable para sostener la vida, lo que conlleva a repensar alternativas que limiten los efectos de la actividad antrópica. Se evidencian conceptos con visión histórica del recurso, así como sus enfoques y funciones, y las causas y consecuencias de su degradación. Luego, se destaca la importancia de la materia orgánica, la cobertura vegetal y las prácticas de conservación. Se añaden apuntes de la importancia del agua en los sistemas, la nutrición vegetal como eje básico de seguridad alimentaria y la jerarquía del suelo en el fenómeno de cambio climático. Por último, se presentan estudios de casos desarrollados por los autores en campo, en los que se resalta la importancia de la cobertura vegetal para la conservación del suelo y la captura de carbono en el trópico seco; se caracteriza el sector agropecuario del Magdalena y la importancia de la conservación del suelo para mitigar el cambio climático, y se finaliza detallando el rol del suelo en la regulación hídrica y térmica en microcuencas del departamento.
... Not only are desert grasslands a significant barrier but they are also important for maintaining the ecological balance of arid desert areas and developing livestock farming [17]. In addition, these grasslands have high carbon sequestration potentials and are important areas for future CO2 fixation [18]. We conducted a field survey to understand the spatial distribution pattern of desert grassland biomass through measured data. ...
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Grassland biomass is a significant parameter for measuring grassland productivity and the ability to sequester carbon. Estimating desert grassland biomass using the best remote sensing inversion model is essential for understanding grassland carbon stocks in arid and semi-arid regions. The present study constructed an optimal inversion model of desert grassland biomass based on actual biomass measurement data and various remote-sensing product data. This model was used to analyze the spatiotemporal variation in desert grassland biomass and climate factor correlation in Xinjiang from 2000 to 2019. The results showed that (1) among the established inversion models of desert grasslands aboveground biomass (AGB), the exponential function model with the normalized differential vegetation index (NDVI) as the independent variable was the best. Furthermore, (2) the NDVI of desert grasslands in Xinjiang showed a highly significant increasing trend from 2000 to 2019 with a spatially concentrated distribution in the north and a more dispersed distribution in the south. In addition, (3) the average AGB value was 52.35 g·m−2 in Xinjiang from 2000 to 2019 and showed a spatial distribution with low values in the southeast and high values in the northwest. Moreover, (4) the low fluctuation in the coefficient of desert grassland variation accounted for 65.26% of overall AGB fluctuation (<0.10) from 2000 to 2019. Desert grassland AGB in most areas (88.65%) showed a significant increase over the last 20 years. Lastly, (5) the correlation between desert grassland precipitation and AGB was stronger than that between temperature and AGB from 2000 to 2019. This study provides a scientific basis and technical support for grassland livestock management and carbon storage assessments in Xinjiang.
... These observable chemical changes are emerging from what are complex systems in a matter of a few decades, suggestive of rapid ecosystem adjustments to changing environmental boundary conditions. Deserts soil C is not likely, as has been proposed, to become a sink for CO 2 (Evans et al., 2014). This research focuses on the warm and dry regions of the Earth, and suggests they may share in common is suggestive. ...
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The Mojave Desert has warmed >2°C, and aridified, in the past 50 years, making it a strategic location to investigate climate change impacts on arid soil processes. We resampled a climosequence of soils in the Mojave first sampled in 1973 and compared current soil properties to those 45+ years earlier. Radiocarbon changes revealed that C is cycling rapidly through the soils, particularly near the surface, with a temperature‐sensitive decomposition rate (Arrhenius Ea = 66 kJ/mol). Significant decreases in soil C/N ratios and increases in δ¹⁵N values occurred, suggestive of enhanced rates of soil C and N cycling and their losses. Covariation between changes in soil radiocarbon, δ¹³C, δ¹⁵N, and C/N point toward emerging chemical impacts on the coupled C and N cycles in response to climate change.
... Afforestation in arid and semiarid desert areas can increase soil carbon sequestration , alleviate atmospheric CO 2 concentration (Evans et al. 2014;Koyama et al. 2019) and improve the ecological environment (Beets and Beets 2020;He et al. 2010;Hong et al. 2020). The SOC and its liable organic carbon (LOC) fractions, including dissolved organic carbon (DOC), microbial biomass carbon (MBC) and readily oxidized organic carbon (ROOC), were obviously increase after afforestation . ...
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Afforestation is helpful to improve soil functions and increase soil organic carbon (SOC) sequestration in semiarid deserts. However, the fine-scale (around a single plant) spatial distribution of SOC and its liable organic carbon (LOC) fractions after afforestation in semiarid deserts are poorly understood. Pinus sylvestris and Salix psammophila afforested on shifting sandy land (Sland) were selected to quantify fine-scale (at 20, 80, 150 and 240 cm away from the trees) spatial distribution of SOC and its LOC fractions in the southeast edge of Mu Us Desert, China. The results showed that the afforested S. psammophila and P. sylvestris significantly increased SOC, total nitrogen, dissolved organic carbon, microbial biomass carbon and readily oxidized organic carbon (ROOC). At 20 cm distance, SOC storage of P. sylvestris was 27.21% higher than S. psammophila in 0–100 cm soil layers, and SOC storage of S. psammophila at 80 and 150 cm distances was 5.50% and 5.66% higher than P. sylvestris, respectively. Compared with Sland, SOC storage under S. psammophila and P. sylvestris significantly increased by 94.90%, 39.50%, 27.10% and 18.50% at 20, 80, 150 and 240 cm distance, respectively. ROOC accounted for 14.09% and 18.93% of SOC under S. psammophila and P. sylvestris, respectively. Our results suggest that afforestation can promote SOC accumulation at different distances from the plants, and that P. sylvestris allocates more organic matter to the closer soil compared with S. psammophila (<80 cm from the tree).
... Although the global C balance includes a large C sink in the terrestrial ecosystem, it is difficult to fully identify the potential of each terrestrial C sink and understand its mechanisms [122]. In a few recent findings, a part of the "missing C sink" could be explained by the removal of atmospheric CO2 through desert soil, capturing CO2 at a magnitude of approximately 100 g C m −2 yr −1 [123]. ...
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Soil organic carbon (SOC) pool has been extensively studied in the carbon (C) cycling of terrestrial ecosystems. In dryland regions, however, soil inorganic carbon (SIC) has received increasing attention due to the high accumulation of SIC in arid soils contributed by its high temperature, low soil moisture, less vegetation, high salinity, and poor microbial activities. SIC storage in dryland soils is a complex process comprising multiple interactions of several factors such as climate, land use types, farm management practices, irrigation, inherent soil properties, soil biotic factors, etc. In addition, soil C studies in deeper layers of drylands have opened-up several study aspects on SIC storage. This review explains the mechanisms of SIC formation in dryland soils and critically discusses the SIC content in arid and semi-arid soils as compared to SOC. It also addresses the complex relationship between SIC and SOC in dryland soils. This review gives an overview of how climate change and anthropogenic management of soil might affect the SIC storage in dryland soils. Dryland soils could be an efficient sink in C sequestration through the formation of secondary carbonates. The review highlights the importance of an in-depth understanding of the C cycle in arid soils and emphasizes that SIC dynamics must be looked into broader perspective vis-à-vis C sequestration and climate change mitigation.
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La captura de carbono es un proceso fundamental que regula el clima y permite contrarrestar el calentamiento global. Este estudio estimó las reservas de carbono en las Lomas de Amancaes, un ecosistema del desierto sudamericano en Lima (Perú). Se tomaron muestras de la biomasa vegetal aérea y del suelo (0 - 20 cm de profundidad), midiendo el carbono almacenado en ambos compartimentos. Los resultados indicaron que la cantidad de carbono almacenado (CA) es de 8 593,97 tC (39,29 tC/ha); el CA fue mayor en el suelo (37,85 tC/ha) que en la biomasa aérea (1,44 tC/ha); al comparar el CA entre rangos altitudinales (300 - 750 m s.n.m.), no se encontraron diferencias significativas (p>0,05). Al compararlo con otros ecosistemas del desierto costero peruano, el CA de las Lomas de Amancaes es mayor a lo encontrado en tillandsiales (3,6 tC/ha), pero fue menor a los reportado para algunos humedales (38,47-305,37 tC/ha). El CA del área de estudio se asemeja a las reservas de varios ecosistemas desérticos del mundo (el valor oscila entre 0,15 - 45,55 tC/ha en desiertos de África, Zona de transición Sahel, Desierto de Negev, Desiertos en China, Desierto Mojave, Cuenca de La Paz y Los Planes) con algunas excepciones (como los desiertos templados de Asia Central, Sabana de Acacia y Túnez que cuentan con un CA = 40,40 -159,2 tC/ha). Estos resultados representan una de las primeras estimaciones de las reservas de carbono en las lomas del desierto del Pacífico Sudamericano y brindan datos valiosos para su conservación.
The increasing of atmospheric carbon dioxide (CO2) has a greater impact on soil microbial diversity and related soil nutrient dynamics under different ecology. In our study, a global database of 572 observations from 202 research publications analysed to explore the impacts of increased atmospheric CO2 on soil microbial diversities. The soil microbial biomass carbon (MBC), structural (microbial populations), and functional (enzymatic activities) microbial diversities were analysed across 22 nations and 108 crops (including forest, grassland and C3 plants). The impact of three elevated CO2 (eCO2) concentrations i.e., <25%, 25–50% and >50% over ambient in three-time scale (1970–1989, 1990–2009 and 2010–2020) and two region (tropical and temperate) on the above parameters were studied. Higher MBC contents were found under eCO2 level (>50%) followed by eCO2 level 25–50% and <25% over ambient in C3 plants and forest ecology, however, in grassland the average MBC content was higher under eCO2 level 25–50%. Soil enzymatic activities were higher under eCO2 (25–50%) than other elevated CO2 conditions in the forest and C3 plants, whereas in grasslands, the enzymatic activities decreased with an increase in CO2 concentrations. These findings suggested that grassland was more sensitive to elevated CO2 as such compared to the forest and C3 plants. Both the bacterial and fungal populations were higher only up to eCO2 level (25–50% over ambient) in all the vegetations. So, higher microbial populations and soil enzymatic activities were noticed up to 50% elevation of CO2 over ambient conditions irrespective of the vegetation and region indicating higher belowground soil activities. Therefore, the findings suggested that there would be higher belowground soil activities in increased CO2 levels (anticipated climate change scenario) in agriculture and forest crop up to a certain threshold elevation of CO2 which needs better water and nutrient management for getting sustainable yield. The finding also suggested region and vegetation-specific (crop/forest/grassland) management options are necessary for fetching advantage of CO2 fertilization and to tackle the abiotic stress management of crops.
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Endpoint impacts related to the transformation of land—including that related to energy infrastructure—have yet to be fully quantified and understood in life cycle assessment (LCA). Concentrated solar power (CSP) which generates electricity by using mirrors to concentrate incoming shortwave radiation onto a receiver, may serve as an alternate source of reliable baseload power in the coming years. As of 2019 (baseline year of the study), the United States (U.S.) had 1.7 GW of installed capacity across a total of eight CSP sites. In this study, we (1) develop an empirical, spatially explicit methodology to categorize physical elements embodied in energy infrastructure using a LCA approach and manual image annotation, (2) use this categorization scheme to quantify land- and ecosystem service-related endpoint impacts, notably potential losses in soil carbon, owing to energy infrastructure development and as a function of electricity generated (i.e., megawatt-hour, MWh); and (3) validate and apply this method to CSP power plants within the U.S. In the Western U.S., CSP projects are sited in Arizona, California, and Nevada. Project infrastructure can be disaggregated into the following physical elements: mirrors (“heliostats”), generators, internal roads, external roads, substations, and water bodies. Of these elements, results reveal that mirrors are the most land intensive element of CSP infrastructure (>90%). Median land transformation and capacity-based land-use efficiency are 0.4 (range of 0.3–6.8) m2/MWh and 40 (range of 11–48) W/m2, respectively. Soil grading and other site preparation disturbances may result in the release of both organic and inorganic carbon—the latter representing the majority stocks in deeper caliche layers—thus leading to potentially significant losses of stored carbon. We estimate three scenarios of soil carbon loss into the atmosphere across 30 years, based on land transformation in m2 per megawatt-hour (m2/MWh) and carbon stock in kilograms of carbon per megawatt-hour (kg C/MWh). Results reveal that potential belowground CO2 released may range from 7 to 137% of total life cycle CO2 emissions. While this study takes a simplistic approach to estimating loss of carbon, the broad methodology provides a valuable baseline for improving comparative analyses of land-related endpoint impacts across energy technologies and other product systems.
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Many terrestrial surfaces, including soils, rocks and plants, are covered by photoautotrophic communities, capable of synthesizing their own food from inorganic substances using sunlight as an energy source . These communities, known as cryptogamic covers, comprise variable proportions of cyanobacteria, algae, fungi, lichens and bryophytes, and are able to fix carbon dioxide and nitrogen from the atmosphere. However, their influence on global and regional biogeochemical cycling of carbon and nitrogen has not yet been assessed. Here, we analyse previously published data on the spatial coverage of cryptogamic communities, and the associated fluxes of carbon and nitrogen, in different types of ecosystem across the globe. We estimate that globally, cryptogamic covers take up around 3.9 Pg carbon per year, corresponding to around 7% of net primary production by terrestrial vegetation. We derive a nitrogen uptake by cryptogamic covers of around 49 Tg per year, suggesting that cryptogamic covers account for nearly half of the biological nitrogen fixation on land. We suggest that nitrogen fixation by cryptogamic covers may be crucial for carbon sequestration by plants.
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1] We examined the effects of elevated CO 2 on soil nitrogen (N) dynamics in the Mojave Desert by measuring plant N isotope composition (d 15 N), soil microbial biomass N, soil respiration, resin-available N, and C and N dynamics during soil incubations. With elevated CO 2 , foliage of Larrea tridentata and Krameria erecta had mean d 15 N 2.1 and 1.1% higher with elevated CO 2 , respectively, and elevated CO 2 increased microbial biomass N in dry soils under a perennial grass (6.8 ± 1.4 versus 3.7 ± 0.3 mg/g). Elevated CO 2 significantly increased cumulative resin-available N in the field by 12%, driven by available soil moisture. Rates of soil respiration with elevated CO 2 were sporadically higher under Pleuraphis and Larrea. Soils under shrubs had greater potential net N mineralization (102.6 ± 24.2 mg/g) than soils under grasses and in plant interspaces (40.0 ± 9.69 mg/g). Rates of recalcitrant N turnover in soil incubations were related to soil substrate availability. Results indicate that shifts in soil microbial structure and/or activity may occur with elevated CO 2 and may result in increases in plant-available N when soil moisture is available.
This book begins with the physical and biological characterization of the four North American deserts and a description of the primary adaptations of plants to environmental stress. In the following chapters the authors present case studies of key species representing dominant growth forms of the North American deserts, and provide an up-to-date and comprehensive review of the major patterns of adaptations in desert plants. One chapter is devoted to several important exotic plants that have invaded North American deserts. The book ends with a synthesis of the adaptations and resource requirements of North American desert plants. Further, it addresses how desert plants may respond to global climate change.
As the largest pool of terrestrial organic carbon, soils interact strongly with atmospheric composition, climate, and land cover change. Our capacity to predict and ameliorate the consequences of global change depends in part on a better understanding of the distributions and controls of soil organic carbon (SOC) and how vegetation change may affect SOC distributions with depth. The goals of this paper are (1) to examine the association of SOC content with climate and soil texture at different soil depths; (2) to test the hypothesis that vegetation type, through patterns of allocation, is a dominant control on the vertical distribution of SOC; and (3) to estimate global SOC storage to 3 m, including an analysis of the potential effects of vegetation change on soil carbon storage. We based our analysis on >2700 soil profiles in three global databases supplemented with data for climate, vegetation, and land use. The analysis focused on mineral soil layers. Plant functional types significantly affected the v...
[1] Satellite observations reveal a greening of the globe over recent decades. The role in this greening of the “CO2 fertilization” effect—the enhancement of photosynthesis due to rising CO2 levels—is yet to be established. The direct CO2 effect on vegetation should be most clearly expressed in warm, arid environments where water is the dominant limit to vegetation growth. Using gas exchange theory, we predict that the 14% increase in atmospheric CO2 (1982–2010) led to a 5 to 10% increase in green foliage cover in warm, arid environments. Satellite observations, analyzed to remove the effect of variations in precipitation, show that cover across these environments has increased by 11%. Our results confirm that the anticipated CO2 fertilization effect is occurring alongside ongoing anthropogenic perturbations to the carbon cycle and that the fertilization effect is now a significant land surface process.
Extensive sampling shows high variability in nitrate concentration within profiles of Mojave Desert soils. This high variability greatly complicates studies of desert soil N and its ecological role. Patterns in nitrate distribution suggest effects of litter decomposition under shrubs, surface leaching in bare areas, and plant uptake in the root zone. Two mechanisms proposed to explain high concentrations found at seemingly random depths are concentration at drying fronts and distribution along water potential gradients.
The decomposition and transformation of above- and below-ground plant detritus (litter) is the main process by which soil organic matter (SOM) is formed. Yet, research on litter decay and SOM formation has been largely uncoupled, failing to provide an effective nexus between these two fundamental processes for carbon (C) and nitrogen (N) cycling and storage. We present the current understanding of the importance of microbial substrate use efficiency and C and N allocation in controlling the proportion of plant-derived C and N that is incorporated into SOM, and of soil matrix interactions in controlling SOM stabilization. We synthesize this understanding into the Microbial Efficiency-Matrix Stabilization (MEMS) framework. This framework leads to the hypothesis that labile plant constituents are the dominant source of microbial products, relative to input rates, because they are utilized more efficiently by microbes. These microbial products of decomposition would thus become the main precursors of stable SOM by promoting aggregation and through strong chemical bonding to the mineral soil matrix.
To realistically simulate climate feedbacks from the land surface to the atmosphere, models must replicate the responses of plants to environmental changes. Several processes, operating at various scales, cause the responses of photosynthesis and plant respiration to temperature and CO2 to change over time of exposure to new or changing environmental conditions. Here, we review the latest empirical evidence that short-term responses of plant carbon exchange rates to temperature and CO2 are modified by plant photosynthetic and respiratory acclimation as well as biogeochemical feedbacks. We assess the frequency with which these responses have been incorporated into vegetation models, and highlight recently designed algorithms that can facilitate their incorporation. Few models currently include representations of the long-term plant responses that have been recorded by empirical studies, likely because these responses are still poorly understood at scales relevant for models. Studies show that, at a regional scale, simulated carbon flux between the atmosphere and vegetation can dramatically differ between versions of models that do and do not include acclimation. However, the realism of these results is difficult to evaluate, as algorithm development is still in an early stage, and a limited number of data are available. We provide a series of recommendations that suggest how a combination of empirical and modeling studies can produce mechanistic algorithms that will realistically simulate longer term responses within global-scale models.
We examined N cycling processes in desert soils exposed to elevated CO 2 to better understand how some features of aridland soil N and C cycling may respond to an altered atmospheric composition. We measured rates of denitrification, potential denitrification, N 2 O fluxes, NH 3 volatilization, and net mineralization in an intact Mojave Desert ecosystem with elevated CO 2 (Free Air Carbon Enrichment technology) over 2 y. All measurements were performed on soil under four different cover types: Larrea tridentata; Lycium spp.; Pleuraphis rigida; and plant interspaces. The mean rate of denitrification was 161 ^ 96 mg N m 22 d 21 . Field fluxes of N 2 O occurred sporadically, with a mean of 30 ^ 20 mg N m 22 d 21 . Rates of NH 3 volatilization experienced less variability than did N 2 O fluxes, with a mean of 120 ^ 45 mg N m 22 d 21 . Mean potential denitrification enzyme activity (DEA) was 146 ^ 8 mg N m 22 d 21 . Rates of net mineralization were highest in soil under L. tridentata and Lycium spp. (398 ^ 108 mg N m 22 d 21) and lowest in the plant interspaces (129 ^ 28 mg N m 22 d 21). There was no effect of elevated CO 2 on N 2 O fluxes or mineralization rates. There was a 39% increase in NH 3 volatilization with elevated CO 2 during March 2000. Potential DEA increased by 193% with elevated CO 2 in October 1999 and decreased by 45% in March 2001. These results suggest that NH 3 volatilization may be a more important component of aridland gaseous N emissions than previously thought, and that the potential for high DEA does not necessarily induce large fluxes of N 2 O under natural conditions, especially in aridlands where rainfall primarily occurs in winter when soil temperatures can limit microbial activity. This study also suggests that the effects of elevated CO 2 on soil microbial activity may not be consistent for all seasons. q