Heterotrophic Respiration (heterotrophic + respiration)

Distribution by Scientific Domains


Selected Abstracts


Tree root and soil heterotrophic respiration as revealed by girdling of boreal Scots pine forest: extending observations beyond the first year

PLANT CELL & ENVIRONMENT, Issue 8 2003
BHUPINDERPAL-SINGH
ABSTRACT Limitations in available techniques to separate autotrophic (root) and soil heterotrophic respiration have hampered the understanding of forest C cycling. The former is here defined as respiration by roots, their associated mycorrhizal fungi and other micro-organisms in the rhizosphere directly dependent on labile C compounds leaked from roots. In order to separate the autotrophic and heterotrophic components of soil respiration, all Scots pine trees in 900 m2 plots were girdled to instantaneously terminate the supply of current photosynthates from the tree canopy to roots. Högberg et al. (Nature 411, 789,792, 2001) reported that autotrophic activity contributed up to 56% of total soil respiration during the first summer of this experiment. They also found that mobilization of stored starch (and likely also sugars) in roots after girdling caused an increased apparent heterotrophic respiration on girdled plots. Herein a transient increase in the ,13C of soil CO2 efflux after girdling, thought to be due to decomposition of 13C-enriched ectomycorrhizal mycelium and root starch and sugar reserves, is reported. In the second year after girdling, when starch reserves of girdled tree roots were exhausted, calculated root respiration increased up to 65% of total soil CO2 efflux. It is suggested that this estimate of its contribution to soil respiration is more precise than the previous based on one year of observation. Heterotrophic respiration declined in response to a 20-day-long 6 °C decline in soil temperature during the second summer, whereas root respiration did not decline. This did not support the idea that root respiration should be more sensitive to variations in soil temperature. It is suggested that above-ground photosynthetic activity and allocation patterns of recent photosynthates to roots should be considered in models of responses of forest C balances to global climate change. [source]


Metagenomic and stable isotopic analyses of modern freshwater microbialites in Cuatro Ciénegas, Mexico

ENVIRONMENTAL MICROBIOLOGY, Issue 1 2009
Mya Breitbart
Summary Ancient biologically mediated sedimentary carbonate deposits, including stromatolites and other microbialites, provide insight into environmental conditions on early Earth. The primary limitation to interpreting these records is our lack of understanding regarding microbial processes and the preservation of geochemical signatures in contemporary microbialite systems. Using a combination of metagenomic sequencing and isotopic analyses, this study describes the identity, metabolic potential and chemical processes of microbial communities from living microbialites from Cuatro Ciénegas, Mexico. Metagenomic sequencing revealed a diverse, redox-dependent microbial community associated with the microbialites. The microbialite community is distinct from other marine and freshwater microbial communities, and demonstrates extensive environmental adaptation. The microbialite metagenomes contain a large number of genes involved in the production of exopolymeric substances and the formation of biofilms, creating a complex, spatially structured environment. In addition to the spatial complexity of the biofilm, microbial activity is tightly controlled by sensory and regulatory systems, which allow for coordination of autotrophic and heterotrophic processes. Isotopic measurements of the intracrystalline organic matter demonstrate the importance of heterotrophic respiration of photoautotrophic biomass in the precipitation of calcium carbonate. The genomic and stable isotopic data presented here significantly enhance our evolving knowledge of contemporary biomineralization processes, and are directly applicable to studies of ancient microbialites. [source]


Molecular investigations into a globally important carbon pool: permafrost-protected carbon in Alaskan soils

GLOBAL CHANGE BIOLOGY, Issue 9 2010
M. P. WALDROP
Abstract The fate of carbon (C) contained within permafrost in boreal forest environments is an important consideration for the current and future carbon cycle as soils warm in northern latitudes. Currently, little is known about the microbiology or chemistry of permafrost soils that may affect its decomposition once soils thaw. We tested the hypothesis that low microbial abundances and activities in permafrost soils limit decomposition rates compared with active layer soils. We examined active layer and permafrost soils near Fairbanks, AK, the Yukon River, and the Arctic Circle. Soils were incubated in the lab under aerobic and anaerobic conditions. Gas fluxes at ,5 and 5 °C were measured to calculate temperature response quotients (Q10). The Q10 was lower in permafrost soils (average 2.7) compared with active layer soils (average 7.5). Soil nutrients, leachable dissolved organic C (DOC) quality and quantity, and nuclear magnetic resonance spectroscopy of the soils revealed that the organic matter within permafrost soils is as labile, or even more so, than surface soils. Microbial abundances (fungi, bacteria, and subgroups: methanogens and Basidiomycetes) and exoenzyme activities involved in decomposition were lower in permafrost soils compared with active layer soils, which, together with the chemical data, supports the reduced Q10 values. CH4 fluxes were correlated with methanogen abundance and the highest CH4 production came from active layer soils. These results suggest that permafrost soils have high inherent decomposability, but low microbial abundances and activities reduce the temperature sensitivity of C fluxes. Despite these inherent limitations, however, respiration per unit soil C was higher in permafrost soils compared with active layer soils, suggesting that decomposition and heterotrophic respiration may contribute to a positive feedback to warming of this eco region. [source]


The response of heterotrophic activity and carbon cycling to nitrogen additions and warming in two tropical soils

GLOBAL CHANGE BIOLOGY, Issue 9 2010
DANIELA F. CUSACK
Abstract Nitrogen (N) deposition is projected to increase significantly in tropical regions in the coming decades, where changes in climate are also expected. Additional N and warming each have the potential to alter soil carbon (C) storage via changes in microbial activity and decomposition, but little is known about the combined effects of these global change factors in tropical ecosystems. In this study, we used controlled laboratory incubations of soils from a long-term N fertilization experiment to explore the sensitivity of soil C to increased N in two N-rich tropical forests. We found that fertilization corresponded to significant increases in bulk soil C concentrations, and decreases in C loss via heterotrophic respiration (P< 0.05). The increase in soil C was not uniform among C pools, however. The active soil C pool decomposed faster with fertilization, while slowly cycling C pools had longer turnover times. These changes in soil C cycling with N additions corresponded to the responses of two groups of microbial extracellular enzymes. Smaller active C pools corresponded to increased hydrolytic enzyme activities; longer turnover times of the slowly cycling C pool corresponded to reduced activity of oxidative enzymes, which degrade more complex C compounds, in fertilized soils. Warming increased soil respiration overall, and N fertilization significantly increased the temperature sensitivity of slowly cycling C pools in both forests. In the lower elevation forest, respired CO2 from fertilized cores had significantly higher ,14C values than control soils, indicating losses of relatively older soil C. These results indicate that soil C storage is sensitive to both N deposition and warming in N-rich tropical soils, with interacting effects of these two global change factors. N deposition has the potential to increase total soil C stocks in tropical forests, but the long-term stability of this added C will likely depend on future changes in temperature. [source]


The European carbon balance.

GLOBAL CHANGE BIOLOGY, Issue 5 2010
Part 3: forests
Abstract We present a new synthesis, based on a suite of complementary approaches, of the primary production and carbon sink in forests of the 25 member states of the European Union (EU-25) during 1990,2005. Upscaled terrestrial observations and model-based approaches agree within 25% on the mean net primary production (NPP) of forests, i.e. 520±75 g C m,2 yr,1 over a forest area of 1.32 × 106 km2 to 1.55 × 106 km2 (EU-25). New estimates of the mean long-term carbon forest sink (net biome production, NBP) of EU-25 forests amounts 75±20 g C m,2 yr,1. The ratio of NBP to NPP is 0.15±0.05. Estimates of the fate of the carbon inputs via NPP in wood harvests, forest fires, losses to lakes and rivers and heterotrophic respiration remain uncertain, which explains the considerable uncertainty of NBP. Inventory-based assessments and assumptions suggest that 29±15% of the NBP (i.e., 22 g C m,2 yr,1) is sequestered in the forest soil, but large uncertainty remains concerning the drivers and future of the soil organic carbon. The remaining 71±15% of the NBP (i.e., 53 g C m,2 yr,1) is realized as woody biomass increments. In the EU-25, the relatively large forest NBP is thought to be the result of a sustained difference between NPP, which increased during the past decades, and carbon losses primarily by harvest and heterotrophic respiration, which increased less over the same period. [source]


Effects of soil frost on soil respiration and its radiocarbon signature in a Norway spruce forest soil

GLOBAL CHANGE BIOLOGY, Issue 4 2009
JAN MUHR
Abstract Apart from a general increase of mean annual air temperature, climate models predict a regional increase of the frequency and intensity of soil frost with possibly strong effects on C cycling of soils. In this study, we induced mild soil frost (up to ,5 °C in a depth of 5 cm below surface) in a Norway spruce forest soil by removing the natural snow cover in the winter of 2005/2006. Soil frost lasted from January to April 2006 and was detected down to 15 cm depth. Soil frost effectively reduced soil respiration in the snow removal plots in comparison to undisturbed control plots. On an annual basis 6.2 t C ha,1 a,1 were emitted in the control plots compared with 5.1 t C ha,1 a,1 in the snow removal plots. Only 14% of this difference was attributed to reduced soil respiration during the soil frost period itself, whereas 63% of this difference originated from differences during the summer of 2006. Radiocarbon (,14C) signature of CO2 revealed a considerable reduction of heterotrophic respiration on the snow removal plots, only partly compensated for by a slight increase of rhizosphere respiration. Similar CO2 concentrations in the uppermost mineral horizons of both treatments indicate that differences between the treatments originated from the organic horizons. Extremely low water contents between June and October of 2006 may have inhibited the recovery of the heterotrophic organisms from the frost period, thereby enhancing the differences between the control and snow removal plots. We conclude that soil frost triggered a change in the composition of the microbial community, leading to an increased sensitivity of heterotrophic respiration to summer drought. A CO2 pulse during thawing, such as described for arable soils several times throughout the literature, with the potential to partly compensate for reduced soil respiration during soil frost, appears to be lacking for this soil. Our results from this experiment indicate that soil frost reduces C emission from forest soils, whereas mild winters may enhance C losses from forest soils. [source]


Modeled interactive effects of precipitation, temperature, and [CO2] on ecosystem carbon and water dynamics in different climatic zones

GLOBAL CHANGE BIOLOGY, Issue 9 2008
YIQI LUO
Abstract Interactive effects of multiple global change factors on ecosystem processes are complex. It is relatively expensive to explore those interactions in manipulative experiments. We conducted a modeling analysis to identify potentially important interactions and to stimulate hypothesis formulation for experimental research. Four models were used to quantify interactive effects of climate warming (T), altered precipitation amounts [doubled (DP) and halved (HP)] and seasonality (SP, moving precipitation in July and August to January and February to create summer drought), and elevated [CO2] (C) on net primary production (NPP), heterotrophic respiration (Rh), net ecosystem production (NEP), transpiration, and runoff. We examined those responses in seven ecosystems, including forests, grasslands, and heathlands in different climate zones. The modeling analysis showed that none of the three-way interactions among T, C, and altered precipitation was substantial for either carbon or water processes, nor consistent among the seven ecosystems. However, two-way interactive effects on NPP, Rh, and NEP were generally positive (i.e. amplification of one factor's effect by the other factor) between T and C or between T and DP. A negative interaction (i.e. depression of one factor's effect by the other factor) occurred for simulated NPP between T and HP. The interactive effects on runoff were positive between T and HP. Four pairs of two-way interactive effects on plant transpiration were positive and two pairs negative. In addition, wet sites generally had smaller relative changes in NPP, Rh, runoff, and transpiration but larger absolute changes in NEP than dry sites in response to the treatments. The modeling results suggest new hypotheses to be tested in multifactor global change experiments. Likewise, more experimental evidence is needed for the further improvement of ecosystem models in order to adequately simulate complex interactive processes. [source]


Partitioning sources of soil respiration in boreal black spruce forest using radiocarbon

GLOBAL CHANGE BIOLOGY, Issue 2 2006
Edward A.G. Schuur
Abstract Separating ecosystem and soil respiration into autotrophic and heterotrophic component sources is necessary for understanding how the net ecosystem exchange of carbon (C) will respond to current and future changes in climate and vegetation. Here, we use an isotope mass balance method based on radiocarbon to partition respiration sources in three mature black spruce forest stands in Alaska. Radiocarbon (,14C) signatures of respired C reflect the age of substrate C and can be used to differentiate source pools within ecosystems. Recently-fixed C that fuels plant or microbial metabolism has ,14C values close to that of current atmospheric CO2, while C respired from litter and soil organic matter decomposition will reflect the longer residence time of C in plant and soil C pools. Contrary to our expectations, the ,14C of C respired by recently excised black spruce roots averaged 14, greater than expected for recently fixed photosynthetic products, indicating that some portion of the C fueling root metabolism was derived from C storage pools with turnover times of at least several years. The ,14C values of C respired by heterotrophs in laboratory incubations of soil organic matter averaged 60, higher than the contemporary atmosphere ,14CO2, indicating that the major contributors to decomposition are derived from a combination of sources consistent with a mean residence time of up to a decade. Comparing autotrophic and heterotrophic ,14C end members with measurements of the ,14C of total soil respiration, we calculated that 47,63% of soil CO2 emissions were derived from heterotrophic respiration across all three sites. Our limited temporal sampling also observed no significant differences in the partitioning of soil respiration in the early season compared with the late season. Future work is needed to address the reasons for high ,14C values in root respiration and issues of whether this method fully captures the contribution of rhizosphere respiration. [source]


Comparing and evaluating process-based ecosystem model predictions of carbon and water fluxes in major European forest biomes

GLOBAL CHANGE BIOLOGY, Issue 12 2005
Pablo Morales
Abstract Process-based models can be classified into: (a) terrestrial biogeochemical models (TBMs), which simulate fluxes of carbon, water and nitrogen coupled within terrestrial ecosystems, and (b) dynamic global vegetation models (DGVMs), which further couple these processes interactively with changes in slow ecosystem processes depending on resource competition, establishment, growth and mortality of different vegetation types. In this study, four models , RHESSys, GOTILWA+, LPJ-GUESS and ORCHIDEE , representing both modelling approaches were compared and evaluated against benchmarks provided by eddy-covariance measurements of carbon and water fluxes at 15 forest sites within the EUROFLUX project. Overall, model-measurement agreement varied greatly among sites. Both modelling approaches have somewhat different strengths, but there was no model among those tested that universally performed well on the two variables evaluated. Small biases and errors suggest that ORCHIDEE and GOTILWA+ performed better in simulating carbon fluxes while LPJ-GUESS and RHESSys did a better job in simulating water fluxes. In general, the models can be considered as useful tools for studies of climate change impacts on carbon and water cycling in forests. However, the various sources of variation among models simulations and between models simulations and observed data described in this study place some constraints on the results and to some extent reduce their reliability. For example, at most sites in the Mediterranean region all models generally performed poorly most likely because of problems in the representation of water stress effects on both carbon uptake by photosynthesis and carbon release by heterotrophic respiration (Rh). The use of flux data as a means of assessing key processes in models of this type is an important approach to improving model performance. Our results show that the models have value but that further model development is necessary with regard to the representation of the some of the key ecosystem processes. [source]


Global climate change and soil carbon stocks; predictions from two contrasting models for the turnover of organic carbon in soil

GLOBAL CHANGE BIOLOGY, Issue 1 2005
Chris Jones
Abstract Enhanced release of CO2 to the atmosphere from soil organic carbon as a result of increased temperatures may lead to a positive feedback between climate change and the carbon cycle, resulting in much higher CO2 levels and accelerated global warming. However, the magnitude of this effect is uncertain and critically dependent on how the decomposition of soil organic C (heterotrophic respiration) responds to changes in climate. Previous studies with the Hadley Centre's coupled climate,carbon cycle general circulation model (GCM) (HadCM3LC) used a simple, single-pool soil carbon model to simulate the response. Here we present results from numerical simulations that use the more sophisticated ,RothC' multipool soil carbon model, driven with the same climate data. The results show strong similarities in the behaviour of the two models, although RothC tends to simulate slightly smaller changes in global soil carbon stocks for the same forcing. RothC simulates global soil carbon stocks decreasing by 54 Gt C by 2100 in a climate change simulation compared with an 80 Gt C decrease in HadCM3LC. The multipool carbon dynamics of RothC cause it to exhibit a slower magnitude of transient response to both increased organic carbon inputs and changes in climate. We conclude that the projection of a positive feedback between climate and carbon cycle is robust, but the magnitude of the feedback is dependent on the structure of the soil carbon model. [source]


Modelling carbon balances of coastal arctic tundra under changing climate

GLOBAL CHANGE BIOLOGY, Issue 1 2003
Robert F. Grant
Abstract Rising air temperatures are believed to be hastening heterotrophic respiration (Rh) in arctic tundra ecosystems, which could lead to substantial losses of soil carbon (C). In order to improve confidence in predicting the likelihood of such loss, the comprehensive ecosystem model ecosys was first tested with carbon dioxide (CO2) fluxes measured over a tundra soil in a growth chamber under various temperatures and soil-water contents (,). The model was then tested with CO2 and energy fluxes measured over a coastal arctic tundra near Barrow, Alaska, under a range of weather conditions during 1998,1999. A rise in growth chamber temperature from 7 to 15 °C caused large, but commensurate, rises in respiration and CO2 fixation, and so no significant effect on net CO2 exchange was modelled or measured. An increase in growth chamber , from field capacity to saturation caused substantial reductions in respiration but not in CO2 fixation, and so an increase in net CO2 exchange was modelled and measured. Long daylengths over the coastal tundra at Barrow caused an almost continuous C sink to be modelled and measured during most of July (2,4 g C m,2 d,1), but shortening daylengths and declining air temperatures caused a C source to be modelled and measured by early September (,1 g C m,2 d,1). At an annual time scale, the coastal tundra was modelled to be a small C sink (4 g C m,2 y,1) during 1998 when average air temperatures were 4 °C above normal, and a larger C sink (16 g C m,2 y,1) during 1999 when air temperatures were close to long-term normals. During 100 years under rising atmospheric CO2 concentration (Ca), air temperature and precipitation driven by the IS92a emissions scenario, modelled Rh rose commensurately with net primary productivity (NPP) under both current and elevated rates of atmospheric nitrogen (N) deposition, so that changes in soil C remained small. However, methane (CH4) emissions were predicted to rise substantially in coastal tundra with IS92a-driven climate change (from ,20 to ,40 g C m,2 y,1), causing a substantial increase in the emission of CO2 equivalents. If the rate of temperature increase hypothesized in the IS92a emissions scenario had been raised by 50%, substantial losses of soil C (,1 kg C m,2) would have been modelled after 100 years, including additional emissions of CH4. [source]


Carbon storage and fluxes in ponderosa pine forests at different developmental stages

GLOBAL CHANGE BIOLOGY, Issue 7 2001
B.E. Law
Abstract We compared carbon storage and fluxes in young and old ponderosa pine stands in Oregon, including plant and soil storage, net primary productivity, respiration fluxes, eddy flux estimates of net ecosystem exchange (NEE), and Biome-BGC simulations of fluxes. The young forest (Y site) was previously an old-growth ponderosa pine forest that had been clearcut in 1978, and the old forest (O site), which has never been logged, consists of two primary age classes (50 and 250 years old). Total ecosystem carbon content (vegetation, detritus and soil) of the O forest was about twice that of the Y site (21 vs. 10 kg C m,2 ground), and significantly more of the total is stored in living vegetation at the O site (61% vs. 15%). Ecosystem respiration (Re) was higher at the O site (1014 vs. 835 g C m,2 year,1), and it was largely from soils at both sites (77% of Re). The biological data show that above-ground net primary productivity (ANPP), NPP and net ecosystem production (NEP) were greater at the O site than the Y site. Monte Carlo estimates of NEP show that the young site is a source of CO2 to the atmosphere, and is significantly lower than NEP(O) by c. 100 g C m,2 year,1. Eddy covariance measurements also show that the O site was a stronger sink for CO2 than the Y site. Across a 15-km swath in the region, ANPP ranged from 76 g C m,2 year,1 at the Y site to 236 g C m,2 year,1 (overall mean 158 ± 14 g C m,2 year,1). The lowest ANPP values were for the youngest and oldest stands, but there was a large range of ANPP for mature stands. Carbon, water and nitrogen cycle simulations with the Biome-BGC model suggest that disturbance type and frequency, time since disturbance, age-dependent changes in below-ground allocation, and increasing atmospheric concentration of CO2 all exert significant control on the net ecosystem exchange of carbon at the two sites. Model estimates of major carbon flux components agree with budget-based observations to within ±,20%, with larger differences for NEP and for several storage terms. Simulations showed the period of regrowth required to replace carbon lost during and after a stand-replacing fire (O) or a clearcut (Y) to be between 50 and 100 years. In both cases, simulations showed a shift from net carbon source to net sink (on an annual basis) 10,20 years after disturbance. These results suggest that the net ecosystem production of young stands may be low because heterotrophic respiration, particularly from soils, is higher than the NPP of the regrowth. The amount of carbon stored in long-term pools (biomass and soils) in addition to short-term fluxes has important implications for management of forests in the Pacific North-west for carbon sequestration. [source]


Tree root and soil heterotrophic respiration as revealed by girdling of boreal Scots pine forest: extending observations beyond the first year

PLANT CELL & ENVIRONMENT, Issue 8 2003
BHUPINDERPAL-SINGH
ABSTRACT Limitations in available techniques to separate autotrophic (root) and soil heterotrophic respiration have hampered the understanding of forest C cycling. The former is here defined as respiration by roots, their associated mycorrhizal fungi and other micro-organisms in the rhizosphere directly dependent on labile C compounds leaked from roots. In order to separate the autotrophic and heterotrophic components of soil respiration, all Scots pine trees in 900 m2 plots were girdled to instantaneously terminate the supply of current photosynthates from the tree canopy to roots. Högberg et al. (Nature 411, 789,792, 2001) reported that autotrophic activity contributed up to 56% of total soil respiration during the first summer of this experiment. They also found that mobilization of stored starch (and likely also sugars) in roots after girdling caused an increased apparent heterotrophic respiration on girdled plots. Herein a transient increase in the ,13C of soil CO2 efflux after girdling, thought to be due to decomposition of 13C-enriched ectomycorrhizal mycelium and root starch and sugar reserves, is reported. In the second year after girdling, when starch reserves of girdled tree roots were exhausted, calculated root respiration increased up to 65% of total soil CO2 efflux. It is suggested that this estimate of its contribution to soil respiration is more precise than the previous based on one year of observation. Heterotrophic respiration declined in response to a 20-day-long 6 °C decline in soil temperature during the second summer, whereas root respiration did not decline. This did not support the idea that root respiration should be more sensitive to variations in soil temperature. It is suggested that above-ground photosynthetic activity and allocation patterns of recent photosynthates to roots should be considered in models of responses of forest C balances to global climate change. [source]