Soil Respiration Carbon Research Articles

Investigating Thaw and Plant Productivity Constraints on Old Soil Carbon Respiration From Permafrost

AbstractIsotopic radiocarbon (Δ14C) signatures of ecosystem respiration (Reco) can identify old soil carbon (C) loss and serve as an early indicator of permafrost destabilization in a warming climate. Warming also stimulates plant productivity causing plant respiration to dominate Reco Δ14C signatures and potentially obscuring old soil C loss. Here, we investigate how a wide spatio‐temporal gradient of permafrost thaw and plant productivity affects Reco Δ14C patterns and isotopic partitioning. Spatial gradients came from a warming experiment with doubling thaw depth and variable biomass, and a vegetation removal manipulation to eliminate plant contributions. We sampled in August and September to capture transitions from high to low plant productivity, decreased surface soil temperature, and relatively small seasonal thaw extensions. We found that surface processes dominate spatial variation in old soil C loss and a process‐based partitioning approach was crucial for constraining old soil C loss. Resampling the same plots in different times of the year revealed that old soil C losses tripled with cooling surface temperature, and the largest old soil C losses were detected when the organic‐to‐mineral soil horizons thawed (∼50–60 cm). We suggest that the measured increase in old soil respiration over the season and when the organic‐to‐mineral horizon thawed, may be explained by mobilization of nitrogen that stimulates microbial decomposition at depth. Our results suggest that soil C in the organic to mineral horizon may be an important source of soil C loss as the entire Arctic region warms and could lead to nonlinearities in projected permafrost climate feedbacks.

IMPACT OF CONVERTING AREAS CULTIVATED WITH SUGARCANE TO EUCALYPT PLANTATIONS ON SOIL QUALITY IN NORTHEASTERN BRAZIL

ABSTRACT Reforestation is considered an effective method to improve soil quality and drain atmospheric CO2 by sequestering carbon, in both soil and vegetation. In this regard, the aim of this study was to evaluate the effects of converting areas cultivated with sugarcane to eucalypt plantations (Eucalyptus spp.) on soil quality and carbon sequestration in a Latossolo (Ferralsol) in the Atlantic Forest region of the Alagoas state, Brazil, through multivariate analysis. The systems under evaluation consisted of four areas: one area cultivated with sugarcane for approximately 20 years, taken as the reference area of this study, and the other three adjacent areas cultivated with eucalypt at 1 (E1), 3 (E3) and 6 (E6) years of age, previously cultivated with sugarcane. Physical (bulk density - BD, Mean weight-diameter - MWD, geometric mean diameter - GMD and aggregate stability index - ASI), chemical (soil organic carbon - SOC, total nitrogen - TN, labile carbon - LC and recalcitrant carbon - RC) and biological (Microbial biomass carbon - MBC, soil carbon respiration - C-CO2 and metabolic quotient - qCO2) properties of soil were evaluated. Data were collected, standardized and submitted to exploratory analysis with principal components. The results show that SOC, LC, TN, GMD, MWD and ASI increased, while BD showed a reduction in E3 and E6 systems. The conversion of sugarcane cultivation with burning of straw and manual harvest into eucalypt plantations was efficient at promoting SOC sequestration and improving physical, chemical and biological properties of soil.

Modeling Transient Soil Moisture Limitations on Microbial Carbon Respiration

AbstractSoil microorganisms are known to survive periods of aridity and to recover rapidly after wetting events, with the ability to transition between a dormant state in dry conditions and an active state in wet conditions. Though this dynamic behavior has been previously incorporated into soil carbon respiration modeling frameworks, a direct comparison between this active‐dormant transition mechanism and a more simplified first‐order model has yet to be made. Here, we demonstrate the necessary extent of model complexity needed to reproduce transient carbon respiration rates obtained from a set of soil incubation experiments implemented over a range of soil depths and time intervals. Two approaches are tested, one uses simplified first‐order kinetics, whereas the other employs a transition between active and dormant biomass. The performance of each model is evaluated using an Akaike Information Criterion (AIC) based on the accuracy with which they reproduce an experimental dataset consisting of two sets of time series soil incubations collected across a range of time and depth resolutions. Based on the AIC evaluation and model‐data comparison, we conclude that a dormancy‐enabled model featuring two distinct microbial strategists performs best for the majority of the soil profile (above 108 cm) for both high and low depth resolution and sampling frequency, despite the added parameters required. In contrast, the first‐order model achieves better AIC scores when simulating our deepest soils (112–165 cm), where moisture fluctuations are expected to be less prevalent. These results guide how and where we choose to apply more cost intensive models.

Long-term deglacial permafrost carbon dynamics in MPI-ESM

Abstract. We have developed a new module to calculate soil organic carbon (SOC) accumulation in perennially frozen ground in the land surface model JSBACH. Running this offline version of MPI-ESM we have modelled long-term permafrost carbon accumulation and release from the Last Glacial Maximum (LGM) to the pre-industrial (PI) age. Our simulated near-surface PI permafrost extent of 16.9 × 106 km2 is close to observational estimates. Glacial boundary conditions, especially ice sheet coverage, result in profoundly different spatial patterns of glacial permafrost extent. Deglacial warming leads to large-scale changes in soil temperatures, manifested in permafrost disappearance in southerly regions, and permafrost aggregation in formerly glaciated grid cells. In contrast to the large spatial shift in simulated permafrost occurrence, we infer an only moderate increase in total LGM permafrost area (18.3 × 106 km2) – together with pronounced changes in the depth of seasonal thaw. Earlier empirical reconstructions suggest a larger spread of permafrost towards more southerly regions under glacial conditions, but with a highly uncertain extent of non-continuous permafrost. Compared to a control simulation without describing the transport of SOC into perennially frozen ground, the implementation of our newly developed module for simulating permafrost SOC accumulation leads to a doubling of simulated LGM permafrost SOC storage (amounting to a total of ∼ 150 PgC). Despite LGM temperatures favouring a larger permafrost extent, simulated cold glacial temperatures – together with low precipitation and low CO2 levels – limit vegetation productivity and therefore prevent a larger glacial SOC build-up in our model. Changes in physical and biogeochemical boundary conditions during deglacial warming lead to an increase in mineral SOC storage towards the Holocene (168 PgC at PI), which is below observational estimates (575 PgC in continuous and discontinuous permafrost). Additional model experiments clarified the sensitivity of simulated SOC storage to model parameters, affecting long-term soil carbon respiration rates and simulated ALDs. Rather than a steady increase in carbon release from the LGM to PI as a consequence of deglacial permafrost degradation, our results suggest alternating phases of soil carbon accumulation and loss as an effect of dynamic changes in permafrost extent, ALDs, soil litter input, and heterotrophic respiration.

Ectomycorrhizal fungi slow soil carbon cycling.

Respiration of soil organic carbon is one of the largest fluxes of CO2 on earth. Understanding the processes that regulate soil respiration is critical for predicting future climate. Recent work has suggested that soil carbon respiration may be reduced by competition for nitrogen between symbiotic ectomycorrhizal fungi that associate with plant roots and free-living microbial decomposers, which is consistent with increased soil carbon storage in ectomycorrhizal ecosystems globally. However, experimental tests of the mycorrhizal competition hypothesis are lacking. Here we show that ectomycorrhizal roots and hyphae decrease soil carbon respiration rates by up to 67% under field conditions in two separate field exclusion experiments, and this likely occurs via competition for soil nitrogen, an effect larger than 2°C soil warming. These findings support mycorrhizal competition for nitrogen as an independent driver of soil carbon balance and demonstrate the need to understand microbial community interactions to predict ecosystem feedbacks to global climate.

Time Domain Similarity of Lightweight Parameters Based Soil Respiration Sensor Network Deployment

Deployment is a basic and key issue for all kinds of wireless sensor networks applications. Most of existing researches on deployment problem of wireless sensor network are on generic network level and not for specific application scenarios and also do not utilize any domain knowledge of practical applications. Focusing on the problem of limited number of sensing nodes in soil respiration sensor networks, using domain knowledge such as some lightweight parameters (temperature, humidity, etc.) influencing soil respiration and soil respiration having a day-periodic trend, we proposed a deployment method, TimSim, for soil respiration sensor network based on time domain similarity of lightweight parameters. Lightweight parameters data from positions in the region to be monitored are collected before the deployment of soil respiration sensing nodes, and then time domain similarities of lightweight data among different positions are analyzed, according to which these positions are divided into some groups. A representative position in each group is chosen to deploy a soil respiration sensing node. The experimental results show that TimSim method can place nodes to proper positions so as to monitor regional soil respiration carbon flux effectively with a smaller estimation error than uniform and random deployment methods.

Measuring and Modeling Soil Carbon Respiration following Repeated Dairy Slurry Application

Farm animal manure slurries are repeatedly applied to soils. The portion of slurry organic matter not decomposed within its application year is left to mineralize over subsequent years, which results in a residual effect of high C mineralization in historically-amended vs. nonamended soils. This process was modeled in laboratory incubation by applying water, ammonium sulfate, heifer (HEI), or dairy cow (COW) slurry between 1 and 4 times (at Day 0, 84, 168, and 252) to soils of contrasting textures [sandy-loam (SL) and clay-loam (CL)]. Respired CO2 was measured 6 to 10 times after each application along the trial period. Results showed daily respiration rates decreased as application frequency increased and that rates were significantly higher in slurry-amended, compared to control treatments. Furthermore, the contribution of slurry-derived CO2 respiration increased as application frequency rose (from 37 to 68% between the first and fourth applications of HEI and from 58 to 80%, respectively, of COW). The labile fraction of potentially mineralizable slurry C, estimated with a first-order kinetic decomposition model, was also increased with application frequency. The two slurries differed in potentially mineralizable C during the 84 d after the application events. However, there were no differences between the two slurries in the potential mineralizable C (1.43% of applied C) that contributed to respiration after 84 d of application. This small residual effect has never been quantified before in an incubation experiment. This small residue C is very important to farm practices in which slurries are continuously applied for decades.

The role of environmental factors and tree injuries in soil carbon respiration response to fire and fuels treatments in pine plantations

The need to understand how forest management practices affect soil CO2 exchange with the atmosphere (soil respiration) has increased with the recognition of a likely feedback effect of climate warming on soil respiration rates. Previous research addressing the mechanisms driving soil respiration has yielded inconsistent and/or conflicting results. This study looked to alternative above-ground forest characteristics to help explain spatial variability in soil respiration in a 30-year-old Sierra Nevada pine plantation. Fire hazard mitigation is one of the predominant management goals in these and other western US forests. Therefore, this analysis examined how fuels treatments, including shredding of understory vegetation (mastication), prescribed fire, and a combination thereof, affected soil respiration and its relationship to environmental factors and post-fire tree injuries. Multiple regression models indicated that mastication had no significant impact on soil respiration, but the roles of soil temperature and forest floor depth (O horizons) in the models increased after the treatment. Burning reduced soil respiration by ∼14%, and increased its sensitivity to tree proximity and the exposure of bare mineral soil. Scorch height in burned stands was negatively correlated with soil respiration. Models incorporating only tree injury or tree proximity parameters explained between 63% and 91% of the variability in burned plantations. This work suggests that measures of above-ground forest features can increase understanding of management impacts on soil respiration, and the mechanisms by which these impacts occur. These results are especially applicable in Mediterranean climates, where moisture stress reduces the effectiveness of soil microclimate in explaining soil respiration.

The effects of fuels treatments on soil carbon respiration in a Sierra Nevada pine plantation

Fire-prone forests in the American west are presently slated for extensive fuels reduction treatments, yet the effect on soil CO 2 efflux rates, or soil respiration, has received little attention. This study utilizes the homogeneity of a Sierra Nevada ponderosa ( Pinus ponderosa Dougl. ex P. & C. Laws)–Jeffrey pine ( Pinus jeffreyi, Grev. & Balf.) plantation to investigate changes in soil respiration following mechanical shredding of understory vegetation, or mastication, in 2004; mastication coupled with prescribed burning in 2005; and burning alone also in 2005 as measured over the growing seasons from 2003 to 2005. Soil respiration, soil temperature and soil moisture were measured in two masticated stands which were burned the following year, and in one burned stand; the three of which were compared with two controls stands. Soil respiration response to treatments was detectable even though spatial variability within sites was high (coefficients of variation of 39–66%). Mastication produced short-term reductions in respiration rates, reduced soil moisture by 20%, and mitigated a year-to-year reduction in soil temperature evidenced by controls. Prescribed fire in masticated stands lowered soil respiration from 3.42 to 2.68 μmol m −2 s −1 while fire in the untreated stand raised rates from 3.41 to 3.83 μmol m −2 s −1, although seasonal increases in control sites were greater than those in the untreated stand. Masticated then burned site soil moisture increased by 52% while soil temperature decreased over the span of the growing season. Microclimate variables were not consistently effective in explaining spatial trends. Exponential models using soil temperature and/or moisture to predict temporal trends in respiration were only significant in treated stands, suggesting that treatment implementation increased sensitivity to environmental factors. These results imply that fuels reduction practices in water-stressed forests may have important consequences for ecosystem carbon dynamics.

A one-compartment model to study soil carbon decomposition rate at equilibrium situation

Based on world-wide observed soil carbon density data and model-simulated net primary production (NPP), we obtained a one-compartment model directly calculating average soil carbon respiration rate and soil carbon density at equilibrium situation. Our formulation shows that the average decomposition rate of soil organic matter, both at dry and wet soil condition, is particularly sensitive to moisture/precipitation changes and it is also sensitive to temperature. The data show that, at wet soil condition, decomposition rate decreases with moisture increasing, while at dry soil condition, it increases with moisture increasing. These results are consistent with previous studies. The temperature effect on soil respiration rate is evident, with Q 10=1.7. The model has a good resolution to describe soil carbon densities at various vegetation types in the Holdridge life ecosystem classification system. Results show that the highest soil carbon densities occur in rain forest/tundra, while the lowest values in deserts and the highest soil respiration rates occur in wet forest/tundra but not in rain forest/tundra, while the lowest rates occur in desert. The calculated present terrestrial carbon pool is ≈1200 PgC. On the basis of model results, some recent conclusions indicating that soil organic carbon decomposition does not vary with temperature should be revised. The soil respiration rates are highly dependent on the combined effects of temperature and precipitation, but not any individual effect. High precipitation rate or soil moisture will greatly prevent soil organic matter from decomposition.