Biology subjects

Slessarev, E.

Publications and source records attributed to Slessarev, E..

5 recordsLinked to original sources

bioRxiv2025

Assessing the Potential of Switchgrass (Panicum virgatum L.) for Storing Carbon Belowground: Insights from a Multi-Site US Study

Agricultural intensification depletes belowground carbon (C) stocks, partly due to the exclusion of deep-rooted perennial species from landscapes where they were once dominant. Reintroducing deep-rooted perennials to cultivated land may help to mitigate SOC loss and restore ecosystem function. We quantified the effect of replacing shallow-rooted annual crops with a deep-rooted perennial grass, switchgrass (Panicum virgatum L.), by comparing 10 to 30 year-old switchgrass stands with paired annual row crop fields across the central and eastern USA. We hypothesized that switchgrass would store more root C and SOC than neighboring shallow-rooted annual crops, and that these effects would extend deeper than 30 cm. We also evaluated whether switchgrass stimulates decomposition of SOC at depth using radiocarbon (14C) to quantify replacement of slow cycling isotopically depleted SOC. Finally, we explored whether the effect of switchgrass on SOC is moderated by soil chemical and physical properties. While the effect of switchgrass on SOC in the surface 100 cm was positive at most sites, the average effect was highly uncertain and statistically indistinguishable from zero (mean difference in SOC = 0.6 kg C m-2 [95% CI -0.8 to +1.9 kg C m-2]). By contrast, we found that root biomass C was consistently more deeply distributed and more abundant under switchgrass, yielding an estimated additional 0.6 kg C m-2 in the surface 100 cm of soil under switchgrass [95% CI +0.5 to +0.7 kg C m-2]. 14C measurements suggested that root C inputs were adding to existing SOC without stimulating decomposition. The effect of switchgrass on belowground C was not strongly related to any of the environmental factors that we evaluated. Our observations show that root biomass C can contribute substantially to belowground C stocks when deep-rooted perennial grasses replace shallow-rooted annual crops.

ecology↗

bioRxiv2025

Drought reduces formation, but enhances persistence, of mineral-associated organic matter in a grassland soil

Drought effects are pervasive in many terrestrial ecosystems, yet little is known about the impact of drought on the transformation of plant C inputs to mineral-associated organic matter (MAOM) - the largest and slowest-cycling pool of organic carbon (C) on land. Using 13C-CO2 greenhouse labeling chambers, we tracked the formation of 13C-MAOM derived from Avena barbata living root inputs (13C-rhizodeposits) versus A. barbata decaying root inputs (13C-root detritus) under normal moisture and spring drought conditions in a semi-arid grassland soil, and then tested the durability of this 13C-MAOM in a subsequent persistence assay. Overall, drought reduced formation of MAOM - both per gram of soil and across the entire soil profile. Notably, drought conditions enhanced the persistence of MAOM derived from root detritus, though not of MAOM derived from rhizodeposition. Drought had the most pronounced effect on MAOM accrual from rhizodeposition late in plant development (week 12) whereas it had the most pronounced effect on MAOM accrual from root detritus early in root decomposition (week 4). These temporal responses were associated with distinct trajectories in microbial community-level growth rates, the average mass of OM compounds, and the number of unique metabolites within each habitat. Our results provide mechanistic evidence that drought reduces overall formation of MAOM but can enhance its persistence in a grassland soil.

ecology↗

bioRxiv2024

Reduced accrual of mineral-associated organic matter after two years of enhanced rock weathering in cropland soils, though no net losses of soil organic carbon

Enhanced rock weathering (ERW), the application of crushed silicate rock to soil, can remove atmospheric carbon dioxide by converting it to (bi)carbonate ions or solid carbonate minerals. However, few field studies have empirically evaluated ERW in field settings. A critical question remains as to whether additions of crushed rock might positively or negatively affect soil organic matter (SOM) - Earths largest terrestrial organic carbon (C) pool and a massive reservoir of organic nitrogen (N). Here, in three irrigated cropland sites in California, USA, we investigated the effect of crushed meta-basalt rock additions on different pools of soil organic carbon and nitrogen (i.e., mineral-associated organic matter and particulate organic matter), active microbial biomass, and microbial community composition. After two years of crushed rock additions, mineral-associated organic matter (MAOM) stocks were lower in the upper surface soil (0-10 cm) compared to unamended controls. At the two sites where baseline pre-treatment data were available, neither total SOC nor SON decreased over the two years of study in crushed rock or unamended control plots. However, the accrual rate of MAOM-C and MAOM-N at 0-10 cm was lower in plots with crushed rock vs. unamended controls. Before ERW is deployed at large scales, our results suggest that field trials should assess the effects of crushed rock on SOM pools, especially over multi-year time scales, to accurately assess changes in net C and understand the mechanisms driving interactions between ERW and SOM cycling.

ecology↗

bioRxiv2022

Divergent microbial traits influence the transformation of living versus dead root inputs to soil carbon

Soil microorganisms influence the global carbon cycle by transforming plant inputs into soil organic carbon (SOC), but the microbial traits that facilitate this process are unresolved. While current theory and biogeochemical models suggest microbial carbon-use efficiency and growth rate are positive predictors of SOC, recent observations demonstrate these relationships can be positive, negative, or neutral. To parse these contradictory effects, we used a 13C-labeling experiment to test whether different microbial traits influenced the transformation of plant C into SOC within the microbial habitats surrounding living root inputs (rhizosphere) versus decaying root litter (detritusphere), under both normal soil moisture and droughted conditions. In the rhizosphere, bacterial-dominated communities with fast growth, high carbon-use efficiency, and high production of extracellular polymeric substances formed microbial-derived SOC under normal moisture conditions. However, in the detritusphere - and the rhizosphere under drought - more fungal-dominated communities with slower growth but higher exoenzyme activity formed plant-derived SOC. These findings emphasize that microbial traits linked with SOC accrual are not universal, but contingent on how microorganisms allocate carbon under different resource conditions and environmental stressors.

ecology↗

bioRxiv2021

Soil depth gradients in microbial growth kinetics under deeply- vs. shallow-rooted plants

AO_SCPLOWBSTRACTC_SCPLOWClimate-smart land management practices that replace shallow-rooted annual crop systems with deeply-rooted perennial plants can contribute to soil carbon sequestration. However, deep soil carbon accrual may be influenced by active microbial biomass and their capacity to assimilate fresh carbon at depth. Incorporating active microbial biomass, dormancy and growth in microbially-explicit models can improve our ability to predict soils capacity to store carbon. But, so far, the microbial parameters that are needed for such modeling are poorly constrained, especially in deep soil layers. Here, we investigated whether a change in crop rooting depth affects microbial growth kinetics in deep soils compared to surface soils. We used a lab incubation experiment and growth kinetics model to estimate how microbial parameters vary along 240 cm of soil depth in profiles under shallow- (soy) and deeply-rooted plants (switchgrass) 11 years after plant cover conversion. We also assessed resource origin and availability (total organic carbon, 14C, dissolved organic carbon, specific UV absorbance, total nitrogen, total dissolved nitrogen) along the soil profiles to examine associations between soil chemical and biological parameters. Even though root biomass was higher and rooting depth was deeper under switchgrass than soy, resource availability and microbial growth parameters were generally similar between vegetation types. Instead, depth significantly influenced soil chemical and biological parameters. For example, resource availability, and total and relative active microbial biomass decreased with soil depth. Decreases in the relative active microbial biomass coincided with increased lag time (response time to external carbon inputs) along the soil profiles. Even at a depth of 210-240 cm, microbial communities were activated to grow by added resources within a day. Maximum specific growth rate decreased to a depth of 90 cm and then remained consistent in deeper layers. Our findings show that > 10 years of vegetation and rooting depth changes may not be long enough to alter microbial growth parameters, and suggest that at least a portion of the microbial community in deep soils can grow rapidly in response to added resources. Our study determined microbial growth parameters that can be used in microbially-explicit models to simulate carbon dynamics in deep soil layers.

microbiology↗