Biology subjects

Grandy, A. S.

Publications and source records attributed to Grandy, A. S..

3 recordsLinked to original sources

bioRxiv2025

Shrub and Sedge Rhizosphere Communities Display Distinct Affinities Toward Exudates and Soil Organic Matter Degradation: a Quantitative Stable Isotope Probing Analysis

Warming temperatures are accelerating permafrost thaw and changing tundra vegetation, where woody shrubs are displacing sedges. Shrubs, such as Betula nana, and sedges, such as Eriophorum vaginatum, exhibit distinct life strategies including unique root-associated, or rhizosphere microbial communities. As permafrost thaws it unlocks previously unavailable carbon and nutrient sources resulting in deeper roots and a translocation of rhizosphere communities. Because permafrost microbial communities contain lower diversity and biomass than rhizosphere communities, the coalescence of rhizosphere and permafrost microbial communities could alter soil organic matter (SOM) degradation rates and increase greenhouse gas emissions. To identify metabolic strategies across distinct rhizosphere and permafrost microbial communities we conducted an isotope tracing incubation experiment. We inoculated thawed permafrost with shrub and sedge rhizosphere communities while adding exudates or water daily and compared this to an uninoculated control. After 46 days, we spiked samples with 18O enriched water or 13C enriched exudates and measured isotope incorporation into microbial DNA with quantitative stable isotope probing (qSIP). Our results indicate that exudate additions had little effect on uninoculated permafrost communities but the addition of exudates and rhizosphere inoculants had a compounding effect on respiration rates. We found that soils inoculated with shrub rhizosphere communities contained a mixture of exudate and SOM degraders while soils inoculated with sedge rhizosphere communities contained mainly SOM degraders. Finally, we found that individual microbial taxa exhibited maximum growth rates in one environment, which was a combination of microbial inoculant communities and exudate addition treatments. Our results reveal that microbial niches are strongly influenced by substrate preferences and community context, and suggest that a reduction in sedges and an expansion of shrubs may provide a mechanism by which permafrost carbon losses are mitigated through corresponding shifts in microbial communities and their substrate preferences.

microbiology↗

bioRxiv2025

Anthropogenic nitrogen deposition decouples relationships with decomposing microbes, altering SOM molecular composition, but not molecular complexity or diversity

Soil organic matter (SOM) consists of diverse biochemical constituents, spanning a spectrum of chemical complexity, and the relative abundance of these substrates influences microbial metabolism and soil carbon persistence. However, mechanistic controls governing these processes and how they may be affected by environmental change remains incomplete. This study aims to assess (1) the molecular-level changes that occur across stages of root decomposition, from undecayed plant root litter to 1-year decomposed root litter, to mineral SOM and (2) how these changes are altered by anthropogenic nitrogen (N) deposition by using SOM biochemical and microbiome datasets and a long-term field experiment. N deposition did not significantly alter undecomposed or 1-year decomposed root litter, but did alter decomposing microbial communities and mineral SOM biochemical composition, specifically in lignin- and lipid-derived compounds. Taken together, this restructuring of microbial communities and alteration of SOM biochemistry likely contributed to the previously observed reduction in SOM decomposition.

ecology↗

bioRxiv2025

Continental-scale relationships of fine root and soil carbon stocks hold in grasslands but not forests

Increasing root carbon inputs into soils has been proposed as a solution to increasing soil organic carbon (SOC). However, while fine root carbon (FRC) inputs can increase SOC accrual in soils, FRC can also enhance SOC loss by stimulating microbial respiration and cause a net loss of SOC through priming. It remains unclear how SOC varies as a function of FRC at broad spatial scales and across ecosystems and depths. Here, we tested the relationship of SOC and FRC using data from 43 sites across the US National Ecological Observatory Network (NEON). We found that total stocks of SOC and FRC in the top 2 meters of soil were positively related with an across-ecosystem slope of 7 {+/-} 3 kg SOC m-2 per kg FRC m-2. However, grassland sites primarily drove this relationship. Grasslands had 15 {+/-} 2 kg SOC m-2 per kg FRC m-2, which is double the across-ecosystem slope. We used deviations from the standardized 1:1 relationship between FRC and SOC to infer whether ecosystems were net priming (indicated by observed SOC being lower than the 1:1 line) or SOC accruing (higher SOC than the 1:1 line). Grassland soils and especially their deep soil layers (>30 cm) showed primarily SOC accrual with increasing fine root abundance. Meanwhile, forest soils had high variability in whether increasing fine roots were associated with net SOC priming or accrual across both shallow and deeper soil layers. We found that in grasslands, FRC inputs are strongly related to SOC accrual, especially at depth and at sites with high moisture and clay content. In contrast, SOC-FRC relationships in forests remain difficult to characterize. Nevertheless, deep grassland soils may serve as optimal environments in which increasing FRC could lead to meaningful increases in SOC stocks.

ecology↗