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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Synthetic microbial communities: Bridging research and application in second-generation bioenergy feedstock microbiomes

The sustainable production of purpose-grown bioenergy feedstocks is essential in transitioning away from fossil fuels. Synthetic communities (SynComs) are consortia of microorganisms that can be used as biological interventions to support objectives like plant growth and stress tolerance. This review examines the state of knowledge regarding microbiomes and SynComs of second-generation bioenergy feedstocks, focusing on the rhizosphere. We first provide an overview of second-generation feedstocks, including switchgrass (Panicum virgatum), miscanthus (Miscanthus × giganteus), sorghum (Sorghum spp.), sugarcane (Saccharum spp.), and poplar (Populus spp.), and summarize our current understanding of their plant-soil-microbiome ecology. We next discuss considerations in the objectives, design, and evaluation of SynComs to enhance feedstock production, and then critically review the literature around their use. Our literature analysis revealed that SynCom performance varied substantially between controlled pilot experiments and field trials, possibly due to system complexity that could not be fully considered in their design and pilot evaluation. We identified a gap in the use of SynComs to support the unique sustainability objectives of biofuel feedstock agriculture, presenting an opportunity to leverage these additional microbial traits in SynCom designs. Finally, we emphasize the importance of targeted research to identify the ecological principles that govern the assembly, activation, and persistence of microbes in the feedstock rhizosphere, thereby enhancing our capacity to manage microbiomes under diverse environmental conditions and ensure their functionality. Beyond biofuels, SynComs are a promising microbiome management strategy for crop production; however, an ecologically informed design and evaluation of SynComs are advised.

SynCom↗
DOE OSTI2022

Biomass Production and Nutrient Removal by Perennial Energy Grasses Produced on a Wet Marginal Land

Growing dedicated bioenergy crops on marginal land can provide beneficial outcomes including biomass production and energy, resource management, and ecosystem services. We investigated the effects of harvest timing (peak standing crop [PEAK] or after killing frost [KF]) and nitrogen (N) fertilizer rates (0, 56, and 112 kg N ha -1 ) on yield, nutrient concentrations, and nutrient removal rates of perennial grasses on a wet marginal land. We evaluated three monocultures, including switchgrass (Panicum virgatum L., SW), Miscanthus x giganteus (MG), prairie cordgrass (Spartina pectinata Link, PCG), and a polyculture mixture of big bluestem (Andropogon gerardii Vitman), Indiangrass (Sorghastrum nutans (L.) Nash), and sideoats grama (Bouteloua curtipendula Torr., MIX). Increasing the application of N did correlate with increased biomass, concentration, and subsequent removal of nutrients across almost all treatment combinations. In all grass treatments except MG, PEAK harvesting increased yield and nutrient removal. At PEAK harvest, switchgrass is ideal for optimizing both biomass production and nutrient removal. While our results also suggest short-term plasticity for farmers when selecting harvest timing for optimal nutrient removal, KF harvest is recommended to ensure long-term stand longevity and adequate nutrient removal. If the KF harvest is adopted, MG would be the ideal option for optimizing biomass yield potential. Additionally, we found that the yield of polyculture did not vary much with harvest timing, suggesting better yield stability. Future studies should give consideration for long-term evaluation of polyculture mixtures to assess their biomass yields and nutrient removal capacities.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Variation in Biomass Yield and Cell Wall Composition in Switchgrass Natural Variants Under Two Nitrogen Regimes

Switchgrass (Panicum virgatum) is a promising lignocellulosic biofuel crop for which biomass and processing quality are important. Inherent plant variability across genotypes and environments challenges uniformity and product quality. In this study, the impact of nitrogen (N) application on switchgrass yield and quality was examined under field conditions using a highly diverse switchgrass panel over a 4-year period at Knoxville, TN. Overall, biomass production was correlated between low (0 kg of added N/ha) and moderate (135 kg of added N/ha) nitrogen treatments, suggesting that the N impact is largely uniform across the genotypes. Nonetheless, high biomass genotypes were identified with high nitrogen-use efficiency ; biomass was congruent or even higher (up to 9-fold) in the low N treatment. Genotypes were also identified with up to 94% nitrogen-remobilization efficiency. Furthermore, nitrogen application appeared to impact lignin content in whole tillers but was neutral to lignin monomer syringyl-to-guaiacyl (S/G) ratio. The same panel grown under natural conditions in Watkinsville, GA, produced significantly more biomass than the Tennessee panel in the first 3 years, but biomass was similar across both sites and treatments in year 4. Top performing genotypes overlapped between sites by 20-37%. There were low correlations in lignin content in whole tillers across the two field sites, but moderate correlations were observed for S/G ratios. The high yielding genotypes from the low N plot identified in this study can be used in breeding programs and management strategies in switchgrass to evade adverse environmental and economic effects.

09 BIOMASS FUELS↗
DOE OSTI2026

The productivity of perennial crops miscanthus and switchgrass is more resistant to vapor pressure deficit stress than maize

Rising atmospheric vapor pressure deficit (D) with warming is an increasingly important driver of crop productivity loss, yet the relative sensitivity of conventional seed crops and alternative perennial crops remains poorly resolved. In this study, we combined a 9-year eddy covariance carbon flux record (2008 – 2016) with 600+ midday leaf water potential (ψ L ) measurements (2024 – 2025) from adjacent maize (Zea mays), miscanthus (Miscanthus x giganteus), and switchgrass (Panicum virgatum) plots to: (1) quantify the limitations of elevated D on crop-specific productivity and (2) evaluate how these responses vary as a function of soil moisture (Θ) status. We found that maize strictly regulated ψ L and its gross primary productivity (GPP) was strongly reduced by increasing D. In contrast, miscanthus and switchgrass allowed larger ψ L declines and sustained higher GPP under similar moisture constraints. D exerted a larger limitation on maize GPP than Θ, but D-driven declines were less severe when accompanied by high Θ. GPP sensitivity to D was also influenced by Θ for miscanthus and switchgrass, but the buffering effect was stronger compared to maize. Specifically, high D paired with high Θ were the most productive conditions for the perennials, reflecting temperature-driven gains in photosynthetic efficiency when evaporative stress was mitigated by sufficient soil water supply. Overall, miscanthus and switchgrass displayed greater resistance to atmospheric drought and more stable GPP across hydroclimate variability than maize. These findings highlight that maize is more vulnerable to future projections of rising D than miscanthus or switchgrass.

drought↗
DOE OSTI2021

Arbuscular mycorrhizal fungal community responses to drought and nitrogen fertilization in switchgrass stands

Anthropogenic global change is increasing the severity and frequency of abiotic stresses such as drought that are likely to affect soil communities. Arbuscular mycorrhizal fungi (AMF) play important roles in many soil processes, so it is important to understand how drought affects AMF biodiversity. This is especially relevant in agricultural systems where crops rely on AMF associations for water and nutrient uptake, and where management decisions such as crop selection and fertilizer application may influence how the AMF community responds to drought. In this study, we examined the effects of reduced precipitation and nitrogen fertilization on AMF richness, community composition, and root and soil colonization in monocultures of two cultivars of switchgrass (Panicum virgatum) grown for bioenergy feedstock. We conducted a two-year field experiment using rain-out shelters to manipulate precipitation in mature stands of switchgrass growing in a long-term nitrogen fertilization (0 or 56 kg N ha –1 ) experiment at the W.K. Kellogg Biological Station Long-Term Ecological Research site in Michigan, USA. We expected that AMF richness and colonization would decrease due to drought, as predicted by the stress exclusion hypothesis. Contrary to our expectations, we found that drought stress increased AMF species richness in fertilized plots by 15%; there was no effect of drought on AMF richness in unfertilized plots. Drought also significantly altered AMF community composition, primarily due to increases in Rhizophagus taxa abundance, and reduced AMF root colonization in switchgrass by 6%. We also found variation in AMF richness and colonization across switchgrass cultivars as well as sampling dates. Furthermore, the changes in AMF richness and composition that we observed in this study may have implications for perennial bioenergy feedstock selection and management as changes in AMF communities may feedback to affect host plants.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Direct root contact among neighboring plants influences activity of soil extracellular enzymes

Composition and diversity of vegetation systems can influence soil microbial activity and extracellular enzyme (EE) dynamics, which are crucial for soil carbon (C) accrual and nutrient cycling. Yet, the impact of plant interactions and competition on EE activities remains a notable knowledge gap. This study examines how direct root contact and neighboring plant identity affect the activity and spatial distribution of four key soil EEs: β-glucosidase (BGlu), chitinase, acid phosphatase (AcidP), and alkaline phosphatase (AlkP). Using three-compartment rhizoboxes with switchgrass (Panicum virgatum L.) grown alongside bush clover (Lespedeza capitata Michx.), and black-eyed Susan (Rudbeckia hirta L.), we assessed enzyme activities using zymography under conditions that either allowed or restricted direct root contact by root barriers. Results show that root proliferation and species interactions significantly influenced EE activity. While BGlu and AcidP activities were strongly correlated with root biomass, AlkP activity was consistently higher in the absence of root barriers, indicating a pronounced microbial response to plant interactions via direct/close root contacts. Additionally, soil phosphorus availability modulated enzyme activity, with higher phosphatase activities in low-P soils. Furthermore, these findings highlight the importance of root-root interactions and plant species composition in shaping soil biochemical processes.

enyzme activity↗
DOE OSTI2023

Interactions among soil texture, pore structure, and labile carbon influence soil carbon gains

Perennial vegetation with high plant diversity, e.g., restored prairie, is known for stimulation of soil carbon (C) gains, due in part to enhanced formation of pore structure beneficial for long-term C storage. However, the prevalence of this phenomenon across soils of different types remains poorly understood. The aim of the study was to assess the associations between pore structure, soil C, and their differences in monoculture switchgrass and polyculture restored prairie vegetation across a wide range of soils dominating the Upper Midwest of the USA. Six experimental sites were sampled, representing three soil types with texture ranging from sandy to silt loams. The two vegetation systems studied at each site were (i) monoculture switchgrass (Panicum virgatum L.), and (ii) polyculture restored prairie, also containing switchgrass as one of its species. X-ray computed micro-tomography (µCT) was employed to analyze soil pore structure. Structural equation modeling and multiple path analyses were used to assess direct and indirect effects of soil texture and pore characteristics on microbial biomass C (MBC), particulate organic matter (POM), dissolved organic C (DOC), short-term respiration (CO 2 ), and, ultimately, soil organic C (SOC). Across studied sites, prairie increased fractions of medium (50–150 µm Ø) pores by 11–45 %, SOC by 3–69 %, and MBC by 18–59 % (except for one site). The greater were the prairie-induced increases in the medium pore volumes, the greater were the prairie-induced SOC gains. Greater C losses via CO 2 and DOC contributed to slower C accumulation in the prairie soil. We surmise that the interactive feedback loop relating medium pores and soil C acts across a wide range of soil textures and is an important mechanism through which perennial vegetation with high plant diversity, such as restored prairie, promotes rapid SOC gains.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Mitigating the soil carbon deficit of annual agriculture with perennial bioenergy crops in the U.S. Midwest

Maize ( Zea mays L.) is the dominant bioenergy feedstock in the US Midwest but its cultivation since the early 1800s has incurred substantial losses in soil organic carbon (SOC). We quantified differences in SOC stocks under perennial bioenergy crops of Panicum virgatum L. (switchgrass) and Miscanthus x giganteus Greef et Deuter (miscanthus) planted on former maize and soybean fields relative to maize-based annual cropping and native prairie. Comparisons were made at seven locations across Illinois, USA, spanning a range of climate and soil types. Across sites, SOC stocks to 1-m depth on an equivalent soil mass basis were 146 Mg C ha −1 under prairie, 107 Mg C ha −1 under miscanthus, 97.9 Mg C ha −1 under switchgrass, and 87.7 Mg C ha −1 under maize. Higher SOC demonstrates the potential of perennial bioenergy crops to rebuild the SOC deficit accrued under nearly two centuries of maize-based annual cropping. SOC stock increased in the first 5 years under mature bioenergy crops at four out of seven sites. Carbon isotope (δ 13 C) analyses of surface depths confirmed short-term increases in SOC to be derived from miscanthus and switchgrass. Stocks of SOC could be increased over time under miscanthus or switchgrass cultivation even with annual harvesting, though our measured rates of SOC accumulation were lower than previous estimates for Illinois and varied by site.

bioenergy↗
DOE OSTI2026

Switchgrass-associated soil microbes have subtle but distinct effects on germination vs. growth under drought

Soil microbial communities can play a large role in plant fitness, including plants’ response to drought. How microbes mediate drought response may also differ across the plants’ life stage, but studies rarely study causal effects of microbes on plant fitness at multiple stages. We conducted a greenhouse experiment on switchgrass (Panicum virgatum L.) to investigate how microbial presence (sterile bulk vs. live bulk soils) and microbial source (communities from bulk vs. rhizosphere soil) affect germination and seedling growth (life-stage) during drought. We also investigated how drought and life-stage alter the assembly of the inoculated communities. Both drought conditions and the absence of microbes reduced germination (49% and 50% fewer seedlings, respectively, p < 0.05), but there were few effects of microbial presence on older seedlings. In addition, microbial source had no effect on the evaluated plant traits, but interestingly, the initially similar bulk and rhizosphere communities became compositionally distinct after 34 days with germinating seeds, but not with seedlings. Therefore, it may be that the plants did respond to microbial source through changes in seed or root exudates, and calls for further study. Finally, while sometimes microbes did benefit plants under drought, we did not find evidence that they are especially beneficial in this condition. We suggest that microbes’ effects differ across plant life stage, and may be both positive and negative. Further research should advance understanding of plant stress tolerance within a framework of plant-microbiome co-development.

drought↗
DOE OSTI2021

Long-term excess nitrogen fertilizer increases sensitivity of soil microbial community to seasonal change revealed by ecological network and metagenome analyses

Nitrogen (N) fertilizer has often been generously applied to increase crop biomass yield. Although the influences of inorganic N fertilizer on soil microbial communities have been widely studied, the effect of N fertilizer on microbial co-occurrence networks and its metagenome is largely unknown. Further, seasonal changes in microbial community responses to N addition have rarely been reported. In this study, three N fertilizer rates (0, 56, 196 kg N/ha) were applied annually in switchgrass (Panicum virgatum L.) grown for bioenergy production in the upper Midwest, USA. The soil microbiome was affected by both fertilizer and low pH in the 7th year of fertilization treatments. The microbial community structures were relatively stable during the growing season for each N fertilizer rate. However, the excess N fertilizer (196N) increased the seasonal variation of bacterial and fungal communities. Network analysis showed that the microbial interactions at the 196N treatment were more intense, with decreased bacteria-fungal interactions compared to 56N and 0N. Furthermore, this suggests that the microbial community became more sensitive to environmental change under the influence of long-term excess N fertilizer. Metagenomic analysis showed that the long-term excess N fertilizer promoted many metabolic processes, especially carbohydrate and amino acid related metabolism and Archaea mediated ammonia oxidation. However, N fertilizer also reduced many other traits, especially N 2 fixation and signal transduction, the latter of which may contribute to the decreased interactions between bacteria and fungi.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Plant root exudates and rhizosphere bacterial communities shift with neighbor context

A plant's neighborhood context can alter its interactions with other organisms, but little is known about how these dynamics occur belowground, especially with soil microbes. Microbial communities in rhizosphere soil are influenced by many factors, including abiotic conditions and root-derived signals. In particular, root exudates have strong effects on rhizosphere assembly, respond to changes in abiotic conditions, and help plants interact with neighbors. Therefore, we predicted that root exudates likely play a central role in neighbor-induced shifts in rhizosphere communities. We conducted a greenhouse experiment to test this and determine how the rhizosphere bacterial community of a focal plant, Panicum virgatum, changed when beside different neighbors, and whether these shifts were mediated by neighbor-induced changes in root exudation. We found that neighbor altered both focal plant exudates and rhizosphere community, and that changes were largest when the focal plant was beside the most competitive neighbor, Rudbeckia hirta, which reduced both focal plant growth and nitrogen uptake. Several factors contributed to neighbor impacts on rhizosphere assembly, including neighbor-induced changes in root exudates during nitrogen-limitation and microbial spillover from roots of larger neighbors. Using an additional soil incubation, we also found that these changes in exudates can have even greater effects on soil nutrients than on microbial assembly. Overall, we show that neighbors influence one another's microbiomes, and highlight neighbor-induced changes in root exudates as one mechanism through which this may occur. Furthermore, this work suggests that rhizosphere assembly may differ in mixed-species communities and thus emphasizes a need for microbiome studies that consider neighborhood context.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Enzymatically hydrolyzed fluorescence-based chemical probe enables in situ mapping of chitinase activity in the rhizosphere

Rhizosphere microbiomes and root exudates play a pivotal biochemical role in helping to catalyze chitin catabolism. Chitin is a recalcitrant and ubiquitous soil biopolymer, estimated to be the second most abundant organic soil biopolymer on Earth. Despite its abundance, role as a source of C and N in soil, and importance to ecosystem function, the biochemical mechanisms controlling chitin fate in the rhizosphere are elusive and poorly understood. To enable spatial mapping of chitinase activity in the rhizosphere, we designed and synthesized an enzymatically activated fluorogenic substrate, chitotriose-TokyoGreen (chitotriose-TG), by incorporating a fluorescein derivative (TG) onto the trimeric unit of chitin. This non-fluorescent substrate is selectively hydrolyzed by chitinase to release TG and yield a high fluorescence signal, which can be used to spatially image and measure chitinase activity in the rhizosphere. To demonstrate the application of this technique, we grew switchgrass (Panicum virgatum) in rhizoboxes amended with a horizontal layer of chitin. We extracted mobile proteins from the rhizobox using a nitrocellulose membrane blotting technique which offer non-destructive enzyme extraction while preserving the 2D spatial position of the enzymes. We then subjected these membranes to the synthesized chitotriose-TG stain to spatially visualize the distribution of chitinase activity within the rhizosphere. Furthermore, we observed increased chitinase activity near plant roots and higher activity within the soil zone enriched in chitin, showing an adaptive response of chitinase activity with spatial focusing in areas of higher chitin abundance. Thus, the enzyme extraction and visualization strategy we describe here can help enlighten efforts to better understand spatial controls on chitin breakdown in rhizosphere, further elucidating the role of chitin as a C and N source in these systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Belowground plant carbon and nitrogen exchange: plant-derived carbon inputs and pore structure formation

Belowground plant transfer of carbon (C) and nitrogen (N) can benefit soil ecosystems, increasing soil C gains and plant N availability, while improving soil pore structure. We explored such transfers among three plant species of North American prairie, where C and N were transferred from a grass (Panicum virgatum L., switchgrass (Sgrass)) to either a legume (Lespedeza capitata Michx., bush clover (Bclover)), a forb (Rudbeckia hirta L., black-eyed Susan (BSforb)), or a mixture of the two. The plants were grown either with/out direct root contact, thus allowing assessment of the relative contributions of fungal- and root-based transfer pathways. The Sgrass was labeled with 13 C and 15 N, and C and N transfers were assessed by measuring isotope enrichment of roots and aboveground biomass of neighboring plants. Soil inputs of plant-derived C and N were assessed by isotope analyses of the rhizosphere soil. X-ray computed tomography was used for pore structure analyses. Carbon transfer was much higher in the presence of direct/close root contact between source and recipient plants, yet N transfers appeared to be mainly fungal driven. Here, while C and N were readily transferred from Sgrass to other Sgrass and Bclover neighbors, transfers to BSforb were negligible. However, in a three species system, the presence of the legume enhanced C and N transfers to BSforb, suggesting non-additive influences of diverse plant community composition. The more plant-derived C and N was found in the rhizosphere of recipient plants, the greater C and N transfers through roots. Greater C and N transfers were associated with increases in 8–30 μm diameter pores and decreases in >150 μm pores. Summarily, diverse plant communities, especially those with legumes, increase C and N transfers, which then benefit soil C inputs and its protection via changes in pore structure.

13 CO 2 pulse labeling↗
DOE OSTI2023

Atomistic Simulations of Polydisperse Lignin Melts Using Simple Polydisperse Residue Input Generator

Understanding the physics of lignin will help rationalize its function in plant cell walls as well as aiding practical applications such as deriving biofuels and bioproducts. Here, in this work, we present SPRIG (Simple Polydisperse Residue Input Generator), a program for generating atomic-detail models of random polydisperse lignin copolymer melts i.e., the state most commonly found in nature. Using these models, we use all-atom molecular dynamics (MD) simulations to investigate the conformational and dynamic properties of polydisperse melts representative of switchgrass (Panicum virgatum L.) lignin. Polydispersity, branching and monolignol sequence are found to not affect the calculated glass transition temperature, T g . The Flory–Huggins scaling parameter for the segmental radius of gyration is 0.42 ± 0.02, indicating that the chains exhibit statistics that lie between a globular chain and an ideal Gaussian chain. Below T g the atomic mean squared displacements are independent of molecular weight. In contrast, above T g , they decrease with increasing molecular weight. Therefore, a monodisperse lignin melt is a good approximation to this polydisperse lignin when only static properties are probed, whereas the molecular weight distribution needs to be considered while analyzing lignin dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Novel Cell-Type-Specific Drought-Responsive Proteins in Root Tips of Field-Grown Perennial Switchgrass

The root-tip region of plants, including the root cap, forms the most basal terminal of the root and exhibits a high degree of cellular complexity in terms of morphology, cytological function, and interaction with environmental cues in the soil. Cells in this region follow a developmental trajectory, transitioning from stem cells to meristematic cells, and ultimately to fully differentiated cell types. However, our understanding of root-tip cell-type specific proteomic responses to abiotic stresses, such as drought, particularly under field conditions, remains limited. This study aimed to identify spatially resolved, cell type-specific proteomes in switchgrass (Panicum virgatum) root tips under drought stress. Root tips were collected from seven-year-old, field-grown switchgrass ‘Alamo’ plants excavated under both well-watered and long-term drought conditions. Cell type-specific proteins were identified using laser capture microdissection (LCM) coupled with nanoPOTS (Nanodroplet Processing in One Pot for Trace Samples) and nano-LC-MS proteomics analysis. Five distinct cell types were targeted: (1) cells in the quiescent center and stem cell niche (QuC), (2) protodermal epidermal cells (PEC) in the meristematic zone, (3) epidermal cells in the transition and elongation zones above the root cap (Epi), (4) peripheral root cap cells (PRC), forming 2–3 layers below the PEC and 1–2 layers above the root border cells, and (5) columella root cap cells (Col) comprising of the columella initials and a single underlying layer of cells undergoing active growth. Principal component analysis (PCA) revealed clear separation among the five targeted cell types, confirming distinct proteomic profiles. Proteins predominantly enriched in each cell type were linked to distinct cellular functions, with QuC cells showing involvement in chromosomal behavior, DNA replication, and mitosis—key processes for stem cell niche regulation. Drought stress resulted in alterations of proteostasis, as evidenced by significant decreases in ribosomal proteins and increases in protein synthesis inhibitors. Moreover, drought stress induced unique cell-type–specific proteins involved in phytohormone biosynthesis and signaling pathways, including auxin, cytokinin, and jasmonic acid. In particular, QuC cells were more highly enriched in proteins associated with DNA repair and mitotic processes. Metabolic pathways related to amino acids, carbohydrates, and lipids were differentially affected in a cell-type–dependent manner, whereas general stress-responsive proteins exhibited consistent changes across all five cell types. Overall, this study provides unique spatially resolved, cell-type-specific proteomic profiles in root tips, representing a significant advancement in our understanding of the cellular mechanisms underlying plant responses to drought stress in natural field conditions.

perennial grass↗
DOE OSTI2026

Assessing the Effect of a Deep‐Rooted Grass on Belowground Carbon Storage in Cultivated Land: Insights From a Multi‐Site US Study

Agriculture depletes soil organic carbon (SOC), partly due to the exclusion of deep-rooted perennials. Reintroducing deep-rooted perennials to cultivated land may help to mitigate SOC loss. We quantified the effect of deep roots on SOC by comparing 8 to 30 year-old stands of switchgrass ( Panicum virgatum L .) with paired annual row crop fields at 12 sites 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 ( 14 C). 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 not statistically significant (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 C was consistently more abundant under switchgrass, yielding an estimated additional 0.6 kg C m −2 in the surface 100 cm of soil [95% CI +0.5 to +0.7 kg C m −2 ]. 14 C 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 soil properties that we evaluated. Our observations show that root C can contribute substantially to belowground C stocks when deep-rooted perennials replace shallow-rooted crops.

60 APPLIED LIFE SCIENCES↗