02866nas a2200145 4500008004100000245012900041210006900170520232200239100001602561700002402577700002402601700001502625700001502640856006502655 2021 eng d00aMechanisms influencing physically sequestered soil carbon in temperate restored grasslands in South Africa and North America0 aMechanisms influencing physically sequestered soil carbon in tem3 a

Sequestering carbon (C) into stable soil pools has potential to mitigate increasing atmospheric carbon dioxide concentrations. Carbon accrues in grassland soil restored from cultivation, but the amount of physically protected C (here measured as microaggregate-within-macroaggregate C) and predominant mechanisms of accrual are not well understood. We modeled the rate of physically protected carbon accrued in three mesic temperate perennial restored grasslands from cross-continental regions using datasets with a wide range of restoration ages from northeast Kansas, USA; southeast Nebraska, USA; and northeast Free State, South Africa. Further, we investigated major controls on the amount of physically protected C in each site using structural equation modeling. Variables in the structural equation model were root biomass, root C:N ratio, soil structure (indicated by bulk density, percent of macroaggregates on a per whole soil mass basis, and percent of microaggregate-within-macroaggregates on a per macroaggregate mass basis), microbial composition (indicated by microbial biomass C, total phospholipid fatty acid [PLFA] biomass, and PLFA biomass of arbuscular mycorrhizae fungi [AMF] biomass), and microaggregate-within-macroaggregate C on a per whole soil mass basis. Across all sites, physically protected C accrued at a rate of 16 ± 5 g m−2 year−1. Data from South Africa fit an a priori metamodel developed for northeast KS that hypothesized physically protected C could be explained as a function of microbial composition, soil structure, root C:N ratio, and root biomass (listed in order of strength of direct effect on physically protected C). In contrast to the model-based hypothesis, root C:N ratio was the strongest influence (negative) on physically protected C in South Africa. The lesser effect of AMF on physically protected C in South Africa was consistent with lower AMF biomass in arid environments. The hypothesized model did not fit southeast Nebraska data possibly due to high (~ 30%) clay content. Overall, these results suggest that physically protected C in soil with moderate amounts of clay (more than 10% and less than 30%) can be predicted with knowledge of roots (biomass and C:N ratio), microbial biomass, and soil aggregation.

1 aScott, D.A.1 aBach, Elizabeth, M.1 aPreez, Chris, C. Du1 aSix, Johan1 aBaer, S.G. uhttps://link.springer.com/article/10.1007/s10533-021-00774-y03107nas a2200169 4500008004100000245011300041210006900154300001100223490000700234520253800241100001502779700001402794700001602808700002002824700002402844856006902868 2020 eng d00aSoil heterogeneity increases plant diversity after twenty years of manipulation during grassland restoration0 aSoil heterogeneity increases plant diversity after twenty years  ae020140 v303 a

The “environmental heterogeneity hypothesis” predicts that variability in resources promotes species coexistence, but few experiments support this hypothesis in plant communities. A previous 15‐yr test of this hypothesis in a prairie restoration experiment demonstrated a weak effect of manipulated soil resource heterogeneity on plant diversity. This response was attributed to a transient increase in richness following a post‐restoration supplemental propagule addition, occasionally higher diversity under nutrient enrichment, and reduced cover of a dominant species in a subset of soil treatments. Here, we report community dynamics under continuous propagule addition in the same experiment, corresponding to 16–20 yr of restoration, in response to altered availability and heterogeneity of soil resources. We also quantified traits of newly added species to determine if heterogeneity increases the amount and variety of niches available for new species to exploit. The heterogeneous treatment contained a factorial combination of altered nutrient availability and soil depth; control plots had no manipulations. Total diversity and richness were higher in the heterogeneous treatment during this 5‐yr study due to higher cover, diversity, and richness of previously established forbs, particularly in the N‐enriched subplots. All new species added to the experiment exhibited unique trait spaces, but there was no evidence that heterogeneous plots contained a greater variety of new species representing a wider range of trait spaces relative to the control treatment. The richness and cover of new species was higher in N‐enriched soil, but the magnitude of this response was small. Communities assembling under long‐term N addition were dominated by different species among subplots receiving added N, leading to greater dispersion of communities among the heterogeneous relative to control plots. Contrary to the deterministic mechanism by which heterogeneity was expected to increase diversity (greater variability in resources for new species to exploit), higher diversity in the heterogeneous plots resulted from destabilization of formerly grass‐dominated communities in N‐enriched subplots. While we do not advocate increasing available soil N at large scales, we conclude that the positive effect of environmental heterogeneity on diversity can take decades to materialize and depend on development of stochastic processes in communities with strong establishment limitation.

1 aBaer, S.G.1 aAdams, T.1 aScott, D.A.1 aBlair, John, M.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/10.1002/eap.201401602nas a2200157 4500008004100000245007500041210006900116300001400185490000700199520109500206100001601301700002101317700001501338700002001353856007101373 2019 eng d00aChanges in potential nitrous oxide efflux during grassland restoration0 aChanges in potential nitrous oxide efflux during grassland resto a1913-19170 v483 a

14 Nitrous oxide efflux from soil is an important ecological process in terms of global climate 15 impacts, stratospheric chemistry, and soil fertility. The effects of grassland restoration on nitrous 16 oxide (N 2 O) efflux in formerly cultivated agricultural soils are not well known. Restoration 17 changes the storage and availability of soil C and N, with potential consequences for N 2 O efflux. 18 We examined changes in potential N 2 O efflux across a 35-year chronosequence of grassland 19 restorations, using lab incubations at moisture levels that maximized N 2 O emissions, to quantify 20 the relationship between N 2 O efflux and soil properties known to change predictably during 21 grassland restoration. We found that restoring cultivated agricultural land to grassland rapidly 22 decreased N 2 O efflux from soils, though native prairie had a potential N 2 O efflux higher than the 23 agricultural land. The oldest restoration had N 2 O efflux 50 times lower than native prairie. 24 Changes in N 2 O efflux were more strongly correlated with N mineralization than C.

1 aScott, D.A.1 aRosenzweig, S.T.1 aBaer, S.G.1 aBlair, John, M. uhttps://acsess.onlinelibrary.wiley.com/doi/10.2134/jeq2019.05.018702672nas a2200133 4500008004100000245011800041210006900159300001600228490000800244520221200252100001602464700001502480856004302495 2019 eng d00aDiversity patterns from sequentially restored grasslands support the ‘environmental heterogeneity hypothesis’0 aDiversity patterns from sequentially restored grasslands support a1116 - 11220 v1283 a

The ‘environmental heterogeneity hypothesis’ (EHH) has been proposed as a mechanism that enables species coexistence through resource partitioning. In accordance with this hypothesis, plant diversity is predicted to increase with variability in resources, but there has been weak support for this hypothesis from experimental studies. The objectives of this research were to 1) characterize how resource availability and heterogeneity (coefficient of variation) change as plant communities develop using sequentially restored grasslands, 2) determine if resource heterogeneity relates to plant diversity (effective number of species, richness, and evenness), and 3) reveal if the strength of resource heterogeneity–diversity relationships is different among levels of resource availability. We quantified means and coefficients of variation in soil nitrate and light availability in grasslands established on former agricultural lands for different times and their relationship to plant diversity using a geostatistically‐informed design. Nitrate availability decreased exponentially with restoration age, but no directional change in nitrate heterogeneity across the chronosequence occurred due to high resource variability in some restorations. Light availability also decreased exponentially across the chronosequence, but there was no directional change in light heterogeneity. Nitrate heterogeneity was positively correlated with both plant richness and plant effective number of species at high levels of nitrate availability. However, no nitrate heterogeneity correlation was detected at low levels of nitrate availability. Light heterogeneity was positively correlated with plant effective number of species at low levels of light availability. However, no light heterogeneity correlation was detected at high levels of light availability. Plant evenness was not correlated with resource heterogeneity at any resource availability level. These results support the positive heterogeneity–diversity relationship predicted by EHH, and uniquely that this relationship develops within a decade of plant community development, but can be obscured by resource availability.

1 aScott, D.A.1 aBaer, S.G. uhttp://doi.wiley.com/10.1111/oik.0587702504nas a2200145 4500008004100000245015200041210006900193300001000262490000700272520195500279100001602234700001502250700002002265856007302285 2017 eng d00aRecovery and relative influence of root, microbial, and structural properties of soil on physically sequestered carbon stocks in restored grassland0 aRecovery and relative influence of root microbial and structural a50-600 v813 a

Managing soil to sequester C can help mitigate increasing CO2 in the atmosphere. To maximize this ecosystem service, more knowledge of factors influencing C sequestration is needed. The objectives of this study were to (i) quantify recovery of the roots, microbial biomass and composition, and soil structure across a chronosequence of grassland restorations and (ii) use a structural equation model to develop a data-based hypothesis on the relative influence of physical and biological soil properties on the soil C aggregate fraction diagnostic of sequestered C. Belowground plant biomass and tissue quality (C/N ratio), soil microbial biomass C, phospholipid fatty acid (PLFA) concentrations, soil structure, and soil C stocks in the bulk soil and each aggregate fraction were quantified from a cultivated field, prairies restored for 1 to 35-yr (n = 6), and a never-cultivated (native) prairie. Root biomass, microbial biomass C, arbuscular mycorrhizal fungi (AMF) PLFA biomass across the chronosequence increase to resemble native prairie following 35 yr of restoration. Many aspects of soil structure (i.e., bulk density, proportional mass of aggregate fractions, and aggregate mean weighted diameter) and the distribution C among soil fractions, including C in the micro-within-macro aggregate fraction (sequestered C), also became representative of native prairie within 35 yr of restoration. Total soil C stock and physically protected C increased at a similar rate (23 and 27 g C m-2 yr-1) respectively, across the chronosequence. After 35 yr of restoration, 50% of the total C pool was physically protected. The structural equation modeling developed by these data hypothesizes that microbial biomass C and AMF biomass (microbial composition) have the strongest causal influence on physically protected C. This model needs to be tested using independent sites to achieve greater inference.

1 aScott, D.A.1 aBaer, S.G.1 aBlair, John, M. uhttps://dl.sciencesocieties.org/publications/sssaj/abstracts/81/1/5000508nas a2200121 4500008004100000245012500041210006900166260006000235490001400295100001600309700001500325856004600340 2015 eng d00aRecovery of whole soil conditions through restoration from agriculture and its role in mediating plant-plant competition0 aRecovery of whole soil conditions through restoration from agric aCarbondale, ILbSouthern Illinois University Carbondale0 vMS Thesis1 aScott, D.A.1 aBaer, S.G. uhttps://opensiuc.lib.siu.edu/theses/1826/