00665nas a2200217 4500008004100000245006500041210006500106300001400171490000800185653003900193653001900232653001400251653000900265653001400274653001800288653002100306100002300327700002100350700002000371856005600391 2021 eng d00aFire history as a key determinant of grassland soil CO2 flux0 aFire history as a key determinant of grassland soil CO2 flux a579–5920 v46010aaboveground net primary production10acarbon cycling10aecosystem10afire10agrassland10asoil CO2 flux10asoil respiration1 aSlette, Ingrid, J.1 aLiebert, Alannah1 aKnapp, Alan, K. uhttp://link.springer.com/10.1007/s11104-020-04781-002697nas a2200193 4500008004100000245009100041210006900132300001000201520208500211653002102296653001202317653002302329653001302352653002102365100001702386700002002403700001602423856006402439 2018 eng d00aCarbon exchange responses of a mesic grassland to an extreme gradient of precipitation0 aCarbon exchange responses of a mesic grassland to an extreme gra a1 -123 a

Growing evidence indicates that ecosystem processes may be differentially sensitive to dry versus wet years, and that current understanding of how precipitation affects ecosystem processes may not be predictive of responses to extremes. In an experiment within a mesic grassland, we addressed this uncertainty by assessing responses of two key carbon exchange processes—aboveground net primary production (ANPP) and soil respiration (Rs) - to an extensive gradient of growing season precipitation. This gradient comprised 11 levels that specifically included extreme values in precipitation; defined as the 1st, 5th, 95th, and 99th percentiles of the 112-year climate record. Across treatments, our experimental precipitation gradient linearly increased soil moisture availability in the rooting zone (upper 20 cm). Relative to ANPP under nominal precipitation amounts (defined as between the 15th and 85th percentiles), the magnitude of ANPP responses were greatest to extreme increases in precipitation, with an underlying linear response to both precipitation and soil moisture gradients. By contrast, Rs exhibited marginally greater responses to dry versus wet extremes, with a saturating relationship best explaining responses of Rs to both precipitation and soil moisture. Our findings indicate a linear relationship between ANPP and precipitation after incorporating responses to precipitation extremes in the ANPP–precipitation relationship, yet in contrast saturating responses of Rs. As a result, current linear ANPP–precipitation relationships (up to ~ 1000 mm) within mesic grasslands appear to hold as appropriate benchmarks for ecosystems models, yet such models should incorporate nonlinearities in responses of Rs amid increased frequencies and magnitudes of precipitation extremes.

10aClimate extremes10aDrought10aPrimary production10aRainfall10asoil respiration1 aFelton, A.J.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007/s00442-018-4284-203012nas a2200229 4500008004100000022001300041245013100054210006900185300001400254490000800268520225400276653001702530653001902547653002102566653001702587653002202604100002102626700001702647700001502664700002002679856008302699 2016 eng d a0929139300aChanges in soil properties, microbial biomass, and fluxes of C and N in soil following post-agricultural grassland restoration0 aChanges in soil properties microbial biomass and fluxes of C and a186 - 1940 v1003 a

Understanding the dynamics of soil C and N pools and fluxes following grassland restoration in formerly cultivated soils is needed to assess the capacity of this land-use change to return soil properties and function to pre-disturbance conditions. We examined changes in physical (bulk density) and chemical (pH, available P and N, and total stocks of C and N) properties, microbial biomass C and N, and transformation rates of C and N in soil (0–10 cm depth) across a 35-year chronosequence of prairie restorations and never-cultivated (native) prairie to evaluate the rate and extent to which sowing native perennial plants into formerly cultivated soils returns soil to steady state conditions. Bulk density, available P, and extractable inorganic N decreased exponentially across the chronosequence. Soil pH increased linearly across the chronosequence to exceed that in native prairie soil. Total C and N stocks in cultivated soil were <50% that of native prairie, and increased at rates of 26.2 g C m−2 year−1 and 1.68 g N m−2 year−1 across the chronosequence. In the oldest restoration, total C and N stocks were 55% and 41% higher than the cultivated soil, respectively. Recovery of C and N stocks to levels comparable to native prairie soil was estimated to take 350 years. Microbial biomass C and N increased 5-fold. Potential C mineralization rate was comparable to native prairie soil following two decades of restoration, and exceeded native prairie in the 35-years restoration. In situ soil CO2 efflux reached equilibrium in <30 years. Potential net N mineralization rate, however, did not exhibit a directional change across the restoration chronosequence, but was lowest in the oldest restored grasslands. Thus, cessation of tillage and sowing native vegetation leads to rapid decreases in available N and P, and promotes rapid (decadal scale) recovery of labile soil organic matter pools, but recovery of total C and N pools requires several centuries. This study suggests that soil properties related to nutrient retention and regulation of nutrient availability can be reestablished within the first few decades of restoration, while C sequestration will continue on a longer time scale.

10aBulk density10achronosequence10asoil respiration10aSOM recovery10atallgrass prairie1 aRosenzweig, S.T.1 aCarson, M.A.1 aBaer, S.G.1 aBlair, John, M. uhttps://www.sciencedirect.com/science/article/pii/S0929139316300014?via%3Dihub02490nas a2200265 4500008004100000245008100041210006900122300001300191490000600204520166200210653001401872653001701886653002501903653002701928653001801955653002001973653002101993100001902014700001602033700001702049700002002066700002002086700001602106856010202122 2005 eng d00aRegional patterns in carbon cycling across the Great Plains of North America0 aRegional patterns in carbon cycling across the Great Plains of N a106 -1210 v83 aThe large organic carbon (C) pools found in noncultivated grassland soils suggest that historically these ecosystems have had high rates of C sequestration. Changes in the soil C pool over time are a function of alterations in C input and output rates. Across the Great Plains and at individual sites through time, inputs of C (via aboveground production) are correlated with precipitation; however, regional trends in C outputs and the sensitivity of these C fluxes to annual variability in precipitation are less well known. To address the role of precipitation in controlling grassland C fluxes, and thereby soil C sequestration rates, we measured aboveground and belowground net primary production (ANPP-C and BNPP-C), soil respiration (SR-C), and litter decomposition rates for 2 years, a relatively dry year followed by a year of average precipitation, at five sites spanning a precipitation gradient in the Great Plains. ANPP-C, SR-C, and litter decomposition increased from shortgrass steppe (36, 454, and 24 g C m−2 y−1) to tallgrass prairie (180, 1221, and 208 g C m−2 y−1 for ANPP-C, SR-C, and litter decomposition, respectively). No significant regional trend in BNPP-C was found. Increasing precipitation between years increased rates of ANPP-C, BNPP-C, SR-C, and litter decomposition at most sites. However, regional patterns of the sensitivity of ANPP-C, BNPP-C, SR-C, and litter decomposition to between-year differences in precipitation varied. BNPP-C was more sensitive to between-year differences in precipitation than were the other C fluxes, and shortgrass steppe was more responsive than were mixed grass and tallgrass prairie.10agrassland10aGreat Plains10alitter decomposition10aNet primary production10aPrecipitation10aRegional trends10asoil respiration1 aMcCulley, R.L.1 aBurke, I.C.1 aNelson, J.A.1 aLauenroth, W.K.1 aKnapp, Alan, K.1 aKelly, E.F. uhttp://knz.lternet.edu/content/regional-patterns-carbon-cycling-across-great-plains-north-america