@article {KNZ002044, title = {Fire history as a key determinant of grassland soil CO2 flux}, journal = {Plant and Soil}, volume = {460}, year = {2021}, pages = {579{\textendash}592}, keywords = {LTER-KNZ, aboveground net primary production, carbon cycling, ecosystem, fire, grassland, soil CO2 flux, soil respiration}, doi = {10.1007/s11104-020-04781-0}, url = {http://link.springer.com/10.1007/s11104-020-04781-0}, author = {Slette, Ingrid J. and Liebert, Alannah and Alan K. Knapp} } @article {KNZ001928, title = {Carbon exchange responses of a mesic grassland to an extreme gradient of precipitation}, journal = {Oecologia}, year = {2018}, pages = {1 -12}, abstract = {

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.

}, keywords = {LTER-KNZ, Climate extremes, Drought, Primary production, Rainfall, soil respiration}, doi = {10.1007/s00442-018-4284-2}, url = {https://link.springer.com/article/10.1007/s00442-018-4284-2}, author = {Felton, A.J. and Alan K. Knapp and M.D. Smith} } @article {KNZ001752, title = {Changes in soil properties, microbial biomass, and fluxes of C and N in soil following post-agricultural grassland restoration}, journal = {Applied Soil Ecology}, volume = {100}, year = {2016}, pages = {186 - 194}, abstract = {

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.

}, keywords = {LTER-KNZ, Bulk density, chronosequence, soil respiration, SOM recovery, tallgrass prairie}, issn = {09291393}, doi = {10.1016/j.apsoil.2016.01.001}, url = {https://www.sciencedirect.com/science/article/pii/S0929139316300014?via\%3Dihub}, author = {Rosenzweig, S.T. and Carson, M.A. and S.G. Baer and John M. Blair} } @article {KNZ00893, title = {Regional patterns in carbon cycling across the Great Plains of North America}, journal = {Ecosystems}, volume = {8}, year = {2005}, pages = {106 -121}, abstract = {The 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.}, keywords = {LTER-KNZ, grassland, Great Plains, litter decomposition, Net primary production, Precipitation, Regional trends, soil respiration}, doi = {10.1007/s10021-004-0117-8}, author = {McCulley, R.L. and Burke, I.C. and Nelson, J.A. and Lauenroth, W.K. and Alan K. Knapp and Kelly, E.F.} }