03493nas a2200217 4500008004100000245013500041210006900176300000900245490000700254520282100261653001003082653001403092653002203106653001303128653001603141653001603157100001803173700001503191700002003206856004903226 2017 eng d00aEffects of grazing and fire frequency on floristic quality and its relationship to indicators of soil quality in tallgrass prairie0 aEffects of grazing and fire frequency on floristic quality and i a10750 v603 a
Fire and grazing are widely used to manage grasslands for conservation purposes, but few studies have evaluated the effects of these drivers on the conservation value of plant communities measured by the floristic quality index (FQI). Further, the influence of fire and grazing on soil properties and functions are difficult for land managers and restoration practitioners to assess. The objectives of this study were to: (1) quantify the independent and interactive effects of grazing and fire frequency on floristic quality in native tallgrass prairie to provide potential benchmarks for community assessment, and (2) to explore whether floristic quality can serve as an indicator of soil structure and function for more holistic ecosystem assessments. A factorial combination of fire frequencies (1–2, 4, and 20 years return intervals) and grazing (by bison or ungrazed) treatments were sampled for plant species composition, and for several indicators of soil quality in lowland tallgrass prairie. Floristic quality, diversity, and richness were higher in grazed than ungrazed prairie over all fire frequencies (P < 0.05). Available inorganic N, microbial biomass N, total N, and soil bulk density were also higher in grazed prairie soil over all fire frequencies (P < 0.05). Microbial biomass C, total organic C, and total soil N were positively correlated with FQI (P < 0.05). This study shows that floristic quality and soil N pools are more strongly influenced by grazing than fire and that floristic quality can be an indicator of total soil C and N stocks in never cultivated lowland prairie.
10abison10agrassland10aMicrobial biomass10anitrogen10arestoration10aSoil carbon1 aManning, G.C.1 aBaer, S.G.1 aBlair, John, M. uhttps://www.ncbi.nlm.nih.gov/pubmed/2896357202039nas a2200193 4500008004100000245011200041210006900153300001200222490000700234520138600241653001101627653001801638653002201656653002601678653002101704100001601725700001701741856008701758 2016 eng d00aMechanisms driving the soil organic matter decomposition response to nitrogen enrichment in grassland soils0 aMechanisms driving the soil organic matter decomposition respons a54 - 650 v993 aEmpirical studies show that nitrogen (N) addition often reduces microbial decomposition of soil organic matter (SOM) and carbon dioxide (CO2) production via microbial respiration. Although predictions from theoretical models support these findings, the mechanisms that drive this response remain unclear. To address this uncertainty, we sampled soils of three grassland sites in the U.S. Central Great Plains that each have received seven years of continuous experimental nutrient addition in the field. Nitrogen addition significantly decreased the decomposition rate of slowly cycling SOM and the cumulative carbon (C) respired per mass soil C. We evaluated whether this effect of N addition on microbial respiration resulted from: 1) increased microbial carbon use efficiency (CUE), 2) decreased microbial oxidative enzyme activity, or 3) decreased microbial biomass due to plant and/or soil mediated responses to N enrichment. In contrast to our hypotheses – as well as results from N addition studies in forest ecosystems and theoretical predictions – N did not increase microbial CUE or decrease microbial oxidative enzyme activity. Instead, reduced microbial biomass likely caused the decreased respiration in response to N enrichment. Identifying what factors drive this decreased microbial biomass response to N should be a priority for further inquiry.
10acarbon10aFertilization10aMicrobial biomass10aMicrobial respiration10aNutrient Network1 aRiggs, C.E.1 aHobbie, S.E. uhttps://www.sciencedirect.com/science/article/abs/pii/S0038071716300608?via%3Dihub03035nas a2200229 4500008004100000245009300041210006900134300001500203490000700218520227700225653001502502653003902517653002202556653002902578653003102607653002202638100001502660700001502675700001602690700001202706856008702718 2011 eng d00aSoil texture affects soil microbial and structural recovery during grassland restoration0 aSoil texture affects soil microbial and structural recovery duri a2182 -21910 v423 aMany biotic and abiotic factors influence recovery of soil communities following prolonged disturbance. We investigated the role of soil texture in the recovery of soil microbial community structure and changes in microbial stress, as indexed by phospholipid fatty acid (PLFA) profiles, using two chronosequences of grasslands restored from 0 to 19 years on silty clay loam and loamy fine sand soils in Nebraska, USA. All restorations were formerly cultivated fields seeded to native warm-season grasses through the USDA’s Conservation Reserve Program. Increases in many PLFA concentrations occurred across the silty clay loam chronosequence including total PLFA biomass, richness, fungi, arbuscular mycorrhizal fungi, Gram-positive bacteria, Gram-negative bacteria, and actinomycetes. Ratios of saturated:monounsaturated and iso:anteiso PLFAs decreased across the silty clay loam chronosequence indicating reduction in nutrient stress of the microbial community as grassland established. Multivariate analysis of entire PLFA profiles across the silty clay loam chronosequence showed recovery of microbial community structure on the trajectory toward native prairie. Conversely, no microbial groups exhibited a directional change across the loamy fine sand chronosequence. Changes in soil structure were also only observed across the silty clay loam chronosequence. Aggregate mean weighted diameter (MWD) exhibited an exponential rise to maximum resulting from an exponential rise to maximum in the proportion of large macroaggregates (>2000 μm) and exponential decay in microaggregates (<250 μm and >53 μm) and the silt and clay fraction (<53 μm). Across both chronosequences, MWD was highly correlated with total PLFA biomass and the biomass of many microbial groups. Strong correlations between many PLFA groups and the MWD of aggregates underscore the interdependence between the recovery of soil microbial communities and soil structure that may explain more variation than time for some soils (i.e., loamy fine sand). This study demonstrates that soil microbial responses to grassland restoration are modulated by soil texture with implications for estimating the true capacity of restoration efforts to rehabilitate ecosystem functions.
10aAggregates10aConservation Reserve Program (CRP)10aMicrobial biomass10aPhospholipid fatty acids10aSoil microbial communities10atallgrass prairie1 aBach, E.M.1 aBaer, S.G.1 aMeyer, C.K.1 aSix, J. uhttps://www.sciencedirect.com/science/article/abs/pii/S0038071710003020?via%3Dihub02839nas a2200265 4500008004100000245010400041210006900145300001500214490000700229520201100236653001802247653002402265653001402289653002102303653001402324653002202338653001902360653001802379653002102397653001202418100001902430700001702449700002002466856008702486 2008 eng d00aConversion of grassland to coniferous woodland has limited effects on soil nitrogen cycle processes0 aConversion of grassland to coniferous woodland has limited effec a2627 -26330 v403 aIn the last century, conversion of native North American grasslands to Juniperus virginiana forests or woodlands has dramatically altered ecosystem structure and significantly increased ecosystem carbon (C) stocks. We compared soils under recently established J. virginiana forests and adjacent native C4-dominated grassland to assess changes in potential soil nitrogen (N) transformations and plant available N. Over a 2-year period, concentrations of extractable inorganic N were measured in soils from forest and grassland sites. Potential gross N ammonification, nitrification, and consumption rates were determined using 15N isotope-dilution under laboratory conditions, controlling for soil temperature and moisture content. Potential nitrification rates (Vmax) and microbial biomass, as well as soil physical and chemical properties were also assessed. Extractable NH4+ concentrations were significantly greater in grassland soils across the study period (P ≤ 0.01), but analysis by date indicated that differences in extractable inorganic N occurred more frequently in fall and winter, when grasses were senescent but J. virginiana was still active. Laboratory-based rates of gross N mineralization (ammonification) and nitrification were greater in grassland soils (P ≤ 0.05), but only on one of four dates. Potential nitrification rates (Vmax) were an order of magnitude greater than gross nitrification rates in both ecosystems, suggesting that nitrification is highly constrained by NH4+ availability. Differences in plant uptake of N, C inputs, and soil microclimate as forests replace grasslands may influence plant available N in the field, as evidenced by seasonal differences in soil extractable NH4+, and total soil C and N accumulation. However, we found few differences in potential soil N transformations under laboratory conditions, suggesting that this grassland-to-forest conversion caused little change in mineralizable organic N pools or potential microbial activity.
10aExtractable N10aForest encroachment10agrassland10aIsotope dilution10aJuniperus10aMicrobial biomass10aMineralization10anitrification10aNitrogen cycling10aprairie1 aMcKinley, D.C.1 aRice, C., W.1 aBlair, John, M. uhttps://www.sciencedirect.com/science/article/abs/pii/S0038071708002320?via%3Dihub02465nas a2200205 4500008004100000245015900041210006900200300001100269490000700280520169400287653001401981653002201995653001302017653002302030653002002053100001902073700002002092700001802112856012902130 2001 eng d00aDifferent behavioral patterns of the earthworms Octolasion tyrtaeum and Diplocardia spp . in tallgrass prairie soils: potential influences on plant growth0 aDifferent behavioral patterns of the earthworms Octolasion tyrta a49 -560 v343 aThis study addressed differences between Diplocardia spp. (a native North American earthworm) and Octolasion tyrtaeum (an introduced European species), with respect to behavior, influence on soil microbial biomass, and plant uptake of N in tallgrass prairie soils. We manipulated earthworms in PVC-encased soil cores (20 cm diameter) over a 45-day period under field conditions. Treatments included: (1) control with no earthworms, (2) Diplocardia spp. only, and (3) O. tyrtaeum only. Prior to addition of earthworms, seedlings of Andropogon gerardii (a dominant tallgrass) were established in each core, and a dilute solution of 13C-labeled glucose and 15N-labeled (NH4)2SO4 was added to the soil to facilitate examination of earthworm/microbe/plant interactions. We found that Diplocardia spp. were significantly more active than O. tyrtaeum, and quickly assimilated 13C and 15N from the tracer. Individuals of Diplocardia spp. were present at shallower soil depths than O. tyrtaeum throughout the study. Contrary to expectation, this greater activity of Diplocardia spp. did not result in increased plant productivity. Rather, the activity of Diplocardia spp. was associated with less plant growth and smaller amounts of N acquired by A. gerardii seedlings compared to controls or O. tyrtaeum treatments. We observed few significant influences of earthworm treatments on microbial biomass C or N pool sizes, but the microbial C/N ratio was consistently greater in the presence of Diplocardia spp. relative to O. tyrtaeum. Results of this study indicate that activity of earthworms may enhance competition for N between microbes and plants during the growing season in tallgrass prairie.10agrassland10aMicrobial biomass10anitrogen10aSoil invertebrates10aStable isotopes1 aCallaham, M.A.1 aBlair, John, M.1 aHendrix, P.F. uhttp://lter.konza.ksu.edu/content/different-behavioral-patterns-earthworms-octolasion-tyrtaeum-and-diplocardia-spp-tallgrass02663nas a2200205 4500008004100000245010000041210006900141300001300210490000800223520195400231653001702185653002302202653002202225653001702247653001502264100001902279700001702298700001802315856012402333 2000 eng d00aCarbon dynamics and microbial activity in tallgrass prairie exposed to elevated CO2 for 8 years0 aCarbon dynamics and microbial activity in tallgrass prairie expo a127 -1370 v2273 aAlterations in microbial mineralization and nutrient cycling may control the long-term response of ecosystems to elevated CO2. Because micro-organisms constitute a labile fraction of potentially available N and are regulators of decomposition, an understanding of microbial activity and microbial biomass is crucial. Tallgrass prairie was exposed to twice ambient CO2 for 8 years beginning in 1989. Starting in 1991 and ending in 1996, soil samples from 0 to 5 and 5 to 15 cm depths were taken for measurement of microbial biomass C and N, total C and N, microbial activity, inorganic N and soil water content. Because of increased water-use-efficiency by plants, soil water content was consistently and significantly greater in elevated CO2 compared to ambient treatments. Soil microbial biomass C and N tended to be greater under elevated CO2 than ambient CO2 in the 5–15 cm depth during most years, and in the month of October, when analyzed over the entire study period. Microbial activity was significantly greater at both depths in elevated CO2 than ambient conditions for most years. During dry periods, the greater water content of the surface 5 cm soil in the elevated CO2 treatments increased microbial activity relative to the ambient CO2 conditions. The increase in microbial activity under elevated CO2 in the 5–15 cm layer was not correlated with differences in soil water contents, but may have been related to increases in soil C inputs from enhanced root growth and possibly greater root exudation. Total soil C and N in the surface 15 cm were, after 8 years, significantly greater under elevated CO2 than ambient CO2. Our results suggest that decomposition is enhanced under elevated CO2 compared with ambient CO2, but that inputs of C are greater than the decomposition rates. Soil C sequestration in tallgrass prairie and other drought-prone grassland systems is, therefore, considered plausible as atmospheric CO2 increases.10aelevated CO210amicrobial activity10aMicrobial biomass10aSoil C and N10asoil water1 aWilliams, M.A.1 aRice, C., W.1 aOwensby, C.E. uhttp://lter.konza.ksu.edu/content/carbon-dynamics-and-microbial-activity-tallgrass-prairie-exposed-elevated-co2-8-years03162nas a2200217 4500008004100000245009700041210006900138300001300207490000700220520243800227653003302665653001202698653001102710653002202721653001402743653001302757100001602770700001902786700001702805856012202822 2000 eng d00aEffects of long-term fungicide application on microbial processes in tallgrass prairie soils0 aEffects of longterm fungicide application on microbial processes a935 -9460 v323 aSeveral studies investigating the role of arbuscular mycorrhizal (AM) fungi in plant communities have included manipulations of AM fungal symbiosis using the fungicide benomyl. The objectives of this study were to evaluate the potential non-target effects of benomyl on soil biota and nutrient cycling in tallgrass prairie and to determine how mycorrhizae may influence these belowground properties. To accomplish these objectives, soil samples were collected during the 1996–1997 growing seasons from long-term benomyl-treated plots established on tallgrass prairie (Manhattan, KS) in 1991, and the following measurements were made: total bacterial and fungal biomass; abundance of nematodes; microbial biomass carbon and nitrogen; substrate-induced respiration; and potentially mineralizable C and N. Long-term benomyl applications resulted in an 80% reduction in mycorrhizal root colonization. By reducing root colonization, benomyl applications resulted in significant decreases in total bacterial biomass and abundance of fungal-feeding and predatory nematodes (20, 12 and 33% reductions compared to control, respectively). Total microbial potential activity (i.e., substrate-induced respiration) increased by 10% with benomyl treatment, whereas the relative contribution of fungi to total microbial activity decreased significantly with benomyl applications. In addition, microbial biomass C increased from 1364 (± 51.2 SE) to 1485 (± 51.2 SE) with benomyl treatment, and total carbon increased significantly (∼8%) only in annually burned soils treated with benomyl. The magnitude of benomyl effects on soil components and processes were small (<33% change with benomyl) relative to effects on mycorrhizal root colonization (80% decrease with benomyl). These results indicate that rather than having large non-target effects, benomyl applications principally affect mycorrhizal root colonization, thereby indirectly influencing soil biota and nutrient availability. Results also indicate that mycorrhizal fungi play an important role in altering the availability and flow of carbon in prairie soil and may influence the composition and abundance of groups of some soil biota. Changes in soil organisms and nutrient availability associated with altered mycorrhizal symbiosis may influence aboveground plant species responses to mycorrhizal suppression, but further research is needed to understand these potential effects.10aArbuscular mycorrhizal fungi10aBenomyl10acarbon10aMicrobial biomass10aNematodes10anitrogen1 aSmith, M.D.1 aHartnett, D.C.1 aRice, C., W. uhttp://lter.konza.ksu.edu/content/effects-long-term-fungicide-application-microbial-processes-tallgrass-prairie-soils