Publications by Colleges and Departments (MSU - Bozeman)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/3
Browse
2 results
Search Results
Item Long-term decline in grassland productivity driven by increasing dryness(2015) Brookshire, E. N. Jack; Weaver, T.Increasing aridity and drought severity forecast for many land areas could reduce the land carbon (C) sink. However, with limited long-term direct measures, it is difficult to distinguish direct drying effects from counter effects of CO2 enrichment and nitrogen (N) deposition. Here, we document a >50% decline in production of a native C3 grassland over four decades and assign the forcing and timing to increasing aridity and specifically to declining late-summer rainfall. Analysis of C and N stable isotopes in biomass suggests that enhanced water use efficiency via CO2 enrichment may have slightly ameliorated the productivity decline but that changes in N had no effects. Identical declines in a long-term snow-addition experiment definitively identified increasing late-summer dryness as the cause. Our results demonstrate lasting consequences of recent climate change on grassland production and underscore the importance of understanding past climate–ecosystem coupling to predicting future responses to changing climate.Item Long-term snowpack manipulation promotes large loss of bioavailable nitrogen and phosphorus in a subalpine grassland(2015-05) Yano, Yuriko; Brookshire, E. N. Jack; Holsinger, Jordan P.; Weaver, T.Nutrient retention in ecosystems requires synchrony between the supply of bioavailable nutrients released via mineralization and nutrient uptake by plants. Though disturbance and chronic nutrient loading are known to alter nitrogen (N) and phosphorus (P) dynamics and induce nutrient export, whether long-term shifts in climate affect source-sink synchrony, and ultimately primary productivity, remains uncertain. This is particularly true for snow-dominated ecosystems, which are naturally subject to lags between nutrient inputs and uptake. To address how climate change may affect nutrient source-sink synchrony we examined the impacts of deepened snowpack on N and P losses in a subalpine grassland in the Northern Rocky Mountains, USA, where we have experimentally increased snowpack depths by two- and four-times ambient snow for 45 years. Long-term snow addition resulted in remarkably high levels of bioavailable-N leaching (up to 16 kg ha^-1 year^-1) that were 11-80 times higher than those under ambient snowpack. Estimated bioavailable-P losses also increased with snow addition, but to a lesser degree (up to 0.3 kg ha^-1 year^-1), indicating greater enhancement of N losses over P losses during snowmelt. Because these losses could not be explained by changes in nutrient inputs in snowpack or by changes in plant-soil turnover, our results suggest that high bioavailable-N leaching under deep snowpack originates not from a lack of N limitation of plant productivity, but rather from enhanced subnivean microbial processes followed by snowmelt leaching prior to the growing season. This is supported by reduced soil N pools in the snow treatments. Snow-dominated regions are projected to experience shifts in seasonal snowpack regime. These shifts may ultimately affect the stoichiometric balance between available N and P and future plant productivity.