Grassland productivity is regulated by both temperature and the amount and timing of precipitation 1,2. Future climate change is therefore expected to influence grassland phenology and growth, with consequences for ecosystems and economies. However, the interacting e ects of major shifts in temperature and precipitation on grasslands remain poorly understood and existing modelling approaches, although typically complex, do not extrapolate or generalize well and tend to disagree under future scenarios 3,4. Here we explore the potential responses of North American grasslands to climate change using a new, data-informed vegetation-hydrological model, a network of high-frequency ground observations across a wide range of grassland ecosystems and CMIP5 climate projections. Our results suggest widespread and consistent increases in vegetation fractional cover for the current range of grassland ecosystems throughout most of North America, despite the increase in aridity projected across most of our study area. Our analysis indicates a likely future shift of vegetation growth towards both earlier spring emergence and delayed autumn senescence, which would compensate for drought-induced reductions in summer fractional cover and productivity. However, because our model does not include the e ects of rising atmospheric CO 2 on photosynthesis and water use e ciency 5,6 , climate change impacts on grassland productivity may be even larger than our results suggest. Increases in the productivity of North American grasslands over this coming century have implications for agriculture, carbon cycling and vegetation feedbacks to the atmosphere. The grassland biome is the largest in the world, covering up to 59 million km 2 (over 30% of the global land surface) 1. Grasslands constitute a key component of the terrestrial biosphere and are fundamental to the meat and dairy industries 1 , but projections of grassland growth and productivity from model intercomparison studies diverge greatly under climate change 3,4. Grassland growth and productivity are highly dynamic on fast (days-to-weeks) timescales, leading to substantial variability between years 7-9. Grassland growth is largely controlled by soil water content and the magnitude, frequency and timing of precipitation events 10-12. The response of grasslands to changes in precipitation
There are inherent challenges in scaling stomatal conductance (g
s) from leaf to canopy particularly over seasonal time scales when species distribution and canopy structure evolve. We address this gap using carbonyl sulfide (OCS) and CO
2 fluxes from a predominantly C3 prairie and C4 maize field in the midwestern United States. The g
s derived from OCS fluxes captured a transition in the stomatal limitation on gross primary productivity (GPP) through the growing season as well as seasonally persistent g
s dynamics such as temperature optimum and a positive response of nighttime g
s to vapor pressure deficit. Near the termination of the prairie growing season, we observed a decrease in the relative OCS to CO
2 flux that we hypothesize emerged from a rising contribution of C4 plants to productivity. The results show how plot‐scale OCS and CO
2 fluxes can be used as a trace gas diagnostic for transitions in the limiting factors for community GPP.
Perennial grasses are promising feedstocks for bioenergy production in the Midwestern USA. Few experiments have addressed how drought influences their carbon fluxes and storage. This study provides a direct comparison of ecosystem-scale measurements of carbon fluxes associated with miscanthus (Miscanthus × giganteus), switchgrass (Panicum virgatum), restored native prairie and maize (Zea mays)/soybean (Glycine max) ecosystems. The main objective of this study was to assess the influence of a naturally occurring drought during 2012 on key components of the carbon cycle and plant development relative to non-extreme years. The perennials reached full maturity 3-5 years after establishment. Miscanthus had the highest gross primary production (GPP) and lowest net ecosystem exchange (NEE) in 2012 followed by similar values for switchgrass and prairie, and the row crops had the lowest GPP and highest NEE. A post-drought effect was observed for miscanthus. Over the duration of the experiment, perennial ecosystems were carbon sinks, as indicated by negative net ecosystem carbon balance (NECB), while maize/soybean was a net carbon source. Our observations suggest that perennial ecosystems, and in particular miscanthus, can provide a high yield and a large potential for CO2 fixation even during drought, although drought may negatively influence carbon uptake in the following year, questioning the long-term consequence of its maintained productivity.
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