Relative effects of precipitation variability and warming on tallgrass prairie ecosystem function

P A Fay,M D Smith,J M Blair,J D Carlisle,J B Nippert,A K Knapp

doi:10.5194/bg-8-3053-2011

Abstract

Abstract. Precipitation and temperature drive many aspects of terrestrial ecosystem function. Climate change scenarios predict increasing precipitation variability and temperature, and long term experiments are required to evaluate the ecosystem consequences of interannual climate variation, increased growing season (intra-annual) rainfall variability, and warming. We present results from an experiment applying increased growing season rainfall variability and year round warming in native tallgrass prairie. During ten years of study, total growing season rainfall varied 2-fold, and we found ~50–200% interannual variability in plant growth and aboveground net primary productivity (ANPP), leaf carbon assimilation (ACO2), and soil CO2 efflux (JCO2) despite only ~40% variation in mean volumetric soil water content (0–15 cm, Θ15). Interannual variation in soil moisture was thus amplified in most measures of ecosystem response. Differences between years in Θ15 explained the greatest portion (14–52%) of the variation in these processes. Experimentally increased intra-annual season rainfall variability doubled the amplitude of intra-annual soil moisture variation and reduced Θ15 by 15%, causing most ecosystem processes to decrease 8–40% in some or all years with increased rainfall variability compared to ambient rainfall timing, suggesting reduced ecosystem rainfall use efficiency. Warming treatments increased soil temperature at 5 cm depth, particularly during spring, fall, and winter. Warming advanced canopy green up in spring, increased winter JCO2, and reduced summer JCO2 and forb ANPP, suggesting that the effects of warming differed in cooler versus warmer parts of the year. We conclude that (1) major ecosystem processes in this grassland may be substantially altered by predicted changes in interannual climate variability, intra-annual rainfall variability, and temperature, (2) interannual climate variation was a larger source of variation in ecosystem function than intra-annual rainfall variability and warming, and (3) effects of increased growing season rainfall variability and warming were small, but ecologically important. The relative effects of these climate drivers are likely to vary for different ecosystem processes and in wetter or drier ecosystems.

Highlights

Terrestrial ecosystems account for large exchanges of carbon (C) with the atmosphere (Denman et al, 2007), but the control of these fluxes by climate remains poorly understood
This study was conducted in the Rainfall Manipulation Plots (RaMPs) facility at the Konza Prairie Biological Station (KPBS) in northeastern Kansas, USA (39◦05 N, 96◦35 W)
There was more interannual variation in ecosystem function than there was from intra-annual rainfall variability and warming

Summary

Introduction

Terrestrial ecosystems account for large exchanges of carbon (C) with the atmosphere (Denman et al, 2007), but the control of these fluxes by climate remains poorly understood. Important variation in precipitation and temperature, from an ecosystem perspective, occurs on daily to decadal time scales (Bonan, 2002; Goodin et al, 2002). Projected increases in atmospheric CO2 and other greenhouse gases are expected to reinforce these trends (Karl et al, 2009). These observed and expected changes in the means and variability of precipitation and temperature on inter- and intra-annual time scales will likely have important impacts on terrestrial ecosystem

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Discussion

Conclusion