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

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 (A CO 2 ), and soil CO 2 efflux (J CO 2 ) despite only ∼40 % variation in mean volumetric soil water content (0-15 cm, 15 ). Interannual variation in soil moisture was thus amplified in most measures of ecosystem response. Differences between years in 15 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 15 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 J CO 2 , and reduced summer J CO 2 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 Correspondence to: P. A. Fay (philip.fay@ars.usda.gov) 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.

Tallgrass prairie soil fungal communities are resilient to climate change

“…The function and composition of the plant communities in grassland ecosystems have been proposed to be sensitive to variability in climatic conditions (Knapp & Smith 2001;Gao & Reynolds 2003). In grassland ecosystems, shifts in timing of precipitation -not in the total quantitycan be important controls of plant productivity Fay et al 2011), soil respiration (Harper et al 2005;Fay et al 2011), as well as function and structure of soil communities (Zeglin et al 2013). As soil moisture and its variability are major controls of the broad scale function and composition of the soil communities on various spatial (Brockett et al 2012) and temporal scales (Zeglin et al 2013), more detailed evaluation of community responses to long-term manipulations are timely.…”

“…While such changes in the per event volume of rainfall as well as in their frequency have been suggested to lead to rapid alterations in soil processes as well as aboveground community composition Fay et al 2003;Harper et al 2005;Swemmer et al 2007;Fay et al 2011), consequences of such alterations for belowground microbial communities have received comparatively less attention (Chou et al 2008;Zeglin et al 2013). This major gap prohibits our understanding of the soil community responses to changes in soil water that far exceed those witnessed for dominant plants (Huxman et al 2004;Ogle & Reynolds 2004;Schwinning & Sala 2004), tend to be more dynamic, and responsive to pulse events (Austin et al 2004;Ogle & Reynolds 2004;Carbone et al 2011).…”

“…While both water and temperature are major abiotic controls of grassland ecosystem carbon exchange (Xu et al 2004;Davidson & Jansens 2006;Fay et al 2011), the effects of altered precipitation are not as well understood as those of elevated CO 2 or temperature (Weltzin et al 2003). Studies focusing on the interactions of multiple global change drivers may be fewer yet (Bardgett et al 2008).…”

Annual grassland resource pools and fluxes: sensitivity to precipitation and dry periods on two contrasting soils

“…Climate projections from general circulation models vary as to whether total precipitation will increase or decrease in different regions over the next century, but most models predict increased variability in rainfall patterns (Cayan et al 2008). Many individual below-and aboveground processes that control water (H 2 O), carbon (C) and nitrogen (N) cycling in terrestrial ecosystems are known to be affected by seasonal rainfall patterns (Knapp et al 2002, Austin et al 2004, Xu and Baldocchi 2004, Nippert et al 2006, Carbone et al 2011, Fay et al 2011, Tiemann and Billings 2011. If soil and plant responses result in the net release of carbon from soils, positive carbon cycle-climate feedback loops may amplify climate change (Heimann and Reichstein 2008).…”

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“…41 It is important to elucidate the mechanisms underlying the relationships between productivity, plant diversity, and 42 precipitation with ongoing global change (Fay et al 2011;Huxman et al 2004; Knapp et al 2008; Knapp et al 2002; 43 Shen et al 2015; Weltzin et al 2003). That is because changing precipitation regimes and other anthropogenic 44 disturbances likely alter community composition and ecosystem functionality, and consequently affect ecosystem 45 services and human welfare (Carmona et 50 A large number of studies have accepted the term of precipitation-use efficiency (PUE, the ratio of ANPP to 51 precipitation) as a proxy of the sensitivity of productivity response to precipitation, because it has normalized the 52 effect of water availability by placing productivity on a per-unit-of-precipitation basis (Bai et Knapp et al (2002) 60 found that PUE was influenced mostly by community composition and that species complementarity ensured greater 61 and more stable productivity in species rich grasslands.…”