Pastures and Climate Extremes: Impacts of Cool Season Warming and Drought on the Productivity of Key Pasture Species in a Field Experiment.

Amber C Churchill ,Haiyang Zhang,Burhan Amiji,Elise Pendall,Vinod Jacob,Yolima Carrillo,Gil Won Kim,Chioma Igwenagu,Karen L M Catunda ,Ian C Anderson ,Mark G Tjoelker ,Jeff R Powell ,Craig V M Barton ,Kathryn J Fuller ,David T Tissue ,Belinda E Medlyn ,Manjunatha H Chandregowda ,Charles B Macdonald ,Jonathan M Plett ,Ben D Moore ,Alison K Post ,Sally A Power

doi:10.3389/fpls.2022.836968

Amber C Churchill , Haiyang Zhang + Show 20 more

Open Access

https://doi.org/10.3389/fpls.2022.836968

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Abstract

Shifts in the timing, intensity and/or frequency of climate extremes, such as severe drought and heatwaves, can generate sustained shifts in ecosystem function with important ecological and economic impacts for rangelands and managed pastures. The Pastures and Climate Extremes experiment (PACE) in Southeast Australia was designed to investigate the impacts of a severe winter/spring drought (60% rainfall reduction) and, for a subset of species, a factorial combination of drought and elevated temperature (ambient +3°C) on pasture productivity. The experiment included nine common pasture and Australian rangeland species from three plant functional groups (C3 grasses, C4 grasses and legumes) planted in monoculture. Winter/spring drought resulted in productivity declines of 45% on average and up to 74% for the most affected species (Digitaria eriantha) during the 6-month treatment period, with eight of the nine species exhibiting significant yield reductions. Despite considerable variation in species’ sensitivity to drought, C4 grasses were more strongly affected by this treatment than C3 grasses or legumes. Warming also had negative effects on cool-season productivity, associated at least partially with exceedance of optimum growth temperatures in spring and indirect effects on soil water content. The combination of winter/spring drought and year-round warming resulted in the greatest yield reductions. We identified responses that were either additive (Festuca), or less-than-additive (Medicago), where warming reduced the magnitude of drought effects. Results from this study highlight the sensitivity of diverse pasture species to increases in winter and spring drought severity similar to those predicted for this region, and that anticipated benefits of cool-season warming are unlikely to be realized. Overall, the substantial negative impacts on productivity suggest that future, warmer, drier climates will result in shortfalls in cool-season forage availability, with profound implications for the livestock industry and natural grazer communities.

Highlights

Climate change is a dominant driver of ecosystem change across the globe (Steffen et al, 2015; Sage, 2019)
We found that eight of the nine C3 and C4 species exposed to extreme winter/spring drought experienced significant reductions in cool season productivity, with 45% declines on average among species and losses of up to 74%, relative to controls
Despite large species differences in drought sensitivity, we did find evidence for functional group-specific responses between C4 grasses, C3 grasses, and legumes, such that C4 grasses had the greatest response to drought

Summary

Introduction

Climate change is a dominant driver of ecosystem change across the globe (Steffen et al, 2015; Sage, 2019). Despite a recent increase in the number of studies focusing on climate extremes (De Boeck et al, 2015, 2019; Power et al, 2016; Knapp et al, 2017; Hanson and Walker, 2019), relatively few have addressed the ecological implications of seasonal shifts in climate, which is important for understanding the underlying trade-offs between plant phenology and associated plant functional group responses (i.e., C3 vs C4, legumes; Beier et al, 2012). In temperate and subtropical climates, grasslands dominated by C3 grasses mainly accrue biomass during cooler periods of the year (i.e., winter or spring), while C4-dominated grasslands typically accumulate biomass later in the growing season, when temperatures are higher (Pearcy and Ehleringer, 1984; Pearcy et al, 1987; Adams et al, 2016; Wilcox et al, 2016) These broad patterns are based on key differences in optimum temperatures for photosynthesis (Figure 1), as well as differences in water-use-efficiency and strategies for nutrient acquisition. It is important to evaluate climate impacts for a wide range of forage species grown in monoculture in order to predict productivity responses and capacity to expand into new regions or vulnerability within current ranges as local climate shifts (Johnston, 1996; Bindi and Olesen, 2011)

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