Does a warmer climate with frequent mild water shortages protect grassland communities against a prolonged drought?

Abstract

Global warming accelerates land surface drying, increasing the incidence of extreme climatic events such as severe droughts with detrimental effects on ecosystem functions and structure. We investigated the effects of an imposed severe drought (24 days) on fully established synthesized grassland communities with three species richness (S) levels (one, three or nine species), grown for 3 years at either ambient air temperatures (unheated) or ambient +3°C (heated). Since water supply during these 3 years was equal in all treatments, heated communities experienced more frequent, short mild droughts, but it was unknown whether this conferred greater or smaller resistance for facing prolonged droughts. During the 24-day drought period, soil matric potential decreased in a similar way over time in both temperature treatments and was lower at increasing S-levels. Although green vegetation cover was significantly reduced by the drought in both temperature treatments, the decrease was higher in heated than unheated communities indicating a lower resistance of heated communities to the drought. After only 13 days of recovery, green vegetation cover of both temperature treatments approached values similar to those observed before the imposed drought, suggesting similar resilience in both treatments. Above-ground biomass was reduced by elevated temperature, consistently in all S-levels, showing that the drought period did not change the biomass production patterns observed in the treatments before the imposed drought. Our results suggest that, regardless of the continuous exposure to elevated temperatures and associated short mild droughts, heated communities had not developed clear mechanisms to better cope with extended summer droughts.

Drought and Carbon Cycling of Grassland Ecosystems under Global Change: A Review

“…On the other hand, droughts are not buffered by increased biodiversity richness. Intriguingly, frequent mild droughts did not change the productivity patterns and point to a higher resistance to severe droughts, with increasing richness levels not necessarily enhancing resistance [91]. Similarly, higher drought stress with increased biodiversity richness led to greater mortality, yet all communities are able to recover similar green cover post-drought [150].…”

“…In grassland communities, mild droughts and warming do not lead to enhanced resistance or recovery from an extreme recurrent drought. Also, grasslands experiencing recurrent drought demonstrate a larger decrease in green vegetation cover [91]. For some drought-affected areas, however, annual NPP and NEE are not reduced, likely because higher temperatures enhance photosynthesis, counteracting the drought effects on NPP in those grasslands [91,92].…”

“…Also, grasslands experiencing recurrent drought demonstrate a larger decrease in green vegetation cover [91]. For some drought-affected areas, however, annual NPP and NEE are not reduced, likely because higher temperatures enhance photosynthesis, counteracting the drought effects on NPP in those grasslands [91,92]. Meanwhile, it is expected that climate warming may directly accelerate soil respiration by stimulating the activities of soil fauna, microbes, and plant roots, and may indirectly accelerate soil respiration by stimulating N mineralization, litter production, and substrate [93,94].…”

Drought, high temperature, and their combination affect ultrastructure of chloroplasts and mitochondria in wheat (Triticum aestivumL.) leaves

“…Although drought and high temperature often occur simultaneously (Zavalloni et al 2008), the underlying mechanisms concerning their combined effect on plants are poorly understood. Very few studies consider mesophyll cell ultrastructure and changes in major cell organelles after exposure to combined stress Cass 1991, 1992;Stoyanova and Yordanov 1999).…”

Effects of low precipitation periods on the herbage yield of mesic semi-natural grasslands under different cutting regimes

“…In botanically diverse grasslands, biodiversity provides a buffer against environmental fluctuations because different species respond differently to these fluctuations, leading to functional compensations among species (Tilman et al, 2006;Zavolloni et al, 2008). In temperate zones, with an adequate water supply and intensive land use, it's likely that fertilization and the cutting or grazing frequency may overcome the influence of climatic conditions…”