Abstract
Heat-waves with higher intensity and frequency and longer durations are expected in the future due to global warming, which could have dramatic impacts in agriculture, economy and ecology. This field study examined how plant responded to heat-stress (HS) treatment at different timing in naturally occurring vegetation. HS treatment (5 days at 40.5°C) were applied to 12 1 m2 plots in restored prairie vegetation dominated by a warm-season C4 grass, Andropogon gerardii, and a warm-season C3 forb, Solidago canadensis, at different growing stages. During and after each heat stress (HS) treatment, temperature were monitored for air, canopy, and soil; net CO2 assimilation (Anet), quantum yield of photosystem II (ΦPSII), stomatal conductance (gs), and internal CO2 level (Ci), specific leaf area (SLA), and chlorophyll content of the dominant species were measured. One week after the last HS treatment, all plots were harvested and the biomass of above-ground tissue and flower weight of the two dominant species were determined. HS decreased physiological performance and growth for both species, with S. canadensis being affected more than A. gerardii, indicated by negative HS effect on both physiological and growth responses for S. canadensis. There were significant timing effect of HS on the two species, with greater reductions in the net photosynthetic rate and productivity occurred when HS was applied at later-growing season. The reduction in aboveground productivity in S. canadensis but not A. gerardii could have important implications for plant community structure by increasing the competitive advantage of A. gerardii in this grassland. The present experiment showed that HS, though ephemeral, may promote long-term effects on plant community structure, vegetation dynamics, biodiversity, and ecosystem functioning of terrestrial biomes when more frequent and severe HS occur in the future.
Highlights
The increased concentration of CO2 and other greenhouse gasses in atmosphere is causing a future climate with higher temperatures and dramatic changes in rainfall patterns (IPCC, 2013)
Leaf area index (LAI) was highest at the plots heat-stressed at early-growing season and lowest at the plots heat-stressed at reproductive-growing stage (Figure 2C)
We found that (1) the physiology of both species and growth of S. canadensis were affected by HS treatment; (2) the degree of HS effect varied when it applied at different growing stages, with greater negative effect associated with HS applied at later-growing season; (3) the physiology and growth of the two dominant species showed differential sensitivity to HS, with S. canadensis being affected more than A. gerardii
Summary
The increased concentration of CO2 and other greenhouse gasses in atmosphere is causing a future climate with higher temperatures and dramatic changes in rainfall patterns (IPCC, 2013). Extreme climate events, in spite of their ephemeral nature, can potentially cause shifts in the structure of plant communities (Smith, 2011) and greatly impact ecosystem productivity (Ciais et al, 2005) and biodiversity (Thomas et al, 2004). It is, difficult to determine whether the ecological response is explicitly attributable to an extreme climate event, since it may not be extreme enough to cause ecological consequences (Niu et al, 2014)
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