Timing Effects of Heat-Stress on Plant Ecophysiological Characteristics and Growth

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 (A_net), quantum yield of photosystem II (Φ_PSII), stomatal conductance (g_s), and internal CO₂ level (C_i), 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.

Keywords: Andropogon gerardii; Solidago canadensis; aboveground productivity; global climate change; photosynthesis.

FIGURE 1

Effects of HS applied at different growing stage on leaf temperature of (A)Andropogon Gerardii and (B)Solidago Canadensis. Measurements were taken during and after each heat-stress treatment. Values are means ± 1 SD; n = 4.

FIGURE 2

Effects of HS applied at different growing stage on (A) the aboveground net primary productivity, productivity of A. gerardii and S. Canadensis; (B) the flower weight of A. gerardii and S. Canadensis; (C) leaf area index (LAI). LAI was measured once during and twice after each heat-stress treatment. Values are means ± 1 SD; n = 4.

FIGURE 3

Effects of HS applied at different growing stage on (A) specific leaf area (SLA) and (B) relative leaf water content of A. gerardii and S. canadensis. Values are means ± 1 SD; n = 4.

FIGURE 4

Effects of HS applied at different growing stage on net photosynthesis (A_net), stomatal conductance (g_s), leaf internal CO₂ (C_i) and intrinsic water use efficiency of A. gerardii and S. canadensis. Measurements were taken once during and twice after each heat-stress treatment. Values are means ± 1 SD; n = 4.

FIGURE 5

Effects of HS applied at different growing stage on quantum yield of photosystem II (Φ_PSII) of (A)A. gerardii and (B)S. canadensis. Measurements were taken during and after each heat-stress treatment. Values are means ± 1 SD; n = 4.

FIGURE 6

Effects of HS applied at different growing stage on relative chlorophyll content of the newly develop, fully developed and senescent leaves of A. gerardii and S. canadensis. Measurements were taken during and after each heat-stress treatment. Values are means ± 1 SD; n = 4.