Impaired photosynthesis and increased leaf construction costs may induce floral stress during episodes of global warming over macroevolutionary timescales

Abstract

Global warming events have coincided with turnover of plant species at intervals in Earth history. As mean global temperatures rise, the number, frequency and duration of heat-waves will increase. Ginkgo biloba was grown under controlled climatic conditions at two different day/night temperature regimes (25/20 °C and 35/30 °C) to investigate the impact of heat stress. Photosynthetic CO2-uptake and electron transport were reduced at the higher temperature, while rates of respiration were greater; suggesting that the carbon balance of the leaves was adversely affected. Stomatal conductance and the potential for evaporative cooling of the leaves was reduced at the higher temperature. Furthermore, the capacity of the leaves to dissipate excess energy was also reduced at 35/30 °C, indicating that photo-protective mechanisms were no longer functioning effectively. Leaf economics were adversely affected by heat stress, exhibiting an increase in leaf mass per area and leaf construction costs. This may be consistent with the selective pressures experienced by fossil Ginkgoales during intervals of global warming such as the Triassic – Jurassic boundary or Early Eocene Climatic Optimum. The physiological and morphological responses of the G. biloba leaves were closely interrelated; these relationships may be used to infer the leaf economics and photosynthetic/stress physiology of fossil plants.

Lipid Peroxidation and Chlorophyll Fluorescence of Photosystem II Performance during Drought and Heat Stress is Associated with the Antioxidant Capacities of C3 Sunflower and C4 Maize Varieties

“…The present study would indicate that heat stress has a more pronounced effect on PSII function than drought ( Table 1 ; Figure 2 , Figure 3 and Figure 4 ); consistent with previous field-based observations of the impact of above 40 °C temperatures when combined with drought [ 16 , 33 , 48 ] and leaf gas exchange analysis ( Figure 1 ). The decrease in G s ( Figure 1 ) would reduce heat loss due to transpiration, resulting in higher leaf temperatures, which may contribute to damage to the thylakoid membranes as PSII photochemistry is reduced [ 18 , 49 ]. The OJIP transient suggested that impairment of PSII was more evident in drought stressed plants than in well-watered plants subject to the 35 °C treatment as more energy was dissipated per reaction center ( Figure 2 , Figure 3 and Figure 4 ).…”

“…Stomatal regulation is one of the most important adaptation mechanisms to environmental changes such as water deficit [ 10 , 22 , 32 , 62 , 63 ]. However, the limitation of CO 2 availability for photosynthesis due to stomatal closure results in an increase in un-utilized light energy ( Figure 1 ) [ 18 , 24 , 25 , 64 ]. This creates an imbalance between the generation and the utilization of electrons by PSII ( Figure 2 ) and PSI ( Figure 1 ) [ 20 , 65 ].…”

“…Analysis of the physiological mechanisms involved in crop responses to drought and heat stress may elucidate the photosynthetic and protective behaviors that underpin tolerance to these stresses. Chlorophyll fluorescence ( ChlF ) allows rapid non-destructive collection of data relating to the performance of photosystem II (PSII) [ 14 ] and is highly sensitive to the deleterious effects of drought [ 15 , 16 ] and heat [ 17 , 18 ] stress. To protect and stabilize the thylakoid membrane where PSII electron transport occurs, plants possess protective antioxidant mechanisms [ 19 , 20 ].…”

The Impact of Heat Stress and Water Deficit on the Photosynthetic and Stomatal Physiology of Olive (Olea europaea L.)—A Case Study of the 2017 Heat Wave

“…In contrast, we observed a reduction in G s H2O in olive during both the heat wave (Figure 1c) and, similar to results obtained in adult olive trees growing in field conditions [53], when exposed to an instantaneous increase in leaf temperature within the leaf cuvette (Figure 5b). Longer-term adaptation to temperature likely affects the response of G s H2O to instantaneous variations in leaf temperature [27,30,31,54]. An increase in leaf to air vapor pressure deficit (VPD) with temperature [50] may have induced stomatal closure in the well-watered olive plants through ABA synthesis [55].…”

“…Heat stress may also adversely affect plant water relations by increasing G s H2O [28,29]. However, longer-term stomatal adaptation to growth at higher temperatures (as oppose to instantaneous increases in leaf temperature) may result in no increase in G s H2O [20,27,30,31]. More detailed analysis of the photosynthetic and stomatal responses to temperature of plants from contrasting environments would enable a greater understanding of the likely impacts of heat waves on different vegetation types.…”