High Temperature Acclimation of Leaf Gas Exchange, Photochemistry, and Metabolomic Profiles in Populus trichocarpa

Abstract

High temperatures alter the thermal sensitivities of numerous physiological and biochemical processes that impact tree growth and productivity. Foliar and root applications of methanol have been implicated in plant acclimation to high temperature via the C 1 pathway. Here, we characterized temperature acclimation at 35°C of leaf gas exchange, chlorophyll fluorescence, and extractable metabolites of potted Populus trichocarpa saplings and examined potential influences of mM concentrations of methanol added during soil watering over a twomonth period. Relative to plants grown under the low growth temperature (LGT), high growth temperature (HGT) plants showed a suppression of leaf water use and carbon cycling including transpiration (E), net photosynthesis (P n ), an estimate of photorespiration (R p ), and dark respiration (R d ), attributed to reductions in stomatal conductance and direct negative effects on gas exchange and photosynthetic machinery. In contrast, HGT plants showed an upregulation of nonphotochemical quenching (NPQ t ), the optimum temperature for ETR, and leaf isoprene emissions at 40°C. A large number of metabolites (867) were induced under HGT, many implicated in flavonoid biosynthesis highlighting a potentially protective role for these compounds. Methanol application did not significantly alter leaf gas exchange but slightly reduced the suppression of R d and R p by the high growth temperature while slightly impairing ETR, Fv′/Fm′, and q p . However, we were unable to determine if soil methanol was sufficiently taken up by the plant to have a direct effect on foliar processes. A small number of extracted leaf tissue metabolites (55 out of 10 015) showed significantly altered abundances under LGT and methanol treatments relative to water controls, and this increased in compound number ( 222) at the HGT. The results demonstrate the large physiological and biochemical impacts of high growth temperature on poplar seedlings and highlight the enhancement of the optimum temperature of ETR as a rapid thermal acclimation mechanism. Although no large effect on leaf physiology was observed, the results are consistent with methanol both impairing photochemistry of the light reactions via formaldehyde toxicity and stimulating photosynthesis and dark respiration through formate oxidation to CO 2 .

Cell wall ester modifications and volatile emission signatures of plant response to abiotic stress

“…Prolonged excessive water loss via transpiration not replaced by water uptake from the soil can result in drought‐induced tissue senescence and mortality, thereby converting individual plants and ecosystems from net sinks of CO 2 to net sources (Jardine et al, 2015 ; Liu et al, 2021 ; McDowell et al, 2008 ). Understanding the biological mechanisms and environmental thresholds that determine plant responses to drought stress is critical for predicting how the structure and function of managed ecosystems will respond to environmental change (Dewhirst et al, 2021 ; McDowell et al, 2008 ).…”

Response Mechanisms of Woody Plants to High-Temperature Stress

“…The electron transfer of photosynthesis was inhibited, and the actual fluorescence value (Ft) decreased [79]. In addition to the above indicators, it also leads to the upregulation of chlorophyll fluorescence nonphotochemical quenching (NPQ) [80]. The efficiency of photosynthesis under high-temperature stress is also related to the antioxidant system and osmotic regulation.…”

Chemical Interactions in the Plant–Atmosphere–Soil System

“…The findings by DeVore et al 7 provide new insights regarding biological and physicochemical processes affecting arsenic accumulation in plants and potential bioremediation applications of fungi. Dewhirst et al 8 describe the effects of hightemperature acclimation in a poplar tree and provide some clues on the potential protective role of methanol against high temperatures. Place et al 9 illustrate how deposition of organic nitrate compounds are driven by leaf stomatal uptake.…”