The temperature optima for tree seedling photosynthesis and growth depend on water inputs

Abstract

Understanding how tree growth is affected by rising temperature is a key to predicting the fate of forests in future warmer climates. Increasing temperature has direct effects on plant physiology, but there are also indirect effects of increased water limitation because evaporative demand increases with temperature in many systems. In this study, we experimentally resolved the direct and indirect effects of temperature on the response of growth and photosynthesis of the widely distributed species Eucalyptus tereticornis. We grew E. tereticornis in an array of six growth temperatures from 18 to 35.5°C, spanning the climatic distribution of the species, with two watering treatments: (a) water inputs increasing with temperature to match plant demand at all temperatures (Wincr), isolating the direct effect of temperature; and (b) water inputs constant for all temperatures, matching demand for coolest grown plants (Wconst), such that water limitation increased with growth temperature. We found that constant water inputs resulted in a reduction of temperature optima for both photosynthesis and growth by ~3°C compared to increasing water inputs. Water limitation particularly reduced the total amount of leaf area displayed at Topt and intermediate growth temperatures. The reduction in photosynthesis could be attributed to lower leaf water potential and consequent stomatal closure. The reduction in growth was a result of decreased photosynthesis, reduced total leaf area display and a reduction in specific leaf area. Water availability had no effect on the response of stem and root respiration to warming, but we observed lower leaf respiration rates under constant water inputs compared to increasing water inputs at higher growth temperatures. Overall, this study demonstrates that the indirect effect of increasing water limitation strongly modifies the potential response of tree growth to rising global temperatures.

Global Patterns and Climate Controls of Terrestrial Ecosystem Light Use Efficiency

“…Increasing evidences had shown that vegetation responses to temperature could be regulated by moisture conditions (e.g., Reich et al, 2018;Wang et al, 2014Wang et al, , 2018. Kumarathunge et al (2020) further showed that the optimum temperature of photosynthesis became higher in more moist conditions, which helped explain more positive S LUE-T with higher mean annual precipitation. This interactive effect, however, was not well captured by data-driven models.…”

Unrevealing water and carbon relations during and after heat and hot drought stress in Pinus sylvestris

“…Further, few experimental studies have focused on the responses of trees to a combination of heat and drought stress (e.g. Zhao et al, 2013;Bauweraerts et al, 2013Bauweraerts et al, , 2014Birami et al, 2020;Kumarathunge et al, 2020), and even less have addressed subsequent recovery trajectories (Ruehr et al, 2016(Ruehr et al, , 2019Birami et al, 2018). In general, our understanding of tree physiological recovery from combined heat waves and drought stress is very limited (Ruehr et al, 2019), thus hindering our ability of forecasting tree responses to climatic extremes.…”

Warming Reduces Net Carbon Gain and Productivity in Medicago sativa L. and Festuca arundinacea

“…These few studies have investigated the response of photosynthesis and respiration to water stress [49], N fertilisation [50,51], shading [52], or only investigated daytime respiration [46]. Importantly, the responses of photosynthesis and respiration to temperature can be confounded by the effect of temperature on evapotranspiration and plant water status [53], which were rarely accounted for in previous studies.…”