No acclimation: instantaneous responses to temperature maintain homeostatic photosynthetic rates under experimental warming across a precipitation gradient in Ulmus americana

Abstract

Past research has shown that plants possess the capacity to alter their instantaneous response of photosynthesis to temperature in response to a longer-term change in temperature (i.e. acclimate). This acclimation is typically the result of processes that influence net photosynthesis (Anet), including leaf biochemical processes such as the maximum rate of Rubisco carboxylation (Vcmax) and the maximum rate of photosynthetic electron transport (Jmax), stomatal conductance (gs) and dark respiration (Rd). However, these processes are rarely examined in the field or in concert with other environmental factors, such as precipitation amount. Here, we use a fully factorial warming (active heating up to +4 °C; mean = +3.1 °C) by precipitation (−50 % ambient to 150 % ambient) manipulation experiment in an old-field ecosystem in the north-eastern USA to examine the degree to which Ulmus americana saplings acclimate through biochemical and stomatal adjustments. We found that rates of Anet at ambient CO2 levels of 400 µmol mol−1 (A400) did not differ across climate treatments or with leaf temperatures from 20 to 30 °C. Canopy temperatures rarely reached above 30 °C in any treatment, suggesting that seasonal carbon assimilation was relatively homeostatic across all treatments. Assessments of the component processes of A400 revealed that decreases in gs with leaf temperature from 20 to 30 °C were balanced by increases in Vcmax, resulting in stable A400 rates despite concurrent increases in Rd. Photosynthesis was not affected by precipitation treatments, likely because the relatively dry year led to small treatment effects on soil moisture. As temperature acclimation is likely to come at a cost to the plant via resource reallocation, it may not benefit plants to acclimate to warming in cases where warming would not otherwise reduce assimilation. These results suggest that photosynthetic temperature acclimation to future warming will be context-specific and that it is important to consider assimilatory benefit when assessing acclimation responses.

Stomatal conductance, not biochemistry, drives low temperature acclimation of photosynthesis in Populus balsamifera, regardless of nitrogen availability

“…2020; but see Smith et al . 2020). The one possible signal of biochemical acclimation that we did observe was a decrease in the JV ratio with increased acclimation temperatures.…”

Temperature acclimation of leaf respiration differs between marsh and mangrove vegetation in a coastal wetland ecotone

“…Consequently, only daytime warming is achieved using this design with minimal warming occurring during cloudy weather, when radiation is limited, or at night. However, unlike infrared heaters, chambers warm air temperatures rather than canopy surface temperatures (e.g., De Boeck et al, 2012; Smith et al, 2020) and do not inhibit dew formation (Feng et al, 2021). In the event of a tropical storm, we removed the polyethylene film from the PVC frames so that chambers would not become airborne.…”

The physiological acclimation and growth response of Populus trichocarpa to warming

“…Warming has been shown to affect soil respiration rates (Bond‐Lamberty & Thomson 2010), and both hetero‐ and autotrophic respiration are predicted to increase as the planet continues to warm (Atkin et al 2005; Atkin & Tjoelker 2003; Bond‐Lamberty & Thomson 2010). Photosynthesis, on the other hand, can acclimate (i.e., adjust to maintain or improve physiological functioning) to increasing temperature (Berry & Björkman 1980; Kamarathunge et al 2018; Sage & Kubien 2007); but, there is little evidence that increases in photosynthetic rates with increasing temperature will keep pace with increases in respiration rates (Smith et al 2020), especially if plants reach critical thermal thresholds. This mismatch could lead to an abrupt decline in C uptake and storage (Jump & Peñuelas 2005).…”