Warming and species range mediate the temperature response of respiration in plants at the temperate-boreal ecotone
Climate change is shifting the ranges of tree species in temperate and boreal forests, and the physiological responses and constraints of these species under environmental change will determine the forests’ future carbon balance and community structure. Respiration, which provides energy for growth and maintenance and, together with photosynthesis, controls plant carbon cycling, responds to temperature in the short-term (minutes to hours) with a dynamic response and in the long-term (days to years) through acclimation. It remains unclear how respiration will respond at moderate and high temperatures in northern- and southern-ranged deciduous and evergreen trees. Here we examine how leaf respiration is altered by growth under warming and drought in species occupying the temperate-boreal ecotone in Northern Minnesota.
At the B4WarmED global change experiment, leaves were sampled from seedlings of five species representing northern (Betula papifera, Picea glauca) and southern (Pinus strobus, Quercus macrocarpa, Acer rubrum) ranges grown under ambient conditions and the following treatments: +3.4 oC warming, partial rain exclusion to simulate drought, and warming with drought. We measured dark respiration as leaves were warmed continuously from 10 oC until a maximum rate (Rmax) was reached (at a temperature, Tmax, of 50-60 oC). For temperatures between 10-45 oC, we analyzed the response curve with a second order polynomial to quantify the curve shape for all replicates, and derived the temperate sensitivity of the respiratory response.
Across the 10-45 °C range, the respiration-temperature response curve shape did not differ between species, and further, this shared temperature sensitivity was unaffected by experimental warming and drought. However, for a northern-ranged deciduous species and both evergreen conifer species, rates at any given measurement temperature were ~30-45% lower in warm-grown plants than their ambient temperature grown counterparts, indicating that respiration acclimated to the higher growth temperature;. However, the southern-ranged deciduous species did not exhibit evidence of thermal acclimation. Elevated growth temperatures also increased values of Tmaxacross all species (e.g. by ~1-4 °C).
These findings imply life-history and range-dependent controls on physiological flexibility in terms of absolute rates of respiration under environmental change. The ability to thermally acclimate, considering the range of measured temperatures from 10 to 45oC, is only observed in northern-ranged deciduous and evergreen species (but with Tmax increasing in all species), suggesting variability in the underlying requirement and/or ability to shift metabolic efficiency under warming and drought conditions.