Precipitation, not air temperature, drives functional responses of trees in semi‐arid ecosystems

Abstract

Summary1. Model scenarios of climate change predict that warming and drought will occur simultaneously in the future in many regions. The capacity of woody species to modify their physiology and morphology in response to environmental conditions is widely recognized, but little is known about the responses of trees to reduced precipitation and increased temperature acting simultaneously. 2. In a semi-arid woodland, we assessed the responses in physiological (needle emergence, maximum photosynthesis, stomatal conductance, water use efficiency (WUE) and shoot elongation) and morphological (needle length and thickness, and leaf mass per area (LMA)) foliar traits of piñon pine (Pinus edulis) in response to three years of a 45% reduction in precipitation, a 4.8°C increase in air temperature and their simultaneous effects. 3. A strong change in physiological and morphological traits in response to reduced precipitation was observed. Precipitation reduction delayed needle emergence, decreased photosynthesis and stomatal conductance, increased WUE, decreased shoot elongation and induced shorter needles with a higher LMA. Trees subjected to simultaneous reductions in precipitation and warming demonstrated a similar response. However, atmospheric warming did not induce a response in any of the measured traits. 4. Physiological and morphological traits of trees in this semi-arid climate were more responsive to changes in soil moisture than air temperature. Long-term exposure to seasonal drought stress in arid sites may have resulted in strong plastic responses to this first stressor. However, atmospheric warming probably was not experienced as a stress for trees in this warm and dry climate. Overall, our results indicate that in semi-arid ecosystems where tree functioning is already highly limited by soil water availability, atmospheric warming as anticipated with climate change may have less impact on foliar trait responses than previously thought.

Phenological and physiological evaluation of first and second cropping periods of sorghum and maize crops

“…Low temperatures may have promoted inhibition in chloroplast function, altering the composition of foliar pigments (Maulana & Tesso, ), as well as lower levels of solar irradiance and water availability, especially during vegetative growth (Righi et al, ). Increases in VPD values, as well as low rainfall levels, probably drove the reduction in stomatal conductance, affecting the diffusion of CO 2 into the leaf, leading to decreases in net assimilation rate (Grossiord et al, ). In general, reductions in net assimilation rate during plant growth after full leaf expansion occur, and this decline is generally driven by a decrease in stomatal conductance and transpiration rates (Locke & Ort, ).…”

Reductions in tree performance during hotter droughts are mitigated by shifts in nitrogen cycling

“…Mean yearly relative extractable water (REW, unitless) calculated using a soil water balance model (Grossiord, Sevanto, Adams, et al, ) and mean yearly air temperature (°C) over the 1997–2016 period at the study site. Starting in 2012 (when treatments started), REW and air temperature are given for each treatment.…”

Using Landlab, a Fine Scale Biogeography Model, to Measure the Sustainability of Semi-Arid Vegetation in a Changing Climate

“…Unlike our findings, however, (Garcia-Forner et al, 2016;Grossiord et al, 2017) found no compounding effect of increased drought in addition to increased temperatures. This discrepancy could simply be the result of differing timescales; while a change in climate might not have a measurable response in vegetation in the short term (such as (Bates et al, 2006) observed in the initial years of their study), or be confounded by previous conditions, this climate pattern can have a large enough effect on tree survival to change species distribution in a climate scenario that has been run until steady state.…”

“…Consistently with our results, (Grossiord et al, 2017) demonstrate that Pinus edulis, a tree species common to North America that grows in semi-arid locations, exhibits plastic changes in response to drought, but has only a moderate response to an increase in temperature alone. Unlike our findings, however, (Garcia-Forner et al, 2016;Grossiord et al, 2017) found no compounding effect of increased drought in addition to increased temperatures.…”

“…Previous work has researched the effects of drought and changes in temperature on Bates et al, 2006;Schwinning, Starr, & Ehleringer, 2005a;Williams et al, 2012;Yetemen et al, 2015), but little work has been done to tease out which of the two is more important, although Grossiord et al (2017) have researched this in a semi-arid woodland. The goal of our research is to promote fundamental understanding of the relative sensitivity of vegetation types to changes in precipitation and temperature in these water-limited environments using a numerical modeling approach.…”