Abstract
Anthropogenic forces are projected to lead to warmer temperatures and altered precipitation patterns globally. The impact of these climatic changes on the uptake of carbon by the land surface will, in part, determine the rate and magnitude of these changes. However, there is a great deal of uncertainty in how terrestrial ecosystems will respond to climate in the future. Here, we used a fully factorial warming (four levels) by precipitation (three levels) manipulation experiment in an old-field ecosystem in the northeastern USA to examine the impact of climatic changes on leaf carbon exchange in five species of deciduous tree seedlings. We found that photosynthesis generally increased in response to increasing precipitation and decreased in response to warming. Respiration was less sensitive to the treatments. The net result was greater leaf carbon uptake in wetter and cooler conditions across all species. Structural equation modelling revealed the primary pathway through which climate impacted leaf carbon exchange. Net photosynthesis increased with increasing stomatal conductance and photosynthetic enzyme capacity (Vcmax), and decreased with increasing respiration of leaves. Soil moisture and leaf temperature at the time of measurement most heavily influenced these primary drivers of net photosynthesis. Leaf respiration increased with increasing soil moisture, leaf temperature, and photosynthetic supply of substrates. Counter to the soil moisture response, respiration decreased with increasing precipitation amount, indicating that the response to short- (i.e. soil moisture) versus long-term (i.e. precipitation amount) water stress differed, possibly as a result of changes in the relative amounts of growth and maintenance demand for respiration over time. These data (>500 paired measurements of light and dark leaf gas exchange), now publicly available, detail the pathways by which climate can impact leaf gas exchange and could be useful for testing assumptions in land surface models.
Highlights
Terrestrial carbon exchange represents the largest flux of carbon between the Earth’s surface and the atmosphere (Le Quereet al. 2012; IPCC, 2013) and studies have shown that land-atmosphere carbon cycle feedbacks are a major source of uncertainty in the Earth System Models used to project climate change (Friedlingstein et al 2013)
All research was conducted at the Boston-Area Climate Experiment (BACE; Rodgers et al 2012; Suseela et al 2012), which is located in an old-field ecosystem at the University of Massachusetts’ Suburban Experiment Station in Waltham, Massachusetts, USA (42 230 300 N, 71 120 5200 W)
We used a climate manipulation experiment in an oldfield ecosystem to examine the responses of net photosynthesis (An) and dark respiration (Rd) to warming and altered precipitation
Summary
Terrestrial carbon exchange represents the largest flux of carbon between the Earth’s surface and the atmosphere (Le Quereet al. 2012; IPCC, 2013) and studies have shown that land-atmosphere carbon cycle feedbacks are a major source of uncertainty in the Earth System Models used to project climate change (Friedlingstein et al 2013). Photosynthesis and plant respiration are variable and strongly influenced by climatic conditions (Wu et al 2011; Lu et al 2012), but scientific understanding of how these fluxes will be altered by climate change remains limited (Arneth et al 2010). Short-term (seconds to minutes) warming typically increases enzymatic rates and, subsequently, rates of photosynthesis and respiration up to a peak, beyond which rates decline. This optimum occurs at a lower temperature in photosynthesis than respiration. Warming may reduce net photosynthesis (i.e. photosynthesis minus leaf respiration) if it increases leaf respiration to a greater degree than photosynthesis
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