Photosynthesis and growth reduction with warming are driven by nonstomatal limitations in a Mediterranean semi‐arid shrub

Abstract

Whereas warming enhances plant nutrient status and photosynthesis in most terrestrial ecosystems, dryland vegetation is vulnerable to the likely increases in evapotranspiration and reductions in soil moisture caused by elevated temperatures. Any warming‐induced declines in plant primary production and cover in drylands would increase erosion, land degradation, and desertification. We conducted a four‐year manipulative experiment in a semi‐arid Mediterranean ecosystem to evaluate the impacts of a ~2°C warming on the photosynthesis, transpiration, leaf nutrient status, chlorophyll content, isotopic composition, biomass growth, and postsummer survival of the native shrub Helianthemum squamatum. We predicted that warmed plants would show reduced photosynthetic activity and growth, primarily due to the greater stomatal limitation imposed by faster and more severe soil drying under warming. On average, warming reduced net photosynthetic rates by 36% across the study period. Despite this strong response, warming did not affect stomatal conductance and transpiration. The reduction of peak photosynthetic rates with warming was more pronounced in a drought year than in years with near‐average rainfall (75% and 25–40% reductions relative to controls, respectively), with no indications of photosynthetic acclimation to warming through time. Warmed plants had lower leaf N and P contents, δ 13C, and sparser and smaller leaves than control plants. Warming reduced shoot dry mass production by 31%. However, warmed plants were able to cope with large reductions in net photosynthesis, leaf area, and shoot biomass production without changes in postsummer survival rates. Our findings highlight the key role of nonstomatal factors (biochemical and/or nutritional) in reducing net carbon assimilation rates and growth under warming, which has important implications for projections of plant carbon balance under the warmer and drier climatic scenario predicted for drylands worldwide. Projected climate warming over the coming decades could reduce net primary production by about one‐third in semi‐arid gypsum shrublands dominated by H. squamatum.

Simulated climate change decreases nutrient resorption from senescing leaves

“…Despite these variable effects of warming on leaf nutrient concentrations, we found an overall decrease in mature leaf nutrient contents (i.e., leaf N, P, K, Ca, Mg, S, Fe, and Zn pools) with warming, either alone (W) or in combination with rainfall reduction (W+RR). This is in contrast to other studies that found minor, neutral, or even positive effects of climate change on leaf nutrients in temperate and boreal ecosystems (Aerts et al, ; Bai et al, ; Chapin, Shaver, Giblin, Nadelhoffer, & Laundre, ; Hobbie & Chapin III, ; Welker, Fahnestock, Sullivan, & Chimner, ; Zong et al, ), but is consistent with previous observations in dry Mediterranean ecosystems (León‐Sánchez et al, , , ; Salazar‐Tortosa et al, ; Sardans et al, ; Sardans, Peñuelas, et al, ; Sardans, Peñuuelas, Estiarte, & Prieto, ).…”

Experimental warming in a dryland community reduced plant photosynthesis and soil CO2 efflux although the relationship between the fluxes remained unchanged

“…Warming of a semi‐arid shrubland also caused a reduction of A net , with no accompanying decline in g s , reducing leaf WUE (León‐Sánchez et al . ). The change in leaf level WUE we observed with warming has significant implications for our understanding of how dryland water and C cycles, and their interactions, will respond to global change.…”

Water use segregation among plants with contrasting root depth and distribution along gypsum hills

“…; León‐Sánchez et al. ). Consequently, they have different mechanisms to adjust their transpiring biomass during summer.…”

“…; León‐Sánchez et al. ). Gypsum crystallization water seems a relatively stable water source for shallow‐rooted plants, but it may come at a cost.…”