title: 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 (13)C, 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.
authors.affiliation: Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC) Campus Universitario de Espinardo PO Box 164 E-30100 Murcia Spain.
authors.forename: Lupe
authors.initials: L
authors.lastname: León-Sánchez
authors.affiliation: Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC) Campus Universitario de Espinardo PO Box 164 E-30100 Murcia Spain.
authors.forename: Emilio
authors.initials: E
authors.lastname: Nicolás
authors.affiliation: Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC) Campus Universitario de Espinardo PO Box 164 E-30100 Murcia Spain.
authors.forename: Pedro A
authors.initials: PA
authors.lastname: Nortes
authors.affiliation: Biodiversity and Conservation Unit Department of Biology and Geology Universidad Rey Juan Carlos Móstoles 28933 Madrid Spain.
authors.forename: Fernando T
authors.initials: FT
authors.lastname: Maestre
authors.affiliation: Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC) Campus Universitario de Espinardo PO Box 164 E-30100 Murcia Spain.
authors.forename: José I
authors.initials: JI
authors.lastname: Querejeta
keywords: Climate change; Helianthemum squamatum; dryland ecosystems; leaf trait plasticity; plant nutrient status; plant survival and growth; plant–climate interactions; stable isotopes