Effects of climate change on native plant communities in semiarid gypsum ecosystems

Abstract

In this thesis, we have simulated the climate conditions projected for the second half of XXI century, by using open top chambers (1-2ºC temperature increase in the wintertime and 4-6ºC in the summertime; W treatment), rainout shelters (-30% rainfall exclusion; RR treatment) and their combination (W+RR treatment) in order to assess the effects of forecasted climate change conditions on the performance of three semiarid Mediterranean shrubland communities located in central (Aranjuez) and southeastern Spain (Sorbas and Sax) throughout 4 hydrological years (2011-2015). Our target species are Helianthemum squamatum (present at the three study sites), Helianthemum syriacum, Gypsohila struthium, Santolina viscosa, Teucrium turredanum and Coris hispanica, which are native shrub species with different sizes/biovolumes, life history traits, phenology, stoichiometry, water use strategies and mycorrhizal association types (ectomycorrhizal or arbuscular mycorrhizal). For this purpose, we measured leaf gas exchange parameters (photosynthesis rate, stomatal conductance, transpiration, maximum efficiency of photosystem II under light conditions, the quantum efficiency of photosystem II and water use efficiency), carbon isotope ratio (δ13C), foliar nutrient status, leaf mass per unit area, shoot dry biomass production, shoot elongation, shoot growth phenology and survival rate at the end of the 4-year study period, as well as mycorrhizal fungal community composition and relative abundances. We hypothesized that warming, rainfall reduction and their combination would reduce soil water availability to an extent that would significantly impair plant nutrient uptake and status, while at the same time increasing stomatal limitation of photosynthesis, thus negatively affecting photosynthesis, productivity and survival across coexisting plant species in these three semiarid ecosystems. Moreover, we predicted that the climate manipulation treatments would impair the performance of both mycorrhizal fungi and their host plants due to the adverse effects of increased heat and drought stress on fungal and plant physiology. Overall, the results of this thesis highlight the potential vulnerability of Mediterraneantype native semiarid shrublands (and their ectomycorrhizal fungal partners in the case of H. squamatum) to forecasted climate change, which will likely cause multiple detrimental feedback loops that could lead to an alternative state of decreased vegetation productivity and push these ecosystems to a degradation and desertification pathway. Therefore, the findings reported in thesis will hopefully contribute to a better understanding and anticipation of the detrimental impacts of ongoing climate warming and aridification on the structure and functioning of plant and mycorrhizal fungal communities in semiarid gypsum ecosystems, which will ultimately aid the long-term management and conservation of biodiversity in these vulnerable habitats.