Climate change and ecohydrological processes in drylands : the effects of C02 enrichment, precipitation regime change and temperature extremes

Abstract

Drylands are the largest terrestrial biome on the planet, and the critically important systems that produce approximately 40% of global net primary productivity to support nearly 2.5 billion of global population. Climate change, increasing populations and resulting anthropogenic effects are all expected to impact dryland regions over the coming decades. Considering that approximately 90% of the more than 2 billion people living in drylands are geographically located within developing countries, improved understanding of these systems is an international imperative. Although considerable progress has been made in recent years in understanding climate change impacts on hydrological cycles, there are still a large number of knowledge gaps in the field of dryland ecohydrology. These knowledge gaps largely hinder our capability to better understand and predict how climate change will affect the hydrological cycles and consequently the soil-vegetation interactions in drylands. The present study used recent technical advances in remote sensing and stable isotopes, and filled some important knowledge gaps in the understanding of the dryland systems. My study presents a novel application of the combined use of customized chambers and a laser-based isotope analyzer to directly quantify isotopic signatures of transpiration (T), evaporation (E) and evapotranspiration (ET) in situ and examine ET partitioning over a field of forage sorghum under extreme environmental conditions. We have developed a useful framework of using satellite data and trend analysis to facilitate the understanding of temporal and spatial rainfall variations in the areas of Africa where the in situ observations are scarce. By using a meta-analysis approach, we have also illustrated that higher concentrations of atmospheric CO2 induce plant water saving and the consequent available soil water increases are a likely driver of the observed greening phenomena. We have further demonstrated that Leuning’s modified Ball-Berry model and RuBP limited optimization model can generally provide a good estimate of stomatal conductance response to CO2 enrichment under different environmental conditions. All these findings provide important insights into dryland water-soil-vegetation interactions.