Print PagePrecipitation patterns are expected to change in the Mediterranean region within the next decades, with projected decreases in total rainfall and increases in extreme events. We manipulated precipitation patterns in a Mediterranean woodland, dominated by Arbutus unedo L., to test the following hypotheses: 1) in an evergreen Mediterranean woodland, plant growth and therefore plant-derived C input to the soil, both from above and below-ground are controlled by soil moisture, so a decrease in precipitation throughout the year will result in significant reduction of soil C input. On the contrary, enhanced water availability during the summer will stimulate NPP and strongly increase soil C input; 2) similarly, soil respiration in Mediterranean woodland is controlled directly and indirectly (i.e. via increased plant-derived C input) by the available soil water, thus a decrease in precipitation throughout the year will suppress soil respiration. Soil respiration will instead be enhanced if soil water increases during summer months. Experimental plots were exposed to either a 20% reduction of throughfall or to a water addition by targeted irrigation during summer months, to maintain soils above a water content of 10% v/v. Treatments were compared to control plots which received ambient rain. In each plot, we measured net annual C input to soil (i.e. litterfall), stem growth and continuous soil respiration and quantified, by the use of stable C isotopes, changes in plant-derived below-ground C input as affected by the water manipulation. Additionally, we discuss the overall implication of the observed treatment effects on soil C fluxes for soil C stores.
Results/Conclusions
Enhanced soil moisture during summer months highly stimulated annual stem primary production, litter fall, soil respiration and net annual plant-derived C input to soil which on average increased by 130%, 26%, 50% and 220%, respectively, as compared to control. On the contrary, the 20% reduction in throughfall (equivalent to 10% reduction of rainfall) did not significantly change soil moisture at the site, and therefore did not significantly affect ANPP or soil respiration. We conclude that minor changes (around 10% reduction) in precipitation amount are not likely to significantly affect ANPP or soil C dynamics in Mediterranean woodland. However, if summer rain will increase, C cycling will significantly accelerate but soil C stocks are not likely to be changed in the short-term.
