Changes In Soil Properties Across A Hydrological Gradient In Saladas From Northeast Spain: Implications For Soil Carbon Stocks, CO2 Efflux And Microbial Communities In A Warming World.

Abstract Numerous permanent and temporary wetlands occur throughout the world’s drylands. Although characterised by diverse hydroperiods, these wetlands in drylands are typically hotspots of biological activity and productivity. The healthy functioning and possibly even existence of many wetlands in drylands, however, is threatened by desiccation resulting from a combination of climate change and human disturbance. Near Alcañiz in arid northeast Spain, three adjacent saladas (playas) with contrasting hydroperiods provide an opportunity to investigate how moisture availability affects their soil carbon (C) stocks, CO2 efflux, and microbial communities. Frequent inundation and/or near-permanent soil saturation supports the generation of organic C from a range of different sources. Soil inorganic C was greatest on the driest salada (3.8 %) compared to the wetter saladas (3.0 % and 2.1 %) owing to evaporative concentration and the reaction of CO2 with available Ca2+, Mg2+ and Na+ ions. CO2 efflux was greatest at intermediate moisture levels (142 mg CO2 m-2 hr-1), but the spatial and temporal variability in CO2 efflux on salada surfaces is very high, demonstrating the need for intensive sampling regimes to provide realistic estimates of their contribution to atmospheric CO2 exchanges. Different microbial community structures also characterise each salada. The saladas near Alcañiz, and many other similar features in northeast Spain, are renowned for their rare and threatened flora and fauna, yet their soil C cycle characteristics and soil microbial communities provide additional reasons to monitor the impacts of climate change and protect these vulnerable environments from further anthropogenic disturbances.