Greenhouse gas fluxes and nutrients availability in Portuguese drylands and their sensitivity to climate change

Drylands are unique and diverse ecosystems that occupy more than 40% of the terrestrial surface. These areas are inhabited by more than 35% of the world population. In the case of Portugal, drylands represent 37% of its territory. In many areas worldwide, climate change (CCh) is increasing the aridity leading to an expansion of drylands. However, the joint effects of different CCh drivers on the features, functions, and services of drylands remain largely unknown. Further, there is large uncertainty on how CCh-driven alterations in biotic and abiotic soil attributes will feedback CCh through greenhouse gas (GHG) fluxes.

This study aims to assess (1) the soil-atmosphere GHG exchange and soil nutrients availability and (2) their response to different CCh scenarios along an aridity gradient made up of 8 humid, arid, and semiarid-natural parks in Portugal. In winter 2019, we installed open top chambers and rainfall shelters (both separately and combined) in 24 plots to simulate the forecasted increase in temperatures (~3 °C) and reduction in precipitation (~35%), respectively. Since then, seasonal field campaigns to collect gas and soil samples as well as to measure in situ nutrients availability have been performed.

Our first data show that soil organic matter and nutrients (N and P) availability decrease along the aridity gradient whereas methanogenesis seems to be constrained along the gradient and there is not a clear response from other GHG to the aridity gradient. Soil respiration was mainly driven by the seasonal variability of soil moisture and temperature. Finally, the different CCh scenarios had their biggest effect on variables with faster turnover and the response of GHG fluxes to different CCh scenarios varied among sites, which highlights the importance of considering other site-dependent ecosystem features when trying to assess the effects of climate change on GHG fluxes.