Biocrusts Modulate Responses of Nitrous Oxide and Methane Soil Fluxes to Simulated Climate Change in a Mediterranean Dryland

Little is known about the role of biocrusts in regulating the responses of N₂O and CH₄ fluxes to climate change in drylands. Here, we aim to help filling this knowledge gap by using an 8-year field experiment in central Spain where temperature and rainfall are being manipulated (~ 1.9°C warming, 33% rainfall reduction and their combination) in areas with and without well-developed biocrust communities. Areas with initial high cover of well-developed biocrusts showed lower N₂O emissions, enhanced CH₄ uptake and higher abundances of functional genes linked to N₂O and CH₄ fluxes compared with areas with poorly developed biocrusts. Moreover, biocrusts modulated the responses of gases emissions and related functional genes to warming and rainfall reductions. Specifically, we found under rainfall exclusion and its combination with warming a sharp reduction in N₂O fluxes (~ 96% and ~ 197%, respectively) only under well-developed biocrust cover. Warming and its combination with rainfall exclusion reduced CH₄ consumption in areas with initial low cover of well-developed biocrust, whereas rainfall exclusion enhanced CH₄ uptake only in areas with high initial cover of well-developed biocrusts. Similarly, the combination of warming and rainfall exclusion increased the abundance of the nosZ gene compared to the rainfall exclusion treatment and increased the abundance of the pmoA gene compared to the control, but only in areas with low biocrust cover. Taken together, our results indicate that well-developed biocrust communities could counteract the impact of warming and altered rainfall patterns on soil N₂O and CH₄ fluxes, highlighting their importance and the need to preserve them to minimize climate change impacts on drylands.