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

Abstract

Little is known about the role of biocrusts in regulating the responses of N 2 O and CH 4 fluxes to climate change in drylands. Here, we aim to help filling this knowledge gap by using an eight-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 N 2 O emissions, enhanced CH 4 uptake and higher abundances of functional genes linked to N 2 O and CH 4 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 N 2 O fluxes (~96% and ~197%, respectively) only under well-developed biocrust cover. Warming and its combination with rainfall exclusion reduced CH 4 consumption in areas with initial low cover of well-developed biocrust, whereas rainfall exclusion enhanced CH 4 uptake only in areas with high initial cover of well-developed biocrusts. Similarly, the combination of warming and rainfall exclusion increased the 3 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 N 2 O and CH 4 fluxes, highlighting their importance and the need to preserve them to minimize climate change impacts on drylands.

Soil-atmosphere fluxes of CO2, CH4, and N2O across an experimentally-grown, successional gradient of biocrust community types

“…While we measured N 2 O efflux from each of the three biocrust treatments, the fluxes were extremely small and, with the exception of moss-lichen biocrusts, not statistically different from blanks or control treatments: fluxes averaged around 0.003 nmol m –2 s –1 for all treatments. Lafuente et al (2020) measured somewhat larger biocrust N 2 O fluxes (mean values up to 0.005 nmol m –2 s –1 ) in a field experiment conducted in a Mediterranean dryland, but noted high temporal variability across measurements. They also observed that climatic manipulations (warming and rainfall exclusion) tended to reduce N 2 O fluxes (relative to controls) in some seasons and increase N 2 O fluxes in other seasons.…”

“…Most studies point to CH 4 consumption (methanotrophy) by dryland soils, but there is some evidence of the potential for CH 4 production (methanogenesis) to occur under the right conditions. Lafuente et al (2020) measured CH 4 consumption of up to 1.45 nmol m –2 s –1 by biocrust-covered soils in a semiarid Mediterranean dryland. Durán et al (2021) measured CH 4 uptake by a range of moss- and lichen-dominated cryptogamic soils in Antarctica, although rates of CH 4 uptake were actually 2–3 × higher in bare soil with no cryptogams.…”

“…While some previous studies have measured biocrust trace gas fluxes under different environmental conditions and for different biocrust types (Lange, 2001;Grote et al, 2010;Jia et al, 2018;Tamm et al, 2018;Lafuente et al, 2020), comparatively few studies have made gas flux measurements along a well-defined biocrust successional gradient, or over time following mechanical disturbance.…”

“…Yet, there remains a general lack of empirical data linking structure (e.g., community composition) and function (e.g., productivity and CO 2 exchange, nitrogen cycling) over the whole trajectory of biocrust succession. While some previous studies have measured biocrust trace gas fluxes under different environmental conditions and for different biocrust types ( Lange, 2001 ; Grote et al, 2010 ; Jia et al, 2018 ; Tamm et al, 2018 ; Lafuente et al, 2020 ), comparatively few studies have made gas flux measurements along a well-defined biocrust successional gradient, or over time following mechanical disturbance.…”

Physical Disturbance Reduces Cyanobacterial Relative Abundance and Substrate Metabolism Potential of Biological Soil Crusts on a Gold Mine Tailing of Central China

“…It is reported that the restoration of biocrusts would take more than 10 years after physical disturbance ( Dojani et al, 2011 ), indicating that physical disturbance is an important factor restricting the development of biocrusts. At large scales, physical disturbance causes the reduction of biocrust coverage, which additionally affects the global soil biogeochemical process ( Steven et al, 2014 ; Ferrenberg et al, 2015 ; Yang et al, 2018 ; Lafuente et al, 2020 ).…”