Environmental and ecological factors influencing soil functionality of biologically crusted soils by different lichen species in dryland

Biocrusts are an essential soil surface cover at drylands where ecosystems are especially fragile to soil degradationprocesses due to climatic peculiarities. In the present work, (micro)biological and physicochemical properties indic-ative of soil functionality were studied in two different biocrust types dominated byDipolschistes diacapsisandLepraria isidiataand in underlying soil at two different depths (SL1, soil layer right below the biocrusts, and SL2,soil layer underlying SL1) at the Tabernas desert (southeast Spain). The influence of climatic factors (rainfall andtemperature) and general soilproperties on the (micro)biological properties were also analyzed in different envi-ronmental (climatic) conditions over a period of two years. PERMANOVA analyses showed significant statisticaldifferences (Pseudo-F = 63.9; P (perm) = 0.001) among biocrust and soil layers. Throughout the study period, en-zyme activities involved in C, N, and P cycles; microbial biomass-C; basal respiration; and several properties directlyrelated to ecosystem productivity (total organic carbon, total nitrogen, concentration of ammonium and nitrate)were higher in both biocrust types than in the underlying soil layers, showing that biocrusts improved soil functionsrelated to nutrient cycling. These properties progressively diminished in successive soil layers under the biocrusts(biocrusts > SL1 > SL2). Biocrusts showed greater similarity to each other and to SL1 than to SL2 in (micro)biologicalproperties. A distance-based linear model analysis showed that total organic carbon, rainfall, pH, mineralized N-NH4+, and total nitrogen were the most important variables for predicting (micro)biological soil properties inbiocrusts. Different biochemical behavior between the biocrusts and successive underlying soil layers has beenfound in wet periods. After rainfall periods, the biocrusts showed important peaks in basal soil respiration and in en-zyme activities involved in C and P cycles. Nevertheless, soil biochemical properties hardly showed any peak in SL1anddidnotchangeinSL2despitesoilmoisturebeinghigherinthesoillayersbelowthebiocrusts.Correlationanal-yses corroborated the existence of different relationships between soil moisture and enzymatic activities. In biocrusts, soil moisture showed a greater number of significant positive correlations with enzymes such asβ-glucosidase, invertase, and phosphomonoesterase among others, whereas in SL1 it was only correlated with cellu-lase and in SL2 with dehydrogenase. A change in rainfall regime, as predicted by models based on climate changein arid and semiarid zones, could affect the activity of soil enzymes in the biocrusts and underlying layers, thus ag-gravating the degradation of these fragile dryland ecosystems.

This study was funded by the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER, through the project CGL2017-88734-R (BIORESOC) MINECO/AEI/FEDER, UE, the FEDER-Junta deAndalucía Research Projects: RESTAGRO (UAL18-RNM-A021-B) andRestoration of Abandoned Agricultural Soils in Semiarid Zones toImprove Productivity and Soil Quality and Enhance Carbon Sequestra-tion (P18-RT-4112), and by the Xunta de Galicia by the projectIN607A 2017/6. Isabel Miralles is grateful for funding received fromthe Ramón y Cajal Research Grant (RYC-2016-21191) from the SpanishMinistry of Economy,Industry andCompetitiveness (MINECO)and Raúl Ortega thanks his postdoctoral contract HIPATIA of the University of Almería Research Plan.

Peer reviewed