Abstract
Biological soil crusts (BSC) are widespread in the Monte desert. BSC, by fixing atmospheric N and retaining soil moisture, may enhance grass emergence, growth, and nutritional value. Our aim was to evaluate the effect of different functional types of BSC from the Monte desert on soil moisture and nutrients, N fixation, respiration, grass emergence, growth, and C/N. We sowed Leptochloa crinita seeds in pots with different BSC types (dominated by cyanobacteria, squamulose phycolichens, squamulose cyanolichens, gelatinous cyanolichens, and mosses) under two irrigation treatments: well watered and drought. We determined soil, BSC and grass properties related to nitrogen, phosphorus, and water cycles. In soils under BSC, we determined moisture, nitrate, and phosphate at two depths. In BSC, we determined total N, organic matter, ammonium, respiration, and δ15N. Finally, in grasses growing under BSC, we determined seedling emergence, grass biomass, C/N, and δ15N. All BSC types except cyanobacteria increased soil total N, ammonium, and respiration rates compared to bare soils under drought conditions. Cyanobacteria BSC increased soil moisture under drought conditions, while squamulose phycolichens and mosses increased it under well watered conditions. All BSC types increased underlying soil nitrate under well watered conditions, and decreased phosphate in at least one experimental condition. All BSC types improved at least one grass variable: cyanobacteria decreased C/N; squamulose cyanolichens increased emergence and decreased C/N; squamulose phycolichens increased emergence and biomass; gelatinous cyanolichens decreased C/N; and mosses increased emergence, biomass, and decreased C/N. The differential effects of each BSC type on soil and grass variables, under drought and well watered conditions, suggest the importance of BSC functional diversity on ecosystem functions of water regulation and nutrient cycling.
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