干旱区生态环境知识资源中心

Soil surface growths dominated by cyanobacteria and the lichen Collema in southeastern Utah are shown to be associated with greater tissue content of several bioessential elements in two co-occurring seed plants (Festuca octoflora, Poaceae, and Mentzelia multiflora, Loasaceae). The elements N, P, K, Ca, Mg, and Fe were present in significantly greater concentrations in Festuca growing on soils heavily encrusted with cyanobacteria and cyanolichens than in plants on the same soil where foot traffic had destroyed the cryptobiotic crusts. With Mentzelia, N, Mg, and Fe were present in significantly greater concentrations in plants from sites with encrusted soil surfaces than on blow-sand sires. The cryptobiota appeared to compete vigorously with Mentzelia for available P: Mentzelia plants from crusted sites contained significantly smaller concentrations of P than plants grown on soils where wind action precluded development of surface crusts. These cryptobiotic crusts fix considerable amounts of N, which apparently becomes available to associated seed plants via decomposition and cellular secretion processes. Other macronutrients are apparently accumulated in forms available to seed plants as the crusts develop in inter-spaces between higher plants. The trace element Fe appears to be rendered more available to higher plants by the cryptobiotic growth. That effect may be related to chelating compounds known to be present in the mucilaginous sheaths of cyanobacteria. Other possible reasons are discussed for the enhanced nutrient uptake of seed plants growing in cryptobiotic crusts.