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Natural History of Biological Soil Crusts in Prairie Ecosystems of the Great Plains: Organismal Composition and Photosynthetic Traits

Biological soil crusts (BSCs) are soil-surface microecosystems composed of a close association of algae, cyanobacteria, fungi, lichens, and nonvascular plants with soil particles. BSCs have several ecological functions including carbon fixation, nitrogen fixation, nutrient relations, soil stabilization, water relations, and floral community development, which make them extremely important in many of the ecosystems where they occur. While BSCs have been studied throughout the American West, little work has been done in the Great Plains region where they are less prominent among the dominant vascular plant communities. This study examined organismal composition and photosynthetic traits of BSCs in four ecosystems within the Great Plains—shortgrass, sandsage, southern mixed grass, and tallgrass prairies. To document the BSCs, seasonal photosynthesis measurements were performed in the field and samples were collected for lab analysis. Prairie BSCs primarily consisted of lichens, bryophytes, and cyanobacteria with lichens being dominant in all ecosystems and varying proportions of bryophytes and cyanobacteria. Bryophyte proportion tended to increase with wetter, cooler climates. Heterocystic (nitrogen-fixing) cyanobacteria, which contribute to soil nitrogen content, and non-heterocystic cyanobacteria were present in lichens at all sites. Photosynthesis rates varied between sites and seasons, ranging from 0.26 to 3.31 µmol CO2 m-2 s-1, and were generally correlated with precipitation and temperature. Results indicate that BSCs of these prairie ecosystems possess diverse communities and perform several important ecological functions.