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Biocrust carbon isotope signature was depleted under a C3 forb compared to interspace

Dettweiler-Robinson, Eva
Plant and soil 2018 v.429 no.1-2 pp. 101-111
Bouteloua gracilis, C3 plants, C4 plants, Cyanobacteria, Gutierrezia sarothrae, arid lands, biological soil crusts, carbon, carbon dioxide, carbon dioxide fixation, forbs, grasses, leaves, lichens, photosynthates, photosynthesis, roots, stable isotopes, trophic relationships
AIMS: Plants and biological soil crusts (biocrusts) are the key producers in drylands, but biocrusts seldom show net CO₂ uptake. I hypothesized that biocrusts could augment CO₂ fixation by incorporating plant-derived carbon. METHODS: I collected biocrusts located at the base of Gutierrezia sarothrae (C₃ forb), Bouteloua gracilis (C₄ grass), and from bare interspaces between plants, and from a mesocosm experiment with live B. gracilis or dead B. gracilis roots. To trace carbon sources, I determined ¹³C values of the biocrust community, isolated cyanobacteria and lichen, and plant leaves because the photosynthetic pathway distinguishes the tissue ¹³C values. RESULTS: Biocrust communities and washed cyanobacteria and cyanolichen in G. sarothrae microsites were depleted by ~2‰ relative to other locations. Biocrust δ¹³C did not differ between the interspace and live or dead B. gracilis. CONCLUSIONS: Potential mechanisms for the trend in biocrust δ¹³C adjacent to C₃ plants include differences in microsite conditions, biocrust communities, use of respired CO₂ in the soil matrix for photosynthesis, or mixotrophic use of plant photosynthates. Further investigation of this observation may improve understanding of the degree to which the activities of dryland primary producers are coupled.