Potential contribution of carbon by microphytic crusts in pinyon-juniper woodlands

Abstract We examined the possibility that microphytic crusts (terrestrial algae, cyanobacteria, lichens, and mosses) contribute organ carbon fixed in photosynthesis directly to the soil ecosystem. Microphytic crusts and their underlying soils were collected from pinyon‐juniper woodlands in the fall and in spring. Samples of these crusts were exposed to 14 CO2‐labeled atmosphere. In general, a downward translocation of photosynthate over time from the crust was demonstrated by an increase in 14C content in the soils beneath the crusts. Following a 30‐min exposure to labeled atmosphere, the crusts accumulated as much as 55 × 103 disintegrations per minute (dpm) for a 0.1‐mL subsample volume (in the spring), leveling off about 25 × 103 dpm 10 and 21 days later. The crusts respired from 34 to 36% of the initial fixed carbon. The underlying soils accumulated significant 14C (relative to background) in both fall and spring samples. The source of this increase in 14C radiation in the soil is attributable to carbohydrates generated by the crust during photosynthesis in the labeled atmosphere. The initial C uptake was correlated with the chlorophyll a content of the crusts in the fall (r 2 = .87) but not in the spring samples.