Responses of Biological Soil Crusts to the Presence of Cheatgrass Litter
Invasion by exotic annual grasses has resulted in an increase in plant litter in sagebrush habitats. This litter tends to cover biological soil crusts (BSCs), which may affect their metabolism and growth. To investigate these possibilities, BSC samples dominated by the moss Bryum argenteum were covered with cheatgrass litter (litter treatment) or left uncovered (control) and exposed to natural conditions during the summer and fall. At the end of the fall, we removed the litter and compared morphological and photosynthetic characteristics of these samples. The presence of litter led to the development of a taller but less dense BSC. Average moss height was 0.8 and 1.5 mm for the control and litter treatment, respectively. In contrast, no differences were observed in chlorophyll content or dry weight per area. The photosynthetic parameter Fv/Fm was higher for the litter than the control, while the opposite was observed for the electron transport rate, which at a light intensity of 700 µmol m-2 s-1 was 25% higher in the control than the litter treatment. This was attributed to higher non-photochemical quenching in the litter treatment. The amount of litter used (25 mg cm-2) severely reduced photosynthesis. However, after litter removal net photosynthesis was somewhat higher in litter than control samples. This was caused by differences in respiration, which was 25% lower in the litter treatment. Overall, the results indicate that BSCs partly adjust to the presence of litter by changing morphology, altering light transfer and dissipation, and decreasing respiration.