Print PageClimate change projections for aridlands include alterations in the magnitude and frequency of rainfall. Plants found in these environments are often living at their physiological limits of tolerance, and water availability exerts prime control on physiological functioning, thus such changes are likely to drive future patterns of distribution and survival. Soil biocrust communities (consisting of moss, lichen, and cyanobacteria) are ubiquitous to aridlands and control biogeochemistry and nutrient dynamics in these ecosystems, yet biocrusts are extremely vulnerable to environmental perturbation. Intact biocrusts subjected to increased frequency of rainfall exhibited a 90% loss of biocrust moss over the course of a single year, suggesting that crust mosses in particular are sensitive to changes in rainfall patterns. Further, loss of the moss component has been shown to severely impair crust structure and biogeochemical function. We sought to gain a mechanistic understanding of moss functionality and decline under projected rainfall patterns by subjecting samples of the common biocrust moss Syntrichia caninervis to alterations in precipitation magnitude and frequency across all seasons of the year. Physiological performance was quantified using carbon balance (net carbon gains and respiratory losses) over the course of individual pulse rainfall events.
Results/Conclusions
Rainfall magnitude was the primary driver of carbon balance in S. caninervis: moss hydrated with ¼ average rainfall events displayed a net carbon loss upon rehydration that was not compensated for by photosynthetic carbon gains during the hydrated period. Conversely, hydration with average rainfall amounts allowed for sustained photosynthetic gains over the course of the event and produced net carbon gains. Rainfall frequency was negatively correlated with carbon balance, such that increasing the dry interval between pulse events reduced carbon balance in a subsequent event. This was due to increased respiratory cost of rehydration with higher desiccation levels between events. Despite identical laboratory treatments and measurement conditions across seasons, respiratory losses and net carbon gains in S. caninervis were 80-120% higher in the winter than in the summer, suggesting that moss is more responsive to rainfall during this time of year. Further, winter moss displayed net carbon gains following 80% of events, compared to only 40% of events for summer moss. Overall, our results suggest that a shift towards smaller rainfall events in the summer will result in a cumulative reduction in carbon gains and reduced survival of biocrust moss.
