Moss nutrient plasticity in desert ecosystems: a hot - cold desert comparison

Desert biology live close to the physical limitations for life, constrained by low availability of water and nutrients. Projections of future climate change suggest that many deserts will experience alterations in water availability, which will reduce limitations to influence soil biology and biogeochemical processes. The McMurdo Dry Valleys, a polar desert in Antarctica, is an extreme habitat that maintains functioning foodwebs and ecosystem processes. As the only above-ground primary producers in the MDV, moss represent a potentially significant contribution to ecosystem biogeochemistry. In both hot and cold deserts, moss may play an important role connecting soil and stream nutrient cycling, where stream nutrients may be taken up by moss growing at the terrestrial-aquatic interface, which may be windblown into the surrounding soil to become an organic matter source in the soil. Despite its importance, very little is known about moss’s role in biogeochemical cycles and how water and nutrient pulses will affect their functional significance as an integrator of nutrient cycling in deserts. We sampled moss in the McMurdo Dry Valleys (MCM-LTER) and the Sonoran Desert (CAP-LTER) to determine whether the nutrient content of the moss varies in relation to environmental gradients of nutrient content (both natural and manipulated). A survey of moss, soil, stream, and groundwater stoichiometry from locations varying in soil and water nutrient status suggests that moss nitrogen (N) and phosphorus (P) content are positively correlated with nutrient availability in the soil, water, or groundwater. When analyzed across all sites, moss growing in soils or water with higher levels of N and P had higher N and P tissue content. However, a comparison of moss stoichiometry to the potential nutrient sources individually (soil, stream water, or groundwater) revealed that the sources most strongly correlated differed for N versus P. For nitrogen, the correlation is strongest with groundwater NO₃+NO₂, followed by that of stream water. For phosphorus, the correlation is strongest for soil NaHCO₃-extractable PO₄-P content, followed by groundwater PO₄. This suggests that terrestrial-aquatic and aboveground-belowground linkages will differ depending upon the nutrient being considered. Forthcoming analyses will clarify how moss stoichiometry responds to short-term pulses of nutrients via fertilization, as opposed to natural gradients.