The role of moss as integrators of soil and stream nutrient status in a polar desert

Background/Question/Methods

The McMurdo Dry Valleys of Antarctica are characterized by distinct, yet connected ecosystem components: glaciers, melt-water streams, stream-fed lakes, and the surrounding soil. The connectivity among these ecosystem components is evident in the movement of nutrients. For example, stream nutrients released from melting glaciers may be taken up by moss growing at the terrestrial-aquatic interface, which may be windblown into the surrounding soil to become an organic source of nutrients for the soil community. Thus, moss reflects habitat nutrient status  and may connect soil and stream nutrient cycling. To understand the functional significance of mosses as an integrator of nutrient cycling, we sampled moss, stream water, and soil to determine (1) whether the nutrient content of the moss relates to the nutrient content of the water source and/or soil; and (2) if moss stoichiometry covaries over natural environmental nutrient gradients (e.g. stream loads, differing native soil content). In addition, moss may contribute significantly to the soil C cycle, which is important due to the fact that carbon is a limiting resource to dry valley soil communities. We are measuring rates of moss photosynthesis and soil respiration adjacent to moss patches to elucidate their relative role in CO₂ flux.

Results/Conclusions

A survey of moss and soil stoichiometry from water sources varying in nutrient status suggests a weak, positive correlation between moss and soil N (as NO₃ and NH₄) and NaHCO₃-extractable P content (R² < 0.5 for both nutrients). When analyzed across all sites spanning three lake basins, moss growing in soils with higher levels of N and P had higher N and P tissue content. However, most soils were low in extractable N and P, and moss growing on low-nutrient soils varied from the lowest measurements of nutrient content to the highest. This suggests that soil nutrient availability is not the main determinant of moss nutrient uptake at lower soil nutrient levels. For stream sites, soil N values were consistently low, and there is no relationship between soil and moss N. This was not the same for P, where the relationship between soil and moss P exists for moss growing at streams and at a snow patch. Forthcoming analyses may clarify whether the remaining variation in moss nutrient status, particularly at low levels of soil nutrients, can be explained by water-source stoichiometry.