The availability of phosphorus (P) controls many aspects of local ecosystem function and global biogeochemistry. While atmospheric inputs of P are typically considered negligible in most terrestrial ecosystems, there is a growing body of work indicating that dust can be a significant source of P. To address this, we focused on a long-term (40-year) snow manipulation experiment in the subalpine environments of the Bangtail Mountains (BTL) in Southwest Montana. We also compared our experimental work with subalpine fir (Abies lasiocarpa) tree islands, which naturally harvest large quantities of snow. Here we evaluate two hypotheses regarding the role of snow in shaping the P cycle: (1) a significant portion of P enters the system via dry and/or wet atmospheric deposition as dust and snow, respectively; or, alternatively (2) increased snowpack elevates P mineralization, resulting in greater P availability. To characterize the P cycle of this grassland system—particularly the role of internal versus external P inputs—and to determine the effects of snow addition, we measured several indices of soil P availability.
Results/Conclusions
Long-term manipulation of snow has dramatically altered the relative abundance of N vs. P relative to controls. While measures of mineral nutrient pools in BTL soils reveal uniformly low supplies of mineral N, mineral P pools are relatively abundant across treatments and islands. Levels of PO4-P increase logarithmically across treatments, consistent with the idea that snow modifies P availability at the scale of the plant-soil system. Further work quantifying the total P available in the soil serves as an indicator of the internal versus external inputs of the system. Understanding the P cycle of this system is integral to understanding nutrient dynamics that govern subalpine environments, and may constitute a significant step in determining the role of snow in high elevation grassland systems.