Phenological shifts are especially important to consider in temperate climates, where winter snowpack has historically insulated soils, protecting them from freezing conditions. In snow-adapted ecosystems, changing climate has led to a paradox between increasing air temperatures, but subsequent lower soil temperatures. These changing conditions have resulted in oscillations of freeze/thaw cycles that can slow or arrest soil arthropod activity during the winter, ultimately affecting nutrient cycling dynamics. This study aimed to compare the abundance of soil-invertebrate detrital food webs in low elevation sites (mimicking a warmer climate) to high elevation sites (mimicking the current climate).
At both “low” and “high” elevations at the Hubbard Brook Experimental Forest, 15N and 13C stable isotope enriched leaf litter was added to forest plots and traced in soil cores and invertebrates over five time periods (December 2011, March, April, July, and October 2012) in three substrates (litter, organic and mineral soil). Litter and soil cores were processed to measure stable isotope content and the invertebrates were identified to order, abundances were recorded, and stable isotope content was measured. Nonmetric multidimensonal scaling (NMS) ordination was used to assess how soil invertebrate communities (based on trophic level) shifted throughout the year and at different depths.
Results/Conclusions
The NMS ordination indicated litter and soil communities were regulated more by seasonal shifts than elevation. Litter invertebrates were most impacted by temperature, with their abundances highly reduced over the winter. All three substrates had similar seasonal shifts in community, but with greater redundancy as depth increased. The NMS ordination indicated that different seasonal conditions likely cause invertebrate community shifts that ultimately affect nutrient cycling.
Linked to seasonal responses of the invertebrate community, 15N and 13C analyses indicated variation in litter decomposition across the two elevations. The rate of nitrogen loss from the litter was similar between elevations, while carbon loss was greater at low elevations. Nitrogen was cycled rapidly by microbes at both low and high elevations, while carbon was regulated by invertebrate community abundance. Carbon loss, as measured by 13C, was lower at high elevation, corresponding to lower invertebrate abundances at this elevation. Slower decomposition of leaf litter resulted in less carbon entering the detrital food web. Ultimately, our results show that the relationship between invertebrate community and nutrient cycling is likely to shift with changing climate and reduced winter snowpack.