The biogeochemistry of moose and soil freezing: Multiple interactions influence on nitrogen cycling in a northern hardwood forest

The winter season has historically been viewed throughout much of northern North America as a season with little biotic activity. As a consequence, limited ecological research has focused on this time of year. Recent research indicates that winter is a biologically important time of year in affecting biogeochemical cycling. Forests in much of New England are experiencing changes in climate, as evidenced by late forming or reduced depths of snowpack. Coupled with these snow changes, this region of North America has also seen the return of a large prominent herbivore to the landscape, the moose. Together, climate change and moose activity will influence forest communities and biogeochemical cycling and a greater understanding of these influences is needed.; My study examined how snow and moose influence both biogeochemical cycling and fate of N in upper elevation forests at Hubbard Brook Experimental Forest, New Hampshire. Experimental field manipulations were employed on small plots and transects and two stable isotopic approaches were used. The first approach used 15N-labelled sugar maple litter and 15N-labelled moose feces that were added to treatment plots to investigate if changes in soil freezing and browsing of plants affected the incorporation and fate of these N sources to the ecosystem. The second stable isotopic approach examined natural abundances of 15N in specific amino acids. This latter approach allowed for characterization and contribution of organic N as amino acids to the ecosystem through moose fecal or plant material.; Results from the labeled experiments indicate that moose feces and sugar maple litter had different responses to soil freezing. Soil freezing made maple litter more 'available' to the soil community than fecal N. However, the mechanism regulating this mobilization remains unclear. There was also a clear indication that 'multiple stresses' (i.e., soil freezing combined with simulated moose activity) elicited the most marked responses. Balsam fir dominated plots had very high soil water NO3- concentrations compared to sugar maple or Viburnum plots, indicating a species response to these multiple stresses. The amino acid studies indicate a higher percent of moose feces N is comprised of this organic N source compared to plant materials. Although moose feces contain small molecular mass amino acids that may contribute significantly to plant N nutrition, further studies investigating the importance of these amino acids in ecosystem N cycling are warranted.