| Our view of an ecological process is influenced by the scale of our hypotheses and experiments. The forest floor can be examined as a system, where processes that affect ecosystem carbon and nutrient cycling are controlled by macroscale variables (seasonal climatic changes), which in turn affect microscale controls over microbial activity. In the forest floor of Alaskan taiga, annual layers of Equisetum (horsetail) litter demarcate cohorts of birch litter. We collected samples of the forest floor monthly during September 1992, and in June-September 1993. Forest floor material was separated into each of the three most recent litter cohorts, plus the Oe layer, and the Oa layer. Overall, respiration potential decreased with depth of litter (litter age), but showed no change over time. Nitrogen mineralization potential increased with depth, and fluctuated over time. Microbial biomass did not vary with depth, but did increase greatly in September in conjunction with increased litter moisture. Litter C:N ratio decreased with time and varied with depth according to the year-to-year variation in litter quality. Our hypothesis that microbial activity on a particular litter cohort is a function of the litter quality, the vertical position of the litter in the forest floor, and the timing of the observation within seasonal macroclimatic cycles was supported.; The distribution of some taxa of soil fauna correlated with depth. In these cases, the fauna were likely constrained mostly by differences in the microclimate of the forest floor strata. Other soil fauna varied over time, likely in response to differences in the microbial community. Yet other faunal distributions showed an interaction between depth and time, apparently responding to a combination of changes in microclimate and changes in food availability. The creatures that live in water pores may also have responded to an increase in habitat space as the top-most litter strata became wetter. "Cascading" microcosms containing material from these forest floor strata showed a temporary suppression of respiration by leachates from the newer litter on underlying forest floor material. Traditional litterbag techniques were also used to show changes in nitrogen that indicate winter microbial activity. |
