Effects of Phosphorous Availability and Litter Type On the Microbial Activity and Elemental Stoichiometry of Detrital Resources

Relationships between litter stoichiometry and microbial processes are rarely examined but could enhance our understanding of litter decomposition and nutritional quality for macroinvertebrates, and, therefore higher trophic levels.  We examined the effects of ten phosphorus (P) concentrations (0, 10, 25, 50, 75, 100, 250, 500, and 1000 µg/L P) on two leaf species (recalcitrant Quercus stellata and labile Acer saccharum) and the associated microbes by measuring decomposition rate, alkaline phosphatase activity (APA), microbial respiration rates, and leaf litter carbon (C):P. Leaf disks, conditioned in laboratory mesocosms at varying P concentrations, were sampled periodically over 30 weeks. We expected APA to decline in a threshold relationship with P concentrations due to alleviation of growth limitation and we hypothesized that APA would decline at a lower threshold concentration in maple compared to oak.  On day 28, changepoint analysis indicated a decrease in APA for maple at 87.5 (p=0.001) and oak at 175 µg/L P (p=0.001). Changepoint concentrations resulting in declines in APA tended to increase over time. These APA threshold concentrations may coincide with increasing decomposition and respiration rates and declines in leaf litter C:P, which could potentially affect aquatic food web dynamics.