The effects of phosphorus enrichment on leaf litter stoichiometry in a forested stream

Background/Question/Methods

The effects of nutrient (N and P) enrichment on leaf litter decomposition in streams have been investigated extensively, but few have explored how P addition alone affects leaf litter stoichiometry (namely the C:P ratio).  This study examined how the P content, C:P ratio and decomposition of two types of leaf litter (the recalcitrant Quercus stellata and the more labile Acer saccharum) responded to P enrichment from nutrient diffusing substrata (NDS) which was either unenriched agar or agar enriched with a moderate or high level of P.   Leaf litter was sealed in 0.05 mm mesh bags, which excluded invertebrates, housed with NDS inside unique PVC containers and placed in an Ozark stream. Leaf C, P, and dry mass remaining were measured for 154 days.  A linear regression analysis was run on the response ratio (RR; ratio of treatment value to control value for a sampling date) for leaf litter P and leaf litter C:P of each leaf type to test the null hypothesis that the slope was equal to 0.  

Results/Conclusions

There was no effect of P enrichment on the decomposition of either oak or maple leaf litter.  The moderate P treatment had no effect on leaf litter P or C:P, therefore the response ratios were calculated using only the high P and control values.  The RR of leaf litter P (m = 0.0023, P = 0.0293) and leaf litter C:P (m = -.0016, P = 0.0294) of oak both indicated a significant increase in leaf litter P and decrease in leaf litter C:P with P addition through time.  The same was true for the RR of maple leaf litter P (m = 0.0041, P = 0.0076) and leaf litter C:P (m = -0.0030, P = 0.0120).  Results of this study indicated that P enrichment increased P content and decreased the C:P ratio of both oak and maple leaf litter.  Maple leaves responded to enrichment faster and at a greater magnitude than oak leaves, possibly due to their greater carbon lability.