Effects of fertilization on leaf decomposition rates mediated by soil microbes and leaf quality

Background/Question/Methods

The rate of decomposition of matter affects the nutrients available in soil for plants, which can impact plant diversity. Rates of decomposition of leaves are influenced by the chemical composition of the decomposing litter as well as the microbial community actively decomposing it. Both of these factors may be influenced by fertilization, and the addition of fertilizers is common. We hypothesized that a common source of litter will decompose more slowly if placed in an area with fertilized soil than in areas with unfertilized soil, and furthermore, that litter from fertilized plants will decompose more slowly than litter from unfertilized plants. To test these hypotheses, we removed and dried leaves of Arundinaria tecta from a long-term experiment that has been running since 2003 containing 8 blocks of plant plots in which half the plots were fertilized three times a year and the remaining half were left unfertilized. We placed these leaves in 192 litter bags and did a reciprocal transplant experiment within the long-term plots. Pairs of litter bags were removed from each plot after 2, 4, 6, 8, 12, and 15 months and the rate of decomposition was calculated.

Results/Conclusions

We calculated the natural log of the proportion of mass remaining from each litter bag and used regression to determine the rate of decomposition for each treatment and plot. We then used a 2-way ANOVA with a block effect to test for treatment differences. Contrary to expectations, preliminary results suggest that there is no significant difference in rates of decomposition between leaves placed in fertilized plots and those placed in unfertilized plots. Furthermore, there is no significant difference between leaves from plants that had been fertilized and those from plants that had not been fertilized.

 Based on these results, it is possible that fertilization of neither soil nor the Arudinaria tecta plant affects the rate of litter decomposition from this species. However, there are other possible explanations. One possibility is that the fertilized plots did not contain enough fertilizer to have a noticeable effect on decomposition even though there are striking differences in plant growth in these plots due to fertilization.  Further research is needed to explain why these results differ from existing ideas in the literature.