Abstract:

To detect the effects of nitrogen deposition on leaf litter decomposition of Eucalyptus grandis, and investigate whether there is a limit value in the decomposition process, a field experiment simulating nitrogen deposition was conducted from January 2008 to January 2010 in a plantation of E. grandis, which is located at a Rainy Region of West China. The levels of nitrogen deposition included control (CK, 0 g N ·m^-2a^-1), low nitrogen (5 g N ·m^-2a^-1), medium nitrogen (15 g N ·m^-2a^-1) and high nitrogen (30 g N ·m^-2a^-1). The total annual amount of nitrogen (NH₄NO₃) application was divided into 12 equal parts, and each part was added to the corresponding N-treated plot by the end of each month started from January of 2008. Results indicated that there was a leaching period at the early stages of leaf litter decomposition of E. grandis. Mass loss became very slow at the late stages after 14 months decomposition, and hereafter the litter was relatively stable. N deposition inhibited the decomposition of litter at the late stages and the inhibiting effect in the low-N treatment was strongest. There was no obvious effect of N deposition on nutrients release in the process of litter decomposition in the plantation of E. grandis. In the natural status, the limit value of leaf litter decomposition of E. grandis was about 90%, and N deposition lowered this value. There was significant difference in the limit value between low-N (72%) and the control (90%). The results in this study suggest that small amount of additional N may increase soil carbon pool through inhibiting litter decomposition process at the late stages.

Key words: nitrogen deposition, Eucalyptus grandis, leaf litter decomposition, nutrient release, Rainy Region of West China