Phosphorus addition reduced microbial respiration during the decomposition of Acacia mangium litter in South Sumatra, Indonesia

Assessing the effects of nutrient addition on organic matter decomposition in tropical tree plantations is essentially important because of the increasing importance of the afforestation along with the increases in the intensified management practices and fertilizer use. We tested the effects of phosphorus (P) addition on microbial respiration during the decomposition of Acacia mangium litters and leaves by using an incubation experiment. Following hypotheses were examined: (i) P addition reduces microbial respiration during the litter decomposition if labile carbon (C) and nitrogen (N) are little; while (ii) the effect is not clear in the fresh leaf decomposition due to the large amount of labile C and N. P addition significantly reduced the rates of microbial respiration during the litter decomposition, with the following possible mechanisms; (i) decrease in C or N investment in phosphatase due to the reduced P requirement makes microbes decompose fewer litters to get C or N, (ii) P addition improved microbial respiratory efficiency and reduced energy required to maintain microbial activity. Meanwhile in high-quality leaf, such decrease in microbial respiration rates during the decomposition by P addition did not occur. We suggested that P fertilization in fast-growing tree plantations in tropics may reduce organic matter decomposition. Since the present study is a short-term incubation study, longer studies or field experiments are required to fully understand the effects of P addition on the organic matter decomposition in P-limited tropical forests.