Effects of phosphorus application on root respiration and heterotrophic microbial respiration in Acacia mangium plantation soil

Abstract

We investigated the effects of phosphorus (P) application on root respiration (RR) and heterotrophic microbial respiration (MR) in an Acacia mangium plantation using a trenching method. Mean RR was 0.46g Cm-2 day-1 in a non-P-applied plot, which accounted for 16% of total soil respiration, exhibiting a lower RR value and proportion of total soil respiration compared with previous studies. Mean MR was 2.41g Cm-2 day-1, accounting for 84% of the whole soil respiration. P application significantly (P <0.01) increased the mean RR from 0.46 to 0.88g Cm-2 day-1. Applied P was readily absorbed by acacia trees, which was inferred from the lower available P and total P in non-trenched plots compared to the trenched plots, and it is likely that the absorbed P stimulated root activities and RR. P application also significantly (P <0.001) increased the mean MR from 2.41 to 2.89g Cm-2 day-1, probably because P application relieved the P shortage and stimulated microbial organic matter decomposition. Our study suggests that when assessing the effects of P fertilization on C cycling in forest plantation, we should take account of the effects on organic matter decomposition and soil respiration, not only the effects on C sequestration by trees.