Contrastive effects of inorganic phosphorus addition on soil microbial respiration and microbial biomass in tropical monoculture tree plantation soils in Thailand

An incubation experiment was conducted to test the effects of inorganic phosphorus (P) addition on soil microbial activities in tropical monoculture tree plantation soils. The soils taken from an experimental tree plantation site in Nakhon Ratchasima, Thailand were incubated for 48 h with and without adding 100 μg of P (KH2PO4) per gram soil after adjusting the water holding capacity to 80%. During the incubation period, the microbial biomass carbon (MBC) contents determined using the chloroform fumigation extraction method decreased and P addition stimulated the decreased rate significantly. On the other hand, the P addition increased the dissolved organic carbon (DOC) contents and CO2 emissions. The study suggested that P addition had changed soil microbial activities, possibly including a soil microbial community change. Furthermore, the study showed that the stimulated soil respiration by P addition is not necessarily accompanied by increased MBC. The assessment of the effects of P limitation on soil microbial activities should measure at least the effects of P addition on both soil respiration and MBC, possibly combined with soil microbial community analyses.