Nutrient fluxes in bulk precipitation, throughfall and stemflow in montane subtropical moist forest on Ailao Mountains in Yunnan, south-west China

A study of nutrient movement through rainfall, throughfall and stemflow, as well as epiphytic bryophyte (moss and liverwort) biomass and its effect on nutrient composition of stemflow, was conducted for 2 y in subtropical montane moist forest (Lithocarpus-Castanopsis association) at Xujiaba, Ailao Mountain National Nature Reserve, Yunnan, south-west China. Base cation and fluxes were increased in throughfall, while NH4+-N and NO3--N were reduced relative to precipitation. Annual throughfall inputs of N, P, Ca and S were mainly from precipitation, while most K and two-thirds of Mg throughfall input was due to canopy leaching. Input of Na in the precipitation and throughfall was low in this forest. Net flux (throughfall flux minus bulk precipitation) and deposition ratios (ratio of throughfall flux to bulk precipitation flux) were in the low part of the range reported for other tropical montane rain forests. The throughfall data for this forest reveal generally low cycling rates for mineral elements. Abundant epiphytic bryophytes on bole bark affected the chemical composition of stemflow by selective uptake or release of elements. Relative to trees without epiphytic bryophytes, the annual amounts of total N, NH4+-N, Mg, Na. and SO42--S were enhanced, while NO3--N, K, P and Ca were depleted in stemflow. Contributions of N from nitrogen-fixing organisms are likely to be constrained by low temperatures.