Abstract:

Based on the small watershed technique and the located observation method,the data collected in 3 consecutive years were used for analyzing the water balance and nutrients geochemical cycling in the second-rotation Chinese fir plantation.The results showed that the average annual rainfall of the ecosystem was 1170.6mm,86.9%,0.3% and 12.8% of which were allocated to throughfall,stemflow and canopy interception,respectively.The annual runoff was 428.05mm,that was 36.57% of the annual rainfall.The surface runoff and ground runoff accounted for 4.31% and 95.69% of the total runoff.The estimated evapotranspiration of the second-rotation Chinese fir plantation was 862.64mm,that was 62.2% of the annual rainfall.In the process of biological cycling,the annual uptake of 5 nutrient elements (N,P,K,Ca and Mg) in the second-rotation Chinese fir plantation was up to 140.658kg·hm^-2·a^-1,annual return and retention was 73.988kg·hm^-2·a^-1 and 66.67kg·hm^-2·a^-1,respectively.The cycling rate accounted for 0.53.The total nutrient input of N,P,K,Ca and Mg reached 53.173kg·hm^-2·a^-1,and output was 42.563kg·hm^-2·a^-1.The net nutrient accumulation was 10.610kg·hm^-2·a^-1. In contrast to the first-rotation Chinese fir plantation,the hydrologic process and nutrient dynamics of the second-rotation had different characteristics.The canopy interception rate in the second-ration was lower than that in the first rotation.In the second-rotation Chinese fir plantation,the monthly runoff varied with the pace of the rainfall,and the annual retention was higher while net nutrient accumulation was lower.These statistics revealed that the second-rotation Chinese fir had lower capacity of water regulation and disturbance resistance.The trees consumed more nutrients and the ecosystem was in the biological restoration stage.

Key words: Second-rotation Chinese fir plantation, Hydrologic process, Nutrient dynamic, Biochemistry, Small watershed