Element characteristics in the precipitation conversion process in Betula platyphlla forest of Xiaoxing’an Mountains, northeastern China

Birch forest as secondary forest after the original natural forest was disturbed plays an important role in northeastern China since it occupies about 20% of the total forest area. To explore the variations of nutrient cycling and nutrient balance in precipitation conversion process in birch forest ecosystem of Xiaoxing’an Mountains, net input of each nutrient element was calculated. The calculation was based on the implementation of long-term fixed-location observation and sampling in the field. We measured the contents of five nutrient elements (K, Ca, Si, Mg and Mn) in precipitation, throughfall, and stemflow using the analyzer of ICP color spectrum, combining the allotment of rainfall water. The results revealed that: 1) in precipitation, the average concentration of each nutrient was significantly different. The concentration of Ca was the highest with 10.807 mg/L and that of Mn only 0.069 mg/L as the lowest. The contents of nutrients in precipitation were in the order as Ca＞K＞Si＞Mg＞Mn, the same order as for the input of nutrients in precipitation. 2) The yearly average concentration of each element in throughfall and stemflow had the same pattern of Ca＞K＞Mg＞Si＞Mn. The contents of nutrients in throughfall and stemflow had increases with different amplitudes if compared to precipitation. 3) All coefficients of variation (CV) in precipitation were higher than 1 except that for Ca, and the greatest CV in precipitation was 1.514 for K and the smallest 0.827 for Ca. The greatest CV for K was 0.989 in throughfall and 0.827 in stemflow. In throughfall, the smallest CV was 0.46 for Si and in stemflow 0.459 for Mn. The CVs in throughfall and stemflow were all smaller than those in precipitation.4) The pattern for the net input amounts of each element in the birch forest was as follows: K＞Mg＞Si＞Mn＞Ca. Furthermore the net input amount of Ca in birch forest was negative.