青冈常绿阔叶林氮的生物循环

Biocycle of nitrogen in a Cyclobalanopsis glauca dominated evergreen broad-leaved forest in East China

对分布于浙江建德的青冈常绿阔叶林N的生物循环进行了研究。群落各代表种类的N浓度在0 .4 9%～1.6 4 %之间,其中下木层、草本层和藤本植物中N的浓度远大于乔木层和亚乔木层的种类;乔木层和亚乔木层4种器官中N的浓度基本为叶>枝>根>干,其他层次的种类则为地上部分>地下部分。乔木层青冈不同器官中N浓度的高低顺序为:花序>嫩叶>老叶>嫩枝>老枝>细根>树干、粗根。各器官中N浓度的季节变化不是很大,其根、枝和叶中的N浓度均在秋季(10月份)最高;下木层青冈各部位N浓度在1月份最高。不同径级青冈中N浓度变化无明显规律。N元素在不同类型凋落物中的浓度范围为0 .74 %～2 .30 % ,降水和穿透水中的N浓度分别为0 .0 0 0 0 38%和0 .0 0 0 0 9% ,N在死地被层中的浓度为1.94 % ,土壤中N的浓度为0 .5 9%。N在植物群落中现存量为10 2 5 .2 8kg/ hm2 ,死地被层中积累量为2 2 4 .88kg/ hm2 ,土壤(A0 ～B层)中储存量为5 5 15 1kg/ hm2 。群落中N的存留量为119.4 7kg/ (hm2 ·a) ;归还量为84 .13kg/ (hm2 ·a) ,其中通过凋落物的为78.4 9kg/ (hm2·a) ,通过穿透水的为5 .6 4 kg/ (hm2 ·a) ;吸收量为2 0 3.6 0 kg/ (hm2 ·a)。降水输入了4 .88kg/ (hm2 ·a)的N。

The nitrogen cycling was elucidated in a about 40-year-old subtropical evergreen broad-leaved forest dominated by Cyclobalanopsis glauca growing on red soil in Zhejiang Province. The samples of the organs in representative species in various layers, litterfall, precipitation, throughfall, litter layer, and soil layer were collected. The concentration of nitrogen in plant materials were analyzed by 2400CHN made by Perkin-Elmer Ltd., and that in water and soil samples was measured using a half dram procedure followed by colorimetric analysis. The results showed that: The concentrations of N in the representative species ranged from 0.49% to 1.64%. The order of which in various layers were liana and herb layers > understory layer> tree and subtree layers, and that in various organs were leaf > branch > root > trunk; overground parts > underground parts. The sequences of the concentrations of N in C. glauca were understory > tree > subtree layer, young and highly growing > old organs, reproductive > vegetative organs. Seasonal dynamics of the concentrations of N in C. glauca in the tree and subtree layers showed comparatively stable, it was less high in autumn (October) in root, branch, and leaf in the tree layer, and was less high in January in the understory. There hadn't evident changing regularity of the concentrations in of N in varying diameter classes. The concentrations of N in the litterfall, precipitation, throughfall, litter layer, and soil were 0.74%～2.30%, 0.000038%, 0.00009%, 1.94%, and 0.59% respectively. The standing crop of N in the plant community was 1025.28 kg/hm^2, accumulation amount in the litter layer was 224.88 kg/hm^2, reserve in the soil was 55151 kg/hm^2. Retention of N was 119.47 kg/(hm^2·a), return of it was about 84.13 kg/(hm^2·a), in which via litterfall was 78.49 kg/(hm^2·a), via throughfall was 5.64kg/(hm^2·a). Absorption of N was 203.60 kg/(hm^2·a). Annual input of N through incident precipitation was 4.88 kg/hm^2. Three indexes of nitrogen cycling rate were used in this study, which were the representative of vegetation. Comparing with other forest types, cycling rate of nitrogen in the community was lower than deciduous broad-leaved forests, rain forests and mangroves; and was moderate among evergreen broad-leaved forests. Two indexes of nitrogen use efficiency were used in this study too, practical definition of them were NPP divided by nitrogen uptake; and is the ratio of litterfall: return via litter fall. Nitrogen use efficiencies mentioned above of this forest were 142 and 61, which were moderate among the forest types cited in this paper. In according to the characters of the biocycle of phosphorous, it was concluded that the nitrogen availability in the soil of this forest was not lower, and phosphorous not nitrogen was the limiting factor of the growth of plants in this community.