土壤氮浓度对油松天然林新生枝叶碳氮磷含量的影响

Effect of soil nitrogen concentration on the contents of carbon,nitrogen and phosphorus of new branches and leaves of Pinus tabuliformis natural forest stand

为更好地理解土壤氮浓度对油松天然林新生枝叶C、N、P含量的影响及其随林龄的变化规律,揭示土壤N、P养分限制阈值,以关帝山地区孝文林场42、55和65年生油松天然林为研究对象,通过5个水平(对照、5、10、15和20 g·m^(-2)·a^(-1))的短期氮添加试验,形成土壤(0~30 cm土层)氮浓度梯度,分析当年生枝叶的全碳(TC)、全氮(TN)、全磷(TP)含量。结果表明:油松天然林新生枝叶C、N、P含量均随土壤氮浓度的升高呈单峰态变化趋势,峰值出现在土壤氮浓度在2.5~3.0 g·kg^(-1)之间;计量比相应地呈倒"U"型的变化趋势;当土壤氮浓度一定时,油松新生枝叶C、N、P含量随林龄增加而减少,计量比除枝N/P外,均随林龄增加而升高;此外,3个林龄的油松天然林新生枝叶生长均受氮限制,且随着林龄的增加和土壤氮浓度的升高,受限制状况有所缓解,其限制效应的土壤氮浓度阈值为2.0~2.5 g·kg^(-1)。

This study aimed to better understand the effect of soil nitrogen concentration on the contents of C,N,and P of new branches and leaves of Pinus tabuliformis natural forest stands of different ages and to reveal the limiting threshold of soil N and P nutrients,to guide the regulation of forest growth environment and forest soil fertility management and provide a reference.In this study,five levels(control,5,10,15,and 20 g·m^(-2)·a^(-1))of short-term nitrogen addition were used to evaluate the effect of nitrogen addition on the growth of P.tabuliformis forest stands at age 42,55,and 65 years in the Xiaowen Forest Farm,Guandi Mountain.The nitrogen concentration gradient of soil(0-30 cm soil layer)was formed,and the contents of total carbon(TC),total nitrogen(TN),and total phosphorus(TP)were analyzed accordingly.Results showed that the contents of C,N,and P in the new shoots and leaves of P.tabuliformis forest stands showed a unimodal change trend with increase in soil N concentration,and the peak value was between 2.5-3.0 g·kg^(-1) of soil N concentration.The measurement ratio showed an inverted U pattern,except for N/P of branches.The stoichiometric ratio increased with an increase in forest age.In addition,the growth of new branches and leaves of natural P.tabuliformis of three forest stand ages in the area were limited by N.Moreover,the increase in forest stand age and soil N concentration alleviated the restricted condition,and the threshold of the limiting effect was 2.0-2.5 g·kg^(-1).