长期氮沉降下杉木人工林凋落物与土壤的C、N、P化学计量特征

为研究长期氮沉降条件下林木凋落物与土壤养分之间的关系,该文以亚热带杉木(Cunninghamia lanceolata)人工林为研究对象,分析了模拟氮沉降处理第12年时杉木林凋落物不同组分(叶、枝、果)与不同土层土壤(0～20 cm、20～40 cm、40～60 cm)的C、N、P含量及其化学计量比。氮沉降处理分4个水平,分别为N0(0 kg N·hm^-2·a^-1)、N1(60 kg N·hm^-2·a^-1)、N2(120 kg N·hm^-2·a^-1)、N3(240 kg N·hm^-2·a^-1),每处理重复3次。结果表明:(1)凋落物各组分的C、N、P含量及其化学计量比均高于土壤; 凋落物和土壤化学计量比均表现为C/P>C/N>N/P; 凋落物不同组分的C、N含量表现为叶>果>枝,而P含量表现为叶>枝>果。(2)12 a氮沉降增加了凋落物叶、枝和果的N含量,增幅分别为4.24%、15.97%、6.47%; 同时增加了凋落物枝N/P,降低了凋落物枝C含量、C/N和C/P; 中-高氮沉降(N2、N3)增加了土壤N含量,低氮沉降(N1)增加了土壤C/P、N/P。(3)相关性分析表明凋落物N与土壤N显著正相关,土壤C/P与凋落物C/P、N/P显著负相关,土壤P与凋落物N/P显著负相关。综上结果说明凋落物N是土壤N的重要N素来源之一,而土壤N可能是决定长期氮沉降后凋落物N/P的主要因素。

C, N and P stoichiometric characteristics of litterfall and soil in a Chinese fir plantation under long-term nitrogen deposition

To reveal the relationship between forest litterfall and soil under long-term nitrogen(N)deposition, litterfall and soil samples were collected in the 12th year of nitrogen deposition in a Chinese fir(Cunninghamia lanceolata)plantation. C, N, and P concentrations and stoichiometric characteristics of litterfall(leaf, branch and fruit)and soil(0-20 cm, 20-40 cm, 40-60 cm)were analyzed. Four simulated nitrogen deposition treatment levels were N0(0 kg N·hm^-2·a^-1), N1(60 kg N·hm^-2·a^-1), N2(120 kg N·hm^-2·a^-1)and N3(240 kg N·hm^-2·a^-1), respectively. Each treatment comprised three replicate plots of 20 m × 20 m which were sprayed with urea on the forest floor at the beginning of each month. The results were as follows:(1)C, N and P contents and stoichiometric ratios of litterfall were higher than that of soil. The stoichiometric ratios of litterfall showed the same order as soil of C/P>C/N>N/P; The C, N contents of litterfall decreased in the order of leaf > fruit > branch, while P decreased in the order of leaf > branch > fruit.(2)N deposition promoted N content in litterfall leaf(+4.24%), branch(+15.97%), and fruit(+6.47%), respectively; N deposition increased N/P while decreased C content, C/N and C/P in litterfall branch; Medium-high level of N deposition(N2 and N3)increased soil N content, and low level of N deposition(N1)increased soil C/P and N/P.(3)Significant positive correlation existed between litterfall N and soil N, while negative correlation between soil C/P and litterfall C/P, N/P, and between soil P and litterfall N/P. It is indicated that litterfall N was one of the important soil N sources, and soil N content mainly influencing the ratio of litterfall N/P after long-term N deposition.