杉木人工林凋落物C,N,P归还量对氮沉降的响应

Impacts of Nitrogen Deposition on C,N,and P Fluxes in the Litterfall of Chinese fir Plantation

为探讨亚热带森林对氮沉降增加的响应,在12年生的杉木人工林中开展4种水平的模拟氮沉降试验,分N0(对照),N1,N2,N3等4种处理,氮沉降量分别为0,60,120,240kg·hm-2a-1。模拟氮沉降2年后,4种不同氮沉降水平杉木人工林的年凋落量分别为1008.83,1164.10,1147.30和976.47kg·hm-2,表明低中氮处理(N1,N2)在一定程度上增加森林凋落物量,而高氮处理(N3)则表现出一定的抑制作用。叶凋落物中C,N元素含量随氮沉降水平的增加而增加,而C/N则呈不断下降的趋势。经不同氮沉降处理后,凋落物C元素的归还量分别为474.70,544.07,538.55和474.02kg·hm-2,N元素的归还量分别为7.21,8.56,9.03和9.04kg·hm-2,P元素的归还量分别为1.17,1.24,1.32和1.09kg·hm-2,说明与N0处理相比,氮沉降显著提高N元素的归还量,而N1,N2处理提高C,P元素归还量,N3处理对C归还量影响不明显,但降低P的归还量。

This field experiment was conducted in a 12-year-old Chinese fir plantation.Four levels of nitrogen,that is 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）,were annually added with three replicates in each level.After seccessive two-years additions of the nitrogen,the annual litterfall production was estimated to be 1 164.10,1 147.30 and 2 599.50 kg·hm-2 ,respectively for N1,N2 and N3 treatments,compared with 976.47 kg·hm-2 for the control （N0）,indicating that the low-to-medium N loads （N1 and N2） increased litterfall amount significantly,while high levels of N deposition （N3） decreased the quantities to some extents.The concentrations of C and N in fallen leaves increased with the increasing nitrogen deposition,but C /N ratios decreased gradually from 65.55 （N0） to 65.38 （N1）,61.77 （N2）,and 53.77 （N3）.The annual C flux through litterfall to the forest floor was estimated at 474.70,544.07,538.55 and 474.02 kg·hm-2 ,and the annual N at 7.21,8.56,9.03 and 9.04 4 kg·hm-2 ,and the P at 1.17,1.24,1.32 and 1.09 g·hm-2 ;respectively,for the above four treatments （N0,N1,N2 and N3）.The annual N flux responded positively to the increased nitrogen loads,C and P fluxes were promoted by N1 and N2 treatments,but inhibited by N3.