鼎湖山苗圃和主要森林土壤CO_2排放和CH_4吸收对模拟N沉降的短期响应

The short-term responses of soil CO_2 emission and CH_4 uptake to simulated N deposition in nursery and forests of Dinghushan in subtropical China

研究了鼎湖山生物圈保护区苗圃(幼苗)、马尾松、混交林和季风常绿阔叶林(季风林)土壤CO2 排放和CH4 吸收的一些特征及其对模拟N沉降增加的响应。结果表明,土壤CO2 日(白天)平均排放量的大小顺序为(平均值±标准误) :苗圃(2 5 8±6 2mg·m- 2 ·h- 1 ) >季风林(177±4 2 mg·m- 2 ·h- 1 ) >马尾松林(16 2±39mg·m- 2 ·h- 1 ) >混交林(12 6±30 mg·m- 2 ·h- 1 )。土壤CH4 日(白天)平均吸收量的大小顺序为:马尾松林(- 0 .15±0 .0 2 mg·m- 2 ·h- 1 ) >季风林(- 0 .0 8±0 .0 1mg·m- 2 ·h- 1 ) >混交林(- 0 .0 7±0 .0 1mg·m- 2·h- 1 ) >苗圃(- 0 .0 5±0 .0 1m g·m- 2·h- 1 )。低N(5 0 kg N·hm- 2·a- 1 )和中N(10 0kg N·hm- 2·a- 1 )处理对苗圃、马尾松林和混交林样地土壤CO2 日平均排放量的影响均不明显,高N(15 0 kg N·hm- 2·a- 1 )处理对苗圃土壤CO2 的日平均排放量也无显著影响,但倍高N(30 0 kg N·hm- 2 ·a- 1 )处理显著促进苗圃样地土壤CO2 的排放。然而,所有N(低N、中N和高N)处理均显著促进季风林土壤CO2 日平均排放量,且这种促进作用随N处理水平的升高而增加。N处理显著促进季风林和马尾松林土壤对CH4 吸收速率,但对混交林土壤CH4 吸收则无明显的影响。在苗圃样地,除倍高N外,N?

The anthropogenic emission of nitrogen (N) compounds is increasing globally. In China, the emission of reactive N increased from 1.4×10~7 t·a^(-1) in 1961 to 6.8×10~7 t·a^(-1) in 2000. Currently this leads to deposition of 30～73 kg·hm^(-2)·a^(-1) in some forests of southern China. The possible impacts of elevated N input on vegetation, N cycling, acidification, and N leaching in tropical and subtropical forests have only been addressed in few studies. In China, the first such studies were carried out in the Dinghushan reserve (an IGBP-GCTE site) based on the design and methods used in the European NITREX project. The principal goal of this study was to measure the effects of nitrogen deposition on soil CO_2 emission and CH_4 uptake in soils of a nursery, pine forest (PF), pine and broadleaf mixed forest (MF), and monsoon evergreen broadleaf forest (MEBF) in the UNESCO/MAB Dinghushan Biosphere Reserve (DHSBR) in southern China. The nursery was dominated by the seedlings of three plant species (Schima superba, Cryptocarya concinna and Castanopsis chinensis). The N addition treatments(in three replicates) were: Control, T50(50 kg N·hm^(-2)·a^(-1)), T100(100 kg N·hm^(-2)·a^(-1)), T150(150 kg N·hm^(-2)·a^(-1)), and T300(300 kg N·hm^(-2)·a^(-1)). The first three treatments were applied to the mixed and pine forests, the first four treatments to the evergreen broadleaf forest, and all five treatments to the nursery. The treatments were applied to 20m × 10m plots surrounded by a 10 m wide buffer strip. All plots and treatments were laid out randomly. NH_4NO_3 solution was sprayed monthly by hand onto the floor of these plots as 12 equal application over the whole year and beginning in July 2003. For this nursery experiment 15 plots (3.5m × 8m) were set up surrounded by a 3.5 m wide buffer strip. All plots and treatments were also laid out randomly. NH_4NO_3 solution was sprayed twice every month by hand onto the floor of these plots as 12 equal application over the whole year and beginning in January of 2003. To examine the short-term responses of soil respiration and CH_4 uptake to N additions, one static chamber was established in each of the plots. Air was sampled from each plot at the time of 8, 10, 12, 14, 16 and 18 hr on the day after nitrogen additions (14～18 October, 2003), and analyzed for CO_2 and CH_4 using gas chromatography (Agilent 4890D) equipped with flame ionization detection (FID) within 24 h. The flux was calculated from a linear regression of concentration versus time using the three data points from each chamber. The daily mean soil CO_2 emission rates in control plots exhibited the following order: seedlings (258±62 mg·m^(-2)·h^(-1)) > MEBF (177±42 mg·m^(-2)·h^(-1))>PF (162±39 mg·m^(-2)·h^(-1)) > MF (126±30 mg·m^(-2)·h^(-1)), while the daily mean soil CH_4 uptake rates were PF (-0.15±0.02 mg·m^(-2)·h^(-1)) > MEBF > (-0.08±0.01 mg·m^(-2)·h^(-1)) > MF (-0.07±0.01 mg·m^(-2)·h^(-1)) > seedlings (-0.05±0.01 mg·m^(-2)·h^(-1)). Nitrogen addition at all levels significantly stimulated soil CO_2 emission in MEBF in comparison with those in control plots, and its effect increased with the levels of nitrogen addition. However, there was no significant effect of nitrogen addition at any level of treatment on soil CO_2 emission in PF and MF. Neither was there a significant effect of nitrogen addition at any levels except for T300 on soil CO_2 emission in seedlings. Nitrogen addition at T300 significantly increased soil CO_2 emission rates in comparison with those in control plots. Nitrogen addition at all levels significantly stimulated soil CH_4 uptake rates in both MEBF and PF in comparison with those in control plots. However, there was no significant effect of nitrogen addition at any levels of treatment except for T300 on soil CH_4 uptake in seedlings. Nitrogen addition at T300 significantly changed the soil function from “CH_4 sink” to “CH_4 source” in the nursery.