模拟氮沉降凋落物管理对樟树人工林土壤呼吸的影响

以湖南省植物园樟树人工林为对象,研究了模拟氮沉降下,不同凋落物处理对土壤呼吸的影响。设置4个施氮水平,分别为CK(0 kg N hm~(-2)a~(-1))、LN(50 kg N hm~(-2)a~(-1))、NM(150 kg N hm~(-2)a~(-1))以及HN(300 kg N hm~(-2)a~(-1));凋落物处理分别为去除凋落物、添加凋落物以及凋落物对照组。经过为期2年的观测研究,结果表明:(1)模拟氮沉降不同凋落物处理下,土壤温度呈现显著的季节性变化,但不存在显著差异;土壤湿度呈现显著的波动性变化,施氮及凋落物管理对土壤温度无影响。土壤湿度仅受凋落物管理的影响。在不同施氮水平下,去除凋落物的土壤湿度与加倍凋落物的土壤湿度均存在显著差异性。(2)模拟氮沉降不同凋落物处理下,土壤呼吸均呈现显著的季节性变化,最大值出现在6—8月;最小值出现在1月,且在生长季期间(4—8月),不同处理下土壤呼吸存在显著差异。(3)施氮对土壤呼吸表现为抑制作用,添加凋落物对土壤呼吸起促进作用,去除凋落物对土壤呼吸起抑制作用。(4)在凋落物对照组中,LN、MN、HN较CK相比,土壤呼吸速率年均值分别降低了35.4%、30.6%、36.8%,且各施氮水平与CK存在显著差异(P0.05);添加凋落物处理下,LN、MN、HN处理较CK相比,土壤呼吸速率年均值土壤呼吸分别降低了23.2%、15.8%、14.7%。去除凋落物处理下,LN、MN、HN较CK相比,土壤呼吸速率年均值分别降低了3.5%、0.5%、-11.6%。且添加或去除凋落物均能削弱施氮对土壤呼吸的抑制作用,且这种作用随着施氮水平的增加而增大。(5)土壤呼吸与5 cm处土壤温度存在显著相关性(P0.05),土壤温度可解释土壤呼吸变异的47.76%—72.61%;与土壤湿度呈现正相关,但未达到显著相关水平(P0.05)。

Effects of litter on soil respiration under simulated nitrogen deposition in a Cinnamomum camphora forest

We evaluated the effects of different litter treatments on soil respiration under the influence of nitrogen deposition in a camphor plantation forest in Hunan Botanical Garden, China.We used four different levels of nitrogen, including CK (0 kg N hm^-2 a^-1), LN (50 kg N hm^-2 a^-1), NM (150 kg N hm^-2 a^-1), and HN (300 kg N hm^-2 a^-1), and three litter treatments, including litter removal, doubled litter, and litter control group (no litter treatment).After two years of observation, the following major results were obtained:(1) Soil temperature showed significant seasonal changes, but no significant difference was observed in soil temperature with different litter treatments under simulated nitrogen deposition. However, soil moisture showed significant fluctuations. Soil moisture was affected only by litter management. A significant difference was observed in soil moisture with litter removal and doubled litter under different levels of nitrogen. (2) With different litter treatments under simulated nitrogen deposition, soil respiration showed significant seasonal changes; the maximum respiration rates were obtained from June to August and the minimum in January. During the growing season (April-August), a significant difference was observed in soil respiration with different treatments. (3) Soil respiration was inhibited by nitrogen applications; however,soil respiration was promoted by the addition of litter and inhibited by its removal. (4)Compared with CK, the soil respiration rates of LN-, MN-, and HN-treated soil significantly decreased by 35.4%, 30.6%, and 36.8% in the litter control group (P < 0.05); by 23.2%, 15.8%, and 14.7% in the doubled litter group; and by 3.5%, 0.5%, -11.6% in the litter removed group. The addition or removal of litter could weaken the inhibitory effect of nitrogen on soil respiration. Moreover, this effect increases with increasing nitrogen levels. (5)A significant correlation was found between soil respiration and soil temperature at a soil depth of 5 cm (P < 0.05). Soil temperature could explain a variation of 47.76%-72.61% in soil respiration, and no significant correlation was found between soil respiration and soil moisture (P > 0.05).