模拟氮沉降对典型阔叶红松林土壤呼吸的影响

阔叶红松(Pinus koraiensis)林是我国东北东部山区的地带性顶极植被,全球氮沉降增加可能影响其碳循环的各个过程。在2010年和2011年的5—10月,对典型阔叶红松林进行了模拟氮沉降实验。实验设置了对照(N₀, 0 kg/(hm²·a))、低氮(N₁, 30 kg/(hm²·a))、中氮(N₂, 60 kg/(hm²·a))和高氮(N₃, 120 kg/(hm²·a))4种模拟氮沉降处理,每隔半个月采用Li-6400-09便携式CO₂/H₂O气体分析仪对土壤呼吸速率进行测定,研究了氮沉降对典型阔叶红松林土壤呼吸的影响。结果表明:① 各处理土壤呼吸速率的季节变化与5 cm深度的土壤温度相似,均呈现出明显的季节变化趋势,最大值出现在6月中旬(3.84～4.55 μmol/(m²·s)),最小值出现在5月初(1.37～1.84 μmol/(m²·s)),土壤温度的变化可解释土壤呼吸速率季节变化的49.9%～69.2%。② 各处理的土壤呼吸速率与土壤温度呈指数相关(R²=0.499～0.692),土壤呼吸速率与土壤温度、湿度及其相互作用的回归模型可以解释各处理土壤呼吸速率52.2%～73.5%的季节变异; ③ N₀、N₁、N₂和N₃样地土壤呼吸温度敏感系数Q₁₀值分别为2.10、1.93、1.97和2.01; ④ 各处理样地土壤呼吸速率的平均值分别为3.09、2.78、3.06和2.90 μmol/(m²·s),与对照样地N₀相比,土壤呼吸速率和凋落物量无明显相关(P> 0.05)。

Effect of simulated nitrogen deposition on soil respiration in the typical mixed broadleaved-korean pine forest

The mixed broadleaved-korean pine(Pinus koraiensis)forest represents the climax vegetation type of the eastern mountainous area of northeast China. The increasing of the global nitrogen deposition may have affects on every process of carbon cycle. Four levels of N treatments: control(N₀, 0 kg/(hm²·a)), low-N(N₁, 30 kg/(hm²·a)), medium-N(N₂, 60 kg/(hm²·a)), and high-N(N₃, 120 kg/(hm²·a))were set in the present study. We measured soil CO₂ efflux about every half a month during the growing seasons from May 2010 to October 2011 using a Li-6400 portable CO₂ infrared gas analyzer. The results showed that the seasonal variation of soil respiration from all treatment plots was obvious and followed a bimodal curve, absolutely parallel to that of the soil temperature. Soil respiration peaked in June, and presented the lowest values in the early growing season. Soil respiration was exponentially related to the soil temperature at 5 cm depth(R²=0.499-0.692). Soil temperature could explain 49.9% to 69.2% of seasonal variation in respiration. Furthermore, soil temperature and moisture, and incorporating soil moisture into the pure soil respiration-temperature model improved the prediction of soil respiration in N₀ and N₂ treatment plots, and their interactions could explain 52.2% to 73.5% of seasonal variation in soil respiration. The average soil respiration rates in the growing season for N₀, N₁, N₂ and N₃ treatment plots were 3.09, 2.78, 3.06 and 2.90 μmol/(m²·s), respectively, and the corresponding apparent Q₁₀ values were 2.10, 1.93, 1.97 and 2.01. The average soil respiration rate, annual litterfall biomass in nitrogen addition plots were not significantly different compared with those in N₀(P> 0.05).