原始红松林退化演替后土壤氮矿化特征变化

Characteristics of soil nitrogen mineralization in the degraded and successional primitive Korean pine forest in the Lesser Khingan Mountain, Northern China

土壤氮矿化是氮素生物地理化学循环的重要环节,表征着土壤的供氮潜力,其变化过程会影响森林生态系统生产力。从小兴安岭典型的原始红松林及其退化形成的次生阔叶林样地采集土壤样品,采用好气室内培养法,研究在不同培养温度(4℃、12℃、20℃、28℃和36℃)和湿度(20%、40%、60%、80%和100%饱和持水量,WHC)下,2种林地土壤氮转化速率的变化。结果表明:与原始红松林相比,次生阔叶林表层土(0—20cm)的有机质、全碳、全氮、硝态氮、碳/氮比、全磷、速效磷、速效钾、pH值均显著升高,铵态氮显著降低(P<0.05)。采用方差分析结果表明:原始红松林表层土壤的净矿化速率、净硝化速率均显著低于次生阔叶林,但净氨化速率的变化则相反;培养温度和湿度及两者的交互作用均对土壤氮转化速率影响显著(P<0.001)。原始红松林和次生阔叶林净矿化速率对温度和湿度变化的响应存在一定差异,最适温度和湿度分别为28℃—36℃和60%(WHC)。原始红松林土壤氮矿化温度敏感性指数(Q10)显著高于次生阔叶林(P<0.05),均值分别为2.08和1.80,Q10与基质质量指数(A)呈负相关,与土壤有机质呈极显著负相关(P<0.01)。

Soil nitrogen mineralization is a key component of the nitrogen biogeochemical cycle, which indicates the potential of the soil nitrogen supply, and its changing process will impact the productivity of forest ecosystems. In this study, soil samples were collected from the typical plots of primitive Korean pine forests and clear cutting-formed the secondary broad-leaved forests in the Lesser Khingan Mountain,Northern China;then they were cultivated aerobically under indoor conditions at different culture temperatures (4℃, 12℃, 20℃, 28℃, and 36℃) and humidity (20%, 40%, 60%, 80%, and 100% saturated water holding capacity;WHC). Soil nitrogen transformation rates were compared between primitive Korean pine forest and the secondary broad-leaved forest. The results showed that the organic matter, total carbon, total nitrogen, nitrate nitrogen, carbon-to-nitrogen ratio, total phosphorus, available phosphorus, available potassium, and pH in the surface soil (0-20 cm) were significantly increased (P< 0.05) and ammonium nitrogen significantly decreased (P< 0.05) in the secondary broad-leaved forest compared to the primitive Korean pine forest. An analyses of variance showed that net mineralization rate and net nitrification rate of the surface soils were significantly lower in the primitive Korean pine forest than the secondary broad-leaved forest;however, net ammonification rates showed the opposite trend when it was compared between the two forest types. Soil nitrogen transformation rates were significantly affected by the temperature and humidity (P< 0.001). There were significant differences in responses of net mineralization rate to changes in temperature and humidity between the primitive Korean pine forest and the secondary broad-leaved forest, the optimum temperature and humidity were 28℃-36℃ and 60% WHC for the soils of both forests. The temperature sensitivity index of soil nitrogen mineralization ( Q10 value) in the primitive Korean pine forest was significantly higher than that of the secondary broad-leaved forest (P< 0.05). The Q10 value was negatively correlated with the matrix quality index (A) and soil organic matter(P< 0.01).