不同无性系杉木人工林土壤氮素转化特征

为揭示福建省洋口林场不同无性系杉木人工林土壤氮素转化特征，以15年林龄的第三代优良组培材料和实生苗(包括洋003（Y003）、洋008（Y008）、洋020（Y020）、洋061（Y061）、洋062（Y062）、第2代种子园良种（Ysec）和无性系混系扦插苗（Ymix）)共计7种无性系杉木人工林土壤为研究对象开展室内培养试验，测定培养期间土壤无机氮含量变化，进而计算不同无性系杉木人工林土壤的净矿化速率和净硝化速率。结果表明：不同无性系杉木人工林土壤的净矿化速率和净硝化速率均处于较低水平（净矿化速率和净硝化速率分别为-0.093~0.118 mg?kg-1?d-1和-0.021~0.051mg?kg-1?d-1）均处于较低水平，表明亚热带地区杉木人工林土壤的供氮能力较弱。但在不同无性系间氮净矿化和硝化速率均存在显著差异。Y061土壤的平均净矿化速率显著高于其他无性系人工林土壤，为0.118 mg?kg-1?d-1，其次为Ymix和Y062无性系，分别为0.046 mg?kg-1?d-1和0.033 mg?kg-1?d-1；而其他4种无性系土壤平均净矿化速率均为负值，表现为无机氮的净同化作用；对不同无性系杉木人工林土壤而言，Y008的净硝化速率最高，为0.051 mg?kg-1?d-1，其次为Ymix和Y020无性系，分别为0.003和0.007 mg?kg-1?d-1，其他4种土壤平均净硝化速率均为负值，表现为硝态氮的净同化作用，因而保氮能力强。综上，Y061和Y062两种无性系杉木人工林土壤的供氮能力和保氮水平显著高于其他无性系，而Y008土壤发生淋溶等氮素损失的风险高于其他无性系，在实际栽植中应当合理选择无性系树种以保证更好的土壤肥力供应。

Characteristics of Soil Nitrogen Transformation in Different Clonal Chinese Fir Plantations

ObjectiveThis study aimed to reveal the characteristics of soil nitrogen (N) transformation in different clonal Chinese fir plantations in Yangkou National Forest Farm of Fujian. This study provided theoretical basis for artificial nitrogen management and improved seed breeding of different clones of Chinese fir plantations.MethodAn incubation experiment was carried out with 7 different kinds of 15-year old third-generation excellent culture materials and seedlings (Y003, Y008, Y020, Y061, Y062, Ysec and Ymix) as the research objects, and the basic physical and chemical properties, net N mineralization and nitrification rate of soil of different clones were evaluated.ResultThe results showed that the net rates of N mineralization and nitrification were significantly affected by different clonal Chinese fir plantations. Specifically, the net mineralization rate and net nitrification rate were -0.09-0.118 mg·kg^-1·d^-1 and -0.021-0.051 mg·kg^-1·d^-1, respectively. During the whole incubation period, the average net soil N mineralization rate of Y061 was 0.117 mg kg^-1 d^-1, which was significantly higher than that of other clones and followed by Ymix (0.046 mg·kg^-1·d^-1) and Y062(0.033 mg·kg^-1·d^-1). In contrast, the average net N mineralization rates of the other four clones were negative, indicating the occurrence of net N immobilization. The average net soil nitrification rate of the Y008 clone was the highest, which was 0.051 mg kg^-1 d^-1, followed by Ymix (0.003 mg·kg^-1·d^-1) and Y020 clone (0.007 mg·kg^-1·d^-1). There were no significant differences in soil pH, ammonium nitrogen, C/N and the composition of silt and sand, but there were significant differences in soil nitrate nitrogen, organic matter, total nitrogen and clay composition. The results showed that ammonium nitrogen, nitrate nitrogen, pH and total nitrogen in soil were the main factors affecting the net nitrification rate and were all positively correlated, In contrast, the average net nitrification rate of the other four clones was negative, indicating the occurrence of net immobilization of nitrate. There were no significant differences in soil pH and carbon (C)/N among different clones, but significant differences in soil particle size composition, organic matter and total N content. Soil pH and total N were positively correlated with net mineralization and net nitrification rate, while soil C/N was negatively correlated with sand content.ConclusionThe results showed that the soil N supply capacity and N retention capacity of Y061 and Y062 clones were significantly higher than those of other clones, and the risk of N loss such as leaching in Y008 clones was higher than that of other clones. Therefore, the clone species should be rationally selected to ensure the soil fertility supply in actual planting. This study provides a theoretical basis for artificial nitrogen management and improved seed breeding of different clones of Chinese fir plantations.