模拟轮伐期长短对杉木人工林氮动态的影响

Simulated nitrogen dynamics for a Cunninghamia lanceolata plantation with selected rotation ages

近年来由于杉木Cunninghamia lanceolata连栽造成生产力日趋下降,已严重影响了杉木人工林的持续经营。运用FORECAST模型模拟杉木人工林在200 a间的生长情况,从而揭示其在不同轮伐期下氮循环的特点。模拟分好、中、差3种立地条件和10,25,50 a等3个不同的轮伐期长度。预测结果显示:杉木人工林氮的吸收量和归还量都随着轮伐期的增长而增加;叶片氮的含量也随着轮伐期的增长而增大;土壤有效氮在25 a轮伐期时下降,而后随着轮伐期变长又有所回升。以中等立地为例,10,25,50 a轮伐期土壤有效氮的200 a的平均值分别为96.24,86.87和96.07 kg.hm-2;吸收氮的平均值分别为49.22,58.44和69.07 kg.hm-2;凋落物形式归还氮的平均值分别为26.75,44.76和60.74 kg.hm-2。随着轮伐期增长,氮的循环系数增大,不同轮伐期的前4个轮伐期(前4代)氮的循环系数分别为0.544,0.766,0.847和0.879。模型预测的氮的吸收量与实测值具有很高的拟合度,达到显著水平。

To show nitrogen dynamics for successive rotations of Cunninghamia lanceolata plantations with declining productivity and the affect on sustainable management,the FORECAST model was used to simulate 200 years of growth for Cunninghamia lanceolata plantations with different rotation ages in China.Results suggested that N uptake,N return to the soil,and foliar N content could increase with a longer rotation age.The model showed that soil available N decreased with a 25-year rotation age and then increased with longer rotation ages.With the medium site,the average soil available N was 96.24 kg·hm-2 for a 10-year rotation age,86.87 kg·hm-2 for a 25-year rotation age,and 96.07 kg·hm-2 for a 50-year rotation age;the average uptake N was 49.22 kg·hm-2 for a 10-year rotation age,58.44 kg·hm-2 for a 25-year rotation age,and 69.07 kg·hm-2 for a 50-year rotation age;and the average return of N to the soil was 26.75 kg·hm-2 for a 10-year rotation age,44.76 kg·hm-2 for a 25-year rotation age,and 60.74 kg·hm-2 for a 50-year rotation age.The recycled N ratios from the first four rotations were 0.544,0.766,0.847,and 0.879.