氮磷添加对亚热带常绿阔叶林凋落物产量及其养分含量的影响

【目的】凋落物是森林净生产量的重要组分,探讨森林凋落物生产及其养分归还量对氮磷添加的响应,为亚热带常绿阔叶林可持续经营提供科学依据。【方法】选择安徽池州亚热带常绿阔叶林,包括甜槠(Castanopsis eyrei)老龄林和苦槠(C. sclerophylla)中龄林,开展氮磷添加试验,设置3个处理,即氮N 100 kg /(hm²·a)]、氮+磷N 100 kg /(hm²·a) +P 50 kg /(hm²·a)]和对照(CK,无氮磷添加)。采用凋落物收集框法,对林分凋落物生产量及其养分归还量进行了为期1年的监测(2017年5月至2018年4月)。【结果】N+P处理下,苦槠林和甜槠林总凋落物量最高值分别为9.502、7.120 t/(hm²·a);其次是N处理,分别为8.393、7.041 t/(hm²·a);CK林分分别为7.724和6.697 t/(hm²·a),氮磷添加提高了总凋落物量,但不同处理间没有显著差异。在N处理和对照条件下,两林分凋落物各组分所占比例由大到小顺序均为:落叶、落枝、碎屑、落花落果。但在N+P处理的苦槠林中由大到小依次为:落叶、落枝、落花落果、碎屑。N处理下,苦槠林和甜槠林凋落物年均氮含量分别为14.199和13.648 g/kg,N+P处理分别为13.863和13.650 g/kg,CK林分分别为13.384和13.094 g/kg。各处理下苦槠林和甜槠林凋落物年均磷含量由大到小顺序为N+P、CK、N处理。两林分凋落物的氮磷含量和年归还量不同处理间差异均不显著;不同处理间的苦槠林和甜槠林凋落物的氮磷比均无明显差异。【结论】氮沉降提高了苦槠和甜槠林凋落物产量,磷添加具有一定的增效作用,表明磷添加缓解了氮沉降引起的磷限制作用。

Effects of nitrogen and phosphorus additions on litterfall production and nutrient dynamics in evergreen broad-leaved forests

【Objective】Litterfall is an important component of net primary productivity of forests. This study deals with the response of litter production and nutrient return to nitrogen (N) and phosphorus (P) additions in subtropical evergreen broad-leaved forests to achieve a sustainable management of the forest. 【Method】A simulated nitrogen deposition experiment was conducted in the evergreen broad-leaved Castanopsis eyrei forest and C. sclerophylla forest; the experiment was commenced from May 2017 to April 2018 in Chizhou, Anhui Province. The experimental design consisted of N N, 100 kg /(hm²·a)), N+P N 100 kg /(hm²·a) + P 50 kg /(hm²·a)] treatments, and a control (CK, stream water only without fertilizer). 【Result】The annual litterfall productions of C. eyrei and C. sclerophylla forests were the highest in N+P treatment with 9.502 and 7.120 t/(hm²·a), respectively, followed by N treatment with the annual litterfall of 8.393 and 7.041 t/(hm²·a), respectively, and then CK with the annual litterfall of 7.724 and 6.697 t/(hm²·a), respectively. There were no significant differences among the treatments. The percentage of the litterfall component was in the following order: foliage > branch > miscellaneous > sexual organs,while the percentage of the litterfall component was in the following order: foliage > branch > sexual organs >miscellaneous for N+P treatment in C. sclerophylla forests. The annual mean weighted N concentrations of litterfall were 14.199 and 13.684 g/kg for N treatment, 13.863 and 13.650 g/kg for N+P treatment, 13.384 and 13.094 g/kg for CK in C. sclerophylla and C. eyrei forests, respectively. The order of annual mean weighted P concentrations of litterfall was ranked as N+P > CK > N for the two forest stands and there was no significant difference among the treatments. Additionally, no significant difference was observed in annual returns of N, P, and ratios of N/P among treatments for the two forest stands. 【Conclusion】The addition of N plus P had a synergistic effect on the litterfall production in subtropical evergreen broad-leaved forests. Our results suggest that the addition of P alleviates the phosphorus limitation caused by the high nitrogen deposition.