施N对云南松凋落叶和枝早期分解过程中养分动态变化的影响

Effects of N application on nutrient dynamics in Pinus yunnanensis forest during the early decomposition of leaf and twig litter

【目的】探讨N沉降条件下森林生态系统凋落物养分的变化规律,以期为亚热带云南松林的保护、生态系统的恢复及其可持续经营发展提供理论依据,并为在全球N沉降普遍持续增加背景下的养分循环变化特征提供基础数据。【方法】本研究以滇中亚高山云南松林凋落叶和枝为研究对象,自2018年2月至2019年1月,采用凋落物分解袋法进行原位分解试验,设置不同施氮水平(对照-CK,0 g·m^(-2)·a^(-1)、低N-LN,5 g·m^(-2)·a^(-1)、中N-MN,15 g·m^(-2)·a^(-1)和高N-HN,30 g·m^(-2)·a^(-1)),探究云南松林凋落物营养元素的动态变化、元素释放以及元素周转率对不同施N水平的响应特征。【结果】1)经过12个月的N沉降实验,云南松林凋落叶和枝在不同施N水平下总体表现为:LN降低、MN和HN提高了C、N、P、K的元素含量;2)凋落叶和枝的元素释放在N沉降过程中表现不同,凋落叶和枝C元素总体表现为直接释放;凋落叶N元素在分解初期(第1个月)呈短暂富集,随后呈释放模式;凋落枝N元素在分解1—10个月均表现为富集状态,在第6个月时残留率达到最高值;凋落叶和枝的P和K的释放过程一致,残留率表现为初期(前3个月)上升,达到峰值后不断下降;3)不同施N处理下,凋落叶和枝整体上呈LN处理促进元素释放,MN和HN处理抑制元素释放;N沉降对各元素周转期影响则表现为:LN缩短了各元素周转期(0.05~0.79 a),MN与HN则分别延长了各元素周转期(0.42~1.93 a和0.07~2.19 a)。【结论】施N并未改变云南松凋落叶和枝分解过程中C、N、P、K元素的释放模式;但随着施N浓度的增加,对分解过程中C、N、P、K元素释放速率表现出持续的抑制作用;施N浓度高于15 g·m^(-2)·a^(-1)均延长了各元素周转期,可能会延缓养分向土壤系统的归还,研究结果为不同水平N沉降对森林碳循环的关键过程提供了理论依据。

【Objective】In order to provide a theoretical basis for the protection,ecosystem restoration and sustainable management and development of subtropical Yunnan pine forest,and provide basic data for the characteristics of nutrient cycling under the background of global N deposition,this paper discussed the changes of forest litter nutrients under the condition of N deposition.【Method】From February 2018 to January 2019,the litter decomposition bag method was used to carry out in-situ decomposition experiments on the leaf and twig litter of Pinus yunnanensis forest in the subalpine of central Yunnan,China.To explore the dynamic changes of nutrient elements,element release and the response characteristics of element turnover ratios to different N deposition levels in the litter of Pinus yunnanensis forest,different N deposition levels were set up as follows:control check(CK,0 g·m^(-2)·a^(-1)),low nitrogen(5 g·m^(-2)·a^(-1)),medium nitrogen(MN,15 g·m^(-2)·a^(-1))and high nitrogen(HN,30 g·m^(-2)·a^(-1)).【Result】The results indicated that 1)After 12 months of the N deposition experiment under different concentrations of N deposition,LN decreased the contents of C,N,P and K,while MN and HN increased the contents of each element.2)There was a slight difference in the release of elements in the litter leaves and twigs.The C element in the leaf and twig litter showed a direct release.The N element in the leaf litter had a short period of enrichment at the initial stage of decomposition(the 1st month),and then turned to a direct release mode.The N element in the twig litter was enriched from the 1st to the 10th month under N deposition,and the residual rate reached the highest value in the 6th month.The release process of P and K elements in the leaf and twig litter was consistent,and the residual rate increased at the initial stage(the first 3 months),then decreased after reaching the peak value.3)Under different N treatments,LN treatments promoted the element release of the leaf and twig litter,while MN and HN treatments inhibited the element release.The influence of N deposition on the element turnover period was as follows:the element turnover period was shortened by LN treatments(0.05-0.79 a),and it was prolonged by MN and HN treatments(0.42-1.93 a and 0.07-2.19 a).【Conclusion】In conclusion,N deposition did not change the release patterns of C,N,P and K elements in the leaf and twig litter of Pinus yunnanensis forest.However,with an increase in N concentration,the release rate of C,N,P and K in the decomposition process showed a continuous inhibition effect.The results of this study provide a theoretical basis for the key process of the forest carbon cycle caused by different levels of N deposition.