凋落物和铵态氮添加对亚热带罗浮栲和杉木林土壤碳氮淋溶的影响

Effects of Litter and Nitrogen Addition on Carbon and Nitrogen in Soil Leaching Solution of Subtropical Castanopsis fabric and Cunninghamia lanceolata Forest

[目的]凋落物是森林土壤碳氮的主要来源,通过分析凋落物或土壤淋溶碳氮的变化,揭示凋落物分解通过淋溶对土壤碳氮的影响及氮添加情况下这种影响的变化,进而探究凋落物分解与土壤碳氮的关系。[方法]以亚热带天然阔叶林和人工针叶林土壤和凋落物为对象,设置6种处理:凋落物、土壤、凋落物+土壤、凋落物+氮、土壤+氮和凋落物+土壤+氮,每个处理3重复。氮添加量(NH_(4)^(+)-N/土壤)为120 mg·kg^(−1),针、阔叶林凋落物添加量分别为12.1、19.7 g·kg^(−1),凋落物放置在土壤或石英石表面,土壤湿度控制在60%饱和持水量,于25℃暗培养箱中,采用氮淋溶模拟氮沉降的方法,进行室内培养试验。培养期间,氮溶液分5次不等氮量淋溶,每次110 mL溶液(按照淋溶次数分配依次为80、10、10、10、10 mg NH_(4)^(+)-N),收集淋溶液,测定其溶解性有机碳(DOC)、氮(DON)和无机氮。[结果]凋落物淋溶液有较低的无机氮和DON,较高的DOC;凋落物添加分别降低针阔叶土壤淋溶液中NO_(3)^(−)-N 22.6%和29.9%、提高针叶林土壤淋溶液中DOC 181.4%,但是降低阔叶林土壤淋溶液中DON 39.2%和阔叶林土壤MBN 53.2%。氮添加后,凋落物对添加氮的截留较少,且阔叶林凋落物截留高于针叶林;凋落物通过淋溶输入土壤的DOC减少,而DON增加。氮添加增加土壤可淋溶的无机氮量和针叶林土壤淋溶液DON,但凋落物降低土壤氮淋溶的作用在氮添加情况下没有减弱。[结论]凋落物具有减缓土壤NO_(3)^(−)-N输出对水环境的负面影响,氮添加可通过改变针阔叶林凋落物DOC和DON的输出影响土壤氮变化。

[Objective]Litter is the main source of carbon and nitrogen in forest soils.The effect of litter decomposition on soil carbon and nitrogen by leaching was studied through analyzing the changes of dissolved carbon and nitrogen in litter or soil leaching solution,for exploring the relationship between litter decomposition and soil carbon and nitrogen.[Method]Soil and litter in broad-leaved and coniferous forests were collected from subtropical forests.Six treatments were set,including litter,soil,litter+soil,nitrogen+litter,nitrogen+soil,and litter+soil+nitrogen.Three replicates were set for each treatment.The nitrogen addition amount was 120mg NH_(4)^(+)-N·kg^(−1) soil.The amount of litter added in coniferous and broad-leaved forests was 12.1 g·kg^(−1) and 19.7 g·kg^(−1),respectively.The litter was placed on the surface of soil or quartzite,and the soil moisture was controlled at 60%water-holding capacity.An incubation experiment was carried out with nitrogen addition by leaching to simulate nitrogen deposition in a dark incubator at 25℃for 220 days.During the incubation period,the nitrogen solution leached in 5 times with different nitrogen amounts,each with 110 mL of solution(80,10,10,10,10 mg NH_(4)^(+)-N in sequence according to the number of leaching times),and the leaching solution was collected and measured..In addition,the dissolved organic carbon(DOC)and nitrogen(DON),and NH_(4)^(+)-N and NO_(3)^(−)-N in the leaching solution were also measured.[Result]The results showed that the litter leaching solution had lower inorganic nitrogen and DON,and higher DOC.Litter addition significantly reduced the NO_(3)^(−)-N by 22.6%and 29.9%in the coniferous forest and broad-leaved forest soil leaching solution,respectively and increased the DOC by 181.4%in the coniferous forest soil leaching solution.However,litter addition significantly decreased the DON by 39.2%in the broad-leaved forest soil leaching solution and MBN by 53.2%in the broad-leaved forest soil.Under nitrogen addition,the interception of added nitrogen by litter was less,and the interception of litter in broad-leaved forest litter was higher than that in coniferous forest.Litter input to soil by leaching decreased DOC,while DON increased.Nitrogen addition increased soil leaching inorganic nitrogen and coniferous forest soil leaching solution DON,but the effect of litter on reducing soil nitrogen leaching was not weakened by nitrogen addition.[Conclusion]The litter slows down the negative impact of soil NO_(3)^(−)-N output on water environment.Nitrogen addition can affect soil nitrogen changes by altering the output of DOC and DON in broad-leaved and coniferous forest litters.