樟树人工林凋落物养分含量及归还量对氮沉降的响应

氮沉降的持续增加对陆地生态系统的健康发展构成严重威胁,森林是陆地生态系统中重要的组成部分,大量的氮沉降对其结构和功能造成严重影响。凋落物是森林生态系统养分循环的重要组成部分,它对土壤肥力、森林生态系统养分循环等方面具有重要作用。为了探讨亚热带常绿阔叶森林凋落物对氮沉降增加的响应,在湖南省森林植物园以樟树人工林为研究对象进行模拟氮沉降的实验,实验设置4种氮添加水平CK(0g N m~(-2)a~(-1),对照)、LN(5g N m~(-2)a~(-1)),MN(15g N m~(-2)a~(-1)),HN(30g N m~(-2)a~(-1)),研究氮沉降对樟树林年凋落物量、凋落物养分含量以及归还量的影响。结果表明:不同施氮水平下(CK、LN、MN、HN),樟树林凋落物的年凋落量分别为(4.53±0.32)t hm~(-2)a~(-1)、(3.95±0.28)t hm~(-2)a~(-1)、(3.56±0.41)t hm~(-2)a~(-1)、(4.46±0.48)t hm~(-2)a~(-1),施氮抑制了樟树林的凋落量,且低、中氮处理下差异显著(P0.05);施氮处理后凋落物的养分含量大小顺序为:CNCaKMg,凋落物的碳含量没有显著变化,但氮含量都有所增加,因此,施氮降低了樟树凋落物各组分的C/N比;凋落物中元素的年归还量大小顺序表现为:CNCaKMg,施氮处理对凋落物C、K、Ca、Mg归还量有抑制作用,但对凋落物N归还量表现为促进作用。

Nutrient contents and fluxes in the litterfall from Cinnamomum camphora plantation in response to simulated nitrogen deposition

Nitrogen deposition is a serious threat to the healthy development of the terrestrial ecosystem. Forests are the important part of terrestrial ecosystem, and high levels of nitrogen deposition seriously influence forest structure and function. Litter is an important part of forest ecosystem nutrient cycling,, which has an important role in the soil, forest ecological. We investigated the effects of Control(CK, no nitrogen fertilization), low nitrogen(LN, 5 g N m^-2 a^-1), medium nitrogen(MN, 15 g N m^-2 a^-1) and high nitrogen(HN, 30 g N m^-2 a^-1) treatments on the, nutrient contents and fluxes caused by litterfalls in a subtropical Cinnamomum camphora plantation located in Hunan Province, China. According to the results, the annual litterfall production in CK, LN, MN, and HN was(4.53±0.32) t hm^-2 a^-1,(3.95±0.28) t hm^-2 a^-1,(3.56±0.41) t hm^-2 a^-1 and(4.46±0.48) t hm^-2 a^-1, respectively, suggesting that low-to-medium N deposition decreased the litterfall production significantly. The order of nutrient contents was C > N > Ca > K > Mg, after nitrogen fertilization. Furthermore, the nitrogen content of litter had little impact on the carbon content. However, the N treatments(LN, MN, HN) decreased C/N ratios, compared with CK. The order of nutrient fluxes was C > N > Ca > K > Mg, and nitrogen fertilization reduced the amount of C, K, Ca, and Mg fluxes, but increased the N flux.