不同年龄毛竹林养分分布及生物循环特征

毛竹林是我国重要的森林资源类型,由于片面追求经济效益,许多竹阔混交林被改造为纯林,造成其土壤质量和立地生产力不同程度退化。因此研究毛竹林生产力和营养元素循环特征,对保持毛竹林持续生产力具有重要意义。以湖南桃江县桃花江林场毛竹林作为研究对象,将同一年龄毛竹的株数占据60%以上林地的标准划分各年龄段毛竹林,并研究不同年龄(1年,3年和5年)毛竹林生态系统营养元素含量、积累和分布格局以及生物循环特征。结果表明:竹林层营养元素平均含量均以N和K含量最高,Ca和P较低,各营养元素在毛竹不同器官的含量存在差异且随竹龄变化而变化;因毛竹林年龄不同,死地被物各层次的营养元素含量不同,并且同一年龄毛竹林亦随层次不同而异;土壤层N、P、K元素随着土层深度的增加而递减,Ca则随土层深度增加而增加。竹林层营养元素总积累量为338.31—1104.72 kg/hm~2,死地被物层为37.69—46.94 kg/hm~2,土壤层为56952.67—63783.22 kg/hm~2。不同年龄毛竹林生态系统营养元素年吸收量为237.41—338.3 kg/hm~2,归还量为20.84—86.47 kg/hm~2,存留量为216.57—267.05 kg/hm~2,利用系数为0.27—1.00,循环系数为0.09—0.25,周转时间在6.17—40.33年之间。

Nutrient distribution and biochemical cycling in different aged moso bamboo (Phyllostachys pubescens) ecosystems

Moso bamboo (Phyllostachys pubescens) is an important forest resource in southern China. The conversion from mixed bamboo and broad-leaf forest to pure bamboo forest may cause a potential degradation of soil fertility in pure bamboo plantations. Therefore, understanding the productivity and biochemical cycling process of bamboo forests is vital for maintaining the sustainability. In this study, we investigated nutrient allocation and biochemical cycling patterns in different aged (1 year, 3 years, and 5 years) bamboo forests. The age category was based on the age distribution of the individual bamboo in one forest site, which accounted for more than 50%-60% of the total individuals. Our results showed that the mean tissue concentrations of N and K were the highest in all the bamboo forests, whereas Ca and P were the lowest. The nutrient concentrations also varied in different organs nested in different aged stands of bamboo. Additionally, the nutrient contents varied in different dead floor layer among different aged stands or even in a same aged stand. N, P, and K in soil decreased with soil depth, while Ca content increased. The accumulated nutrients ranged 338.31-1104.72 kg/hm² in the whole forest ecosystem, 37.69-46.94 kg/hm² in dead floor, and 56952.67-63783.22 kg/hm² in soil layers, respectively. The nutrient cycling index ranged from 237.41-338.30 kg hm^-2 a^-1 for annual absorption, 20.84-86.47 kg hm^-2 a^-1 for annual return, and 216.57-267.05 kg hm^-2 a^-1 for annual retention, respectively. The nutrients utilization coefficient was 0.27-1.00, 0.09-0.25 for cycling coefficient, and 6.17-40.33 years for recycling period, respectively. Our results indicated that bamboo forests had relatively high absorption, low return, and high retention of nutrient elements on an annual basis. Thus, more nutrients are needed and advanced scientific management is required in order to maintain a long-term productivity of bamboo forests comparing to other common forest types in this area.