西藏东南部色季拉山主要类型森林叶片和枯落物养分含量特征

为阐明不同生长年限森林叶片和不同分解程度枯落物养分含量特征,为植物-土壤养分循环研究提供科学依据。以藏东南色季拉山几种典型森林植被(雪山杜鹃(Rhododendron aganniphum)、海拔4000 m和3900 m区域急尖长苞冷杉(Abies georgei var. smithii)、川滇高山栎(Quercus aquifolioides))为研究对象,分析了1年生和2年生植物叶片及不同分解程度枯落物有机碳(OC)、全氮(TN)、全磷(TP)和全钾(TK)含量。结果表明:色季拉山森林叶片和枯落物OC含量表现为2年生叶片1年生叶片未分解枯落物(ND)半分解枯落物(SD)完全分解枯落物(CD),即老叶片以C积累为主,而枯落物OC含量随分解程度的增加而下降,叶片OC平均含量(68.5%)显著高于中国平均水平(45.5%);叶片N、P、K含量表现为1年生2年生,即新叶以N、P、K等营养物质的吸收积累为主。枯落物TN含量低于中国森林的平均水平(12.03 g/kg),而TP含量显著高于中国森林平均水平(0.74 g/kg),枯落物TN和TP以SD最高,即分解初期表现为净固定,而后期则呈净释放,TK含量随分解程度的增加而增加,表现为K的净固定;叶片C∶N,C∶P和C∶K表现为2年生1年生,枯落物C∶N,C∶P和C∶K随着分解程度的增加而显著降低;叶片N∶P处于较低水平(6.08),显著低于全球平均水平(16.0),表现出明显的N限制营养型;研究结果为科学阐明藏东南森林生态系统植被-土壤养分循环研究提供了数据支撑。

Stoichiometric characteristics of leaves and litter in typical forest types on Sejila Mountain, southeastern Tibet

The contents and dynamics of nutrients in leaves and litter are important for plant-soil nutrient cycling in forest ecosystems. Forests are one of the most important terrestrial ecosystems in southeastern Tibet, where the litter layer develops in an alpine climate. In this study we investigated the contents and stoichiometry of the most important nutrients (carbon, nitrogen, phosphorus, and potassium) in relation to the leaf age and stage of forest litter decomposition on Sejila Mountain (elevation approximately 3400-4150 m) in southeastern Tibet. We measured the organic carbon (OC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) contents in 1-a-old and 2-a-old leaves, and at different stages of litter decomposition (non-decomposedND], semi-decomposedSD], and completely decomposedCD]), in typical forest types (Rhododendron aganniphum, Abies forrestii, and Quercus aquifolioides). The OC contents of the leaf and litter showed the following rank order:2-a-old leaf > 1-a-old leaf > ND > SD > CD (65.71%, 71.29%, 60.58%, 41.15%, and 29.86%, respectively). The litter OC content decreased with an increasing litter decomposition. The leaf OC contents were higher than the average for China (45.5%). The leaf OC contents were significantly higher in the coniferous forest than in the broad-leaved forest, and those in both forest types were higher in older leaves than in new leaves (72.89% and 58.32% for 1-a-old leaves, and 78.31% and 64.29% for 2-a-old leaves, in the coniferous and broad-leaved forests, respectively). The contents of N, P, and K in the leaf were higher in the 1-a-old leaves than in the 2-a-old leaves. The TN content of the 1-a-old leaves was higher in the broad-leaved forest (11.23 g/kg) than in the coniferous forest (10.55 g/kg), whereas the TN content of the 2-a-old leaves in the coniferous forest (9.39 g/kg) was higher than that in the broad-leaved forest (7.15 g/kg). The TN and TP contents of litter were highest in the SD forest, which indicated that net fixation occurred during initial decomposition, whereas complete decomposition resulted in a net release of nitrogen and phosphorus. The litter TK content was elevated with increased decomposition, and thus showed net fixation during the decomposition process. The litter TN contents were lower than the average for Chinese forests (12.03 g/kg), and the average values were 6.59, 8.24, and 9.55 g/kg for ND, SD, and CD forests, respectively. The litter TP contents were higher than the average for Chinese forests (0.74 g/kg), and the average values were 1.17, 2.49, and 1.87 g/kg for ND, SD, and CD forests, respectively. The litter TK contents were 2.19, 3.33, and 4.67 g/kg for ND, SD, and CD forests, respectively. The leaf C:N, C:P, and C:K ratios were higher in the 2-a-old leaves than in the 1-a-old leaves; the ratios at each leaf age were 87.81 and 60.79 for C:N, 539.25 and 375.49 for C:P, and 139.15 and 101.20 for C:K, respectively. The litter C:N, C:P, and C:K ratios were decreased with increased decomposition. The ND, SD, and CD ratios were 90.20, 43.36, and 35.68 for C:N; 520.34, 167.60, and 159.13 for C:P; and 297.73, 129.97, and 64.42 for C:K, respectively. The leaf N:P ratios were low (6.09 and 4.76), and significantly lower than the global average (16.0), which was indicative of nitrogen limitation. The litter N:P ratios for ND, CD, and SD were 5.86, 4.51, and 3.90, respectively. The results provide valuable information on plant-soil nutrient cycling in forest ecosystems in southeastern Tibet.