Effects of forest gap on the seedling growth of a canopy tree species Pometia tomentosa in tropical rainforest of Xishuangbanna.
在林窗中央、林窗边缘和林冠下3种不同光照梯度的森林生境中,研究了西双版纳季节雨林冠层树种绒毛番龙眼幼苗的早期 (种子萌发后10周内) 生长和定居后 (实生苗生长3个月以上) 的生长特点.结果表明: 绒毛番龙眼幼苗在早期生长阶段,林窗中央的株高、基径、总干质量、单株叶面积和相对生长率最大,分别为24.45 cm、3.17 mm、0.79 g、122.45 cm2和14.78×10-3 g·d-1.林冠下根冠比 (0.87) 高于林窗中央 (0.20) ,可能是光照和水分共同作用的结果.林窗中央较强的光照有利于定居后幼苗的生长,株高、基径、总干质量、单株叶面积、相对生长率和净同化率均在林窗中央最大,实验结束时分别达到31.48 cm、3.80 mm、2.22 g、174.52 cm2、2.29×10-3 g·d-1和2.54×10-5 g·cm-2·d-1.幼苗死亡可能与水分胁迫密切相关,由水分胁迫引起的幼苗死亡率在林冠下最高 (26.88%),但林冠下由脊椎动物捕食引起的幼苗死亡率较低(2.93%),从而使林冠下幼苗的最终存活率最高 (70.19%).光照是影响绒毛番龙眼幼苗形态学调节的重要因素, 林窗中央不同生长阶段幼苗的比叶面积最低,但相对生长率和净同化率最大.水分胁迫和光照在幼苗定居后仍是影响幼苗生物量分配的重要因素, 林窗边缘幼苗的根冠比最高 (0.33).
In this paper, the seedling’s early growth and establishment of Pometia tomentosa, a canopy tree species in Xishuangbanna tropical seasonal rainforest, were investigated under different illumination gradients (gap center, gap edge, and under canopy). The seedling height, basal stem diameter, total dry mass, leaf area per seedling, and relative growth rate at early stage peaked in gap center, with the values of 24.45 cm, 3.17 mm, 0.79 g, 122.45 cm2, and 14.78×10-3 g·d-1, respectively. The seedlings had a higher root-shoot ratio under canopy (0.87) than in gap center (0.20) due to the influence of both illumination and water. The brighter illumination in gap center facilitated the growth of established seedlings, with the peaks of seedling height (31.48 cm), basal stem diameter (3.80 mm), total dry mass (2.22 g), leaf area per seedling (174.52 cm2), relative growth rate (2.29×10-3 g·d-1), and net assimilation rate (2.54×10-5 g·cm-2·d-1) attained by the end of the investigation. The death of established seedlings might be closely related to water stress. Under canopy, the death rate caused by water stress was the highest (26.88%) but that caused by the predation of vertebrates was the lowest (2.93%), which in final, induced the highest survival rate (70.19%) of the seedlings. Illumination was the important factor affecting the morphological regulation of P. tomentosa eedlings. In gap center, the specific leaf area of the seedlings at their different growth stages was the smallest, but their relative growth rate and net assimilation rate were the greatest. The root-shoot ratio of established seedlings peaked at gap edge (0.33), suggesting that water stress and illumination were the important factors affecting the biomass allocation of established seedlings.