两种光强下木质藤本与树木幼苗的竞争关系

ABOVE-AND BELOW-GROUND COMPETITION BETWEEN SEEDLINGS OF LIANAS AND TREES UNDER TWO LIGHT IRRADIANCES

为了探讨木质藤本和树木幼苗的相互作用关系,对两种光强(4%和35%的光强)、4种竞争处理下(全竞争、地上竞争、地下竞争和无竞争),一种需光木质藤本(刺果藤(Byttneria grandifolia))和3个树种(耐荫种:五桠果木姜子(Litsea dilleniifolia)和绒毛番龙眼(Pometia tomentosa);需光种:羊蹄甲(Bauhinia variegata))幼苗的地上部分和地下部分的竞争关系进行了研究。结果表明:木质藤本的竞争显著影响着3种树木幼苗的光合能力、形态特征和生长,但生长环境的不同光强影响地上部分竞争和地下部分竞争的相对强度。在低光下,地上部分竞争比地下部分竞争对3种树木幼苗的相对生长速率(Relative growth rate,RGR)和光合能力造成更大的影响;而高光下,地下竞争对树木幼苗的生长有更强的抑制作用。不同的竞争处理和光强对树木幼苗的生物量积累造成显著的影响。光强对3种树种的比叶面积(Specific leaf area,SLA)和叶面积比(Leaf area ratio,LAR)有显著的抑制作用,但竞争只对需光的羊蹄甲的SLA和LAR有显著影响。不同的光照和竞争处理之间,同种植物表现出不同的表型特征。由于竞争的影响,苗木在形态上较为矮小、叶片数目较少、叶面积减小,但是长细比改变较少。

Aims Lianas are an important component of forests, especially in the tropics. They strongly influence regeneration of trees and maintenance of species diversity in tropical forests, but little is known about competition between trees and lianas. In this study, we investigate the effects of lianas on the morphology, photosynthesis and growth of trees and examine the relative importance of above- and below-ground competition between tree and liana seedlings under different light irradiances. Methods We used four different competition treatments （AC： all competition; RC： root competition; SC： shoot competition; NC： no competition） between seedlings of one shade-intolerant liana （Byttneria grandifolia） and three tree species （shade-tolerant Litsea dilleniifolia and Pometia tomentosa and shade-intolerant Bauhinia variegata）. Seedlings were grown in a shade house under two levels of light availability （4% and 35% light intensity）. Important findings Competition from lianas substantially reduced the growth of tree seedlings, but the relative importance of above- and below-ground competition differed between the two light levels. At low light intensity, the relative growth rate （RGR） and photosynthetic capacity （maximum net photosynthetic rate, Pmax） in seedlings of all three tree species were reduced more strongly by SC than RC. However, SC rather than RC greatly reduced RGR and Pmax of tree seedlings grown under high light intensity. Different competition combinations （above- and below-ground competition） of liana seedlings resulted in distinctive morphological traits in seedlings of the three tree species. The specific leaf area and leaf area ratio of the three tree species were significantly influenced by light intensity. Meanwhile, only those of the light demanding species, B. variegata, were affected by the liana competition. Tree seedlings had small diameter, low height, leaf numbers and leaf area with slight changes in slenderness （stem length/diameter） under the competitive environments of liana seedlings. In conclusion, our findings suggest that competition from liana seedlings can greatly suppress growth in tree seedlings of both shade-intolerant and shade-tolerant species and the effects of lianas on tree seedlings can differ with type of competition. Above- and below-ground competition can interactively limit the growth of tree seedlings.