光强对马尾松幼苗出土和早期生长的影响

Effects of light intensities on seedling emergency and early growth of Pinus massoniana

先锋树种马尾松(Pinus massoniana)在南方红壤丘陵区退化生态系统恢复和水土流失治理中发挥重要作用。但绝大多数马尾松人工林质量不高,存在大量的"稀疏小老头林",林下幼苗更新困难。本研究设置5个光强处理(透光率分别为自然光的5%、15%、40%、60%、100%),探讨马尾松幼苗出土、存活、生长、形态可塑性对不同光强的响应策略,揭示光是否是限制马尾松幼苗出土和生长的限制因子。结果表明,马尾松出苗率、出苗指数、活力指数在不同光强处理间差异显著(P<0.05),最大值均出现在40%光强处理。随光强增大,苗高逐渐降低,地径逐渐增粗,根长逐渐增长。幼苗总生物量,根、茎、叶生物量,粗壮度均在全光照下达到最大值。随光强增大,根冠比、根生物量比呈递增趋势,茎生物量比、叶生物量比呈降低趋势。研究证明,光照过强和过弱均不利于马尾松幼苗出土,弱光环境不利于幼苗生长,验证了林下弱光环境可能是马尾松人工林林下更新能力差的一个主要因素。

Pinus massoniana,a pioneer species,plays an important role in restoration of degraded ecosystem and controlling soil erosion in south China. Most P. massoniana plantations are sparse and dwarfish,with low quality and poor natural regeneration. To test whether light is a limiting factor for seedling emergence and growth of P. massoniana,the effects of five light intensities( 5%,15%,40%,60%,100% of full sun light) on seedling emergence,survival,growth,and morphological plasticity were investigated. The results showed that seedling emergency,germination index,and vitality index were significantly affected by light intensity( P<0.05).Seedling emergency,germination index,and vitality index reached the maximum at 40% light intensity. With increasing light intensity,stem length decreased,while root collar diameter and root length increased. The highest total biomass,root biomass,stem biomass,leaf biomass,and robustness of seedlings were observed under 100% light intensity. With increasing light intensity,the ratio of root to shoot and root biomass allocation increased,while the stem and leaf biomass allocation declined. The results suggested that seedling emergence was inhibited under high and low light intensity while low light intensity inhibited seedling growth. Our results provided experimental evidence that light is a key ecological factor affecting seedling emergence and growth of P.massoniana.