[Responses of seed germination and seedling growth of Cunninghamia lanceolata and Schima superba to different light intensities.]

Light is a key factor affecting seed germination and seedling growth. In this study, seed germination and seedling growth of Cunninghamia lanceolata and Schima superba were compared under controlled conditions with five light treatments (100%, 60%, 40%, 15% and 5% of full sunlight). The results showed that light intensity significantly impacted seed germination and seedling growth of both species. With decreasing light intensity, the germination rate and germination index of C. lanceolata increased, while those of S. superba showed a trend which increased first and then decreased, with the maximum at 40% light intensity. The seedling survival rate of both species was 0 under full sunlight, while significantly decreased with decreasing light intensity from 60% to 5%. Root length, basal stem diameter and height showed a consistent trend with the change of light availability in both species. Root length significantly decreased, basal stem diameter and height increased first and then decreased with decreasing light intensity, with the minimum at 5% light intensity. With decreasing light intensity, root biomass, stem biomass, leaf biomass and total biomass of C. lanceolata seedlings declined, while high biomass accumulation of S. superba seedlings were observed in 15%-60% light intensities, and lowest at 5% light intensity. Biomass accumulation in each organ of S. superba seedlings was greater than that of C. lanceolata seedlings under the same light intensity. High stem biomass and leaf biomass, low root biomass and root to shoot ratio were a phenotypic response to low light intensity in C. lanceolata and S. superba seedlings grown under poor light condition. The growth of C. lanceolata is better under relatively high light intensity than S. superba. Whereas S. superba is moderately shade-tolerant at the seedling stage, thus is more suitable for planting under closed canopy. 光是影响种子萌发和幼苗生长的关键因素.为理解不同树种种子萌发及幼苗生长对光梯度变化的响应机制,本文研究了不同光照强度(分别为自然光强的100%、60%、40%、15%和5%)对杉木和木荷种子萌发及幼苗生长的影响,探讨了两树种种子萌发和幼苗生长对光照响应的差异性.结果表明: 光照强度对两树种的种子萌发和幼苗生长均具有显著影响. 随着光照强度的减弱, 杉木种子萌发率增大,萌发指数增大,木荷种子萌发率和萌发指数则先增大后减小,在40%光照强度下达到最大值.两树种幼苗存活率在全光照(100%光照)下均为0,在5%～60%光照处理下则随着光照强度的减弱而显著降低.两树种幼苗根长、地径和株高对光梯度变化的响应趋势一致,随着光照强度的减弱,根长显著减小,地径和株高则先增大后减小,在5%光照强度下达到最小.随着光照强度的减弱,杉木幼苗根、茎、叶及总生物量降低,木荷幼苗生物量积累在15%～60%光照强度下较高, 5%光照强度下最小,且相同光照强度下,木荷幼苗各部分生物量均大于杉木.两树种幼苗应对低光环境时,表现出较大的茎和叶的生物量分配比,而根生物量比和根冠比降低.表明杉木苗期生长不耐阴,需要相对较强的光照,而木荷苗期具有较强的耐阴性,对弱光环境的适应性更强,能够在郁闭的林冠下定植和正常生长.