Leakey A D B, Press M C, Scholes J D
Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK.
Oecologia. 2003 Apr;135(2):184-93. doi: 10.1007/s00442-003-1178-7. Epub 2003 Mar 4.
In the deeply shaded understorey of S.E. Asian rain forests the growth and survival of dipterocarp seedlings is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain in understorey plants. To test the sensitivity of photosynthesis and growth to variation in the pattern of dynamic irradiance, dipterocarp tree seedlings (Shorea leprosula and Hopea nervosa) were grown for 370 days under shaded forest light treatments of equal total daily photosynthetic photon flux density (approximately 3.3 mol m(-2) day(-1)), but characterised by either long flecks (LF) or short flecks (SF). Seedling growth was more than 4-fold greater under LF, compared with SF, in both species. Variation in the relative growth rates (RGR) and light saturated rates of photosynthesis (A(max)) were strongly positively correlated with the mean duration of sunflecks. Variation in RGR was strongly correlated with greater unit leaf rate growth, indicating that photosynthetic carbon gain per unit leaf area was greater under LF. The accumulation of starch in leaves over the diurnal period was 117% greater in both species under LF, compared with SF. Greater carbon gain in seedlings under LF is likely to have resulted from the combination of (1) greater A(max) (S. leprosula 35%, H. nervosa 40%), (2) more efficient dynamic photosynthesis, and (3) greater incident photosynthetic quantum yield, compared with seedlings receiving the SF irradiance treatment. The pattern of dynamic irradiance received by seedlings may significantly impact their growth and survival to a previously unrecognised extent, with important consequences for regeneration processes and hence forest structure and composition.
在东南亚雨林阴暗的林下叶层中，龙脑香科幼苗的生长和存活受其维持正碳平衡能力的限制。光斑期间的光合作用是林下叶层植物碳获取的重要组成部分。为了测试光合作用和生长对动态光照模式变化的敏感性，将龙脑香科树苗（轻坡垒和多脉坡垒）在总日光合光子通量密度相等（约3.3摩尔·米⁻²·天⁻¹）但具有长光斑（LF）或短光斑（SF）特征的林下遮荫光照处理下培养370天。在这两个物种中，与短光斑处理相比，长光斑处理下的幼苗生长速度快4倍多。相对生长率（RGR）和光合作用光饱和率（A(max)）的变化与光斑的平均持续时间呈强正相关。RGR的变化与单位叶面积生长率的增加密切相关，这表明在长光斑处理下单位叶面积的光合碳获取量更大。与短光斑处理相比，两个物种在长光斑处理下叶片中淀粉在昼夜期间的积累量都高出117%。与接受短光斑光照处理的幼苗相比，长光斑处理下的幼苗碳获取量更大，这可能是由于以下因素共同作用的结果：（1）更高的A(max)（轻坡垒增加35%，多脉坡垒增加40%），（2）更高效的动态光合作用，以及（3）更高的入射光合量子产率。幼苗接收到的动态光照模式可能会在以前未被认识到的程度上显著影响它们的生长和存活，这对更新过程以及森林结构和组成具有重要影响。
