落叶阔叶树种蒙古栎(Quercus mongolica)对林缘不同光环境光能和水分的利用

Solar energy and water utilization of Quercus mongolica, a deciduous broadleaf tree, in different light regimes across the edge of a deciduous broad-leaved forest

由于砍伐、林火等形成的林缘是典型的生态过渡区,并以高生物多样性和快速变化的光环境为最显著特征。研究植物在林缘附近不同光环境下对光能和水分的利用特征有利于在个体层次揭示林木更新、森林群落动态的生理生态学基础,具有重要意义。蒙古栎是长白山地区落叶阔叶林及阔叶红松林中的常见阳性树种。通过对长白山白桦林林缘及附近蒙古栎的野外观测研究,结果表明:①林冠对林缘光照等的影响随距离林缘远近的不同而不同。林缘及附近区域的光环境存在巨大差异,温度和水分条件等也有显著变化。②蒙古栎光合的日进程为单峰型,净光合速率的高峰值达20μmolCO2·m-2·s-1,未见明显午休;林外蒙古栎的净光合速率及日光合总量均大于(或远大于)林缘和林内的净光合速率及日光合总量,表明蒙古栎在林外强光下生长最快;此外,对低光的高效利用显示蒙古栎可在林内低光环境正常生长。③蒙古栎在不同光环境下蒸腾速率的日进程为单峰型,林外最高可达近8mmolH2O·m-2·s-1。虽然蒙古栎在林外的蒸腾速率、日蒸腾量及水分利用率均较高,但与林内弱光环境相比,水分利用率增加的趋势略有降低,这是蒙古栎对林外强光环境的一种适应。④蒙古栎叶片的气孔导度随光照的增加而增大,这有利于植物在强光下增加净光合速率和蒸腾速率,有利于植物在强光下快速生长。另外,蒙古栎的叶片胞间CO2浓度从早至晚呈增加趋势;随日PAR总量的增加,蒙古栎的叶片胞间CO2浓度呈降低趋势。弱光环境下胞间CO2浓度的增加,有利于植物固定CO2、增加对光能和水分的利用效率。

The forest edge usually formed by felling trees and forest fire is a typical ecotone with high biodiversity and rapid changing light. It is of important significance to study on how the different functional groups to use the solar energy use and water so as to understand the physiological ecological basis of forest regeneration, forest community dynamics and evolution at individual level. Quercus mongolica is a common sun plant in deciduous broad-leaved forests and broad-leaved Pinus korinsis forests in Changbaishan Mountains. Based on the field experiment on Q. mongolica trees near the edge of the natural secondary white birch forest, the following results could be achieved： ① The effect of forest canopy on forest edge light varies according to the distance from the forest edge. The light in the forest edge and near the edge changes enormously. The total amount of daily PAR of the forest edge is about 50 % of that outside the forest, while the total amount of daily PAR within the forest is about 5 % of that outside the forest. Moreover, the air temperature, land temperature and humidity across the forest edge change significantly. ② Q. mongolica tree has a single peak curve in the daily process of photosynthesis, and net photosynthetic rate （Pn） reaches a peak （about 20μmol CO2·m^-2· s^-1） at 10：00 ～ 12 ：00. No significant midday photosynthetic depression is observed in sunny day in summer, and the reason should be further studied. Meanwhile, the net photosynthetic rate and total amount of daily photosynthesis of Q. mongolica tree are greater （or far greater） than those in forest edge and within the forest. This indicates that Q. mongolica tree grows the most rapidly under strong light outside the forest. In addition, this deciduous tree has so high utilization efficiency to low light within the forest that Q. mongolica trees can normally grow within the forest. ③The daily process of transpiration rate of Q. mongolica trees under different light environment is single peaked with a maximum of about 8 mmol H2O· m^-2·s^-1 outside the forest. Although Mongolia oak has fairly high transpiration rate, daily transpiration amount and water utilization efficiency, yet as compared with low light environment outside the forest, this increasing trend of water utilization has slightly reduced. So, this could be thought as a kind of acclimation to strong light environment outside the forest. ④ The stomatal conductance of Mongolia oak leaves increases along with the increase of light. It is beneficial to increase net photosynthesis rate and transpiration rate of plant under strong light conditions, and beneficial to rapid growth of plant under strong light conditions. In addition, the leaf intercellular CO2 concentration of Q. mongolica trees has a trend of increasing from morning till night. Along with the increase of the total amount of solar radiation under different light regimes, the leaf intercellular CO2 concentration of Mongolia oak has a trend of decrease. Under low light conditions, the increase of leaf intercellular CO2 concentration is beneficial for plants in CO2 fixation, increases solar energy utilization and improves water utilization efficiency.