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Seasonal changes in the physiological activity of regeneration under a natural light gradient in a Pinus pinea regular stand

机译：松树常规林分在自然光梯度下再生生理活动的季节性变化

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摘要

Seasonal courses of chlorophyll a fluorescence, gas exchange parameters and water status, joined to environmental variables, were measured in four age classes of stone pine (Pinus pinea L.) natural regeneration, selected within a natural light gradient in order to cover the whole range of incident light detected within a stone pine regular stand throughout 2007 and 2008. Selection of light conditions was based a priori on the distance of seedlings to the parent trees, expressed by crown radius distances. One-year old seedlings were worse acclimated to the extreme drought conditions recorded in summer (especially in 2008), showing lower predawn and midday Fv/Fm values, slightly lower photosynthetic rates at midday, lower Phi PSII values, lower water potentials (Psi(pd) and Psi(min)), and high mortality (90%). The oldest seedlings (class 4, 51-200 cm high), although they do not experience the lowest Psi(min). in July 2008, were not able to maintain a positive carbon gain at midday, even showing the lowest photosynthetic rates. However, they rapidly recovered once the climatic conditions were softened in early autumn. During late autumn low Fv/Fm values were found especially in one-year old seedlings, indicating that maximal photochemical efficiency of PSII is sensitive to the autumn temperatures below cero recorded during both years. Thus, stone pine regeneration acclimates its physiology to the seasonal course of temperature and water availability, and this acclimation depended on age class. However, seedling physiology is only slightly affected by differences in light environment, probably related to the low variability recorded in GSF values (0.55 +/- 0.01), due to the low density of the stand. We suggest that such low stand densities cannot assure one-year old seedlings' survival, but are sufficient for older seedlings.
机译：在四个自然年龄的石松（Pinus pinea L.）自然再生中测量了叶绿素a荧光，气体交换参数和水状态随季节变化的季节性变化，以覆盖整个范围整个2007年和2008年在石松常规林中检测到的入射光的数量。光条件的选择是先验地基于幼苗到亲本树的距离，用树冠半径距离表示。一岁的幼苗更难适应夏季（尤其是2008年）记录的极端干旱条件，显示出较低的黎明前和中午Fv / Fm值，中午的光合速率略低，Phi PSII值较低，水势较低（Psi（ （pd）和Psi（min）），死亡率高（90％）。最老的幼苗（4级，高度51-200 cm），尽管它们的Psi（min）最低。在2008年7月，即使显示出最低的光合速率，也无法在正午时保持正的碳增加。但是，一旦秋初的气候条件减弱，它们便迅速恢复。在深秋期间，特别是在一岁的幼苗中发现较低的Fv / Fm值，这表明PSII的最大光化学效率对这两年记录的低于秋季的秋季温度敏感。因此，石松的再生使其生理适应温度和水的季节性变化，而这种适应取决于年龄段。但是，由于光密度低，幼苗的生理仅受光照环境差异的轻微影响，可能与GSF值记录的低变异性（0.55 +/- 0.01）有关。我们建议，如此低的林分密度不能确保一岁的幼苗的存活，但足以用于较老的幼苗。

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