Wayne P M, Bazzaz F A
Department of Organismic and Evolutionary Biology, Harvard University, 02138, Cambridge, MA, USA.
Oecologia. 1993 May;94(2):235-243. doi: 10.1007/BF00341322.
We investigated whether the timing of high light availability as sun patches within forest gaps, independent of total or peak photosynthetic photon flux (PPF), influences the physiology and growth of four coexisting birch species (Betula alleghaniensis, B. lenta, B. papyrifera, and B. populifolia). Birch seedlings were grown for two years along either the east or west sides of experimental gap structures and at two moisture levels. Seedlings positioned in the west received sun patches earlier in the day than those in the east, and environmental conditions for carbon gain were generally more favorable during the earlier sunpatches in the west; air and leaf temperatures were lower, and relative humidity higher, relative to conditions during sun patches in the cats, simulating patterns observed in natural forest gaps. Seedlings positioned along the west edges of gaps fixed more carbon earlier in the day than those in the east, and in many cases, peak net photosynthetic rates were greater for west positioned seedlings. In year two, leaf-level integrated daily carbon gain was greater for west- than eastpositioned plants, and for the most pioneer species, B. populifolia, differences between west and east seedlings were greatest at lower soil moisture levels. Despite some small effects on leaf gas exchange, the timing of high light availability, and its temporal congruence with other factors critical to carbon gain, had no significant effects on first or second year seedling biomass. The responses of birch seedlings to controlled variations in the timing of high light availability were generally much smaller than birch seedling responses to variations in other components of daily light regimes such as total integrated and peak PPF.
我们研究了森林林窗内高光可利用时间（独立于总光合光子通量或峰值光合光子通量）是否会影响四种共存桦树物种（黄桦、黑桦、纸皮桦和美洲山杨桦）的生理和生长。桦树苗沿着实验林窗结构的东侧或西侧生长两年，并设置了两种水分水平。西侧的树苗比东侧的树苗更早接受阳光照射，并且在西侧较早的阳光照射期间，碳获取的环境条件通常更有利；相对于东侧阳光照射期间的条件，空气和叶片温度更低，相对湿度更高，模拟了天然林窗中观察到的模式。位于林窗西侧边缘的树苗比东侧的树苗在一天中更早固定更多碳，并且在许多情况下，西侧树苗的净光合速率峰值更高。在第二年，西侧植株的叶片水平日碳积累量大于东侧植株，对于最先锋的物种美洲山杨桦来说，西侧和东侧树苗之间的差异在较低土壤湿度水平下最为明显。尽管对叶片气体交换有一些小影响，但高光可利用时间及其与碳获取关键的其他因素的时间一致性，对第一年或第二年树苗生物量没有显著影响。桦树苗对高光可利用时间控制变化的响应通常远小于桦树苗对每日光照模式其他组成部分变化的响应，如总积分光合光子通量和峰值光合光子通量。
