Myneni Ranga B, Yang Wenze, Nemani Ramakrishna R, Huete Alfredo R, Dickinson Robert E, Knyazikhin Yuri, Didan Kamel, Fu Rong, Negrón Juárez Robinson I, Saatchi Sasan S, Hashimoto Hirofumi, Ichii Kazuhito, Shabanov Nikolay V, Tan Bin, Ratana Piyachat, Privette Jeffrey L, Morisette Jeffrey T, Vermote Eric F, Roy David P, Wolfe Robert E, Friedl Mark A, Running Steven W, Votava Petr, El-Saleous Nazmi, Devadiga Sadashiva, Su Yin, Salomonson Vincent V
Department of Geography and Environment, Boston University, 675 Commonwealth Avenue, Boston, MA 02215, USA.
Proc Natl Acad Sci U S A. 2007 Mar 20;104(12):4820-3. doi: 10.1073/pnas.0611338104. Epub 2007 Mar 13.
Despite early speculation to the contrary, all tropical forests studied to date display seasonal variations in the presence of new leaves, flowers, and fruits. Past studies were focused on the timing of phenological events and their cues but not on the accompanying changes in leaf area that regulate vegetation-atmosphere exchanges of energy, momentum, and mass. Here we report, from analysis of 5 years of recent satellite data, seasonal swings in green leaf area of approximately 25% in a majority of the Amazon rainforests. This seasonal cycle is timed to the seasonality of solar radiation in a manner that is suggestive of anticipatory and opportunistic patterns of net leaf flushing during the early to mid part of the light-rich dry season and net leaf abscission during the cloudy wet season. These seasonal swings in leaf area may be critical to initiation of the transition from dry to wet season, seasonal carbon balance between photosynthetic gains and respiratory losses, and litterfall nutrient cycling in moist tropical forests.
尽管早期有相反的推测，但迄今为止所研究的所有热带森林在新叶、花朵和果实的出现方面都呈现出季节性变化。过去的研究集中在物候事件的时间及其线索上，而不是调节植被与大气之间能量、动量和质量交换的叶面积的伴随变化。在此，我们通过对最近5年卫星数据的分析报告称，大多数亚马逊雨林的绿叶面积季节性波动约为25%。这个季节性周期与太阳辐射的季节性同步，这表明在光照充足的旱季早期到中期有预期的和机会主义的净叶片萌发模式，以及在多云的雨季有净叶片脱落模式。叶面积的这些季节性波动可能对从旱季到雨季的过渡开始、光合增益与呼吸损失之间的季节性碳平衡以及潮湿热带森林中的凋落物养分循环至关重要。
