Despite a perennial evergreen canopy, tropical evergreen forests continuously shed old leaves and grow new leaves at different time across different tropical regions. To examine how water and light availability control the leaf phenology of tropical evergreen forests, we used monthly litterfall mass data from 30 sites in Pan-Asian tropics and solar-induced chlorophyll fluorescence (SIF) as leaf shedding and a proxy for canopy photosynthetic activity and productivity, respectively. Two types of climate were identified depending on the positive and negative corrections between seasonal precipitation (Pre) and shortwave radiation (SW), named as synchronous and asynchronous climates, respectively. In regions where Pre and SW are positively correlated, litterfall and SIF are parabolically greater in the wet season (named as synchronous-unimodal regime), or show bimodal litterfall peaks in the dry and wet seasons (named as synchronous-bimodal regime). In regions where Pre and SW are negatively correlated, litterfall is parabolically greater in the dry-sunny season (named as asynchronous-unimodal regime), or show multiple peaks at the wet season, coincides with relatively high SIF (named as asynchronous-multimodal regime). The adaptive strategies of leaf phenology could be generated as a response to water and light availability balancing the benefits and costs from the plant perspective. On the one hand, plant prioritizes light acquisition by exchanging old, senescent leaves for new, efficient leaves to optimize photosynthesis with sufficient water availability. On the other hand, plant sheds old leaves to minimize maintenance costs and to avoid hydraulic failure under water stress during dry season. Our findings are crucial for assessing both the impacts of future climate change on tropical evergreen forests and the feedbacks of tropical evergreen forests on the terrestrial carbon cycle. This study also suggests that the ongoing changes in tropical rainfall seasonality relative to radiation seasonality may significantly alter canopy leaf phenology under future climate conditions.

尽管有多年生常绿树冠，但热带常绿森林在不同热带地区的不同时间不断脱落旧叶并长出新叶。为了研究水和光的可用性如何控制热带常绿森林的叶子物候，我们使用来自泛亚热带地区 30 个地点的每月凋落物质量数据和太阳诱导的叶绿素荧光 (SIF) 作为叶子脱落和冠层光合活动的代理和生产力，分别。根据季节性降水（Pre）和短波辐射（SW）之间的正负校正，确定了两种类型的气候，命名为同步和异步气候，分别。在 Pre 和 SW 正相关的地区，凋落物和 SIF 在雨季（称为同步单峰体制）呈抛物线状较大，或在旱季和湿季表现出双峰凋落物峰值（称为同步双峰体制）。在 Pre 和 SW 呈负相关的地区，凋落物在干晴季节（称为异步单峰制度）呈抛物线状较大，或在雨季出现多个高峰，与相对较高的 SIF 重合（称为异步多峰制度）政权）。叶子物候的适应性策略可以作为对水和光可用性的响应，从植物的角度平衡收益和成本。一方面，植物通过将旧的、衰老的叶子换成新的、有效的叶子来优先获取光，以优化光合作用并提供充足的水分。另一方面，植物会脱落老叶，以最大限度地降低维护成本，并避免旱季在水分胁迫下出现水力故障。我们的发现对于评估未来气候变化对热带常绿森林的影响以及热带常绿森林对陆地碳循环的反馈至关重要。