ABSTRACT Lack of information on water use of key agroforestry species is an obstacle to understanding their influence on crop productivity. Cordia africana and Albizia coriaria are the dominant tree species of smallholder farming systems in the Mt Elgon region of Uganda and have multiple uses in agroforestry systems. This study deployed six sap flow meters on stems of three selected trees each of C. africana and A. coriaria on-farm. The objective of the study was to assess the daily water use patterns of these agroforestry tree species at different times of the year. We measured the daily sap flow of these two species using the heat ratio method over a period of 18 months. There was a significant main effect of the interaction between tree species and season on daily water use. The two species show contrasting patterns of seasonal water use across leaf shedding stages characterised by episodes of reverse flow in A. coriaria at specific periods of the year. We propose that reverse flows in A. coriaria were triggered by leaf shading while the zero flows in C. africana, which occurred during rainfall events, could have resulted from a lag phase, an indication that the two species may have different water-use strategies. Although C. africana uses 12–15 l day−1 and A. coriaria uses 20–32 l day−1 based on the study trees, C. africana generally uses 12% more water than A. coriaria on a standardised daily basis. Albizia coriaria exhibited radial variation of sap velocities between the inner and outer thermocouples at different periods of measurement, a phenomenon worth investigating further. The leaf shedding patterns of the two trees provide an opportunity for maximising the temporal complementarities of agroforestry systems where these trees exist. This knowledge of C. africana and A. coriaria tree water use provides critical insight for developing successful long-term tree monitoring and management programs in agroforestry systems.

中文翻译：

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乌干达埃尔贡山地区两种重要农林业树种的用水模式对比

摘要 缺乏有关主要农林业物种用水的信息是了解其对作物生产力影响的障碍。Cordia Africana 和 Albizia coriaria 是乌干达埃尔贡山地区小农农业系统的主要树种，在农林业系统中具有多种用途。该研究在农场上的三棵选定的 C.africana 和 A. coriaria 树的茎上部署了六个树液流量计。该研究的目的是评估这些农林树种在一年中不同时间的日常用水模式。我们在 18 个月的时间里使用热比法测量了这两个物种的每日树液流量。树种和季节的交互作用对日常用水有显着的主效应。这两个物种在叶子脱落阶段表现出不同的季节性用水模式，其特征是一年中特定时期 A. coriaria 的逆流事件。我们提出 A. coriaria 的逆流是由叶子遮蔽引发的，而在降雨事件期间发生的 C. Africana 中的零流量可能是由于滞后阶段造成的，这表明这两个物种可能具有不同的用水策略. 尽管根据研究树的数据，C.africana 使用 12-15 l day-1 和 A. coriaria 使用 20-32 l day-1，但在标准化的基础上，C. Africana 通常比 A. coriaria 使用多 12% 的水。合欢在不同的测量周期内表现出内部和外部热电偶之间汁液速度的径向变化，这一现象值得进一步研究。两棵树的落叶模式为最大化存在这些树木的农林业系统的时间互补性提供了机会。C.africana 和 A. coriaria 树木用水的这些知识为在农林业系统中制定成功的长期树木监测和管理计划提供了重要的见解。