Transpiration Source Water and Embolism Resistance Across a Topographic Gradient in the Eastern Amazon Rainforest

Transpiration contributes up to 70% of regional rainfall during the dry season in the Amazon through precipitation recycling. But the source, spatial distribution of transpiration and the key plant hydraulic drivers of transpiration source water remains unclear. Here, we quantify transpiration sources across a topographic gradient in the eastern Amazon, at the Tapajós National Forest. We leverage embolism resistance data collected on the same sites during this same campaign. We asked: i) What is the source of transpiration? And ii) how do transpiration depth and origin vary across topographic gradients and species with different embolism resistance growing under the same climate? Our data show that on hills, dry-season transpiration sources are mostly shallow soil water mainly recharged by current dry-season rainfall. In contrast, transpiration source water in the valley includes both shallow and deep soil layers, with both dry and wet season contributions. The observed pattern in transpiration source water is largely explained by species embolism resistance, but with contrasting trade-offs between hill- and valley-species. The significant relationship between embolism resistance and depth of water uptake in both topographic positions influencing transpiration age could be used to parameterize vegetation water use in land surface models.