Introduction Water table depth (WTD) is an overlooked component of local hydrological conditions that impacts soil water availability to plants in tropical forests. The extremes of a WTD gradient may impose soil water deficit or excess to plants, and little is known about how plant traits interact with the groundwater and how this impacts plant strategies and distribution.
Hypothesis We hypothesize that WTD acts as a filter of plant traits, determining ecological strategies, species distribution patterns and intraspecific variation across tropical forest landscapes.
Methods We summarized the knowledge accumulated over the past 10 years of our sampling efforts of morphological (leaf, wood) and physiological traits in 102 tree and 115 liana species, at local scale and across the Amazon basin. These species occur along the WTD gradient, either along the whole gradient or on its extremes, growing in non-flooded (terra-firme) forests.
Results We found that tree species occurring strictly in the extremes of the WTD gradient differ in their hydraulic architecture traits and resistance to embolism. Tree species occurring in shallow WTD forests have higher specific leaf area (SLA), and preliminary results suggest higher photosynthetic capacity. These species have lower wood density, wider xylem vessels and lower embolism resistance compared to deep water table forests. Low resistance to embolism in shallow WTD holds when considering intraspecific variation. Across the Amazon, the combination of shallow WTD and high soil fertility results in a risky hydraulic strategy with a high vulnerability to embolism in sites with high productivity. Some lianas’ trait changes along the WTD gradient differ from trees, e.g. higher SLA in shallow WTD, but others go in the similar direction (larger stomatal size and lower WD).
Conclusions/Implications Our results indicate WTD is an important filter of plant traits explaining ecological strategies, species distribution and intraspecific variation across Amazon forest landscapes. Shallow WTD tends to select traits that maximize water transportation and resource acquisition and minimize drought resistance in trees. Lianas seem to have different strategies to deal with WTD conditions and data on resistance to embolism may help to unravel mechanisms behind these differences. Understanding species distribution patterns through their trait interactions with soil water availability is essential to predict tolerance/resistance capacity of tropical species against climate change.
Amazon, hydraulic traits, plant strategies, infraspecific variability, species distribution.