How do droughts affect growth of tropical trees? An evaluation of source and sink limitation

Drought effects on diel and seasonal tree growth responses

Tropical forests will become more water limited due to global warming and increased incidence of extreme droughts, threatening their roles in biodiversity conservation and climate change mitigation. At present, predicting tropical forest responses to droughts is hampered by a poor mechanistic understanding of tree growth responses to water limitation. Two mechanisms of drought-induced growth responses are currently debated: (i) low availability of sugars due to stomatal closure, reducing water loss but impairing photosynthesis (source limitation) and (ii) lack of cell multiplication and expansion due to low cell turgor pressure (sink limitation).

We will study tree species from two widespread and abundant tree genera that form annual tree rings. We will conduct intensive field studies at two sites to assess the effect of water availability on diel and seasonal patterns of plant hydration and stem growth (with dendrometers), sap flow (sap flow sensors) and leaf phenology (automized cameras). We will parameterize and apply a mechanistic model that simulates tree-level photosynthesis and turgor-limited growth at hourly resolution. This model allows evaluating the roles of source and sink limitation in driving diel and seasonal growth dynamics.

This study will greatly improve our understanding of the roles of source and sink limitation in shaping tropical tree responses to droughts. Such insights are crucial to predicting growth responses of tropical forest trees to shifting water variability in a changing climate.

The project is lead by Frank Sterck and Pieter A. Zuidema, supported by Jorad de Vries, Peter Groenendijk and Richard L. Peters.

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