Tropical forests are experiencing increases in vapour pressure deficit (D), with possible negative impacts on tree growth. However, the mechanisms by which climatic variability drives tree growth are poorly understood. The role of turgor limitation in driving the growth of tropical trees also remained largely unexplored. 

In a study published in Plant, Cell & Environment, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and their collaborators explored how environmental conditions induced turgor-limitation in stem growth and, in turn, could explain diel and seasonal patterns in stem diameter growth in the widespread tropical tree species Toona ciliata (red cedar). 

The researchers conducted continuous monitoring for one year in a tropical rainforest near XTBG, Yunnan province in southwest China. They applied a turgor-driven mechanistic model to quantify the environmental conditions causing turgor to limit intra-annual stem diameter growth rates in Toona ciliata. 

To simulate tugor-driven growth during the growing season, the researchers collected hourly sap flow and dendrometer measurements. They found that the simulated seasonal patterns of radial growth matched well with growth observations. Growth mainly occurred at night and its pre-dawn build-up appeared to be limited under higher vapor pressure deficit.  

They further found that the night-time turgor pressure required for growth was   

 negatively related to previous midday vapor pressure deficit across seasons. “It is possibly due to relatively high canopy conductance at high vapor pressure deficit, relative to stem rehydration,”said FAN Zexin of XTBG. 

The study showed that the mechanistic modelling of turgor dynamics in the cambium was an effective tool to simulate and understand diel and seasonal growth dynamics of a tropical tree species. Inred cedar, turgor limitation was highly sensitive to changes in atmospheric drought, probably driven by poor stomatal control.  

"Our findings provide the first evidence that tropical trees grow at night and that turgor pressure limits tree growth," said FAN Zexin of XTBG. 

Contact 

FAN Zexin Ph.D Principal Investigator      

Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China        

E-mail: fanzexin@xtbg.org.cn   

First published: 10 July 2023