High vapour pressure deficit enhances turgor limitation of stem growth in an Asian tropical rainforest tree

Abstract

Tropical forests are experiencing increases in vapour pressure deficit (D), with possible negative impacts on tree growth. Tree‐growth reduction due to rising D is commonly attributed to carbon limitation, thus overlooking the potentially important mechanism of D‐induced impairment of wood formation due to an increase in turgor limitation. Here we calibrate a mechanistic tree‐growth model to simulate turgor limitation of radial stem growth in mature Toona cilitata trees in an Asian tropical forest. Hourly sap flow and dendrometer measurements were collected to simulate turgor‐driven growth during the growing season. Simulated seasonal patterns of radial stem growth matched well with growth observations. Growth mainly occurred at night and its pre‐dawn build‐up appeared to be limited under higher D. Across seasons, the night‐time turgor pressure required for growth was negatively related to previous midday D, possibly due to a relatively high canopy conductance at high D, relative to stem rehydration. These findings provide the first evidence that tropical trees grow at night and that turgor pressure limits tree growth. We suggest including turgor limitation of tree stem growth in models also for tropical forest carbon dynamics, in particular, if these models simulate effects of warming and increased frequency of droughts.

Diel and seasonal stem growth responses to climatic variation are consistent across species in a subtropical tree community

“…Such VPD effects on subtropical trees are consistent with results from temperate ecosystems where VPD combined with soil moisture determined the variability in diel stem growth (Zweifel et al, 2007(Zweifel et al, , 2021. Specifically, temperate trees mainly grew under conditions with VPD < 0.4 kPa (Zweifel et al, 2021), since such conditions allow cambial tissues to rehydrate at night and increase turgor pressure to reach the threshold required for stem growth (occurrence; Steppe et al, 2006;Zweifel et al, 2007;Peters et al, 2023). The much lower VPD (0.1 kPa) at night and early morning hours for our study trees are thus expected to favour stem growth in our study (Fig.…”

“…Furthermore, daily growth rates need to be interpreted with care, as they were aggregated from hourly values of stem diameter changes that are result from both structural growth as well as diel stem shrinking and swelling caused by negative pressure in xylem and refilling of vessels (Steppe et al, 2006(Steppe et al, , 2015Zweifel et al, 2016;Meng et al, 2021). Detailed tree growth modelling can help to unravel the contributions of these processes to stem dynamics and provide a clear understanding of stem growth (Peters et al, 2023).…”

Variation of floristic diversity, community composition, endemism, and conservation status of tree species in tropical rainforests of Sri Lanka across a wide altitudinal gradient

“…Monthly mean SVP was computed as the mean of SVPs computed based on T max and T mean . Vapour pressure deficit is a measure of atmospheric dryness and exerts direct influences on stomatal conductance 98 – 100 , transpiration 101 , photosynthesis 102 and growth 103 of forest communities.…”

Beyond source and sink control – toward an integrated approach to understand the carbon balance in plants

“…As an example, a low fraction of leaf mass relative to the whole plant biomass might cause a higher probability for C limitation (and thus source control) under drought than a higher proportion of leaves. On the contrary, a high leaf mass fraction and thus a high transpiration demand might more likely cause tree water potentials to drop, thus directly restricting sink activities such as stem growth (Steppe et al, 2015;Peters et al, 2021Peters et al, , 2023a.…”

“…If we, for example, assume that source control is a dominant factor, increasing CO 2 concentrations should clearly stimulate photosynthesis in C 3 plants and subsequently increase growth. If, by contrast, sink control is dominating, it will be rather the change in environmental factors such as the water vapor pressure deficit that strongly influence sink activity (Zweifel et al ., 2021; Tumajer et al ., 2022; Peters et al ., 2023a) and subsequently may determine the C sequestration potential of the vegetation.…”