Why trees grow at night

Abstract

 The timing of diel stem growth of mature forest trees is still largely unknown, as empirical data with high temporal resolution have not been available so far. Consequently, the effects of day-night conditions on tree growth remained uncertain.  Here we present the first comprehensive field study of hourly-resolved radial stem growth of seven temperate tree species, based on 57 million underlying data points over a period of up to 8 years.  We show that trees grow mainly at night, with a peak after midnight, when the vapour pressure deficit (VPD) is among the lowest. A high VPD strictly limits radial stem growth and allows little growth during daylight hours, except in the early morning. Surprisingly, trees also grow in moderately dry soil when the VPD is low. Speciesspecific differences in diel growth dynamics show that species able to grow earlier during the night are associated with the highest number of hours with growth per year and the largest annual growth increment.  We conclude that species with the ability to overcome daily water deficits faster have greater growth potential. Furthermore, we conclude that growth is more sensitive than carbon uptake to dry air, as growth stops before stomata are known to close.

Limitation by vapour pressure deficit shapes different intra‐annual growth patterns of diffuse‐ and ring‐porous temperate broadleaves

“…The observed responses of growth rates to climatic conditions are in line with existing experimental and empirical knowledge (Ziaco & Biondi, 2018;Güney et al, 2020;Zweifel et al, 2021).…”

“…Consequently, the growth rate peaked at timestamps with optimal or slightly suboptimal VPD, mainly at night after replenishment of the stem water content (Fig. S4; Zweifel et al, 2021). We observed a stronger coupling of radial growth to relative air humidity and VPD compared to soil moisture availability (Fig.…”

“…For instance, variations in intra‐annual cambial activity, specifically the production and maturation of new xylem and phloem cells, exert control over the carbon sequestration capacity of the entire ecosystems dominated by woody species (Pan et al ., 2011; Cuny et al ., 2015). Although shifting climatic limitation of annual growth rates has recently been described using tree‐ring widths across space (Babst et al ., 2019; Cook et al ., 2020) and over time (Wilmking et al ., 2020), the understanding of high‐frequency variability in sub‐daily growth rates is limited (but see Zweifel et al ., 2021).…”

Wood Formation Modeling – A Research Review and Future Perspectives

“…Nevertheless, dendrometers are essential tools to determine the critical sub-daily time periods during which growth variations actually occur and which environmental factors matter. For example, Zweifel et al ( 2021 ) determine that wood radial growth is most likely to occur during the night or at dawn, when vpd is low. Their findings make clear that daily aggregation of environmental variables to drive wood formation models must be done with care.…”

The dual C and O isotope – gas exchange model: A concept review for understanding plant responses to the environment and its application in tree rings

“…Moreover, the apparent 13 C fractionation increases considerably in the low light range (near light compensation point, , Busch et al, 2020Liu et al, 2021; see also Breakout Box 1). Yet the large part of carbon acquisition occurs mostly under high light and biomass production under non-limiting growth conditions (Körner, 2015;Zweifel et al;2021). Therefore, except for understorey plants the low light impact on 13 C fractionation is hardly visible in tree rings.…”