Are trees able to grow in periods of stem shrinkage?

Abstract

SummarySeparating continuously measured stem radius (SR) fluctuations into growth-induced irreversible stem expansion (GRO) and tree water deficit-induced reversible stem shrinkage (TWD) requires a conceptualization of potential growth processes that may occur during periods of shrinking and expanding SR below a precedent maximum. Here, we investigated two physiological concepts: the linear growth (LG) concept, assuming linear growth, versus the zero growth (ZG) concept, assuming no growth during periods of stem shrinkage.We evaluated the physiological mechanisms underlying these two concepts and assessed their respective plausibilities using SR data obtained from 15 deciduous and evergreen trees.The application of the LG concept produced steady growth rates, whereas growth rates varied strongly under the ZG concept, more in accordance with mechanistic expectations. Further, growth increased for a maximum of 120 min after periods of stem shrinkage, indicating limited growth activity during those periods. However, this extra growth was found to be a small fraction of total growth only. Furthermore, TWD under the ZG concept was better explained by a hydraulic plant model than TWD under the LG concept.We conclude that periods of stem shrinkage allow for very little growth in the four tree species investigated. However, further studies should focus on obtaining independent growth data to ultimately validate these findings.

No role for xylem embolism or carbohydrate shortage in temperate trees during the severe 2015 drought

“…SDV were also used to calculate the daily radial increment for all 24 trees. We considered growth to only occur during periods of effective diameter increases, and assumed no growth during periods of stem shrinkage (Zweifel, Haeni, Buchmann, & Eugster, ). Hence, during times of radial shrinkage, stem diameter was set to the last maximum measured before shrinkage for the calculation of daily increment growth.…”

Ecophysiological modeling of photosynthesis and carbon allocation to the tree stem in the boreal forest

“…However, empirical studies have shown that the correlation between photosynthetic production and the diameter growth of trees is far from perfect Rocha et al, 2006;Berninger et al, 2004). This imperfect correlation is due to the fact that plant hydraulics (e.g., turgor pressure) and thermal limitations during very short periods of time can be more important than carbon (C) availability for secondary tree growth (Kirdyanov et al, 2003;Rossi et al, 2016;Zweifel et al, 2016;Fatichi et al, 2014; secondary growth is the increase in the girth of the plant roots and stems). These factors influence the proportion of net primary productivity allocated to stem growth each year, dampening the correlation between gross primary production (GPP) and growth.…”

Growing Season Stem Water Status Assessment of Qinghai Spruce through the Sap Flow and Stem Radial Variations in the Qilian Mountains of China

“…Dendrometer data of stem radial changes include water content variability and growth; therefore, stem radial changes of each tree were detrended for growth based on the zero-growth concept as described in Zweifel [23] (Figure 1a,b), and used to indicate drought stress in trees [21,43]. Tree water deficit (∆W) was calculated as the difference between the past highest stem radial record (SRmax) and current stem radial reading (SRt) when SRt < SRmax, with ∆W = 0 when SRt > SRmax [24], that is, the difference between growth trend and stem radial fluctuations ( Figure 1a,b and Figure 2d). A ∆W of zero indicated an optimal water content of the cambial zone, while increasingly positive values meant increasing water stress.…”

“…In early May, stem radial changes were due to spring rehydration following winter desiccation and subsequent precipitation [63][64][65]. Stem radial growth ended by late August and fluctuations in stem radial measurements were caused by tree water status [24]. Based on this, we focused on the periods from middle May to early August.…”

“…During these periods, precipitation increased, driving cell division and irreversible expansion of the already existing cells [9,16,38], supplying tree water prompting expansion of stem radial growth, and decreasing the rate of sap flow due to reduced transpiration. A relatively long time period with large ∆W occurred before late May and early July ( Figure 2); at that time, the newly-divided cells were likely not elongating due to the low cambium turgor pressure, and commenced elongation when water became available in late May and early July [24]. In the middle of July, precipitation decreased and transpiration increased, resulting in tree storage-water loss and stem radial contraction.…”