Leaf water maintains daytime transpiration in young Cryptomeria japonica trees.

Sawa Himeno,H Roaki Ishii,Koichiro Gyokusen,Wakana Azuma

doi:10.1093/treephys/tpx056

Sawa Himeno, H Roaki Ishii + Show 2 more

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https://doi.org/10.1093/treephys/tpx056

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Abstract

Compared with stem water storage, leaf water storage is understudied although it may be important for alleviating water stress by contributing quickly and directly to transpiration demand. To quantify the relative contribution of stem versus leaf water storage to daily water deficit, we measured diurnal changes in transpiration rate, sap-flow velocity and stem radius of 10-year-old Cryptomeria japonica D. Don trees. We assumed that the duration of time lags between transpiration rate and sap-flow velocity reflected stored water in the stem and leaf, and that stem volume change represented water content of elastic tissue. The relationship between fresh mass and water potential of the whole tree indicated that the study trees had capacity to store, on average, 91.4 ml of water per kg fresh mass at turgor loss. Leaves, sapwood and elastic tissue contributed around 51%, 29% and 20% of stored water, respectively. During morning, transpiration rates were higher than sap-flow velocity suggesting depletion of stored water. During the first 2 h after onset of transpiration, stored water contributed more than 100% of whole-tree transpiration. Depletion of leaf water (PLeaf) and sapwood water (PSap) coincided with the onset of transpiration and became maximum around 15:00 h. Depletion of elastic tissue water (PElastic) lagged behind that of PLeaf and PSap by 1-2 h, indicating that replenishment of stored water occurs late in the day when low leaf water potentials resulting from daytime transpiration drive water uptake. Maximum depletion of PLeaf was about 1-3 times and 5-10 times that of PSap and PElastic, respectively. The contribution of PLeaf to total daily transpiration was 5-8%, while those of PSap and PElastic were 3-4% and 0.7-1%, respectively. Our results suggest the importance of leaf water storage in maintaining daily transpiration in young C. japonica trees.

Highlights

Foliar water storage is an important mechanism for maintaining physiological function, especially in arid environments (Chaves et al 2002, Von Willert et al 1990)
Replenishment of stored water coincided with the decrease in whole-tree water loss, as a result stored water contribution became negative after 15:00 (Table 3, Figure 6a). These results indicated that replenishment of stored water occurs in late afternoon when low leaf water potentials resulting from day-time transpiration drive water uptake
We found that stored water contributed 100% of outflow for approximately 2 hour after transpiration began in the morning, indicating that stored water plays an important role in maintaining transpiration rates in early morning before sap-flow rates begin to increase

Summary

Introduction

Foliar water storage is an important mechanism for maintaining physiological function, especially in arid environments (Chaves et al 2002, Von Willert et al 1990). Treetop leaves experience water-stressed environments with high levels of solar radiation and evapo-transpirational demand. Water stored in sapwood, is important for compensating this deficit (Waring and Running 1978; Meinzer et al 2003, Phillips et al 2003) and maintaining daytime transpiration rates (Goldstein et al 1998). Estimates of the contribution of sapwood water storage to daily transpiration vary widely among species (e.g., Waring et al 1979; Lostau et al 1996; Goldstein et al 1998; Kobayashi & Tanaka 2001) and with tree size (Phillips et al 2003)

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