Link between diurnal stem radius changes and tree water relations

Abstract

Internal water reserves are depleted and replenished daily, not only in succulent plants, but also in trees. The significance of these changes in tissue water storage for tree water relations was investigated by monitoring diurnal fluctuations in stem radius. In 6-year-old potted Norway spruce (Picea abies (L.) Karst.) trees, whole-tree transpiration rate (T), sap flow at the stem base and fluctuations in stem radius were measured at 10-min intervals over eight successive weeks. The dynamics of diurnal water storage in relation to the daily course of water movement was simulated and the contribution of stored water to T quantified. The finding that, in P. abies, the course of bark water content is linearly coupled to stem radius fluctuations provided the basis for linking stem radius changes to a functional flow and storage model for tree water relations. This model, which consists of physical functions only and is driven by a single input variable (T), accurately simulates the diurnal course of changes in stem radius and water storage of the tree crown and stem. It was concluded that fluctuations were mainly determined by the course of transpiration. The availability of soil water and the degree to which storage tissues were saturated were also factors affecting the diurnal course of stem radius changes. Internally stored water contributed to daily transpiration even in well-watered trees, indicating that stored water plays an important role not only during periods of drought, but whenever water transport occurs within the tree. Needle and bark water reserves were most heavily depleted during transpiration. Together they supplied approximately 10% of daily T on sunny days, and up to 65% on cloudy days. On a daily basis, the crown (mainly needles) contributed approximately eight times more water to T than the stem (mainly bark). The depletion of the two storage pools and the water movements observed in the trees always occurred in the same sequence. In the morning, T first caused a depletion of the water stored in the crown. It then caused depletion of bark storage tissues at ever increasing distances from the needles. Up to 75% of the transpired water could be withdrawn from storage tissues when the increase in T reached a maximum.

Model analysis of the effects of atmospheric drivers on storage water use in Scots pine

“…The maximum contribution of the storage water to daily transpiration varied between 28 and 45%. These values fall within the wide range of values that can be found in the literature: ranging from 1 up to 50% (Čermák et al, 2007) or even up to 65% (Zweifel et al, 2001). -s t o r a g e w a t e r u s e S t o r a g e w a t e r f l o w ( k g h -1 ) V P D ( k P a ) + s t o r a g e w a t e r r e c h a r g e …”

“…Nonetheless, storage water contributes substantially to daily transpiration, irrespective of the climatic conditions. These results confirm that stored water plays an important role not only during periods of drought, but whenever water transport occurs within the tree (Zweifel et al, 2001). These last mentioned authors found that even in well-watered soils the tree water reserves were depleted every morning.…”

“…Therefore, the xylem water potential is smoothed along the flow path, which may help avoid xylem cavitation. Trees can use stored water to allow continued photosynthesis when transpiration exceeds soil water uptake (Zweifel et al, 2001). Despite the importance of water storage in regulating the water budget of trees, limited information exists on the contribution of internal water storage to their total daily water consumption (Meinzer et al, 2001).…”

Diurnal dynamics of water transport, storage and hydraulic conductivity in pine trees under seasonal drought

“…A T vs. SF lag was discussed (Cruiziat et al 2002) but not frequently tested, presumably due to the differentiation between studies using gas (T) and liquid phase (SF) measurement techniques. Two notable exceptions are Zweifel et al (2001) and Fisher et al (2007), who showed time lags between T and SF of 0.5-3 hr. Comparing SF rates at the bottom and high crown of large tropical trees, Meinzer et al (2003) found up to a 2 hr lag time.…”

“…Comparing SF rates at the bottom and high crown of large tropical trees, Meinzer et al (2003) found up to a 2 hr lag time. The role of tree water storage was shown in many studies (Zweifel et al 2001, Meinzer et al 2003, McLaughlin et al 2003, Fisher et al 2007, Meinzer et al 2009), some showing a major storage contribu-tion, e.g., 10-75% of daily T in potted, young Norway spruce (Picea abies -Zweifel et al 2001), or a more minor contribution of 2-10% in adult yellow poplar (Lirodendron tulipifera -McLaughlin et al 2003) and down to zero stem storage in the woody monocot Bamboo suffering from cavitation (Yang et al 2012).…”