Articles
Saving some for later: seasonal variations in sap flow, withdrawal and elastic storage in large trees under throughfall exclusion
Article number
1419_18
Pages
143 – 152
Language
English
Abstract
Transpiration is influenced by vapor pressure deficit, solar radiation and soil moisture but these factors fluctuate at different time scales ranging from hours to days to weeks and months.
Furthermore, when using sap flow to infer transpiration, withdrawal from stem water stores complicates estimates of timing and amounts of transpiration, particularly in large trees.
Kauri (Agathis australis) is one of the largest and longest-lived conifers in the world with sapwood depths of up to 20 cm.
Published P50 values indicate stems and roots are highly vulnerable to xylem embolism and regular summer droughts are increasing in intensity and frequency with climate change.
We established a throughfall exclusion experiment in kauri forest in West Auckland, Aotearoa New Zealand to explore responses of water relations to drying soils in mature trees.
Our three year experiment indicated sap flow was responsive to soil moisture at seasonal time-steps.
Seasonal sap flow significantly increased as seasonal soil moisture increased but the slope of the curve was steeper for control compared to drought trees.
Stem water withdrawal was responsible for a higher proportion of daily water-use for drought trees (8-28%) compared to control trees (5-12%) but the volume of withdrawal (in L) increased as seasonal tree water-use (per unit sapwood area) increased.
Elastic storage (as a percentage of tree water use) increased as stem water withdrawal increased.
These results indicate the importance of withdrawal and elastic storage in large trees during drought conditions and that withdrawal and storage are likely reducing the incidence of embolism in these iconic trees.
Analyzing such relationships between seasonal soil moisture and seasonal sap flow provides a clearer picture of the influence of soil moisture on sap flow patterns.
Furthermore, when using sap flow to infer transpiration, withdrawal from stem water stores complicates estimates of timing and amounts of transpiration, particularly in large trees.
Kauri (Agathis australis) is one of the largest and longest-lived conifers in the world with sapwood depths of up to 20 cm.
Published P50 values indicate stems and roots are highly vulnerable to xylem embolism and regular summer droughts are increasing in intensity and frequency with climate change.
We established a throughfall exclusion experiment in kauri forest in West Auckland, Aotearoa New Zealand to explore responses of water relations to drying soils in mature trees.
Our three year experiment indicated sap flow was responsive to soil moisture at seasonal time-steps.
Seasonal sap flow significantly increased as seasonal soil moisture increased but the slope of the curve was steeper for control compared to drought trees.
Stem water withdrawal was responsible for a higher proportion of daily water-use for drought trees (8-28%) compared to control trees (5-12%) but the volume of withdrawal (in L) increased as seasonal tree water-use (per unit sapwood area) increased.
Elastic storage (as a percentage of tree water use) increased as stem water withdrawal increased.
These results indicate the importance of withdrawal and elastic storage in large trees during drought conditions and that withdrawal and storage are likely reducing the incidence of embolism in these iconic trees.
Analyzing such relationships between seasonal soil moisture and seasonal sap flow provides a clearer picture of the influence of soil moisture on sap flow patterns.
Publication
Authors
B. Cranston, C. Macinnis-Ng
Keywords
stem withdrawal, throughfall exclusion, southern conifer, large trees
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