Canopy-level stomatal narrowing in adult Fagus sylvatica under O3 stress – Means of preventing enhanced O3 uptake under high O3 exposure?

Matyssek, R.; Baumgarten, M.; Hummel, U.; Häberle, K.-H.; Kitao, M.; Wieser, G.

Canopy-level stomatal narrowing in adult Fagus sylvatica under O3 stress – Means of preventing enhanced O3 uptake under high O3 exposure?

2015

Spatio-temporally consistent O3 doses are demonstrated in adult Fagus sylvatica from the Kranzberg Forest free-air fumigation experiment, covering cross-canopy and whole-seasonal scopes through sap flow measurement. Given O3-driven closure of stomata, we hypothesized enhanced whole-tree level O3 influx to be prevented under enhanced O3 exposure. Although foliage transpiration rate was lowered under twice-ambient O3 around noon by 30% along with canopy conductance, the hypothesis was falsified, as O3 influx was raised by 25%. Nevertheless, the twice-ambient/ambient ratio of O3 uptake was smaller by about 20% than that of O3 exposure, suggesting stomatal limitation of uptake. The O3 response was traceable from leaves across branches to the canopy, where peak transpiration rates resembled those of shade rather than sun branches. Rainy/overcast-day and nightly O3 uptake is quantified and discussed. Whole-seasonal canopy-level validation of modelled with sap flow-derived O3 flux becomes available in assessing O3 risk for forest trees.

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