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Tree Physiology Advance Access originally published online on December 5, 2008
Tree Physiology 2009 29(1):137-145; doi:10.1093/treephys/tpn014
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© The Author 2008. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Large-scale canopy opening causes decreased photosynthesis in the saplings of shade-tolerant conifer, Abies veitchii

Masako Mitamura1,2, Yasuo Yamamura1 and Takashi Nakano3

1 Laboratory of Ecology, Faculty of Science, Ibaraki University, 2-1-1, Bunkyo, Mito 310-8512, Japan
2 Corresponding author (rico3886ra{at}yahoo.co.jp)
3 Yamanashi Institute of Environmental Sciences, Yamanashi 403-0005, Japan


  Abstract

Although the environmental change by canopy gap formation in a forest improves the light availability for the saplings on the forest floor, it may result in stresses on the saplings due to high radiation and drought. In large-scale gaps, the photosynthesis of shade-tolerant species may be inhibited by high radiation and drought stress if they lack effective tolerance or avoidance mechanisms for the stresses. We investigated the photosynthetic traits and water relations of Abies veitchii Lindl. saplings in an open habitat created by an avalanche and in a nearby forest floor habitat undisturbed by the avalanche. We analyzed the influence of exposed conditions on sapling photosynthesis. The maximum photosynthetic rate of the saplings in the open habitat was lower than that in the forest habitat. The ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) was lower in the open habitat than that in the forest habitat during the late growing season, indicating that the open habitat saplings suffer photoinhibition of photosystem II for a long period. A lower Rubisco concentration in needles in the open habitat indicated the breakdown of this photosynthetic protein because of excess solar energy resulting from serious photoinhibition. The shoot water potential of the saplings in the open habitat at daytime was higher than that of the saplings in the forest habitat because of less transpiration caused by the remarkable stomatal closure in the open habitat. Although these acclimations to high radiation improve the tolerance of A. veitchii saplings to high radiation and drought stress, they would result in low gain of daily carbon and a reduction in growth in the open habitat.

Keywords: avalanche, canopy gap, chlorophyll fluorescence, light acclimation, photoinhibition, Rubisco

Received July 3, 2008; Accepted September 15, 2008


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