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Effect of light availability on the carbon gain of beech ( Fagus crenata ) seedlings with reference to the density of dwarf bamboo ( Sasa kurilensis ) in an understory of Japan Sea type beech forest
Author(s) -
KOBAYASHI TSUYOSHI,
SHIMANO KOJI,
MURAOKA HIROYUKI
Publication year - 2004
Publication title -
plant species biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.419
H-Index - 36
eISSN - 1442-1984
pISSN - 0913-557X
DOI - 10.1111/j.1442-1984.2004.00099.x
Subject(s) - beech , fagus crenata , understory , canopy , bamboo , sasa , seedling , botany , fagus orientalis , photosynthesis , biology , horticulture
In the understory of Japan Sea type beech ( Fagus crenata Bl.) forests, a beech seedling bank persists at the forest floor where the seedlings are shaded by dwarf bamboo ( Sasa kurilensis Makino et Shibata). The culm density of dwarf bamboo is reduced by shading from the overstory. To determine the effect of the dwarf bamboo on the photosynthetic productivity of beech seedlings, we evaluated the leaf carbon gain of the beech seedlings with respect to the spatiotemporal variation in light regimes and CO 2 concentration in a forest at Buna‐Daira, Fukushima Prefecture, central Japan. In midsummer, we measured photosynthetic photon flux density (PPFD) and air CO 2 concentration ( C amb ) at the beech seedling height in the understory beneath the forest canopy with less dwarf bamboo, and in a canopy gap with dense dwarf bamboo. A frequency distribution of log 10 ‐transformed PPFD showed that the mode PPFD class was greater beneath the closed canopy patch than in the gap (51–109 µmol/m 2 per s vs 24–52 µmol/m 2 per s), which was close to the estimated mean background PPFD (diffuse light) in each understory. The total sunfleck period during the midday hours and the mean PPFD of each sunfleck were also greater beneath the closed canopy than in the gap. From the diurnal course of PPFD and C amb , we simulated the midday carbon gain of beech seedlings using the CO 2 assimilation ( A )–PPFD and A – CO 2 curves of beech leaves in the closed canopy patch. The total carbon gain of beech leaves beneath the canopy was 2.35‐fold greater than that in the gap, whether the simulation incorporated photosynthetic induction responses to sunflecks or not. High C amb at the forest floor (380–420 µmol/mol) enhanced the total carbon gain 1.12‐fold. The simulation indicated that an increase in diffuse light under sparse dwarf bamboo, which could accelerate the photosynthetic responses to sunflecks and high C amb , contributed to the photosynthetic carbon gain of beech leaves beneath the forest canopy. These findings suggest that the light environment of the understory can be determined by the effects of forest canopy structure on the density of understory dwarf bamboo and that the photosynthetic productivity of beech seedlings mainly depends on the diffuse light intensity.