Photosynthetic responses to lightflecks ofFagus crenata seedlings grown in a gap and understory of a deciduous forest |
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Authors: | Masaaki Naramoto Qingmin Han Yoshitaka Kakubari |
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Institution: | (1) Department of Forest Resources, Faculty of Agriculture, University of Shizuoka, 422-8529 Shizuoka, Japan;(2) Present address: Department of Plant Ecology, Forestry and Forest Products Research Institute, 305-8687 Tsukuba, Japan |
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Abstract: | Photosynthetic responses to a series of 1-min lightflecks (1,000μmol m−2 s−1) superimposed on a background with different duration (1, 5, and 10 min) and intensity (25 and 50μmol m−2 s−1) of low background photosynthetic photon flux density (PPFD) were measured in the leaves ofFagus crenata grown in a gap and understory of aFagus crenata forest in the Naeba Mountains. The two background PPFD intensities most frequently occurred in understory and gap sites respectively.
The maximum net photosynthetic rate (P
Nmax) and maximum stomatal conductance (g
smax) were higher in the gap seedlings than in the understory seedlings. However, when the background PPFD was 25μmol m−2s−1, the net photosynthetic rate (P
25) and stomatal conductance (g
s25) were almost the same between the gap and understory. When the background PPFD duration was 1-min, the net photosynthetic
rate (P
N
) at the end of each lightfleck increased progressively. When the background PPFD duration was 5- and 10-min, the increase
inP
N
at the end of each lightfleck was less. This indicates that background PPFD duration is important to photosynthetic responses
to lightflecks. The higher ratios ofP
25/P
Nmax andg
s25/g
smax in the understory seedlings indicate that the understory seedlings can maintain relatively lower levels of biochemical and
stomatal limitations than the gap seedlings under low light conditions. The ratios ofP
N
/P
Nmax at the end of each lightfleck (IS) and light utilization efficiency of single lightflecks (LUE
s) that showed the influence of lightflecks on carbon gain were higher in the understory seedlings than in the gap seedlings
when the background PPFD was 25μmol m−2 s−1. This means that understory seedling are capable of utilizing fluctuating light more efficiently under low light conditions
than the gap seedlings although the net carbon gain of single lightflecks (CG
s) in the understory seedlings was not higher than that in the gap seedlings. There were no significant differences inIS andLUE
s between understory seedlings at a background PPFD of 25μmol m−2 s−1 and gap seedlings at a background PPFD of 50μmol m−2 s−1. However,CG
s in gap seedlings was higher than in understory seedlings. These results provide more evidence thatF. crenata acclimate to a natural light environment in respect to relative induction state at low background PPFD and can capture the
fluctuating light at the same efficiency in both the gap and understory seedlings under natural light environments.
This study was funded by the research project, Evaluation of Total CO2 Budget in Forest Ecosystems, coordinated by the Ministry of Agriculture, Forestry and Fisheries of Japan. |
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Keywords: | background light intensity and duration carbon gain induction state light utilization efficiency |
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