Seasonal Variations of Leaf Order and Leaf Age whenReaching Maximum Photosynthetic Rate in SevenTree Species

• Main Authors: Kuo, Shin-Yi, 郭欣儀
• Other Authors: Kuo, Yau-Lun
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/93378735146402818893

碩士 === 國立屏東科技大學 === 森林系所 === 103 === In the past, researchers normally chose newly matured leaves, or leaves at the 3~5 sprouting orders from top of a branch, to measure the photosynthetic rate of a plant. However, this measuring method which based on past experiences did not provide quantitative data for references. The objectives of this research were to investigate the differences of maximum photosynthetic rate (Amax) in different leaf orders of a species during various seasons, and at which leaf order does the Amax occur. Seven species of various shade tolerance classes, including shade-intolerant species Broussonetia papyrifera and Premna serratifolia, moderate shade-tolerant species including Margaritaria indica, Michelia formosana and Heritiera littoralis, shade-tolerant species Gelonium aequoreum and Drypetes littoralis were selected for this study. Ten branches from 3~4 saplings within the range of 1.5~3.0 m in height of each species were tagged for their newly sprout leaves. Photosynthetic rates of each leaf during the four seasons were measured since August, 2013. With these obtained informations, we then knew the leaf order at the branch and leaf age when it reached Amax in various seasons, and thereby calculated leaf sprouting rates in different seasons. Our results showed that, during spring and summer seasons, leaves which had reached Amax were mostly at the 4th~6th leaf orders of morphologically matured leaves in B. papyrifera, Mar. indica, H. littoralis, and D. littoralis, while they were mostly at the 3rd leaf order in P. serratifolia, Mic. formosana, and G. aequoreum. During autumn and winter seasons, leaves which had reached Amax were mostly at the 2nd~4th leaf order in all species besides Mar. indica. We found that the leaf order at which a leaf reached Amax in various seasons was influenced by both the leaf age when physiologically mature and the leaf sprouting rate during that season. A species would have leaves reached Amax at an front position of a branch when a shorter time is needed for reaching Amax. During a faster sprouting season, leaf order of reaching Amax would be at a position relatively away from the branch tip. However, leaf sprouting rates were slower during winter season such that leaves of physiologically mature would be at an front position. In addition, we also found that leaf age of leaf reaching Amax were the shortest during spring or summer seasons. Five species showed the longest leaf age of leaf reaching Amax during winter season, while that of H. littoralis and D. littoralis were during the spring season. For leaf sprouting rates, B. papyrifera, P. serratifolia, and Mar. indica grew 5~9 new leaves per month during spring and summer seasons; Mic. formosana, and H. littoralis grew 3 new leaves; and G. aequoreum and D. littoralis grew 2~3 leaves. To summarize results from the above 7 species, we found that leaves of a same branch reached Amax mostly at 3~5 leaf orders. In addition, leaves reached the highest photosynthetic capacity were at the front 1/4 position and not at the middle position of a branch. Keywords：leaf age, leaf generating speed, leaf order, maximum photosynthetic rate, seasonal variation.