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The Effects of Shade on the Gas Exchange of Seedlings of Four Tropical Trees from Mexico

J. Ramos and J. Grace
Functional Ecology
Vol. 4, No. 5 (1990), pp. 667-677
DOI: 10.2307/2389735
Stable URL: http://www.jstor.org/stable/2389735
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Effects of Shade on the Gas Exchange of Seedlings of Four Tropical Trees from Mexico
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Abstract

The effects of two light regimes, `sun' and `shade', on the gas exchange of four tropical tree species from Mexico were evaluated. Photosynthetic and stomatal responses to light and humidity were studied using a controlled environment cabinet and an infra-red gas analyser. A non-linear model was fitted to the photosynthetic responses and the physiological parameters found were used to compare treatments and species. Species from the secondary forest displayed higher maximal values of photosynthesis than those species normally found in primary forests. These species were also more sensitive to shade, i.e. maximal rates of photosynthesis were reduced to a greater extent when plants were grown in `shade'. Plants grown under `sun' conditions displayed enhanced dark respiration, higher values of photosynthesis and their rate of photosynthesis continued to increase above a photon flux density of 400 μmol m-2 s-1. When plants were raised in `sun' conditions, their leaves contained more nitrogen (on a leaf area basis) and this was associated with an increased mesophyll conductance. The species differed from each other much more in their growth than in their rates of photosynthesis and it is concluded that assimilate distribution may be more diagnostic of the ecological status of a species than its rate of assimilate production per area of leaf.

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