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Photosynthetic Rate and Diffusion Conductance as a Function of Age in Leaves of Bean Plants 1
Author(s) -
Davis S. D.,
McCree K. J.
Publication year - 1978
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1978.0011183x001800020021x
Subject(s) - photosynthesis , phaseolus , biology , conductance , stomatal conductance , botany , horticulture , diffusion , mathematics , thermodynamics , physics , combinatorics
Bush beans ( Phaseolus vulgaris L.) were grown and tested under constant environmental conditions. Simultaneous measurements of CO 2 exchange rates and H 2 O diffusion conductances were made on individual leaves, throughout all stages of leaf and plant development. Both exchange rate and leaf conductance (reciprocal of resistance) declined with leaf age. In both cases the data for all leaves fell on a single straight line, when plotted against time expressed as a percentage of the time from maturity to death. The decline in conductance was not sufficient to explain the decline in the exchange rate. There was a proportionate decline in the internal photosynthetic capacities of the leaves. Since the CO 2 concentration in the substomatal cavity was found to remain almost constant, and the external conditions (light, temperature, water status) were kept constant, the decline in conductance was either due to a real decrease in the abilities of the stomates to stay open or a compensating adjustment of stomates by a CO 2 feedback process.