Abstract
We investigated the patterns of response to a long-term drought in the field in cotton cultivars (genotypes) with known differences in their drought tolerance. Four cotton genotypes with varying physiological and morphological traits, suited to different cropping conditions, were grown in the field and subjected to a long-term moderate drought. In general, cotton leaves developed under drought had significantly higher area-based leaf nitrogen content (Narea ) than those under well irrigation. Droughted plants showed a lower light-saturated net photosynthetic rate (Asat ) with lower stomatal conductance (gs ) and intercellular CO2 concentration (Ci ) than irrigated ones. Based on the responses of Asat to gs and Ci , there was no decreasing trend in Asat at a given gs and Ci in droughted leaves, suggesting that the decline in Asat in field-grown cotton plants under a long-term drought can be attributed mainly to stomatal closure, but not to nonstomatal limitations. There was little evidence of an increase in thermal energy dissipation as indicated by the lack of a decrease in the photochemical efficiency of open PSII (Fv ′/Fm ′) in droughted plants. On the basis of electron transport (ETR) and photochemical quenching (qP ), however, we found evidence indicating that droughted cotton plants can circumvent the risk of excessive excitation energy in photosystem (PS) II by maintaining higher electron transport rates associated with higher Narea , even while photosynthetic rates were reduced by stomatal closure.
Key words
Chlorophyll fluorescence - cultivars - gas exchange -
Gossypium
- water deficit
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tomlei@rins.ryukoku.ac.jp
Editor: R. C. Leegood
