Interaction of water stress and nitrogen supply on the photosynthetic parameters of two upland rices and two upland weeds
1991
Migo, T.R. | Pamplona, R.R. | Dingkuhn, M. | De Datta, S.K. (International Rice Research Inst., Los Banos, Laguna (Philippines))
The effects of water stress and nitrogen (N) application on photosynthetic capacities of ecologically similar annuals--two upland rices (var. IR43 and Kinandang Patong, C3 species and two upland weeds (Echinochloa colona (L.) Link and Rottboellia cochinchinensis (Lour.) W.D. Clayton, C4 species) were studied in a greenhouse during the 1990 wet season. Under well-watered and water-stressed conditions, leaf water potential (LWP) was lower in plants with high N application than those without N. The N content of water-stressed plants was higher than those of well-watered plants, suggesting that water-stressed slowed down or delayed metabolism of absorbed N. Under well-watered conditions, E. colona and R. cochinchinensis had higher CO2 exchange rates (CER) at leaf level than IR43 and Kinandang Patong with or without any N applied. There was high CER in R. cochinchinensis throughout its growing period but decreased with age in E. colona. In water-stressed treatment with no N application, particularly at the 10-day stress period, CER of R. cochinchinensis was 73% and E. colona was 60% higher than that of the two rices suggesting the high water use efficiency (WUE) of both weeds under this condition. In contrast, CER when averaged over all species decreased by 78% with high N compared with that when no N was applied under water-stressed conditions indicating strong water stress and N interactions. The high CER of C4 weeds were associated with higher quantum efficiency (QE), higher WUE and CO2 fixed/N available. Also, the two-way interaction of water stressed and N supply was clearly manifested in QE and WUE as in CER. Results showed the physiological and morphological advantages of these weeds over the crop, thus rendering them highly competitive.
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