The effect of nitrogen fertilization and water stress on the spectral signature of winter wheat Triticum aestivum cv. Astral were measured with a field radiometer over two years. Spectral reflectance of the canopy has been related to the most indicative physiological parameters (nitrogen and photosynthetic pigment content, biomass, leaf area and LAI), but only a few of these parameters can be estimated independently of plant treatment.The normalized difference vegetation index seems the most powerful spectral combination with which to estimate the total area of plant leaves and LAI. The nitrogen content of plants can also be related to a linear combination of green and red canopy refleetances independently of plant treatment. Relations between canopy reflectance and other physiological parameters are not independent of plant treatment.

Ecophysiological differences related to photosynthesis were compared in holm oak Quercus ilex leaves from undisturbed holm-oak vegetation, resprouts after fire and resprouts after tree-fell. No significant differences in any parameter measured were observed between the two kinds of resprout throughout the first growing season following disturbance. Resprouting leaves showed lower carbon isotope discrimination (Δ) and intercellular CO concentration (p ), and higher photosynthesis, leaf conductance and transpiration rates than leaves from undisturbed stands. Nitrogen, soluble protein content and ribulose bisphosphate carboxylase (RuBPCase) activity were 88%, 96% and 45% higher respectively, in both kinds of resprout. The results indicate that photosynthetic capacity, rather than stomatal conductance, is the limiting factor in photosynthesis in resprouts, Chlorophyll content and chlorophyll a/b ratio did not differ between resprouts and undisturbed leaves, indicating that the observed differences were not a result of differences in light environment during leaf development. Leaf mass per area (LMA), was 80% higher in the resprouts, and was negatively related (r=-0.86) to Δ and positively related (r=0.87) to N content. Enhanced carbon assimilation after disturbances resulted in higher water use efficiency, as indicated by lower Δ values in the resprouts. We conclude that the cause of defoliation was not relevant in the physiology of the resprouts, suggesting the importance of underground organs.

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Anatomical and physiological leaf characteristics and biomass production of Fatsiajaponica plants were studied. Plants were grown in a growth chamber at 300 umol m ? S-I (high light) and 50 umol m ? S-I (low light) photosynthetic photon flux density. Plants grown under high light showed a net maximum photosynthetic rate 44% higher than plants grown under low light; the light compensation point and the light saturation point were also higher in high-light plants. Photosynthetic oxygen evolution in isolated chloroplasts was about 40% higher in high-light plants. However, chlorophyll content on a dry weight basis, on a leaf area basis, and per chloroplast was greater in plants grown under low light. Leaf thickness in high-light plants was 13% higher than in low-light plants. The number of chloroplasts was 30% higher in high-light leaves, while chloroplast size was only slightly higher. Chloroplast ultrastructure was also affected by light. Leaf dry weight, leaf area, and biomass production per plant were drastically reduced under low light. Thus, F. japonica is a plant that is able to acclimate to different photosynthetic photon flux density by altering its anatomical and physiological characteristics. However, lowlight acclimation of this plant has a considerable limiting effect on biomass production. 1149

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The effects of the herbicide methabenzthiazuron (175 and 220 g ha-~) on vegetative and reproductive growth, nodulation and nitrogenase activity of Vicia faba were studied in the field under Mediterranean conditions. Nitrogenase activity of excised nodules was estimated using the acetylene reduction assay four times during the developmental period. Leaf area index, dry weight and nitrogen content of the different parts of the plants were measured. Methabenzthiazuron-treated plants showed an increase in nodulation, nitrogenase activity and vegetative growth at early pod fill. Methabenzthiazuron also caused an increase in leaf N content and fruits. These were transient effects found during early and mid pot fill. Nevertheless, plants treated with these sublethal doses of herbicide improved seed production and nitrogen content of seeds at harvest time. The stimulatory effect of methabenzthiazuron on N 2 fixation and vegetative growth seems not be related with the transient stimulatory effect on photosynthetic capacity, also caused by the herbicide, since the stimulatory effect on N 2 fixation was apparent during pod fill, when photosynthetic capacity declined and was not modified by methabenzthiazuron.

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