Despite continuing efforts to correlate unit area rates of photosynthesis of crop varieties with growth rates, there has been little or no success. It is reasonable to assume that partitioning of photosynthate into new leaf area is an important component of growth. Accordingly, an expression was developed to measure leaf area partitioning. Using growth analysis techniques, relative growth rates were compared to net assimilation rates, partitioning of daily weight gain into new leaf area, and partitioning of daily weight gain into new leaf weight of nine species grown in growth chambers under three temperature regimes. Day/night temperatures of 21/10, 32/21, and 38/27 C caused large differences in relative growth rates. Relative growth rates were closely correlated with leaf area partitioning in seven of the nine species, but were inversely correlated with leaf weight partitioning for six of the nine species.Relative growth rates were poorly correlated with net assimilation rates for five of the nine species. The product of net assimilation rate times leaf area partitioning is shown to be equal to the relative leaf area expansion rate.These results indicate that growth responses due to temperature shifts were more sensitive to changes in leaf area partitioning or relative leaf area expansion rates than to net assimilation rates. Because changes in leaf area partitioning or relative leaf area expansion rates can have an effect on relative growth rates that overshadow changes in net assmilation rates, and because net assimilation rates are largely a function of unit area rates of photosynthesis, the correlation of unit area rates of photosynthesis with growth should include consideration of leaf area partitioning or relative leaf area expansion rates.For more than a decade, considerable effort has been expended in the search for crop varieties or ecotypes that have high unit leaf area photosynthetic rates (3-6, 11, 13, 14, 16, 22). These investigations have been based on the assumption that high unit area photosynthetic rates should correlate well with growth. Generally, it has been found that growth is not well correlated with unit area rates of photosynthesis (4,13,15,16,18,23), although some authors have reported otherwise (9). However, good correlations between growth and rates of leaf area expansion (5-7, 11, 22, 24, 26) analysis has permitted the accurate and rapid measurement of short term photosynthetic rates. Second, the discovery that the pathways and rates of photosynthesis differ greatly among species has led plant scientists to re-examine the role of photosynthesis in plant growth. Coupled with this renewed interest in photosynthesis is a growing awareness that partitioning of photosynthate into new leaf growth is also an important factor in plant growth (2,10,17,19,21). This paper is an assessment of the relation between growth, NAR, and the partitioning of daily weight gain into new leaf area and new leaf weight. MATERIALS AND METHODS

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Drought resistance of mycorrhizal pepper plants independent of leaf P concentration -response in gas exchange and water relations, -Physiol, Plant. 87: 45-53.Pepper (Capsicum annuum L.) plants with and without the VA-mycorrhizal fungus Giomus desenicola Trappe, Bloss and Menge (VAM and NVAM, respectively), were drought acclimated by four drought cycles (DA) or kept well watered (NDA). All plants were then subjected to an additional drought followed by a 3-day irrigation recovery period. Measurements of water relations, gas exchange and carbohydrates were made at selected intervals throughout the drought cycles and recovery. To equalize growth and avoid higher P in VAM plants, NVAM plants received higher P fertilization. Consequently, similar transpirational surfaee and shoot mass were achieved in all treatments, but NVAM had a higher tissue P concentration than VAM plants. Plants that were either VAM or DA, but especially the VAM-DA plants, tended to be high in net photosynthetic flux (A), A per unit of tissue P concentration (A/F), stomata] conductance (g) or leaf turgor (ip_) during high environmental stress or recovery from stress. During this time, NVAM-NDA plants had low A, A/P and leaf chlorophyll, but high soluble carbohydrate concentrations in their leaves. All VAM and DA plants had some osmotic adjustment compared to the NVAM-NDA plants, but VAM-DA plants had the most. Osmotic adjustment was not due to accumulation of soluble carbohydrate. The high turgor, A and g in the VAM-DA plants during and following environmental stress indicated superior drought resistance of these plants; however, osmotic adjustment was only apparent during recovery and cannot account for the observed drought resistance during environmental stress. Drought resistance of VAM-DA plants was not attributable to high leaf P concentration or confounded by differences in plant transpirational surface.