JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. In many plants, extrafloral nectars attract ants that protect the plant from herbivory. Previous work indicates that both sugars and amino acids contribute to ant attraction and that herbivory may affect nectar production or composition. This study was designed to measure the effect of defoliation on sugar and amino acid concentrations in the extrafloral nectar of Impatiens sultan. Twenty-nine fall-raised plants and 45 springraised plants were subjected to varying degrees of defoliation in which 25, 50, or 75% of each leaf was removed. Extrafloral nectar was collected immediately before and 24 h after defoliation for the fall-raised plants; additionally, nectar was collected 24 h before and 48 and 72 h after defoliation in the spring-raised plants. Nectars were analyzed for sugar and amino acid content by means of high-pressure liquid chromatography (HPLC). Twentyfour hours after defoliation, amino acid content increased dramatically in plants subjected to all three levels of defoliation; amino acid concentrations of nectars 72 h after defoliation were indistinguishable from predefoliation levels. No change in sugar concentrations or nectar volumes was detected. Additional work is needed to determine if the increase in amino acids is adaptive and serves to attract more plant protectors.
Although the volume and chemical composition of nectars are known to vary among plant species and to affect pollinator response to plants, relatively little is known of the variation in volume, and sugar and amino acid composition within species. We collected nectar from Impatiens capensis in a nested design: three flowers from each of three plants from each of three populations. This design enabled us to quantify variation within individual plants, among plants within populations, and among populations. Using high performance liquid chromatography, we analyzed the sugar and amino composition of the 27 flowers. Analysis of variance showed that none of the parameters (volume, concentrations of three sugars and 24 amino compounds) varied within individuals. Variation in nectar volume was not significant among plants but was nearly significant among populations. Of the three sugars detected (sucrose, glucose, and fructose), the only significant variation was that of sucrose among populations. Concentrations of 12 amino compounds varied significantly at the plant level while 7 amino compounds varied among populations. The results indicate that: (1) pooling of nectar samples from flowers of individual plants can be an acceptable methodology for those seeking to understand within species variation; (2) amino compounds appear to vary more than either volumes or sugar concentrations; (3) future studies should assess how much of the observed variation is due to genetic versus environmental differences; (4) additional studies should examine the geographic variation in nectar parameters and pollinators of I. capensis in order to assess the role different pollinators play in shaping nectar composition.
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