Damián A. Ravetta

Long-term effect of carbohydrate reserves on growth and reproduction of Prosopis denudans (Fabaceae): implications for conservation of woody perennials

We evaluated the usefulness of long-term plant carbon economy of a xerophyte shrub as a tool in conservation. Reserves manipulation through defoliation decreased reproduction in the long-term but not growth. Root and shoot reserves can be used as indicators of how much biomass can be harvested without threatening future reproduction

The impact of reproductive output on Prosopis denudans pod partition and chemical composition: Implications for economic utilization

The impact of reproductive output on Prosopis denudans pod partition and chemical composition: Implications for economic utilization.m Located in southern Argentina where the climate is dry, cold, and windy, the economy of the Patagonian shrub-steppes is based almost exclusively on sheep husbandry. In this ecosystem, grazing has been identified as one of the main causes of degradation, a process that hampers the sustainability of the region (1). A sustainable alternative that could increase the economic return in this area is to harvest native stands of target species capable of yielding raw industrial materials. One of the target species identified for the Chubut province (42 ~ S) is Prosopis denudans Bentham (2). Prosopis pods, which are rich in sugar, protein, and carbohydrates (3), are mostly consumed by wildlife and domestic herbivores (4). The importance of Prosopis pods for Indian cultures in North and South America has been very great in the past and is still considerable. The edible fruits are used as food in the form of meal or fermented beverages. The pod mesocarp, which is the spongy pulp between the pod exterior (exocarp) and the stony endocarp, is a source of flour and gum, both of which are suitable for human consumption (5). Because the taste and aroma of Prosopis flour is in the same general class as coffee/cacao/cinnamon/mocha, its greatest economic value will be achieved in flavoring/aroma applications of the food industry (5). The mesocarp of the fruits of Prosopis denudans also could be used as a source of gum (up to 10% of the fruits dry weight; 6). Because the development of Prosopis as a crop would be enhanced if the annual pod crop is efficiently utilized, much effort has been devoted to develop products suitable for use as a food ingredient (7, 8, 9). Despite the fact that the industrial technology to produce Prosopis flour seems to be ready, the great variation shown both in reproductive output and fruit quality does not allow for intensive utilization (10, 11) and, at the present time, flour is not used in any commercial application on a significant scale. In this regard, the proportion of the mesocarp of a fruit is a key factor for pod industrial utilization because it has a clear influence on the cost of the processes involved in the production of flours (5). See Figure 1. With this in mind, we tested the hypothesis that fruit size and partition (i.e., mesocarp proportion) are strongly influenced by the number of fruits produced by the plant in a given season. The objective of this work was to compare green and ripe pods partition into pericarp and seeds and their chemical composition in P. denudans individuals differing in reproductive output (highand low-pod yield individuals). Four morphological variables (fruit dry weight, pericarp:seed ratio, number of seeds, and seed dry weight) and two chemical variables (protein and total non-structural carbohydrate content) are described for four growth stages of Prosopis denudans pods. The results are discussed in the context of the economic utilization of the crop. Materials and methods: Three native populations of Prosopis denudans, located in the Patagonian province of Cbubut (Argentina), were selected for this study. In late spring (December), individuals bearing high quantities (HY) and low quantities (LY) of green pods were identified (10 reps/population). Two groups of plants with no significant differences in height (t test; P=0.47) and diameter (t test; P=0.23) were chosen for this study. Reproductive output as measured in grams (g) of mature fruits (12) and reproductive allocation [reproductive output (g)/aerial biomass produced during the last growing season in grams of dry weight (g D.W.; 13)] significantly differed (p<0.05) between HY (32.9 _+ 6.8 g fruit per plant and 0.053 -+ 0.007 g fruit [ g bi . . . . . ) and LY (5.8 -+ 0.8 g fruit per plant; 0.01 +0.003 g fruit [ g bi . . . . . ) individuals. Green pods were harvested and oven-dried at 50~ to constant weight. Growth stages were identified according to a pods width (stage 1 <_ 3 mm; stage 2 = 3.1-5 mm; stage 3 >_ 5.1 mm; and stage 4 (full size) = mature pod). Total non-structural carbohydrates (TNC) were determined by the anthrone method (14). Nitrogen determination was based