Reproductive allocation in plants in terms of biomass, energy or nutrients

Reproductive allocation (RA), the proportion of total resources that are invested in reproductive structures, is a key component of plant life histories. A major methodological issue is to identify the allocation currency that better estimates RA: biomass, energy or some mineral nutrient. Despite considerable effort to ascertain whether biomass could serve as an integrated estimate of the allocation of other resources, no clear guideline has emerged from the currency issue. Here, we reappraised this problem at an interespecific scale. We compiled a data base of 38 studies that estimated RA in terms of two or more different resources for 82 plant species. We tested the equivalence of allocation currencies by means of both bi- and multivariate correlations among currencies. We also tested for differences in allocation patterns between growth forms. RA was estimated in 18 different currencies, including biomass, energy and 16 mineral nutrients. Nitrogen, P, K, Mg and Ca were the main nutrients used as allocation currency. Growth form accounted for 20-30% of differences in the resource allocation of multiple resources. The six resources most frequently used as estimates RA were roughly equivalent at an interspecific scale. Nevertheless, covariation patterns among currencies suggested that RA in plants should be better considered a multivariate trait and not estimated using a single currency. In particular, multivariate estimates of RA can contribute to the ongoing comparative studies of life histories and functional traits.