Ecological implications of seed characteristics of the native Prosopis cineraria and the alien P. juliflora

Seed weight, percentage germination, seedling growth, and nutrient concentrations (Mg, Na, K, Zn, Cu and P) of whole seeds, and of seed coats and embryos separately of two tree species, the native Prosopis cineraria and the invasive alien P. juliflora from semi-arid and arid areas of north and north-west India, were analysed to understand the differences in their ecology. Seeds of P. cineraria were heavier than those of P. juliflora. Percent germination was similar in the two species, but seedling growth was faster in P. juliflora than in P. cineraria. Nutrient concentrations of seeds of the two species were similar (except Cu). Nutrient concentrations in the embryo were higher in P. cineraria, while those in the seed coat were higher in P. juliflora. The relative allocation of nutrients to seed coat was higher in P. juliflora than in P. cineraria. Nutrient-rich embryos and slow growth, along with a staggered seed germination pattern in the native P. cineraria could be linked to delayed establishment as well, in the substratum. Faster growth of the nutrient-poor embryos in P. juliflora along with its simultaneous seed germination pattern, and creation of a favourable microenvironment through leaching of nutrients from a nutrient-rich seed coat can facilitate immediate and successful establishment of this alien species in the invaded habitats.