Effects of conspecific and congeneric soils and litters on the nodulation and growth of non-native invasive and native Prosopis species in arid deserts

Allelochemical production is a plausible mechanism promoting the invasion of Prosopis species in their introduced ranges. This study assessed how allelopathy affects the nodulation and growth of non-native Prosopis species (P. juliflora and P. pallida) and native P. cineraria congeners in the United Arab Emirates (UAE). In two experiments, seeds of the three Prosopis species were grown in conspecific and congeneric soils, and litter was collected from underneath their canopies. Prosopis juliflora and P. pallida seedlings, on average, formed a higher number of nodules than native P. cineraria seedlings. Prosopis juliflora seedlings had the heaviest dry shoots and nodules, whereas P. pallida had the heaviest dry roots. The soil source played an important role in the nodule production of each species, with P. pallida and P. cineraria seedlings producing more nodules when growing in conspecific soils. Nodulation and growth were generally reduced across all species when conspecific litters were added, with P. juliflora being the least affected. The success of non-native invasive Prosopis trees in their introduced ranges could be attributed to their capacity to nodulate profusely and to use the biologically fixed nitrogen to enhance aboveground growth in soils with low nitrogen content.