Temporal differentiation in maximum biomass and nutrient accumulation rates in two coexisting annual plant species

Abstract

The temporal patterns of growth and nutrient accumulation into above-ground biomass of two annual coexisting plant species were studied in a semi-arid unfertile grassland. The hypothesis that temporal differences in growth and in nutrient accumulation into above-ground biomass facilitate species coexistence was also tested. Of the annual species identified, only the growth data of Vulpia myuros (L.) C.C. Gmel. and Trifolium campestre Schreb., for two growing seasons, 1991 (wet) and 1993 (dry) were used. The timing of maximum rates were estimated for above-ground biomass growth and accumulation of N, P, and K in above-ground biomass, as well as for the respective rates from the best fitted curves to data of the seven harvests for 1991 and six for 1993 made. The mean timing of maximum rates for the species, averaged over all growth parameters (absolute growth rates, and rates of nutrient accumulation) and years were significantly earlier for the Vulpia. Mean maximum rates of growth parameters, averaged over all species and years followed this order: significantly earlier K<P=N<biomass. Absolute growth rates, averaged over all species were significantly earlier in the dry than in the wet year. On the contrary, the K accumulation rates were earlier in the wet than in the dry year. In the wet year 1991 in comparison to dry 1993, higher moisture levels affected the growing period, and the temporal separation of species maxima was more pronounced, which may have resulted in moderate interspecific competition between Vulpia and Trifolium.