Effect of Resource Reallocation on Pollen Limitation and Reproductive Assurance of Apocynum venetum L. in an Arid Region

Pollen limitation is considered to be a strong force driving the evolution of reproductive strategies in flowering plants. However, resource reallocation may occur among seeds because of variation in the quantity or quality of pollen received. We performed single-flower and whole-plant pollen supplementation and emasculation of flowers of Apocynum venetum L. to estimate pollen limitation and reproductive assurance. In addition, we calculated the visiting patterns of the pollinators, frequency of pollinators to estimate the effect of pollinator activity and further on the reproductive success of A. venetum. Our results indicated estimates from single-flower manipulations were not biased, closely resembling those from whole-plant manipulations. We found Apis mellifera was the dominant pollinator during the pollination process. In addition, insect pollination played a more important role in the outcrossing system, which could explain the differences in reproductive success. Our results also showed that autonomous self-pollination eliminates pollen limitation and provides reproductive assurance.