Reproductive Biology of T. chinensis and T. ramosissima (Tamaricaceae: Theineae) from Gansu, Northwestern China

Abstract

Tamarix. chinensis and Tamarix. ramosissima are ecologically important species in the arid region of Northwest China, and have been widely studied in recent years. The reproductive biology of T. chinensis and T. ramosissima was studied to determine the main pollination system and pollen limitation of these species, providing the first experimental data on reproductive success in the Tamaricaceae. This study was conducted, including observations on phenology and floral trait of flowers, insect visits and pollinator behavior. Experimental pollination treatments were performed to assess self-compatibility, outcrossing and self-pollination. Pollen limitation and reproductive success were assessed by fruit-and seed-set. The blooming duration and flowering peak were different between T. chinensis and T. ramosissima, being longer in the former. Both species were pollen-limited, and pollen limitation was more intense in T. ramosissima than that in T. chinensis. In T. chinensis, Megachile (Amegachile) kagiana was found to be the most frequent and effective pollinator, Apis mellifera was the frequent visitor in T. ramosissima. We suggested that pollinator behavior is closely associated with floral phenology. Some important differences were found from the study on two species in floral phenology and the primary pollinator behavior. Outcrossing was dominant and that self-pollination played a complementary role to assure production. Both species display a highly adaptive breeding system, and it's also the evolution of reproductive biology.Keywords: reproductive, pollination, pollen limitation, pollinator, breeding system IntroductionReproductive success in variable environments in which pollination may be uncertain is a common problem that confronts many plants (Ai et al., 2013). Pollination is a key process as the first stage in sexual reproduction of plants, and an essential prerequisite for the development of fruits and seeds (Kevan et al., 1990). Therefore, pollination affects a variety of ecological and evolutionary processes of many plant species, such as floral attraction, plant mating system and population persistence (Bond, 1994;Kearns et al., 1998;Ashman et al., 2004;Ashman & Morgan, 2004). During the short growing seasons, harsh weather and low densities of pollinators could affect the effective pollination (Ai et al., 2013;Ashman et al., 2004). Studying reproductive biology is helpful to understanding of pollination success, as well as natural factors influencing dynamics of populations (Arias-Cóyotl et al., 2006). The flowering plants under natural pollination conditions often suffer from pollen limitation (Ashman et al., 2004; Knight et al., 2006). Pollen limitation occurs when plant reproduction is limited by the quantity or quality of pollen received (Byers, 1995;Aizen & Harder, 2007). When pollen limitation is observed in fragmented habitat, it is often interpreted as evidence for pollinator limitation of reproduction (Stuart & Stephanie, 2010). Sexual selection theory once optimistically predicted t...