Comparative effects of pollen limitation, floral traits and pollinators on reproductive success of Hedysarum scoparium Fisch. et Mey. in different habitats.

BACKGROUND: Reproduction in most flowering plants may be limited because of the decreased visitation or activity of pollinators in fragmented habitats. Hedysarum scoparium Fisch. et Mey. is an arid region shrub with ecological importance. We explored the pollen limitation and seed set of Hedysarum scoparium in fragmented and restored environments, and examined whether pollen limitation is a significant limiting factor for seed set. We also compared floral traits and pollinator visitation between both habitats, and we determined the difference of floral traits and pollinators influenced reproductive success in Hedysarum scoparium. RESULTS: Our results indicated that supplementation with pollen significantly increased seed set per flower, which is pollen-limited in this species. Furthermore, there was greater seed set of the hand cross-pollination group in the restored habitat compared to the fragmented environment. More visits by Apis mellifera were recorded in the restored habitats, which may explain the difference in seed production between the fragmented and restored habitats. CONCLUSIONS: In this study, a positive association between pollinator visitation frequency and open flower number was observed. The findings of this study are important for experimentally quantifying the effects of floral traits and pollinators on plant reproductive success in different habitats.

Effects of sand burial on the survival and growth of two shrubs dominant in different habitats of northern China.

Plants that grow in dune ecosystems always suffer from sand burial. Shrubs play implications on the healthy functioning of dune ecosystems due to control blowing sand. However, the survival and growth responses of shrubs to sand burial remain poorly understood. The survival rate and seedling height of two shrubs (Artemisia halodendron and Lespedeza davurica) along with the soil properties under different burial depths were examined in order to reveal the causing ecophysiological attributes of sand burial on shrubs in the desertified region. It was found that A. halodendron can survive a burial depth of 6 cm greater than its seedling height, which is a dominant shrub in mobile dunes with intense burial, whereas a burial depth equivalent to three fourths of its seedling height is detrimental to L. davurica, which is dominant in fixed dunes with less burial. The reasons for the shrub death under sand burial were associated with the physical barrier to vertical growth and the reduction in photosynthetic area. In conclusion, A. halodendron can facilitate the stabilization of mobile dunes because of their high tolerance to the frequent and intensive sand burial, while L. davurica can be beneficial for the recovery process because of their higher survival rates under shallow burial following restoration of mobile dunes.

[Crust development and subsurface soil properties under dominant shrubs in the process of dune restoration, Horqin Sand Land].

Soil crust is a common and widespread phenomenon in desert areas all over the world due to its extraordinary ability to survive desiccation and extreme temperatures, high pH and salinity. Despite its unassuming appearance, biological soil crusts play a significant role in desert ecosystems, including involvement in the process of formation, stability and fertility of soil, preventing soil erosion by water or wind, increasing the possibility of vascular plant colonization, and being responsible for the stabilization of sand dunes. This study taking Horqin Sand Land as research region, by field sampling, crust and topsoil (0-2.5 cm and 2.5-5 cm under crust) samples in different dune habitats and shrub communities were collected, and their physicochemical properties were analyzed, including particle size distribution, bulk density, total nutrients and available nutrients, pH, EC and CaCO3 content. The result revealed that Artemisia halodendron in semi-mobile dune, Caragana microphylla in semi-fix dune, Artemisia frigida in fix dune and Salix microstachya in interdunal lowland were respectively developed physical soil crust, algae crust, lichen crust and moss crust. Crust thickness, hardness, water content, fine fraction, total and available nutrients gradually increased by semi-mobile dune < semi-fix dune < fix dune < interdunal lowland in terms of different dune habitats, and by physical soil crust < algae crust < lichen crust < moss crust in terms of different crust types. There were significant differences among crust types on nutrient content and particle size distribution (p < 0.01). Meanwhile, crust enhanced the < 0.05 mm content and nutrient content of topsoil, following an increasing trend from semi-mobile dune to interdunal lowland. As to each crust, the parameters of 0-2.5 cm subsurface soil layer were higher than that in 2.5-5 cm soil layer. The result also showed that the fine fraction and nutrient content of moss crust under Salix microstachya in interdunal lowland were higher than others, so did the 0-5 cm subsurface soil under it.