Ammopiptanthus nanus (M. Pop.) Cheng f. is a very important resource plant that integrates soil and water conservation, afforestation of barren mountains, and ornamental, medicinal, and scientific research functions and is also a critically endangered plant in China, remaining in only six small fragmented populations in the wild. These populations have been suffering from severe anthropomorphic disturbances, causing further losses in genetic diversity. However, its genetic diversity level and genetic differentiation degree among the fragmented populations are still unclear. Inthis study, DNA was extracted from fresh leaves from the remnant populations of A. nanus, and the inter-simple-sequence repeat (ISSR) molecular marker system was used to assess its level of genetic diversity and differentiation. The result was that its genetic diversity is low at both species and population levels, with only 51.70% and 26.84% polymorphic loci, respectively. The Akeqi population had the highest genetic diversity, whereas the Ohsalur and Xiaoerbulak populations had the lowest. There was significant genetic differentiation among the populations, and the value of the genetic differentiation coefficient (Gst) was as high as 0.73, while the gene flow value was as low as 0.19 owing to spatial fragmentation and a serious genetic exchange barrier among the populations. It is suggested that a nature reserve and germplasm banks should be established as soon as possible for elimination of the anthropomorphic disturbances, and mutual introductions between the populations and introduced patches of the species, such as with habitat corridors or stepping stones, should be performed simultaneously to improve the genetic diversity of the isolated populations for the conservation of this plant.
The alien weed Xanthium italicum (Italian cocklebur) severely decreases the Helianthus annuus (oil sunflower) seed yield; however, its mechanisms remain unknown. To explore the relative intensity of competition between the two plants and to test the hypothesis that interspecific competitive pressure from Italian cocklebur causes a reduction in the yield and quality of oil sunflower seeds, a replacement experiment using the two species was performed under simulated common water-supply conditions of sunflower farmlands, and differences in growth parameters, seed yield, and seed quality of oil sunflower between monoculture and interplanting conditions were compared. The results showed that compared with those under monoculture conditions, the seed yield (biomass), oil content, and 1000-seed weight of oil sunflower interplanted with Italian cocklebur decreased by 7.75%, 23.48%, and 13.86%, respectively, under low water supply. Moreover, these parameters were reduced by 19.85%, 24.36%, and 16.19%, respectively, under high water supply. The interspecific competitive intensity of X. italicum was significantly higher than that of oil sunflower under both water-supply conditions. Given the competitive inhibition from the exotic plant, the vegetative and reproductive growth of the native crop was significantly impaired, and its seed yield and oil content were significantly reduced.
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