To estimate genetic diversity of the residual northern populations of Oryza rufipogon, a total of 232 individuals from six populations were analyzed using microsatellites (SSRs). The O. rufipogon populations with different status included three from Dongxiang (Jiangxi Province) and three from Chaling (Hunan Province) in China. The 23 rice SSR primer pairs selected from the RiceGenes Database detected a total of 115 alleles, indicating that all the SSR loci were polymorphic in this study. The total gene diversity was 0.919 in the six O. rufipogon populations, and the Donxiang populations showed higher diversity than the Chaling populations. More significant genetic differentiation and less gene flow were found among the Dongxiang populations than those from Chaling. The two putative introgressed populations showed relatively high genetic variation. One in situ conserved population from Dongxiang had the lowest level of genetic diversity. The re-introduced population from Chaling restored about 90% of the genetic variation, compared with the original source population. It is concluded from these results that a relatively high level of genetic variation resided in the northern O. rufipogon populations and continued efforts of conservation of these populations are needed; and that the conservation of some Chaling and Dongxiang populations has been effective in preventing gene flow from cultivated rice. Introgression of cultivated rice demonstrated significant impacts on genetic variability of the O. rufipogon populations, and should be carefully considered in conserving this wild rice. This study also suggested that re-introduction to its original habitats is an effective approach to restore O. rufipogon populations.

A common but often less tested explanation for the successful invasion of alien species is that invasive alien species outcompete their co-occurring natives, which may not always be the case. In this study, we established artificial environmental gradients in a series of pot experiments with controlled environments to investigate the effects of salinity, sediment type and waterlogging on the performance of and interactions between Phragmites australis (native) and Spartina alterniflora (alien), which generally co-exist in the saline intertidal zones of Chinese and American coasts. Significant effects of salinity and waterlogging were detected on biomass production and morphological characteristics of S. alterniflora and P. australis, and the competitive interactions between the two species were found to vary with all three environmental factors in our experiments. Relative Neighbor Effect (RNE) analyses indicate that competitive dominance of S. alterniflora occurred under the conditions of high salinity, sandy sediment and full immersion, whereas P. australis showed competitive dominance under the conditions of low salinity and non-immersion. Our results suggest that S. alterniflora might outcompete P. australis under conditions present in early salt marsh succession, which support the viewpoint that the outcomes of competition between co-occurring native and invasive alien plants depend on the growing conditions. The implication of this study is that in response to the environmental changes expected from seawater intrusion and sea-level rise, the range of S. alterniflora is expected to expand further in the Yangtze River estuary in the future.

SU MMARYThis study was conducted to determine the effects of plastic film mulch on percentage of abortive tillers and harvest index (HI) in two spring wheat populations, and to explore its mechanism in relation to size inequality and life-history strategies theory. Field-grown spring wheat mulched with plastic film shows a remarkable increase in grain yield (an average increase of 38 . 5 % over nonmulched control), which mainly results from the significant increase in above-ground biomass (+44 . 7 %). At the same time, however, reproductive allocation (spike weight/above-ground biomass, x5 . 2 %) and harvest index (x4 . 5 %) were significantly lower (P<0 . 05) in mulched than unmulched populations in both of the two cultivars used. Meanwhile, the number and weight of barren shoots and the ratio of barren shoot biomass to total shoot biomass were significantly greater in mulched populations than unmulched controls both at booting, flowering and ripening stages. From tillering to ripening stages, the tendency of G (Gini coefficient) shows obvious differences between mulched populations ('^' type with the peak of G at booting stages) and non-mulched controls ('_' type with the lowest G at flowering and rebounded at ripening stage). At booting and flowering, the G was significantly higher in mulched populations than unmulched controls, and it was just contrary at ripening. Reproductive allocation and HI were both negatively correlated to average G of the populations, which indicated that resource use efficiency of a crop is inversely related to plant-to-plant variability and also provided further evidence for the views that stand uniformity of field crops is an important aspect of high yield formation. From these results, it was concluded that appreciable growth redundancy occurred in spring wheat populations mulched with plastic film, which may result from the exacerbated inter-plant competition and self-thinning (evidenced by the increased degree of Gini coefficient at booting and flowering stages). Thus, spring wheat cultivation with plastic film mulching does not always mean efficiency, although there is a remarkable increase in grain yields.

Fourteen efficient inter-simple sequence repeat (ISSR) primers were screened and optimized for detecting the genetic diversity in wild populations of Glycyrrhiza uralensis Fisch. By using these primers, 249 polymorphic bands out of a total of 270 (92.2 %) were generated from 70 individuals of 4 wild G. uralensis populations sampled from Inner Mongolia Province of China. Nei's gene diversity (h) and Shannon index (I) calculated from the data matrix of the ISSR phenotypes revealed a high level of genetic diversity with h = 0.268 and I = 0.415 within this plant. Analysis of molecular variation (AMOVA) showed that most of the genetic variation (81 %) occurred within the populations, whereas the variance among populations was only 19 %. The UPGMA tree based on Nei's unbiased genetic diversity illustrated that populations from Bulage and Bayanwusu were genetically close related, while the population from Shanghaimiao was found to be the most diverse from the other three. The high genetic diversity implies that the wild resources of this species could be restored soon if an appropriate and efficient protection strategy was employed. Our results also provided an optimized method for evaluating genetic diversity of G. uralensis using ISSR markers which was useful for further investigation.