Effect of clonal integration on nitrogen cycling in rhizosphere of rhizomatous clonal plant, Phyllostachys bissetii, under heterogeneous light.

Clonal integration plays an important role in clonal plant adapting to heterogeneous habitats. It was postulated that clonal integration could exhibit positive effects on nitrogen cycling in the rhizosphere of clonal plant subjected to heterogeneous light conditions. An in-situ experiment was conducted using clonal fragments of Phyllostachys bissetii with two successive ramets. Shading treatments were applied to offspring or mother ramets, respectively, whereas counterparts were treated to full sunlight. Rhizomes between two successive ramets were either severed or connected. Extracellular enzyme activities and nitrogen turnover were measured, as well as soil properties. Abundance of functional genes (archaeal or bacterial amoA, nifH) in the rhizosphere of shaded, offspring or mother ramets were determined using quantitative polymerase chain reaction. Carbon or nitrogen availabilities were significantly influenced by clonal integration in the rhizosphere of shaded ramets. Clonal integration significantly increased extracellular enzyme activities and abundance of functional genes in the rhizosphere of shaded ramets. When rhizomes were connected, higher nitrogen turnover (nitrogen mineralization or nitrification rates) was exhibited in the rhizosphere of shaded offspring ramets. However, nitrogen turnover was significantly decreased by clonal integration in the rhizosphere of shaded mother ramets. Path analysis indicated that nitrogen turnover in the rhizosphere of shaded, offspring or mother ramets were primarily driven by the response of soil microorganisms to dissolved organic carbon or nitrogen. This unique in-situ experiment provided insights into the mechanism of nutrient recycling mediated by clonal integration. It was suggested that effects of clonal integration on the rhizosphere microbial processes were dependent on direction of photosynthates transport in clonal plant subjected to heterogeneous light conditions.

Genetic structure in dwarf bamboo (Bashania fangiana) clonal populations with different genet ages.

Amplified fragment length polymorphism (AFLP) fingerprints were used to reveal genotypic diversity of dwarf bamboo (Bashania fangiana) clonal populations with two different genet ages (≤30 years versus >70 years) at Wolong National Natural Reserve, Sichuan province, China. We generated AFLP fingerprints for 96 leaf samples, collected at 30 m intervals in the two populations, using ten selective primer pairs. A total of 92 genotypes were identified from the both populations. The mean proportion of distinguishable genotypes (G/N) was 0.9583 (0.9375 to 0.9792) and Simpson's index of diversity (D) was 0.9982 (0.9973 to 0.9991). So, two B. fangiana populations were multiclonal and highly diverse. The largest single clone may occur over a distance of about 30 m. Our results demonstrated that the genotypic diversity and genet density of B. fangiana clonal population did not change significantly (47 versus 45) with genet aging and low partitioned genetic differentiation was between the two populations (Gst = 0.0571). The analysis of molecular variance consistently showed that a large proportion of the genetic variation (87.79%) existed among the individuals within populations, whereas only 12.21% were found among populations. In addition, the high level of genotypic diversity in the two populations implies that the further works were needed to investigate the reasons for the poor seed set in B. fangiana after flowering.

The evolution and utility of ribosomal ITS sequences in Bambusinae and related species: divergence, pseudogenes, and implications for phylogeny.

Ribosomal internal transcribed spacer (ITS) sequences are commonly used for phylogenetic reconstruction because they are highly reiterated as components of rDNA repeats, and hence are often subject to rapid homogenization through concerted evolution. Concerted evolution leads to intragenomic uniformity of repeats even between loci on nonhomologous chromosomes. However, a number of studies have shown that the ITS polymorphism within individuals is quite common. The molecular systematics of Bambusinae and related species were recently assessed by different teams using independently generated ITS sequences, and the results disagreed in some remarkable features. Here we compared the ITS sequences of the members of Bambusa s. l., the genera Dendrocalamus, Dinochloa, Gigantochloa, Guadua, Melocalamus, Monocladus, Oxytenanthera, Thyrsostachys, Pleioblastus, Pseudosasa and Schizostachyum.We have reanalysed the ITS sequences used by different research teams to reveal the underlying patterns of their different results. After excluding the sequences suspected to represent paralogous loci, a phylogenetic analysis of the subtribe Bambusinae species were performed using maximum parsimony and maximum-likelihood methods. The implications of the findings are discussed. The risk of incorporating ITS paralogues in plant evolutionary studies that can distort the phylogenetic signal should caution molecular systematists.

Effects of aqueous extracts of Paeonia decomposita seeds on germination and some metabolic activities associated with growth of wheat seedlings.

Paeonia decomposita is a perennial deciduous shrub with great ornamental and medicinal values. Unfortunately, the distribution region, population size and individual numbers of P. decomposita rapidly decrease in the wild. It is a particularly rare, highly endangered, protective plant endemic to Southwest China. To understand the causes of seed dormancy of P. decomposita, the effects of aqueous extracts of the seed coat, endosperm of P. decomposita on germination, seedling growth and amylases activities of wheat seeds were examined in this paper. The results showed that the seed, especially the endosperm tissue of P. decomposita contained substances that strongly suppressed seed germination. The crude extract of endosperm of P. decomposita, which significantly reduced the activities of α and ß-amylase, showed a more significant inhibition than that of seed coat at the same dose. It was concluded that the presence of inhibitory substances in seed, especially in endosperm tissue, seem to be responsible for P. decomposita seed dormancy.

[Point pattern analysis of Phyllostachys bissetti ramet population in West China Rainy Area].

In this paper, point pattern analysis was conducted to study the spatial distribution of Phyllostachys bissetii ramet population and the spatial association between different age-class P. bissetii ramet populations in West China Rainy Area. The ramet population had a clumped distribution at the scale 0-0.32 m, a regular distribution at the scale 0.64-4.48 m, and a random distribution at the scale > 4.48 m. Different age-class ramet populations mainly had a random distribution at the scale 0-8.00 m, though a slight difference was observed among different age-classes. The spatial association between age-class I and age-classes II and III at the scale 1.76 - 4.16 m and 0.32-4.16 m approached to or reached to negative, respectively, while the spatial association between age-classes I and IV at the scale 0.32-3.04 m was significantly negative, indicating that the spatial negative association between younger and elder ramet populations increased with enlarged age-class difference. The spatial pattern of P. bissetii ramet population and the spatial association between different age-class ramet populations were depended on spatial scale, ramet age, and environmental factors.

[Species diversity of AMF community colonized in herbages roots in calcareous soil and purple soil].

A total of 17 herbages belonging to 12 families were selected as the host plants of arbuscular mycorrhizal fungi (AMF). They were grown on calcareous soil and purple soil, respectively, and sampled on the 120th day after seedling emergence. The DNA of AMF in the herbages roots was extracted by CTAB method, the partial rDNA sequence encoding ribosomal 28S big unit was amplified with special primers U1/U2 for fungi, and the PCR products were analyzed with PAGE silver staining method. In calcareous soil, 29 AMF bands were found in the roots of the 17 host plant species, and each host plant was colonized by 8.29 AMF bands; while in purple soil, only twenty-four AMF bands were found, with 9.47 bands in each host plant. All the AMF bands included unique bands and common bands. Cluster analysis showed that the AMF colonization in host plant roots was family-specific, and affected by soil factors. The feasibility of applying AMF in ecological restoration of limestone area was also discussed in this paper.

[Growth response of Broussonetia papyrifera seedlings to VA mycorrhizal fungi inoculation].

In an experiment with single inoculation (SI) and co-inoculation (CI) of three VA mycorrhizal fungi, i. e., Glomus mosseea (GM), Glomus versiforme (GV) and Glomus diaphanum (GD), the growth response of Broussonetia papyrifera seedlings in limestone area was studied. The results showed that after 3 months of growth, the aboveground-, underground-, and total biomass were increased significantly by the inoculation, being 2.49-8.19 times as much as the control. Treatment CI had the highest biomass, but the leaf number had little difference with the control. In SI, GD inoculation had the greatest effect; and CI was more effective than SI. The ground diameter, height, and total leaf area in CI were 1.5, 2.2, and 6.0 times as much as those in CK, respectively, and the root/shoot ratio in CI was the highest (0.446). There existed an interactive selection between host plants and VA mycorrhizal fungi.

Competition between plasmid-bearing and plasmid-free organisms in the host: population dynamics and antibiotic resistance.

OBJECTIVE: To clarify the effects of antibiotic exposure on bacterial antibiotic resistance. MATERIALS AND METHODS: A competitive population dynamics model for plasmid-bearing organisms and plasmid-free organisms in the host was established. The Poincaré-Bendixson theorem was used for analysis. RESULTS: All possible results of the competition dependent on biologically meaningful parameters were obtained, which can be classified into eight categories. With the outcomes of the plasmid model, we discussed the sterilizing effect if an antibiotic was added to the host. CONCLUSION: When antibiotic-resistant bacteria existed in a host, a higher dosage of antibiotics was needed with an increased risk of survival of plasmid-bearing organisms and greater danger of resistance to antibiotics.