Biomass allocation strategies and Pb-enrichment characteristics of six dwarf bamboos under soil Pb stress.

Dwarf bamboos are clonal plants with potential applications in the remediation of heavy metal-polluted soils, although their pollution adaptation strategies are unknown. This study examined the biomass allocation strategies and lead (Pb) enrichment characteristics of various dwarf bamboo tissues by the end of the growing season and explored their potential for phytoremediation of Pb stress in the soils. Six dwarf bamboo genotypes were treated with three levels (0, 300, and 1500 mg kg-1) of soil Pb stress. The majority of the bamboos adopted two biomass allocation strategies to adapt to Pb stress, namely, "reducing biomass allocation into new bamboo growth" and "increasing/stabilizing biomass allocation into rhizomes". Pb accumulation was highest in the roots, rhizomes, and old stems and showed the following trend: rhizomes/old stems> new roots/old roots> old leaves> new leaves> new stems among various tissues. Moreover, the six bamboos used three different Pb-enrichment strategies, as follows: (i) "rhizome domination and old stem synergy" (Sasaella glabra (Nakai) f. albo-striata Muroi, Sasa auricoma (Mitford) E.G. Camus, Sasa fortunei (Van Houtte) Fiori, and Shibataea lanceifolia C.H. Hu); (ii) "old stem domination and rhizome synergy" (Indocalamus decorus Q.H. Dai); and (iii) "old stem domination and new root synergy" (Sasa argenteostriata (Regel) E.G. Camus). In Pb-contaminated soils, genotypes with TFs greater than 1 were Sasa fortunei (Van Houtte) Fiori, Sasa argenteostriata (Regel) E.G. Camus, and Indocalamus decorus Q.H. Dai; in addition, only S. argenteostriata had BCF values greater than 1. Furthermore, this study provides the first evidence that S. argenteostriata can extract 0.22 and 0.58 mgplant-1 of Pb ions in soil polluted with 300 and 1500 mg kg-1 Pb, respectively. S. argenteostriata showed the greatest potential for phytoremediation among the bamboo genotypes in both Pb-contaminated urban and mining sites.

EDTA-facilitated toxic tolerance, absorption and translocation and phytoremediation of lead by dwarf bamboos.

Bamboos are considered as potential plants for phytoremediation. However, the mechanisms of EDTA-assisted bamboo for lead (Pb) control has not been described. The objective of this study was to examine the tolerance and behaviors of Pb to screen bamboos for Pb-contaminated soil and to explore the effects of EDTA on their phytoremediation. In this regard, five dwarf bamboos were treated with various doses Pb (0-1500 mg kg-1) and/or EDTA (500 or 250-1000 mg kg-1) to investigate antioxidant systems and Pb accumulation/species. Our findings showed that different doses of Pb significantly affect lipid peroxidation and antioxidant compounds in studied bamboos. EDTA increased the absorption of soil Pb2+ in all tissues with increasing Pb doses, while the Pb concentrations in all bamboo roots was higher than those in other tissues. Among these plants, Arundinaria argenteostriata (AA) and A. fortunei (AF) showed greater oxidative tolerance than other bamboos. Moreover, Pb accumulation showed the highest values in AA and AF plants relative to other bamboos. With increasing EDTA doses, levels of reducible and residual Pb decreased but the weak acid-soluble and total Pb increased in Pb-stressed AA/AF soils. Similarly, EDTA increased Pb2+ concentration in both bamboo tissues, while the Pb2+ level in leaves was higher than that in other organs at the highest EDTA dose. This study provides the first comprehensive evidence regarding EDTA enhancing the availability, absorption, and translocation of Pb in bamboo/soil, suggesting the application of EDTA may be an effective strategy for phytoremediation with two Arundinaria bamboos in Pb-contaminated soils.

The shifting pattern of CO2 source sink in a subtropical urbanizing lightly eutrophic lake.

Globally, numerous freshwater lakes exist, and rapid urbanization has impacted carbon biogeochemical cycling at the interface where water meets air in these bodies. However, there is still a limited understanding of CO2 absorption/emission in eutrophic urbanizing lakes. This study therefore involved biweekly in-situ monitoring to evaluate fluctuations in the partial pressure (pCO2) and flux (fCO2) of CO2 and associated parameters from January to September 2020 (7:00-17:00 CST) in an urbanizing lake in southwestern China. Our study revealed that during the daylight hours of the 11 sampling days, both pCO2 and fCO2 consistently demonstrated decreasing trends from the early morning period to the late afternoon period, with notable increases on May 7th and August 15th, respectively. Interestingly, unlike our previous findings, an nonsignificant difference (p > 0.05) in mean pCO2 and fCO2 was observed between the morning period and the afternoon period (n = 22). Furthermore, the mean pCO2 in January (~105 µatm; n = 4) and April (133-212 µatm; n = 8) was below the typical atmospheric CO2 level (C-sink), while that in the other months surpassed 410 µatm (C-source), although the average values (n = 44) of pCO2 and fCO2 were 960 ± 841 µatm and 57 ± 85 mmol m-2 h-1, respectively. Moreover, the pCO2 concentration was significantly greater in summer (May to August, locally reaching 1087 µatm) than in spring (January to April at 112 µatm), indicating a seasonal shift between the C-sink (spring) and the C-source (summer). In addition, a significant positive correlation in pCO2/fCO2 with chlorophyll-a/nitrate but a negative correlation in dissolved oxygen and total phosphorus were recorded, suggesting that photosynthesis and respiration were identified as the main drivers of CO2 absorption/emissions, while changes in nitrate and phosphorus may be attributed to urbanization. Overall, our investigations indicated that this lightly eutrophic lake demonstrated a distinct shifting pattern of CO2 source-sink variability at daily and seasonal scales.

Influence of the size of clonal fragment on the nitrogen turnover processes in a bamboo ecosystem.

Different sizes of clonal fragments contain various number of ramets with different spacer lengths, which strongly affects the redistribution of photosynthetic assimilates. Although clonal integration significantly affects rhizosphere processes via microbial enzymes under heterogeneous conditions, the effects of clonal fragment size (ramet number and spacer length) on rhizosphere N turnover processes remain poorly understood. Here, we sampled clonal fragments of Phyllostachys bissetii with different ramet numbers and spacer lengths to determine the relative effects of clonal integration and fragment size on rhizosphere processes and resource availability. We found that clonal integration had positive effects on the C and N availability of shaded ramets in clonal fragments with different ramet numbers, owing to the large resource storage in the fragment. However, it only promoted the dissolved organic carbon of the shaded ramets in clonal fragments with different spacer lengths. Results of regression analyses indicated that the response ratios of the soil variables of the shaded ramets first increased when the spacer length was about less than 30 cm and then decreased when the spacer became longer (about >30 cm), suggesting a cost-benefit tradeoff in the fragment. The contribution of the size of clonal fragment to the soil N turnover process was higher than that of clonal integration, whereas its contribution to soil C availability had the opposite effect. These results further revealed the mechanism of the size of clonal fragment in affecting the rhizosphere processes of stressed ramets, which is critical for the adaptation of P. bissetii to stressed habitats and further bamboo ecosystem N turnover under climate change.

The key to improving the beauty of the giant retaining wall in valleys: Increasing visual extension.

The retaining wall is a passive engineering measure to prevent and control unsafe factors caused by rock collapse in the valleys. Existing studies have mainly focused on its functional robustness and safety features, with few exploring its visual quality in the landscape. A multiple regression analysis was applied to evaluate the Scenic Beauty Estimation (SBE) of the giant retaining wall in Jiuzhaigou's (a world natural heritage site) Heye Village, then the factors affecting SBE were analyzed. It is found that enhancing the sense of perspective and spatial hierarchy of retaining-wall murals in narrow roads contributes to the extension of observers' sight, which is the key to improving SBE. Furthermore, the showcase of folk culture in murals can realize the beautification function of the giant retaining walls. In addition, the SBE of giant retaining walls is also linked to coordination, where the walls embellished with the natural landscape and folk culture murals have better SBE performance than those with local stones. This study provides a reference for constructing scenic beauty after fulfilling the safety function of retaining wall engineering.

Population structure and phylogeography of three closely related tree peonies.

Paeonia decomposita, Paeonia rotundiloba, and Paeonia rockii are three closely related species of Sect. Moutan is distributed in the montane area of the Eastern Hengduan Mountain region. Understanding the population history of these three tree peony species could contribute to unraveling the evolutionary patterns of undergrowth species in this hotspot area. We used one nuclear DNA marker (internal transcribed spacer region, ITS) and two chloroplast DNA markers (matK, ycf1) to reconstruct the phylogeographic pattern of the populations. In total, 228 individuals from 17 populations of the three species were analyzed in this study. Three nuclear clades (Clade I - Clade III) and four maternal clades (Clade A - Clade D) were reconstructed. Molecular dating suggested that young lineages diverged during the late Pliocene and early Pleistocene, younger than the uplift of the Hengduan Mountains but older than the last glacial maximum (LGM). Significant population and phylogeographic structures were detected at both markers. Furthermore, the populations of these tree peonies were overall at equilibrium during the climatic oscillations of the Pleistocene. The simulated palaeoranges of the three species during the LGM period mostly overlapped, which could have led to cross-breeding events. We propose an evolutionary scenario in which mountain orogenesis around the Hengduan Mountain area triggered parapatric isolation between maternal lineages of tree peonies. Subsequent climatic fluctuations drove migration and range recontact of these populations along the valleys. This detailed evolutionary history provides new insights into the phylogeographic pattern of species from mountain-valley systems.

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.

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.

Differentiating Thamnocalamus Munro from Fargesia Franchet emend. Yi (Bambusoideae, Poaceae): novel evidence from morphological and neural-network analyses.

Fargesia Franchet emend. Yi is closely allied with Thamnocalamus Munro but differs in many major morphological characteristics. Based on traditional morphological characters, it is difficult to differentiate these two genera. The current study measured 19 species in these two genera to determine whether variations in 12 categories of major characters are continuous. In addition, a self-organizing map (SOM) and cluster analysis were used together to reveal whether the known species of Fargesia represent discontinuous sampling of Thamnocalamus. The results show that 46 morphological characteristics exhibited high variation at the generic and species levels. In addition, the cluster analysis showed that 32 morphological characteristics of Thamnocalamus and Fargesia were divided between two species and well separated from the outgroup. Additionally, significant differences (P < 0.01) were observed in the reproductive structures between these two genera. The unrooted dendrogram, which was based on the SOM neural network, shows the same results as the cluster analysis of morphological characteristics. These data indicate that Fargesia is not a result of discontinuous sampling of Thamnocalamus; thus, Fargesia should not be treated as a synonym for Thamnocalamus.

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.

[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.

[Relationship between plant community succession and fertility variation of mountain yellow soil in east Chongqing].

Based on the analyses of soil physical and chemical properties, this paper studied the relationship between plant community succession and fertility variation of mountain yellow soil in east Chongqing. The results showed that the values of integrated soil fertility index of Pinus massoniana, Cunninghamia lanceolata, deciduous oak, Camellia sinensis and evergreen broad-leaved forest soils were 0.1256, 0.2085, 0.3514, 0.2479 and 0.9329, respectively, implying that soil development had a close relation to plant community succession.

[A comparative study on life-form spectra of evergreen broad-leaved forest in different successions in Jinyun Mountain].

The life-form of plant communities in different succession stages in Jinyun Mountain was studied and the life-form spectrum was established. The results showed that according to the characters of life-form of plant communities, the vegetation in Jinyun Mountain belonged to typical subtropical evergreen broad-leaved forest vegetation. Evergreen phaenerophytes were absolutely dominant in the life-form spectrum and its quantity accounted for more than 80%. Among phaenerophyte, quantity of microphanerophyte was the most, and quantities of mesophanerophtye and nanophanerophyte were less. Different successions had different life-form spectra. With the development of succession, the percentage of phaenerophytes increased, and other life-forms decreased correspondingly. According to the development of life-form and comparative analysis of environmental factors in different succession stages, coniferous species would be replaced by evergreen phaenerophytes.