Regulation of potential denitrification rates in sediments by microbial-driven elemental coupled metabolisms.

Microbial driven coupled processes between denitrification and methane/sulfur metabolism play a very substantial role in accelerating nitrogen removal in river sediments. Until now, little is known about how element coupling processes alter nitrogen metabolism by the microbial functional communities. The primary objective of this research was to clarify the contributory role of microbial-mediated coupled processes in controlling denitrification. Specifically, the study sought to identify the key bioindicators (or metabolic pathway) for preferably regulating and predicting potential denitrification rate (PDR). Here, a total of 40 sediment samples were collected from the inflow rivers of Chaohu Lake under nitrogen stress. The results revealed the ecological importance of methanogens and sulfate reducing bacteria in the microbial interaction network. Correlations between quantitative or predicted genes showed that the methanogenic gene (mcrA) was synergistic with denitrifying genes, further unraveling that the key role of methanogenesis in denitrification process for facilitating nitrogen removal. The PDR of sediments ranged from 0.03 to 133.21 µg N·g-1·h-1. The study uncovered specific environmental factors (NH4+ and OM) and microbial indicators (nosZ, mcrA, Paracoccus, Thauera, Methanobrevibacter and Desulfomicrobium) as potential contributors to the variations in PDR. Structural Equation Model (SEM) analysis revealed a significant direct effect of NH4+ on PDR, evidenced by a standardized coefficient (λ) of 0.77 (P < 0.001). Additionally, the findings also emphasized the salient role of methanogens (Methanobrevibacter) and methanogenic gene (mcrA) in indicating PDR. The research's aforementioned findings shed light on the substantial consequences of methanogenesis on nitrogen metabolism in coupled processes, enabling improved control of nitrogen pollution in river sediments. This study provided fresh perspectives on the effects of multiple functional taxa on denitrification, and reinforces the significance of coupling processes for nitrogen removal.

Identification of surface polysaccharides in akinetes, heterocysts and vegetative cells of Anabaena cylindrica using fluorescein-labeled lectins.

In response to environmental changes, Anabaena cylindrica differentiate three cell types: vegetative cells for photosynthesis, heterocysts for nitrogen fixation, and akinetes for stress survival. Cell-surface polysaccharides play important roles in cyanobacterial ecophysiology. In this study, specific cell-surface sugars were discovered in heterocysts, akinetes and vegetative cells of A. cylindrica using 20 fluorescein-labeled lectins. Both N-acetylglucosamine-binding lectins WGA and succinylated WGA bound specifically to the vegetative cells. Akinetes bound to three mannose-binding lectins (LCA, PSA, and ConA), and one of the galactose-binding lectins (GSL-I). Heterocyst also bound to ConA. However, the heterocysts in all4388 mutant of Anabaena sp. PCC 7120, in which the putative polysaccharide export protein gene all4388 was disrupted, exhibited diminished binding to ConA. Identification of distinct cell-surface sugar helped us to understand the role of polysaccharide for each cell type. Fluorescence-activated cell sorting may be applicable in isolating each cell type for comparative "omics" studies among the three cell types.

Inorganic and organic nitrogen acquisition by a fern Dicranopteris dichotoma in a subtropical forest in South China.

The fern Dicranopteris dichotoma is an important pioneer species of the understory in Masson pine (Pinus massoniana) forests growing on acidic soils in the subtropical and tropical China. To improve our understanding of the role of D. dichotoma in nitrogen (N) uptake of these forests, a short-term (15)N experiment was conducted at mountain ridge (MR, with low N level) and mountain foot (MF, with high N level). We injected (15)N tracers as (15)NH4, (15)NO3 or (15)N-glycine into the soil surrounding each plant at both MR and MF sites. Three hours after tracer injection, the fern D. dichotoma took up 15NH4+ significantly faster at MF than at MR, but it showed significantly slower uptake of (15)NO3- at MF than at MR. Consequently, (15)NO3- made greater contribution to the total N uptake (50% to the total N uptake) at MR than at MF, but (15)N-glycine only contributed around 11% at both sites. Twenty-four hours after tracer injection, D. dichotoma preferred (15)NH4+ (63%) at MR, whereas it preferred (15)NO3- (47%) at MF. We concluded that the D. dichotoma responds distinctly in its uptake pattern for three available N species over temporal and spatial scales, but mainly relies on inorganic N species in the subtropical forest. This suggests that the fern employs different strategies to acquire available N which depends on N levels and time.

[Content and distribution of active components in cultivated and wild Taxus chinensis var. mairei plants].

Taxus chinensis var. mairei is an endemic and endangered plant species in China. The resources of T. chinensis var. mairei have been excessively exploited due to its anti-cancer potential, accordingly, the extant T. chinensis var. mairei population is decreasing. In this paper, ultrasonic extraction and HPLC were adopted to determine the contents of active components paclitaxel, 7-xylosyltaxol and cephalomannine in cultivated and wild T. chinensis var. mairei plants, with the content distribution of these components in different parts of the plants having grown for different years and at different slope aspects investigated. There existed obvious differences in the contents of these active components between cultivated and wild T. chinensis var. mairei plants. The paclitaxel content in the wild plants was about 0.78 times more than that in the cultivated plants, whereas the 7-xylosyltaxol and cephalomannine contents were slishtly higher in the cultivated plants. The differences in the three active components contents between different parts and tree canopies of the plants were notable, being higher in barks and upper tree canopies. Four-year old plants had comparatively higher contents of paclitaxel, 7-xylosyltaxol and cephalomannine (0.08, 0.91 and 0.32 mg x g(-1), respectively), and the plants growing at sunny slope had higher contents of the three active components, with significant differences in the paclitaxel and 7-xylosyltaxol contents and unapparent difference in the cephalomannine content of the plants at shady slope. It was suggested that the accumulation of the three active components in T. chinensis var. mairei plants were closely related to the sunshine conditions. To appropriately increase the sunshine during the artificial cultivation of T. chinensis var. mairei would be beneficial to the accumulation of the three active components in T. chinensis var. mairei plants.

[Point pattern analysis of different age-class Taxus chinensis var. mairei individuals in mountainous area of southern Anhui Province].

By using O-ring statistics in point pattern analysis and Programita software, this paper studied the spatial distribution patterns and associations of different age-class individuals of Taxus chinensis var. mairei populations at Xianyu and Xiaxiang in the mountainous area of southern Anhui Province. The Xianyu population had a random spatial distribution at the scales from 2 m to 25 m but a clumped distribution at the scales < 2 m, while the Xiaxiang population distributed randomly at all the scales. As for Xianyu population, its individuals of age-class I had a clumped distribution at the scales < 5 m, while the individuals of elder age-classes tended to be non-randomly distributed at more scales than < 5 m, which might be related to the features of population regeneration. With increasingly enlarged age-class differences, the spatial association between younger and elder age-classes individuals turned to be negative, but less spatial association was observed between adjacent age-classes individuals. Such a spatial relationship between different age-classes individuals of T. chinensis was beneficial to the effective use of resources. With the growth of the individuals, T. chinensis population had a transition from clumped to random distribution.

[Effects of copper mine tailings on seed germination and seedling growth of five legumes species].

Through solution culture and soil culture experiments, effects of Tongling copper mine tailings on seed germination and seeding growth of five legumes species were studied in this paper. The results showed that the seeds of five legumes species could germinate in the normal and acidified tailings extracted solution, but germination percentage was lower than that under control. It indicated that tailings extracted solution had inhibition effect on seed germination, however, acidified tailings extracted solution promoted absorbing water of the seeds in early stage. In five amelioration substrates between tailings and soils, the tailings also inhibited seed germination of the five species. No dead seedlings of Glycine max, Phaseolus angularis, P. calacaratus were found within 70 days.

[Studies on the adaptation of five legumes species to copper tailings].

Pot experiments with five legumes were conducted in five different amendment substrates for the reclamation of copper tailings in Tongling, Anhui province. The five tested legumes species are Glycine max, Phaseolus angularis, P. calcaratus, P. radiatus, P. mininus. The results showed that the main factors to restrict growing of the vegetation are poor nutrient and high concentration of Cu. The seeds of the legumes species could germinate, but they germinated later in the substrates with higher proportion of copper tailings than in the substrates with lower proportion of copper tailings. After clipping, G. max, P. angularis, P. calcaratus, P. radiatus were alive all the time, but some of the other two legumes species were dead because of the their non-adaptation to the copper tailings. At the same amendment group, the chlorophyll contents of G. max and P. calcaratus were higher than that of other three experimental species on the 50th day. The height and the biomass of G. max and P. calcaratus were higher than that of other three experimental species on the 70th day too. According to the biological characteristics of the five species during the growth periods about indexes of the seeding survival, chlorophyll content, height and biomass, G. max and P. calcaratus are more adaptive and tolerant than the other legumes and the TA75 amendment approach is the more reasonable for the reclamation of copper tailings.