Determining the Optimal Sowing Density for a Mixture of Native Plants Used to Revegetate Degraded Ecosystems

No standardized, objective methodology exists for optimizing seeding rates when establishing herbaceous plant cover for pastures, hay fields, ecological restoration, or other revegetation activities. Seeding densities, fertilizer use, season of seeding, and the interaction of these treatments were tested using native plants on degraded sites in northern British Columbia, Canada. A mixture of 20% Achillea millefolium, 20% Carex aenea, 20% Elymus glaucus, 20% Festuca occidentalis, 16% Geum macrophyllum, and 4% Lupinus polyphyllus seed was applied at 0, 375, 750, 1,500, 3,000, and 6,000 pure live seed (PLS) per m² in 2.5 × 2.5–m rototilled test plots, established in the fall and spring, with and without fertilizer. There was no significant difference in plant cover of sown species between fall seeding and spring seeding, and few treatment interactions were identified in the first 2 years after sowing. There was no significant difference in cover between seed densities of 3,000 and 6,000 PLS/m² in the first year, nor among 1,500, 3,000, and 6,000 PLS/m² treatments in the second year. Seed densities as low as 375 PLS/m² produced year 2 plant cover equivalent to that observed at 3,000 PLS/m² in year 1. Plots sown to seed densities less than or equal to 750 PLS/m² generally exhibited an increase (infilling) in plant density from year 1 to year 2, whereas plots sown to seed densities greater than or equal to 1,500 PLS/m² generally exhibited a decrease (density‐dependent mortality) in plant density. These results imply a most efficient sowing density between 750 and 1,500 PLS/m² (corresponding to 190–301 established plants^.m^?2 after two growing seasons). It is suggested that net changes in plant populations observed over a range of sowing densities are a robust and objective means of determining optimal sowing densities for the establishment of herbaceous perennials.     

宁夏生态足迹影响因子的偏最小二乘回归分析

生态足迹分析方法是一种度量区域生态可持续程度的有效方法,偏最小二乘回归法(PLS)能有效解决多元回归分析中变量的多重相关性问题,具有容易操作,相关分析精度高等特点。以宁夏为研究区域,在计算了宁夏2001—2010年人均生态足迹的基础上,应用偏最小二乘回归分析法,对影响宁夏生态足迹的各因子的重要程度进行了分析。通过变量投影重要性分析、特异点分析和预测分析,证明所得偏最小二乘回归模型具有较好的精度。研究结果为:2001—2010年,宁夏人均生态足迹由1.818103793 hm2上升至2.894958909 hm2,生态赤字由1.28352051 hm2上升至2.42316627 hm2,生态承载力由0.53458328 hm2下降至0.47179264 hm2;全区GDP、城镇居民人均生活消费支出、第二产业产值和第一产业产值是影响宁夏生态足迹的显著因子。     

Conformational preferences of helix foldamers of γ‐peptides based on 2‐(aminomethyl)cyclohexanecarboxylic acid

The conformational preferences of helix foldamers having different sizes of the H‐bonded pseudocycles have been studied for di‐ to octa‐γ^2,3‐peptides based on 2‐(aminomethyl)cyclohexanecarboxylic acid (γAmc₆) with a cyclohexyl constraint on the C^α–C^β bond using density functional methods. The helical structures of the γAmc₆ oligopeptides with homochiral configurations are known to be much stable than those with heterochiral configurations in the gas phase and in solution (chloroform and water). In particular, it is found that the (P/M)?2.5₁₄‐helices are most preferred in the gas phase and in chloroform, whereas the (P/M)?2.3₁₂‐helices become most populated in water due to the larger helix dipole moments. As the peptide sequence becomes longer, the helix propensities of 14‐ and 12‐helices are found to increase both in the gas phase and in solution. The γAmc₆ peptides longer than octapeptide are expected to exist as a mixture of 12‐ and 14‐helices with the similar populations in water. The mean backbone torsion angles and helical parameters of the 14‐helix foldamers of γAmc₆ oligopeptides are quite similar to those of 2‐aminocyclohexylacetic acid oligopeptides and γ^2,3,4‐aminobutyric acid tetrapeptide in the solid state, despite the different substituents on the backbone. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 87–95, 2014.     

Design and development of topoisomerase inhibitors using molecular modelling studies

Topoisomerase inhibitors are used as anticancer and antibacterial agents. A series of novel 2,4,6-tri-substituted pyridine derivatives reported as topoisomerase inhibitors were used for quantitative structure–activity relationship (QSAR) study. In order to understand the structural requirement of these topoisomerase inhibitors, a ligand-based pharmacophore and atom-based 3D-QSAR model have been developed. A five-point pharmacophore with one hydrophobic group (H4), four aromatic rings (R5, R6, R7 and R8) was obtained. The pharmacophore hypothesis yielded a 3D-QSAR model with good partial least-square (PLS) statistic results. The training set correlation is characterized by PLS factors (r² = 0.7892, SD = 0.2948, F = 49.9, P = 1.379). The test set correlation is characterized by PLS factors (q² = 0.7776, root mean squared error = 0.2764, Pearson R = 0.8926). The docking study revealed the binding orientations of these inhibitors at active site amino acid residues of topoisomerases enzyme. The results of pharmacophore hypothesis and 3D-QSAR provided the detail structural insights as well as highlighted the important binding features of novel 2,4,6-tri-substituted pyridine derivatives and can be developed as potent topoisomerase inhibitors.

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Open in a separate windowKey structural requirement for topoisomerase activity