Influence of Reduced Leaching on Growth of Seedlings of Black Locust Inoculated with Rhizobia

Seedlings of black locust (Robinia pseudoacacia L.) were inoculated with compatible rhizobia and irrigated twice each week with solution containing either 50 or 150 mg nitrogen/L. Leaching fraction treatments of 0, 0.2, or 0.4 were maintained for 6 weeks. Seedlings supplied 50 mg nitrogen/L grew poorly compared co planes supplied 150 mg nitrogen/L regardless of leaching fraction. Dry masses of shoots and of entire planes were lower for seedlings in the 0 and 0.2 leaching fraction treatments compared with chose in the 0.4 treatment. Neither leaching fraction nor applied nitrogen concentration appeared co affect the number of nodules per plant, but nodule diameter seemed greater on planes irrigated with the more dilute solution. We conclude that reducing leaching can reduce shoot growth of containerized black locust, but the monetary and environmental benefits of lower water and fertilizer use should be considered before the commercial significance of the growth reduction is judged

At the interface of phylogenetics and population genetics, the phylogeography of Dirca occidentalis (Thymelaeaceae)

Dirca occidentalis is a rare shrub indigenous to only six counties near the San Francisco Bay in California, United States. We used intersimple sequence repeat (ISSR) markers and automated genotyping to probe 29 colonies of D. occidentalis from four geographically disjunct populations (East Bay, North Bay, Salmon Creek, and Peninsula) and used methods of phylogenetics and population genetics to model variation across the species. Results show that the four disjunct populations are genetically isolated and have undergone divergence. Phylogenetic analyses indicate that the East Bay population was the first to diverge, followed by the North Bay, then the Salmon Creek and Peninsula populations. This order of divergence suggests an intriguing natural history for D. occidentalis that is explained by the dynamic geological and climatic history of the Bay Area. Spatial genetic structure detected for the species suggests an interaction of four factors: limited seed dispersal, clonal regeneration, distances traveled by pollinators, and genetic isolation of the four populations. Genetic diversity within the North Bay and Salmon Creek populations is low, indicating poor ecological fitness and risk of decline. ISSRs resolved phylogeographic structure within D. occidentalis, results unattainable with ITS methods, and the integration of tools of phylogenetics and population biology led to an enhanced understanding of this endemic species

A Molecular Dynamics Study of Monomer Melt Properties of Cyanate Ester Monomer Melt Properties

The objective of this work was to computationally predict the melting temperature and melt properties of thermosetting monomers used in aerospace applications. In this study, we applied an existing voids method by Solca. to examine four cyanate ester monomers with a wide range of melting temperatures. Voids were introduced into some simulations by removal of molecules from lattice positions to lower the free-energy barrier to melting to directly simulate the transition from a stable crystal to amorphous solid and capture the melting temperature. We validated model predictions by comparing melting temperature against previously reported literature values. Additionally, the torsion and orientational order parameters were used to examine the monomers’ freedom of motion to investigate structure–property relationships. Ultimately, the voids method provided reasonable estimates of melting temperature while the torsion and order parameter analysis provided insight into sources of the differing melt properties between the thermosetting monomers. As a whole, the results shed light on how freedom of molecular motions in the monomer melt state may affect melting temperature and can be utilized to inspire the development of thermosetting monomers with optimal monomer melt properties for demanding applications