No abstract

We used a long-term fire experiment in south-east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soilstored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 1971-1972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil-stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 3-7.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil-stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.

In this study, hydrogels based on acetylated galactoglucomannan (AcGGM)-a hemicellulose present in softwood-were synthesized and examined for their properties in drug-release systems using two model substances of different molecular weight, size, and polarity (caffeine and vitasyn blue). Neutral hydrogels were produced from functionalized AcGGM using hydroxyethyl methacrylate (HEMA) coupled via carbonyldiimidazole (CDI) and a co-monomer in a radical-initiated polymerization. Through a second modification reaction between the HEMA-modified AcGGM (M-AcGGM-methacrylated AcGGM) and maleic anhydride, a ''double-modified'' AcGGM (CM-AcGGM-carboxylated M-AcGGM) was successfully formed that could be cross-linked to form ionic hydrogels by the very same polymerization method. The neutral hydrogels showed drug release kinetics that could be easily regulated by changing the relative amount of the methacrylated AcGGM and its corresponding degree of methacrylation. The drug release rate and the Fickian swelling decreased with an increase in these two aforementioned parameters. The ionic hydrogels showed quicker release kinetics and higher swelling capabilities than the corresponding nonionic gels did, especially at neutral conditions. Under acidic conditions, the release speed was lowered as expected because of protonation of carboxylic functionalities. Based on the findings we conclude that these novel hemicellulose-containing hydrogels have future prospects in drug release formulations, e.g., in a later stage of development for application in oral drug administration technology.

No abstract

No abstract

No abstract

No abstract

No abstract