Acacia angustissima: Its anti-nutrients constituents, toxicity and possible mechanisms to alleviate the toxicity – a short review

In most tropical countries poor nutrition limits ruminant productivity. The main feed resources include native pasture and crop residues, which are low in nitrogen (6.2-10.6 g/kg DM) and high in fibre (676-772 g/kg DM). Nutritional deficiencies of these feeds can be alleviated by supplementation with fodder trees such as Acacia angustissima, which are multipurpose, have outstanding agronomical attributes and are rich in nitrogen (33.2-40.8 g/kg DM). However, feeding A. angustissima without adaptation caused toxicity to sheep. Rats fed diets containing 20% A. angustissima died within 2-5 d. Intake and average daily gain (6.0 and 0.5 g/d) were significantly (P 0.05) reduced in rats fed a diet containing 70% acetone extract compared to the rats fed the control diet (8.8 and 3.1 g/d). Addition of polyethylene glycol (PEG) improved in-vitro gas and ammonia production from A. angustissima leaves (gas, 3.9 to 13.4 ml/100g DM; ammonia, 2.8 to 8.5 mM). PEG also increased DM intake (696 and 860 g /d) in sheep fed A. angustissima. These results suggested that tannin contributed to the negative effects of A. angustissima. Non-protein amino acids (4-N-acetyl-2, 4-diaminobutanoic acid, acetyl diaminopropionic acid, oxalyl diamino butyric, oxalyl diaminopropionic) have also been isolated from A. angustissima leaves. Feeding A. angustissima to sheep by gradually increasing levels in the diet prevented toxicity. Additionally, transfer of rumen contents from adapted to non-adapted sheep prevented toxicity of A. angustissima. These observations suggested that adaptation was at the microbial level. Current work to alleviate the toxicity of A. angustissima is therefore focused on microbial adaptation and detoxification. Tannin-tolerant bacteria have been isolated from sheep adapted to A. angustissima and free-ranging animals. Work on non-protein amino acids is underway. Overcoming the negative effects of the anti-nutritional factors in A. angustissima would not only improve livestock productivity but also result in improvement of the environment. This revised version was published online in June 2006 with corrections to the Cover Date.     

Gold nanoelectrodes of varied size: transition to molecule-like charging

A transition from metal-like double-layer capacitive charging to redox-like charging was observed in electrochemical ensemble Coulomb staircase experiments on solutions of gold nanoparticles of varied core size. The monodisperse gold nanoparticles are stabilized by short-chain alkanethiolate monolayers and have 8 to 38 kilodaltons core mass (1.1 to 1.9 nanometers in diameter). Larger cores display Coulomb staircase responses consistent with double-layer charging of metal-electrolyte interfaces, whereas smaller core nanoparticles exhibit redox chemical character, including a large central gap. The change in behavior is consistent with new near-infrared spectroscopic data showing an emerging gap between the highest occupied and lowest unoccupied orbitals of 0.4 to 0.9 electron volt.     

Primary production of the biosphere: integrating terrestrial and oceanic components

Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.