Growth of lucerne (Medicago sativa,L.) in response to frequency of irrigation and gypsum application on a heavy clay soil

Summary Effects of weekly (W) and fortnightly (F) irrigation schedules on established stands of lucerne (Medicago sativa L.) grown on gypsum treated (G) and untreated (C) heavy clay soil were investigated. Two irrigations were applied under the fortnightly regime and four under the weekly schedule during a single cutting cycle. Growth and light interception were measured during both the vegetative and mature phases of growth.Leaf expansion, light interception and dry matter production were greater under treatments W _G and W _C, with yield increasing from 3.4 t ha^–1 under the fortnightly schedule to 5.0 t ha-1 with weekly irrigation. Gypsum treatment was effective under the more frequent irrigation schedule. Specific leaf area and the proportion of stem were both increased by treatments W _G and W _C. The responses to irrigation were therefore characteristic of those elicited by a more favourable plant moisture status. Growth was analysed in terms of light interception, the efficiency of utilisation of intercepted light, the proportion of the daily dry matter gain retained by the leaves and leaf expansion. The analysis demonstrated that impaired leaf expansion contributed to a decline of approximately 15% in yield, and that impaired efficiencies of utilisation of intercepted light contributed to losses of approximately 30% under the less frequent irrigation schedule.A comparison of growth rates and efficiencies of energy conversion with published data showed that satisfactory rates of growth and levels of productivity were achieved on the heavy soils of the local region using gypsum treatment and the more frequent irrigation schedule.     

New insights into the structural characteristics of the arabinogalactan-protein (AGP) fraction of gum arabic

The structural characteristics of the gum exudate of Acacia senegal (gum arabic) have been investigated by monitoring the composition and physicochemical properties before and after treatment with proteolytic enzyme and various alkaline systems. Molecular mass ( M w) and radius of gyration ( R g) measurements were performed using gel permeation chromatography (GPC) coupled to refractive index, UV absorbance, and multiangle light scattering detectors and indicated that the macromolecules present have a compact structure. It was found that treatment with proteolytic enzyme caused the arabinogalactan-protein component (AGP) with average molecular mass approximately 2 x 10 (6) Da to degrade, yielding material of molecular mass approximately 4 x 10 (5) Da, whereas the bulk of the material corresponding to the protein-deficient arabinogalactan component (AG) with molecular mass 4 x 10 (5) remained unaffected. Barium hydroxide was found to hydrolyze the polysaccharide component (AG) itself in addition to the proteinaceous component as demonstrated in control experiments using dextran. However, sodium borohydride/sodium hydroxide treatments were unable to hydrolyze dextran and were assumed to hydrolyze only the proteinaceous component of gum arabic. The AGP component was completely degraded, yielding material of molecular mass approximately 4.5 x 10 (4) Da. It has been concluded, therefore, that the enzyme did not fully hydrolyze all of the protein present and that the AGP component of gum arabic consists of carbohydrate blocks of approximately 4.5 x 10 (4) Da linked to a polypeptide chain consistent with the wattle blossom structure. Because the AGP was degraded to differing extents using a mild and more severe sodium borohydride/sodium hydroxide treatment, it was concluded that the polysaccharide moieties were linked through both O-serine and O-hydroxyproline residues. The gum arabic sample was deglycosylated by treatment with anhydrous hydrogen fluoride and revealed the presence of two putative core proteins of approximately 3 x 10 (4) and approximately 5 x 10 (3) Da, respectively, which correspond to proteins of approximately 250 and 45 amino acids in length. A new model for the structure of the AGP component has been proposed.     

Synthesis of angiotensin I-converting enzyme (ACE)-inhibitory peptides and gamma-aminobutyric acid (GABA) during sourdough fermentation by selected lactic acid bacteria

This article aimed at investigating the synthesis of angiotensin I-converting enzyme (ACE)-inhibitory peptides and gamma-aminobutyric acid (GABA) during sourdough fermentation of white wheat, wholemeal wheat, and rye flours. Sourdough lactic acid bacteria, selected previously for proteinase and peptidase activities toward wheat proteins or for the capacity of synthesizing GABA, were used. The highest ACE-inhibitory activity was found by fermenting flour under semiliquid conditions (dough yield 330) and, especially, by using wholemeal wheat flour. Fourteen peptides, not previously reported as ACE-inhibitory, were identified from the water/salt-soluble extract of wholemeal wheat sourdough (IC 50 0.19-0.54 mg/mL). The major part of the identified peptides contained the well-known antihypertensive epitope VAP. The synthesis of GABA increased when the dough yield was decreased to 160. The highest synthesis of GABA (258.71 mg/kg) was found in wholemeal wheat sourdough.     

Differential and successive effects of residue quality and soil mineral N on water-stable aggregation during crop residue decomposition

Residue quality has been shown to influence soil water-stable aggregation (WSA) during crop residue decomposition, but there is still little information about its interactive effect with soil mineral N availability. The aim of this study was to determine the effect of soil mineral N on WSA during the decomposition of two high-C/N crop residues (wheat straw with C/N = 125.6 and miscanthus straw with C/N = 311.3). The two crop residues were combined with three mineral N addition rates (0, 60, and 120 mg N kg⁻¹ dry soil). Respiration, soil mineral N content, and WSA (expressed as mean-weight diameter, MWD) were measured on several dates during a 56-d incubation. The effect of decomposing crop residues on WSA followed two phases. (i) Between 0 and 7 d, the increase in WSA was related to intrinsic residue quality with higher decomposability of the wheat straw resulting in higher WSA. (ii) Thereafter, and until the end of the experiment, mineral N addition rates had a predominant but negative influence on WSA. In this second phase, the average MWD of residue-treated soils was 0.92, 0.55, and 0.44 mm for the 0, 60 and 120 mg N kg⁻¹ dry soil addition rates, respectively. Mineral N addition which did result in higher crop residue decomposition did not lead to higher WSA. WSA during crop residue decomposition is therefore not simply positively related to the induced microbial activity, and changes in microbial community composition with differential effects on WSA must be involved. The impact of high-C/N crop residues inputs on WSA, initially assumed to be low, could actually be strong and long-lasting in situations with low soil mineral N content.     

Plot-scale manipulations of organic matter inputs to soils correlate with shifts in microbial community composition in a lowland tropical rain forest

Little is known about the organisms responsible for decomposition in terrestrial ecosystems, or how variations in their relative abundance may influence soil carbon (C) cycling. Here, we altered organic matter in situ by manipulating both litter and throughfall inputs to tropical rain forest soils, and then used qPCR and error-corrected bar-coded pyrosequencing to investigate how the resulting changes in soil chemical properties affected microbial community structure. The plot-scale manipulations drove significant changes in microbial community composition: Acidobacteria were present in greater relative abundance in litter removal plots than in double-litter plots, while Alphaproteobacteria were found in higher relative abundance in double-litter and throughfall reduction plots than in control or litter removal plots. In addition, the bacterial:archaeal ratio was higher in double-litter than no-litter plots. The relative abundances of Actinobacteria, Alphaproteobacteria and Gammaproteobacteria were positively correlated with microbial biomass C and nitrogen (N), and soil N and C pools, while acidobacterial relative abundance was negatively correlated with these same factors. Bacterial:archaeal ratios were positively correlated with soil moisture, total soil C and N, extractable ammonium pools, and soil C:N ratios. Additionally, bacterial:archaeal ratios were positively related to the relative abundance of Actinobacteria, Gammaproteobacteria, and Actinobacteria, and negatively correlated to the relative abundance of Nitrospira and Acidobacteria. Together, our results support the copiotrophic/oligotrophic model of soil heterotrophic microbes suggested by Fierer et al. (2007).     

Developmental neuroethology: changes in escape and defensive behavior during growth of the lobster

The changes in relative efficacy of two incompatible behaviors was investigated during growth of the lobster, Homarus americanus. In larval and early juvenile stages, physiological and morphological factors favor use of the escape response over defensive behavior. In large animals, defensive behavior is preferred almost exclusively to escape behavior unless the claws are lost. The interaction of escape and defensive behavior is modified by neural and morphological factors, which are dependent on the stage in the life cycle of the organism.     

Biological bulldozers and the evolution of marine benthic communities

During the Phanerozoic, the diversity of immobile suspension feeders living on the surface of soft substrata (ISOSS) declined significantly. Immobile taxa on hard surfaces and mobile taxa diversified. Extinction rates of ISOSS were significantly greater than in other benthos. These changes in the structure of benthic communities are attributed to increased biological disturbance of the sediment (bioturbation) by diversifying deposit feeders.     

Plant growth-rate dependence of detrital carbon storage in ecosystems

Detrital carbon accumulation accounts for most of an ecosystem's capacity to store organic carbon because the carbon contained as plant detritus exceeds that stored in living plants by about threefold. A comparative analysis of the mass and turnover of detrital carbon in ecosystems demonstrates that these properties are strongly related to the turnover rate of the dominant primary producers and are poorly related to ecosystem primary production. These results contribute to an understanding of the factors that control carbon storage in ecosystems and the role of carbon storage in the global carbon budget.     

Autumn bloom of antarctic pack-ice algae

An autumn bloom of sea-ice algae was observed from February to June of 1992 within the upper 0.4 meter of multiyear ice in the Western Weddell Sea, Antarctica. The bloom was reliant on the freezing of porous areas within the ice that initiated a vertical exchange of nutrient-depleted brine with nutrient-rich seawater. This replenishment of nutrients to the algal community allowed the net production of 1760 milligrams of carbon and 200 milligrams of nitrogen per square meter of ice. The location of this autumn bloom is unlike that of spring blooms previously observed in both polar regions.