Optimizing the Irrigation Scheduling Strategy and the Water Use Efficiency in Steppe and Irrigated Crop Production Ecosystems in the Northwestern China

ＩｎｔｒｏｄｕｃｔｉｏｎＳｉｎｃｅｔｈｅｌａｔｅ 1970ｓａｌａｒｇｅｎｕｍｂｅｒｏｆｓｔｕｄｉｅｓｈａｖｅｃｏｎｓｉｄｅｒｅｄｉｒｒｉｇａｔｉｏｎｓｃｈｅｄｕｌｉｎｇｉｎｉｒｒｉｇａｔｉｏｎｍａｎａｇｅｍｅｎｔ[1- 7] ａｎｄｉｔｈａｓｂｅｅｎｓｈｏｗｎｔｈａｔｅｆｆｉｃｉｅｎｔａｎｄ ｐｒｏｆｉｔａｂｌｅｉｒｒｉｇａｔｉｏｎｓｃｈｅｄｕｌｉｎｇｓｔｒａｔｅｇｉｅｓａｒｅｎｅｅｄｅｄ ,ｐａｒｔｉｃｕｌａｒｌｙｗｈｅｒｅｗａｔｅｒａｖａｉｌａｂｌｅｆｏｒｉｒｒｉｇａｔｉｏｎｉｓｌｉｍｉｔｅｄ .Ｉｎｎｏ…     

Modelling of Energy Flow, Rotational Grazing and Potential Productivity in an Alpine Meadow Grazing Ecosystem

An eight-compartment model of the energy dynamics of an alpine meadow-sheep grazing ecosystem was proposed based on SHIYOMI's system approach. The compartments were the above-ground plant portion, the underground live portion including roots, the underground dead portion including roots, the above-ground litter Ⅰ (degradable portion), the above-ground litter Ⅱ (undegradable portion), the sheep intake, the sheep liveweight, and the faeces. Energy flows between the eight compartments were described by eight simultaneous differential equations. All parameters in the model were determined from paddock experiments.The model was designed to provide a practical method for estimating the effects of the number of rotational grazing subplots, grazing period, and grazing pressure on the performance of grazing systems for perennial alpine meadow pasture. The model provides at least 28 different attributes for characterizing the performance of the grazing system. Analyses of 270 simulated rotational grazing systems of summer-autumn meadow pasture (grazing from 1st June to 30 October each year) provided an inference base to support two recommendations concerning management variables. First, with a three-paddock, 29-day grazing period and 30.14kJ·m-2·day-1 grazing pressure scheme, the system has the highest total grazing intake, 4250.44 kJ·m-2, during the grazing season. Secondly, with a three-paddock, 7-day grazing period and 28.89kJ·m-2·day-1 grazing pressure scheme, the accumulated graze is 4073.34kJ*m-2.The potential productivity of the alpine meadow under grazing is defined in this paper as the maximal dry biomass of herbage grazed by the grazing animals over the whole growing season. It has been analysed by applying optimal control theory to the model. The productivity is regarded as the objective function to be maximized through optimization of the time course of the grazing pressure, the control variable. The results show that: (1) under constant grazing pressure, the optimal grazing pressure is f16=25.90kJ·m-2·day-1 (f46=f56=0) with the highest accumulated intake of J(1)=3268.17kJ·m-2; and (2) the optimal grazing pressure is f16=25.94kJ·m-2·day-1 (f46≠0, f56≠0) with the maxial accumulated intake J(145)=3500.39kJ·m-2. Under variable grazing pressure, the dynamics of optimal grazing pressure is shown in Fig.6(a) and Eqs. (9)(11), while the potential productivity (the highest accumulated intake) is J(145)=8749.01kJ·m-2, 2.5 times the constant grazing pressure.     

A natural polymorphism alters odour and DEET sensitivity in an insect odorant receptor

Blood-feeding insects such as mosquitoes are efficient vectors of human infectious diseases because they are strongly attracted by body heat, carbon dioxide and odours produced by their vertebrate hosts. Insect repellents containing DEET (N,N-diethyl-meta-toluamide) are highly effective, but the mechanism by which this chemical wards off biting insects remains controversial despite decades of investigation. DEET seems to act both at close range as a contact chemorepellent, by affecting insect gustatory receptors, and at long range, by affecting the olfactory system. Two opposing mechanisms for the observed behavioural effects of DEET in the gas phase have been proposed: that DEET interferes with the olfactory system to block host odour recognition and that DEET actively repels insects by activating olfactory neurons that elicit avoidance behaviour. Here we show that DEET functions as a modulator of the odour-gated ion channel formed by the insect odorant receptor complex. The functional insect odorant receptor complex consists of a common co-receptor, ORCO (ref. 15) (formerly called OR83B; ref. 16), and one or more variable odorant receptor subunits that confer odour selectivity. DEET acts on this complex to potentiate or inhibit odour-evoked activity or to inhibit odour-evoked suppression of spontaneous activity. This modulation depends on the specific odorant receptor and the concentration and identity of the odour ligand. We identify a single amino-acid polymorphism in the second transmembrane domain of receptor OR59B in a Drosophila melanogaster strain from Brazil that renders OR59B insensitive to inhibition by the odour ligand and modulation by DEET. Our data indicate that natural variation can modify the sensitivity of an odour-specific insect odorant receptor to odour ligands and DEET. Furthermore, they support the hypothesis that DEET acts as a molecular 'confusant' that scrambles the insect odour code, and provide a compelling explanation for the broad-spectrum efficacy of DEET against multiple insect species.