L-cysteine Stimulates Selenite Uptake through GSH Involving in Selenite Reduction in Rice Roots

The effect of L-cysteine on selenite uptake rate in rice roots was investigated in this study. The results indicated that L-cysteine stimulated selenite uptake significantly, but D-cysteine had no effect on selenite uptake. Selenite uptake increased significantly when the roots were exposed to the L-cysteine solution following a cleanup of the adsorbed L-cysteine on the root surface. Exogenous reduced glutathione stimulated selenite uptake significantly, but oxidized glutathione had no effect on selenite uptake. Split-root experiments showed that exogenous L-cysteine and reduced glutathione applied to one-half of the root system induced selenite uptake by the untreated half. Furthermore, reduced glutathione concentration in rice roots was increased or reduced significantly when exposed to L-cysteine or selenite solution, respectively. A correlation analysis revealed selenite uptake rate was positively correlated with reduced glutathione concentration in rice roots but not in rice leaves. L-cysteine stimulates selenite uptake through reduced glutathione involving in selenite reduction in rice roots.     

氧化还原条件对土壤磷素固定与释放的影响

为探讨水稻土由氧化环境转为还原条件时对土壤磷素固定与释放的影响,选择18种水稻土样品进行室内模拟实验,通过测定不同条件下磷的等温吸附曲线和采用氧化铁试纸测定法进行多次提取以对比淹水前后土壤磷的累计解吸量,发现大部分供试样品的固磷能力在淹水条件下有了显著的提高,全部样品在淹水后磷的释放量都有不同程度的减少。进一步的研究表明淹水条件下土壤对磷的固定与释放的变化主要与淹水后土壤Eh的降低和pH的升高而导致的大量无定形铁的形成有关。     

Reduced glutathione decreases energy expenditure in chicks exposed to separation stress

Recently, we reported that intracerebroventricular (i.c.v.) injection of reduced glutathione (GSH) induces hypnotic and sedative effects under an acute stressful condition in chicks. However, no information is available on the effects of GSH on energy expenditure (EE) under stressful conditions. The purpose of the present study was to clarify whether i.c.v. injection of GSH affects EE of neonatal chicks, and whether EE is correlated with behavioral changes after isolation-induced stress. The EE was rapidly decreased by i.c.v. injection of GSH, but was increased 27 min after injection. This change in EE was correlated with behavioral changes in which GSH induced hypnotic and sedative effects shortly after injection, followed by a period in which activity increased. The present study demonstrates that central GSH initially causes lowered EE through hypnotic and sedative effects under an acute stressful condition in chicks.     

河流水环境容量的估算和分配研究

在水污染物综合降解系数率定、分析和验证的基础上,估算不同设计条件下曹娥江上游主要支流的水环境容量,并给出了综合体现社会性、经济性和历史性的水环境容量分配方案。结果表明,河流中CODMn和NH4^＋-N的综合降解系数受到水温和流量的影响,而具有显著的时间变异性,变异范围分别为0.078～0.29/d和0.087～0.3/d,其中以冬季枯水期（11月,10月,12月,1月）的值最小。不同设计条件下,CODMn和NH4＋-N全年水环境容量分别为139.74～633.80 t和56.47～151.09 t。通过增加设计流量、降低水质目标、采用段末控制的方法均能不同程度地增加河流水环境容量,但加大污染治理力度、削减流域内各业的排污量,才是提高河流水质的根本方法。为保证社会、经济、水环境的协调发展,河段沿岸的部分排污企业需削减当前CODMn排放量的27.5%～70.5%,所有NH4＋-N排污企业需削减当前NH＋4-N排放量的12.6%～70%。这样的分配结果不但具有实际的可操作性,而且有利于促进排污权交易市场的形成。     

Reduced tillage in temperate organic farming: implications for crop management and forage production

To promote conservation tillage in organic farming systems, weed control and ley removal within arable-ley rotations need to be optimized. A long-term field trial was thus established in Frick, Switzerland in 2002 on a clayey soil and with a mean precipitation of 1000 mm/year. The tillage experiment distinguished between conventional tillage with mouldboard ploughing (CT, 15 cm depth) and reduced tillage (RT), including a chisel plough (15 cm) and a stubble cleaner (5 cm). Results of a 2-year grass-clover ley (2006/2007) and silage maize (2008) are presented. Due to dry conditions, mean grass-clover yields were 25% higher in RT than in CT, indicating better water retention of RT soils. Clover cover and mineral contents of the fodder mixture were also higher in RT. The ley was successfully removed in autumn 2007 in RT plots, and a winter pea catch crop was sown before maize. In CT, ploughing took place in spring 2008. Maize yields were 34% higher in RT than in CT, despite a two- to three-fold higher but still tolerable weed infestation. Maize in RT plots benefited from an additional 61.5 kg of easily decomposable organic N/ha incorporated into the soil via the pea mulch. Measurement of arbuscular mycorrhizal colonization of maize roots indicated a similar mechanical disturbance of the topsoil through the reduced ley removal system compared with ploughing. It is suggested that RT is applicable in organic farming, even in arable-ley rotations, but long-term effects need further assessment.     

干湿交替对半干旱地区一些铅盐污染土壤中铅再分配的影响

Mobility and bioavailability of lead (Pb) could be affected considerably by soil physicochemical properties;however,less is known about the effect of Pb levels and aging time.This study was conducted to evaluate the effects of Pb levels and wetting-drying (WD) cycles on distribution and bioavailability of Pb in three semi-arid zone soils treated with different levels of Pb(NO 3) 2.Wetting-drying cycles simulated the actual field irrigation in the semi-arid soils.A soil with a long history of Pb contamination was also taken as a reference soil.The soils were spiked with various levels of Pb and incubated under WD cycles for 160 d.Sequential extractions and batch sorption experiments were performed to assess the fractionation of Pb in the spiked soils.Redistribution index (U ts) and reduced partitioning parameter (I R) were applied to semi-quantify the distribution of Pb in the spiked soils.A small amount of Pb sorbed was desorbed by the soils,indicating a strong and irreversible binding of Pb in the studied soils.Contribution of carbonate-bound (Car) and residual (Res) Pb fractions to the total Pb of the soils was more than 97%.The Car,soluble plus exchangeable (SE),and organic matter-bound (OMB) fractions of Pb were transferred to the Res fraction under the WD cycles.The I R and U ts values were influenced by Pb loading levels and WD;therefore,the Pb lability and/or redistribution pattern could semi-quantitatively be assessed via these parameters.At the end of the experiment,the I R and U ts values for the Pb salt-spiked soils did not show the quasi-equilibrium state.The lability of Pb in the soils decreased with increasing incubation time and showed a strong dependence on Pb levels and soil chemical composition.WD cycles significantly affected the overall lability of Pb in soils through influencing the redistribution of Pb among solid-phase components.     

肥料减施下玉米-大豆间作对作物产量和昆虫群落组成及多样性的影响

为探究肥料减施下玉米-大豆间作对作物产量和昆虫群落组成及多样性的影响,在玉米、大豆单作及二者间作下施以标准肥料750 kg/hm~2和减半肥料375 kg/hm~2,于作物生长期调查田间昆虫群落组成及多样性,并在收获期对玉米和大豆进行测产。结果表明:与单作玉米相比,间作玉米在施用标准肥料下的百株生物量、百株籽粒重和千粒重分别显著增加78.33%、85.35%和38.71%,而在施用减半肥料下则分别显著增加90.91%、135.73%和33.33%;相同种植模式下,与施用标准肥料相比,减半肥料使单作玉米百株籽粒重显著降低22.45%。与单作大豆相比,在施用标准肥料下,间作大豆的百株籽粒重和千粒重分别显著降低49.47%和11.54%,在施用减半肥料下,间作大豆的百株生物量、百株籽粒重和千粒重分别显著降低73.94%、50.51%和17.39%;相同种植模式下,与施用标准肥料相比,减半肥料使大豆在单作和间作下的百株籽粒重分别显著降低65.02%和65.73%,使间作下大豆的百株生物量和千粒重分别显著降低73.14%和17.39%。与单作相比,间作均显著降低了标准肥料和减半肥料处理下玉米和大豆害虫群落的物种数、多样性指数和均匀度指数,还显著降低了标准肥料和减半肥料处理下玉米天敌昆虫群落的物种数和优势度指数以及大豆天敌昆虫群落的物种数和均匀度指数。表明玉米-大豆间作能有效提高玉米产量,降低虫害发生,但对大豆生产不利,而间作条件下减施肥料对玉米产量的影响更小。建议在田间生产中可将夏玉米和大豆间作种植,更有利于通过生态学方法控制田间害虫发生和增加作物总体产量。