Seed traits and rodent community interact to determine seed fate: evidence from both enclosure and field experiments

Animal-mediated seed dispersal is an important ecological process in which a strong mutualism between animals and plants can arise. However, few studies have examined how a community of potential seed dispersers interacts with sympatric seed trees. We employed a series of experiments in the Qinling Mountains in both semi-natural enclosure and the field to assess the interactions among 3 sympatric rodent species and 3 Fagaceae tree seeds. Seed traits all showed similar tannin levels but markedly different physical traits and nutritional contents. We found that seeds with heavy weight, thick coat, and high nutritional contents were less likely to be eaten in situ but more often to be eaten after dispersal or hoarded by rodents. These results support both the handling time hypothesis and the high nutrition hypothesis. Surprisingly, we also found that rodents, maybe, preferred to consume seeds with low levels of crude fiber in situ, and to harvest and hoard those with high levels of crude fiber for later consumption. The sympatric rodent species, Cansumys canus, the largest rodent in our study, harvested and hoarded more Quercus variabilis seeds with high physical and nutritional traits, while Apodemus draco, the smallest rodent, harvested more Q. serrata seeds with low physical and nutritional traits, and Niviventer confucianus harvested and hoarded more Q. aliena seeds with medium physical and nutritional traits. Our study demonstrates that different seed traits play different roles in influencing the seed fate and the shaping of mutualism and predation interactions within a community of rodent species.     

移栽叶龄对水稻氮素吸收利用及~(15)N-肥料去向影响

利用15N示踪技术研究了不同叶龄移栽对水稻产量、氮肥吸收利用及其氮素去向的差异。结果表明,随移栽叶龄推迟,水稻产量显著降低,籽粒与秸秆氮肥吸收量、肥料利用率及其残留量也降低,而氮素损失增加。水稻所吸收的氮素约2/3来源于土壤氮,1/3来源于当季肥料施的氮。肥料利用率为20.8%~25.7%,氮肥残留率为17.9%~32.2%,有42.1%~61.3%的肥料损失。无论哪种叶龄移栽条件下,肥料主要残留在0~20cm土层中。研究表明水稻早栽能增加产量、提高肥料利用率,减少肥料损失,降低氮素对环境的污染。     

太湖和滇池流域保护地蔬菜氮肥去向研究

为了研究化肥氮在保护地土壤-蔬菜系统中的当季利用与损失,在浙江嘉兴和云南昆明15个点位上进行15N田间微区试验。结果表明,保护地莴苣化肥氮当季利用率为8.32%~14.52%,保护地西芹化肥氮当季利用率为6.34%~13.85%,保护地结球生菜化肥氮当季利用率为11.34%。相同土壤、同一种类蔬菜保护地种植中,随着保护地种植年限的增加,蔬菜对化肥氮当季利用率显著降低。莴苣和西芹吸收化肥氮和土壤氮的比例在不同种植年限保护地土壤上差异不显著。当季蔬菜收获后,0～20 cm土层15N丰度和化肥氮残留量显著高于20 cm以下各土层。在保护地莴苣种植系统中,施入土壤中的化肥氮有18.98%～42.5%损失。在保护地西芹种植系统中,有11.7%~18.9%损失。在保护地生菜种植系统中,施入土壤中的化肥氮有16.0%损失。     

干旱区稳定蒸发条件下土壤盐溶质迁移的动态预测

<正> 1.导言土壤盐碱化是世界干旱区共同性的问题,也是人类遇到的最古老的环境问题。近30年来,迫于人口压力和食物需求,许多容易开发的土地均已得到利用,人们正在将注意力转向干旱区。由于干旱区自身的特征,土地开发和盐渍化防治,在强烈蒸发条件下土壤盐溶质浓度目标C(Z,t)及迁移预测已成为近代土壤—水环境研究热点之一,成为中国北     

Pesticide paddy field model (PADDY) for predicting pesticide concentrations in water and soil in paddy fields

To evaluate the fate of pesticides in paddy fields, the pesticide paddy field model (PADDY) has been developed for predicting pesticide concentrations in paddy fields and the run-off amount of pesticides to the aquatic environment. This model focused particularly on granule formulation because these formulations have been used widely as herbicides on paddy fields in Japan. The behavior of pesticides in paddy fields was assessed by considering the main processes on the basis of a compartment system and the mass-balance equations of pesticides in the compartments were derived from kinetic data. The mathematical model, PADDY, was constructed by numerical solution techniques. A method for measuring the pesticide parameters for this model was also developed. To validate the model, a field experiment was carried out on a paddy field and the concentration changes of pesticides in water and soil were measured. These were in reasonably good agreement with those predicted by PADDY. © 1999 Society of Chemical Industry     

农药登记环境影响试验试材使用现状及管理建议

农药环境影响试验数据是开展农药环境风险评估的重要依据,而试验试材又是影响试验数据可靠性的关键因素。农药生态毒理学和环境归趋试验涉及的试材种类繁多,主要包括土壤试材和20多种生物试材,规范化管理难度较大。本文归纳总结了国内外农药环境影响试验准则中对试材的要求,调研了目前国内农药环境影响实验室的试材使用情况,并对试材规范化管理提出了建议。     

气候变化对农药应用风险的影响

全球气候变化的影响已成为世界关注的热点。它不仅影响作物产量,还会影响农药应用风险问题,包括农药使用量、农药环境行为、毒性效应等。我国是农药生产和使用大国,农药应用风险问题受到高度关注。本文结合国内外的相关研究分析了气温升高、降雨变化以及极端天气频发对农药应用的直接影响,气候变化所引起的土地利用变化对农药应用的间接影响,为气候变化下农药应用风险评估和控制提供科学依据和参考。     

Fate of chlorsulfuron in the environment. 1. Laboratory evaluations

The behaviour and fate of chlorsulfuron in aqueous and soil systems were examined in laboratory studies. Aqueous hydrolysis was pH-dependent and followed pseudo-first-order degradation kinetics at 25°C, with faster hydrolysis occurring at pH 5 (half-life 24 days) than at either pH 7 or 9 (half-lives >365 days). Degradation occurred primarily by cleavage of the sulfonylurea bridge to form the major metabolites chlorobenzenesulfonamide (2-chlorobenzenesulfonamide) and triazine amine (4-methoxy-6-methyl-1,3,5-triazin-2-amine). This route is a major degradation pathway in water and soil systems. Aqueous photolysis (corrected for hydrolysis) proceeded much more slowly (half-life 198 days) than aqueous hydrolysis and is not expected to contribute significantly to overall degradation. Hydrolysis in soil thin-layer plates exposed to light (half-life 80 days), however, progressed at a much faster rate than in dark controls (half life 130 days), which suggests that a mechanism other than direct photolysis may have been operative. An aerobic soil metabolism study (25°C) in a Keyport silt loam soil (pH 6·4, 2·8% OM) showed that degradation was rapid (half-life 20 days). Dissipation in an anaerobic sediment/water system (initial pH of water phase 6·7, final pH 7·4) progressed much more slowly (half-life >365 days) than in aerobic soil systems. Major degradation products in aerobic soil included the chlorobenzenesulfonamide and triazine amine as in the aqueous hydrolysis study. Neither of these degradation products exhibited phytotoxicity to a variety of crop and weed species in a glasshouse experiment, and both exhibited an acute toxicological profile similar to that of chlorsulfuron in a battery of standard tests. Demethylation of the 4-methoxy group on the triazine moiety and subsequent cleavage of the triazine ring is another pathway found in both aqueous solution and soils, though different bonds on the triazine amine appear to be cleaved in the two systems. Hydroxylation of the benzenesulfonamide moiety is a minor degradation pathway found in soils. Two soils amended with 0·1 and 1·0 mg kg^-1 chlorsulfuron showed slight stimulation of nitrification. The 1·0 mg kg^-1 concentration of chlorsulfuron resulted in minor stimulation and inhibition of ¹⁴C-cellulose and ¹⁴C-protein degradation, respectively, in the same soils. Batch equilibrium adsorption studies conducted on four soils showed that adsorption was low in this system (K_oc 13–54). Soil thin-layer chromatography of chlorsulfuron (R_f=0·55–0·86) and its major degradation products demonstrated that the chlorobenzenesulfonamide (R_f=0·34–0·68) had slightly less mobility and that the triazine amine (R_f=0·035–0·40) was much less mobile than chlorsulfuron. In an aged column leaching study, subsamples of a Fallsington sandy loam (pH_water 5·6, OM 1·4%) or a Flanagan silt loam (pH_water 6·4, OM 4·0%) were treated with chlorsulfuron, aged moist for 30 days in a glasshouse and then placed upon a prewet column of the same soil type prior to initiation of leaching. This treatment resulted in the retention of much more total radioactivity (including degradation products) than by a prewet column, where initiation of leaching began immediately after chlorsulfuron application, without aging (primarily chlorsulfuron parent). © 1998 SCI     

机无机肥料配施对棉田氮素去向影响的研究

在等N、P、K条件下．应用^15N示踪的方法研究了盆栽条件下不同肥料结构对棉花的生物学效应及N素去向的影响。所得主要结果如下：(1)与单施化肥相比，绿肥 沼肥 化肥配施有利于N向生殖器官转移．增产效果较好．绿肥 化肥配施效果次之。(2)有机无机配施吸收的土壤N和肥料N明显大于单施化肥。棉株生育前期对土壤N的依赖性较高，后期对肥料N的依赖性较高，不同时期施N对各器官的贡献率也说明重施化肥做花铃肥的重要性。(3)有机无机肥配施肥料N在土壤中的残留量为单施化肥的1．57～3．31倍．而损失量后者为前者的1．21～2．57倍，其生态效益十分明显。