河南省封邱县低产土壤上小麦黄叶病的发生及防治对策

河南省封邱县位于黄河下游的大冲积扇平原上。小麦是本县主要作物。本文主要根据野外调查结果讨论了小麦生理性黄叶病和土壤性质的关系。低产土壤包括盐土、碱土、风沙土及低肥力的两合土等。 主要论点及结论如下： l、调查了各种土壤上的小麦黄叶病。这种生理上的黄叶病导因于土壤的不良性质。次生盐渍化旱地上的小麦黄叶病是由于土壤中高量的可溶性盐分不但提高了土壤溶液的渗透势，而且损坏了根系的吸收功能，使得其得不到大量营养元素的补充而引起。次生盐渍化水浇地上的小麦黄叶病的原因是和土壤的水盐动态有关，田间高持水量和盐分使小麦根系黑，田间土体构型改变了盐分在土壤中的再分配。县西牛皮碱地区小麦黄叶病的原因是土壤结构、土壤高PH值。土壤结构呈层片状使小麦根系难以深扎、水稳性差，土壤高PH值损害作物的组织和吸收功能。 2、由于土壤的盐渍化，次生盐渍化的发生，由于土壤的水盐动态关系，土壤的微生物性质、土体构型及微地形差异都发生程度不同的黄叶病。本文还从大环境角度分析了次生盐渍化发生的原因是背河洼地边缘种稻引起地下水位抬高，从而导致大范围小麦生态环境条件恶化。 3、由于沙土、低肥力两合土的保水保肥能力较差，使小麦在主要发育期（拔节）产生生理性的黄叶病。 4、本文根据作者自己的调查结果认为，地下水在盐渍化作用中的影响是有条件的，土壤质地、微地形、土体构型、植被和降水蒸发比是重要因素;认为认为不同的土体构型中浅位粘层返盐效果最显著;认为盐渍土壤温度低是小麦黄叶病的重要原因。

Physiological and biochemical microcystin-RR toxicity to the Synechococcus elongatus

Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 mug (.) L-1 significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (F-v/F-m) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article. (C) 2004 Wiley Periodicals, Inc.