中美洲原产地鳗鲡苗种对几种生态因子的耐受性研究

初步研究了产自中美洲地区的美洲鳗鲡（Anguilla rostrata）苗种对于温度、pH值、溶解氧、亚硝酸盐、氨氮、光强等生态因子的适宜范围及耐受极限。结果显示：鳗苗适宜水温是20℃～28℃,临界上限和下限分别是38℃及0℃;鳗苗正常活动的溶氧临界值是1.0 mg L-1,半数窒息点为0.7 mg L-1;适宜pH为4～10,耐受的上下限分别为11和3;非离子态氨对鳗苗24、48、72、96h的半致死浓度分别是4.54、4.08、4.08、2.62 mg L-1,安全浓度为0.26 mg L-1;亚硝酸盐对鳗苗24、48、72、96h的半致死浓度分别是92.05、65.81、45.54、37.06 mg L-1,安全浓度为3.71 mg L-1;引起鳗苗不安的光强阈值是5.88 µE/m2/s。     

中美绿色开敞空间体系比较与启示

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Pre-maturity α-amylase in wheat: The role of abscisic acid and gibberellins

The occurrence of pre-maturity α-amylase (PMA) is a major cause of poor bread-making quality (low Hagberg Falling Number) in wheat grain. In susceptible genotypes, it involves the excessive accumulation of high isoelectric point (pI) α-amylase in mature grain prior to germination and in the absence of pre-harvest sprouting. Several factors regulate PMA formation in developing grain, including genotype, agronomy, and environmental conditions. In particular, a cold period during mid-grain development has been found to be a major stimulus for PMA induction. Although the factors affecting the PMA occurrence are well known, little is known about the molecular mechanism governing its induction. The plant hormones abscisic acid (ABA) and gibberellins (GAs) influence various aspects of grain development, and it has been suggested that PMA involves changes in the amount of these hormones or the sensitivity of the grain to these hormones. This review summarizes recent studies investigating the role of ABA and GAs in PMA induction and PMA occurrence.     

Large reservoirs as ecological barriers to downstream movements of Neotropical migratory fish

Most large rivers in South America are fragmented by large dams, and a common management strategy to mitigate impacts has been construction of fish passes. Recent studies, however, indicate that downstream passage of adults and young fish is nil or minimal. Better understanding of this phenomenon is needed if fishways are to provide any tangible conservation value in South America. We propose, in this article, that large reservoirs impose a different kind of barrier to migrating fish: impoundments create a diffuse gradient of hydraulic/limnological conditions that affects fish behaviour and functions as an extensive environmental filter that discourages downstream movements. To develop this idea, we characterize the barriers created by dams and reservoirs by describing their distinct nature, the effects on fish migration and potential solutions. We show, for example, that dams generally prevent upstream movements, whereas reservoirs impede mainly downstream movements. In this context, we explain how fish passes, in some instances, can partially mitigate fragmentation caused by dams, but there is no technical solution to solve the barrier effect of reservoirs. In addition, we present a body of empirical evidence that supports the theory that large reservoirs are important barriers to fish migration in South America, we offer an overview of the size of reservoirs to show that impoundments typically have large dimensions, and we discuss the significance of this theory for other regions. Based on current and proposed river regulation scenarios, we conclude that conservation of Neotropical migratory fish will be much more complicated than previously believed.     

The native South American crayfishes (Crustacea,Parastacidae): state of knowledge and conservation status

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