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Concentrations of total nitrogen in squash,cucumber and melon in relation to growth,and to a piper‐steenbjerg effect

Abstract

Squash (Cucurbita pepo), cucumber (Cucranis sativus), and sweet melon (Cucumis dudain) were grown in sand cultures with N supply concentrations as the variable. For several reasons, total‐N values were found to be less satisfactory than NO ‐N for the purpose of determining the critical nitrogen concentration for maximum growth. Concentrations of total‐N in mature petioles were higher in plants severely deficient in N than in less deficient plants, characteristic of a Piper‐Steenbjerg effect.     

“三次论战”与李大钊对马克思主义的捍卫

马克思主义是在与各种非马克思主义反复斗争的过程中发展起来的 ,李大钊在“三次论战”中态度坚决、立场鲜明 ,体现了他对马克思主义的坚决捍卫     

Influence of extreme K:Na ratios and high substrate salinity on plant metabolism of crops differing in salt tolerance

K⁺/Na⁺ and Cl^‐ effects on activity of amylases as well as on their isoenzyme pattern in leaves of bushbeans and sugarbeets at the beginning of salinity stress were investigated, in plants grown in water culture under controlled environmental conditions. Alpha‐ and beta‐amylase activity in beans increased, particularly due to K⁺ and Cl^‐ supplied. In sugarbeets amylase activity remained unchanged as a result of K/Na treatment in combination with Cl and decreased using SO₄ ^2‐ as counterion. A direct correlation of amylase activity to the starch content of both species was not detctable. Particularly α‐but also ß‐amylase was most strongly inhibited by KCl “in vitro”. Independent on their origin, amylases from bushbeans and sugarbeets did not show any differences in ionic inhibition “in vitro”. The isoenzyme pattern of the species was different, but no clear ionic effect was detectable. Amylolytic activity is evidently not a causative factor for restricted starch mobilization in leaves under an early salinity stress. It is suggested that amylases are indirectly involved in starch formation via degradation due to a lack of a carbohydrate sink under salinity stress. Differences in salt tolerance of the investigated crops are obviously not related to different “in vitro” properties of amylases.     

Behavior of iron‐supplying materials in incubated calcareous soils 1

Two Fe chlorosis‐inducing calcareous soils were incubated for up to 5 months, at room temperature and field capacity, with Fe‐EDDHA, Fe‐DTPA, FeSO₄, an amino acid chelate “Fe‐Metalosate”;, an oxide “Micronized‐Iron”;, and a precipitated Fe‐S compound “Iron‐Sul”;. Other treatments included DTPA chelate alone, elemental S and H₂SO₄ at comparable rates. Both water‐soluble, and DTPA‐extractable Fe fractions were measured periodically from each sample. All water‐soluble sources decreased with time. Soluble Fe was highest after Fe‐EDDHA addition but was not detectable after “Fe‐Metalosate”; and FeSO₄. Acidification to neutralize CaCO₃ significantly increased DTPA‐extractable Fe, which remained high with increasing incubation time. “Micronized‐Iron”; and S had only a slight effect on DTPA‐ extractable Fe. Though Fe‐EDDHA is the most efficient Fe material, pelleted acidified Fe sources, i.e., “Iron‐Sul”;, may be more economical for some crops in the long term.     

The Prevalence and Distribution of Fusarium species in Norwegian Cereals: a Survey

In the period 1994–1996 a post-harvest survey was conducted in wheat, barley and oats to assess the occurrence and geographic distribution of Fusarium species in Norwegian cereals. The number of samples investigated was adjusted proportionally to the production of each cereal species within the regions. A total of 695 grain samples were analysed. The amount of Fusarium infection varied with cereal species and region of origin. The most frequently isolated Fusarium spp. from all samples were F. avenaceum, F. poae, F. tricinctum and F. culmorum. Other important toxigenic Fusarium spp. were F. graminearum, “powdery F. poae”, F. equiseti and F. sporotrichioides. A north-south gradient was valid for F. tricinctum, F. poae and in 1994 for “powdery F. poae”. In 1994 “powdery F. poae” was the most abundant potential producer of HT-2 and T-2 toxins in Norwegian cereals. Distribution of F. graminearum and F. culmorum demonstrated in this study, corresponded to previously reported DON-distribution, although DON seems to be produced by different species in different regions. Distribution of the isolated Fusarium species and comparison between cereals and locations are discussed.     

Prophage region and short tandem repeats of “Candidatus Liberibacter asiaticus” reveal significant population structure in China

Whole-genome sequencing of “Candidatus Liberibacter asiaticus” (Las) indicated some polymorphic gene regions enabling the molecular characterization of this bacterium. Although the population diversity of Las in China has been previously studied, no reports have used a combination of a prophage region and short tandem repeat (STR) loci for phylogenetic relationship characterization. In this study, we investigated the genetic diversity and structure of 667 Las strains from nine provinces in southern China using multiple genetic loci including three type-specific prophage loci, two STR loci, and a miniature inverted-repeat transposable element (MITE) region. The results indicated that the genetic diversity varied according to the gene loci used. The prophage regions, including the MITEs, revealed significant genetic differences of Las populations in Yunnan and Guizhou from other provinces, while the STR loci only indicated a difference of Las population in Guizhou from those of other provinces. In particular, the Las population shown to be diverse in Jiangxi at the CLIBASIA_01215_STR locus was not diverse when measured using the other loci. Considering all loci, the Las populations from Yunnan and Guizhou were different, those from Guangdong and Guangxi were complex, while the Las population in Jiangxi was comparatively simple. Las populations from five neighbouring provinces, including Guangdong, Guangxi, Hunan, Fujian, and Jiangxi were grouped in a big cluster. The Las population structure changed with age according to the prophage type. This study evaluated the method used for studying the molecular diversity of Las populations and provided more detailed information on the geographical origin and epidemic trend of Chinese Las populations.     

应用耗散结构理论分析地下水系统演化

地下水系统的演化是在天然或人为因素影响下,以新的宏观状态取代旧的宏观状态的耗散过程。提出基于耗散结构理论研究地下水系统演化机制的新思路。地下水系统是一个复杂的开放系统,其演化过程处于非平衡有序状态且不可逆,与地下水系统相关的各子系统之间的作用是非线性的,强烈的人为因素对地下水系统演变的影响显著。华北平原中部“冀枣衡”深层地下水漏斗是人类活动强烈干扰下地下水系统异常涨落的产物。大规模超量开采地下水导致衡水市地下水动力场、水化学场和含水介质空间结构变异等问题,地下水系统进入人为活动强烈干扰下的新的演化时期。