环境内分泌干扰物对睾丸间质细胞功能的影响

近年来,环境内分泌干扰物(environmental endocrine disrupting chemicals,EDCs)对雄性动物的生殖毒性引起了广泛的关注。大量资料显示EDCs可引起雄性生殖发育障碍,如隐睾、尿道下裂、睾丸癌、精液品质不良等。作者就几种典型的EDCs对睾丸间质细胞分泌睾酮的影响机制作一综述。     

Microbial biomass and activity along a natural pH gradient in forest soils in a karst region of the upper Yangtze River,China

Mountain closure, considered an effective and economic measure for natural restoration of degraded forest ecosystems, has been widely carried out in the karst region of southwest China. The aim of this study was to evaluate microbial aspects of soil quality after mountain closure by analyzing soil microbial biomass, basal respiration, metabolic quotient, and relationships with basic chemical properties in Guizhou Province, a karst region of the upper Yangtze River. Soil quality was considered poor from the low levels of microbial biomass carbon (MBC), nitrogen (MBN), and microbial quotient (MBC/total C and MBN/total N), but high metabolic quotient (qCO₂). Soil pH, showing marked variation from 4.1 to 7.9 in this karst region, was proved to significantly affect soil microbial biomass and activity. Soil microbial biomass, microbial quotient, and soil basal respiration declined significantly with decreasing soil pH, while qCO₂ showed an apparently increasing, but not statistically significant, trend. The changes in microbial biomass and activity following the change in soil pH could possibly be because of a change in soil microbial composition, and more detailed research is necessary. Compared with soil pH, soil organic matter content was another, more important, factor that directly restricted microbial growth because of the serious loss as a result of disturbance. As a practical application based on microbial aspects, introduction of some N-fixing tree species may be an active and effective measure to improve soil fertility and thus to accelerate restoration of the forest ecosystem in the karst region.     

Interrelationships between herd management practices and udder health status using canonical correspondence analysis

The relationships between the herd-level distribution of udder health measures (traumatic, physical, functional and congestive udder disorders, clinical mastitis and somatic cell counts (SCC) greater than 400 × 10³, ml⁻¹) and farm (general hygiene, milking practices and housing system) and aggregated individual characteristics were studied by canonical correspondence analysis (CCA). This is a correspondence-analysis technique in which the axes representing disease patterns are expressed as linear combinations of potentially explanatory variables. These main axes can be drawn so that the distribution of diseases for combinations of the main-explanatory managerial variables can be visualized. The type of quarantine for newcomers, type of animal housing, presence of shelter at pasture, use of udder towel before milking, milk production and loss of body condition after calving, were strongly correlated with udder health status. Mastitis and physical udder disorders were associated with the combination of no introduction of replacement heifers and low loss of body condition after calving. Congestive disorders were more common on farms when no quarantine for newcomers was combined with high loss of body condition after calving. Higher clinical and subclinical mastitis incidence risks were associated with the combination of no udder towel, loose housing with high animal density and high milk production. In most cases, clinical mastitis and high SCC were explained by the same covariates but with contrasting levels of those covariates.     

多胺对甜瓜幼苗抗冷性的影响机理研究

本文研究了外源多胺对在低温胁迫下甜瓜幼苗体内DNA、RNA、可溶性蛋白质、超氧物歧化酶(SOD)及细胞质膜透性的影响.结果表明,多胺处理的甜瓜幼苗在低温(2±1℃)下处理10h后,RNA和DNA含量明显增多,蛋白质的图谱发生显著变化,SOD活性增强,细胞膜的破损渗漏较少,尤以0.4mmol的腐胺处理最为显著.多胺与核酸的相互作用调节了植物体内的代谢过程,与膜的相互作用增强了机体的抗冷性.     

向日葵菌核病生防放线菌的分离筛选及拮抗作用的初探

根据微生物间的拮抗作用,试从病地土壤中分离拮抗放线菌,探索利用放线菌对向日葵菌核病进行生物防治的途径。从内蒙古呼和浩特市、巴彦淖尔、包头等地所采集的土壤中分离出38个放线菌菌株,经过平板拮抗作用初测,有8个菌株(F-1、F-3、F-6、F-8、F-11、F-15、F-21、F-25)对向日葵核盘菌(Sclerotinia sclerotiorum)有拮抗作用。选出其中2个作用最明显的菌株(F-6、F-8),观察其在平板对峙培养中对向日葵核盘菌的抑制作用及其代谢产物对向日葵核盘菌的作用。结果表明:F-6、F-8菌株及其代谢产物对向日葵核盘菌均有明显的抑菌作用。同时,对F-6、F-8两菌株的培养性状和形态特征进行了初步观察。     

Stage of development affects penetration of calcium chloride into apple fruits

Using young fruits or fruit segments, rates of penetration of ⁴⁵CaCl₂ across apple fruit cuticles (Malus x domestica) were studied during fruit development in two consecutive years (’?Golden Delicious’ in 2000, ’?Cox Orange Pippin’ and ’?Boskoop’ in 2001). The aqueous donor solutions contained 5 g l^—1 CaCl₂ and 0.2 g l^—1 Glucopon 215 CSUP as wetter. A droplet (5 μl) was applied to each fruit disc and allowed to dry within 1 h. Amounts penetrated were estimated immediately after droplet drying (0 h) and after 6 and 24 h penetration, respectively. Temperature during penetration was 20 ?C and 100 % humidity was maintained throughout the experiment, once the droplet had dried. Rates of penetration were greatly affected by the stage of fruit development. With all varieties tested, highest rates were measured during the early stages of fruit development (before June drop) when approx. 100 % of the CaCl₂ applied penetrated within 24 h. After June drop, when trichomes had vanished and most stomata developed into lenticels, penetration rates decreased rapidly and large variability among the samples developed. This pattern was similar with all three varieties. The involvement of trichomes, stomata, and lenticels as preferential sites of penetration of calcium chloride across the apple fruit cuticles is discussed. Using a model calculation, it is argued that ten or more spray applications are needed to significantly increase calcium contents of apples. This has two causes: Only a small fraction of the spray liquid is intercepted by the fruits, and penetration can be rather slow.     

Organic matter accumulation and fertilizer-induced acidification interact to affect soil microbial and enzyme activity on a long-term sugarcane management experiment

The effects of crop residue management and fertilizer applications on the size and activity of the microbial community and the activity of exocellular enzymes involved in mineralization of C, N, P and S were examined on a long-term (60 years) field trial under sugarcane situated at Mount Edgecombe, South Africa. Treatments at the site included pre-harvest burning with harvest residues removed (B), burning with harvest residues (unburnt tops) left on the soil surface (B_t) and green cane harvesting with retention of a trash blanket (T). Plots were either fertilized annually with N, P and K or unfertilized. The size and activity of the microbial community and the activity of soil enzymes assayed increased with increasing inputs of crop residues (B < B_t < T) and this effect was evident to a depth of 30 cm. The metabolic quotient was decreased by inputs of both crop residues and fertilizers. Annual fertilizer additions did not affect basal respiration, increased fluorescein diacetate (FDA) hydrolysis rate and acid phosphatase, invertase and protease activities and decreased arginine ammonification rate and dehydrogenase, alkaline phosphatase, arylsulphatase and histidase activities. These effects were attributed to an interaction between the positive effect of fertilizer in increasing the size of the microbial biomass and the negative effect of fertilizer-N-induced soil acidification on microbial activity and on the activity of exocellular enzymes. Such results demonstrate the importance of using a range of measurements of microbial and enzyme activity when determining the effects of management on soil microbial and biochemical properties.     

Chemical and biochemical properties in a silty loam soil under conventional and organic management

To improve soil fertility, efforts need to be made to increase soil organic matter content. Conventional farming practice generally leads to a reduction of soil organic matter. This study compared inorganic and organic fertilisers in a crop rotation system over two cultivation cycles: first crop broad bean (Vicia faba L.) and second crop mixed cropped melon-water melon (Cucumis melo-Citrullus vulgaris) under semi-arid conditions. Total organic carbon (TOC), Kjeldahl-N, available-P, microbial biomass C (Cmic), and N (Nmic), soil respiration and enzymatic activities (protease, urease, and alkaline phosphatase) were determined in soils between the fourth and sixth year of management comparison. The metabolic quotient (qCO₂), the Cmic/Nmic ratio, and the Cmic/TOC ratio were also calculated. Organic management resulted in significant increases in TOC and Kjeldahl-N, available-P, soil respiration, microbial biomass, and enzymatic activities compared with those found under conventional management. Crop yield was greater from organic than conventional fertilizer. The qCO₂ showed a progressive increase for both treatments during the study, although qCO₂ was greater with conventional than organic fertilizer. In both treatments, an increase in the Cmic/Nmic ratio from first to second crop cycle was observed, indicating a change in the microbial populations. Biochemical properties were positively correlated (p < 0.01) with TOC and nutrient content. These results indicated that organic management positively affected soil organic matter content, thus improving soil quality and productivity.     

Organic matter status and the size,activity and metabolic diversity of the soil microflora as indicators of the success of rehabilitation of mined sand dunes

The effectiveness of the rehabilitation of mined sand dunes on the northern coast of KwaZulu–Natal, South Africa, was assessed based on measurements of the total and labile organic matter content and the size, activity and metabolic diversity of the soil microflora. Soil was sampled (0–10 cm) after 0, 5, 10, 20 and 25 years of rehabilitation and compared with soil under undisturbed native forest and under long-term commercial pine forest. Following topsoil removal, stockpiling and respreading on reformed dunes, there was a massive loss of organic C such that, at time zero, organic C content was only 24% of that present under native forest. Soil organic C content increased progressively during rehabilitation until, after 25 years, it represented 93% of that present under native forest. The pattern of change in light-fraction C, KMnO₄-extractable C, water-soluble C, microbial biomass C, basal respiration and arginine ammonification rate was broadly similar to that for organic C, but the extent of the initial loss and the magnitude of the subsequent increase differed. Microbial biomass C, water-soluble C and KMnO₄-extractable C, expressed as a percentage of organic C, declined during rehabilitation as humic substances progressively accumulated. Principal component (PC) analysis of catabolic response profiles to 36 substrates revealed that the catabolic diversity of microbial communities differed greatly between native forest, commercial pine forest, 0 years and 10 years of rehabilitation. On the PC1 axis, values for soils under native forest and after 25 years rehabilitation were similar, but there was still separation on the PC2 axis. The main factor explaining variation in response profiles on the PC1 axis was organic C content; and the greatest catabolic diversity occurred in soils under native forest and after 25 years of rehabilitation.     

Responses of microbial biomass and respiration of soil to topography,burning, and nitrogen fertilization in a temperate steppe

Temporal dynamics of microbial biomass and respiration of soil and their responses to topography, burning, N fertilization, and their interactions were determined in a temperate steppe in northern China. Soil microbial indices showed strong temporal variability over the growing season. Soil microbial biomass C (MBC) and N (MBN) were 14.8 and 11.5% greater in the lower than upper slope, respectively. However, the percentage of organic C present as MBC and the percentage of total N present as MBN were 16.9 and 26.2% higher in the upper than lower slope, respectively. Neither microbial respiration (MR) nor metabolic quotient (qCO₂) was affected by topography. Both MBC and MBN were increased by burning, on average, by 29.8 and 14.2% over the growing season, and MR and qCO₂ tended to reduce depending on the sampling date, especially in August. Burning stimulated the percentage of organic C present as MBC and the percentage of total N present as MBN in the upper slope, but did not change these two parameters in the lower slope. No effects of N fertilization on soil microbial indices were observed in the first growing season after the treatment. Further research is needed to study the long-term relationships between changes in soil microbial diversity and activity and plant community in response to burning and N fertilization.