Ecological thresholds of Suaeda salsa to the environmental gradients of water table depth and soil salinity

The responses of Suaeda salsa to the environmental gradients of water table depth and soil salinity in the Yellow River Delta, China were analyzed from the aspect of ecological thresholds which were developed from the Gaussian model. Based on the correlation analysis of population biomass, density, height, coverage and abundance of Suaeda salsa, population biomass was selected as the population index for further analysis. The results indicated that the optimum water table depth for the growth of Suaeda salsa was about −0.42 m, the ecological thresholds were from −0.92 m to 0.08 m, and the optimum ecological thresholds were from −0.67 m to −0.17 m. To the soil salinity gradient, the optimum was about 12.71 g/kg, the ecological thresholds were from 5.17 g/kg to 20.25 g/kg, and the optimum ecological thresholds were from 8.94 g/kg to 16.48 g/kg. However, the effect of water-salinity interaction seemed to be important to the growth of Suaeda salsa, which was discussed through analyzing the water table depth-soil salinity relationship and their interactions. By using Ward cluster analysis and Gamma distances, 69 sampling sites were classified into 7 kinds of Suaeda salsa communities. It was found that there was a remarkable response of the community structure of Suaeda salsa to the water table depth and soil salinity gradients, which can be a switchover from xeromorphic and saline-alkali plants to limnophytes, and vice versa.     

黄河口岔尖岛、大口河岛和望子岛潮间带秋季大型底栖动物生态学调查

2005年11月(秋季)对位于黄河口的岔尖岛、大口河岛和望子岛三岛的高、中、低潮带(岔尖岛:C1、C2、C3;大口河岛D1、D2、D3;望子岛W1、W2、W3)所设的9个采样站进行大型底栖动物调查,分析所获得的样品.结果表明,本次秋季调查共采到大型底栖动物34种,其中多毛类种类最多,13种,软体动物11种,甲壳动物8种,其他类群2种;大型底栖动物总平均栖息密度为164 ind./m2,总平均生物量为61.12 g/m2;9个采样站底栖生物的种类组成和数量特征有较大差异,其中物种数最高的为D3站,最低的为C1站.黄河口潮间带大型底栖动物生态特征主要受底质、潮汐、季节和人为干扰等因素的影响.     

小麦黄色素合成途径中Psy基因的克隆及分子特性

对普通小麦(Ttiticum aestivum)黄色素(YP)合成途径中的首要限速酶——八氢番茄红素合成酶(Psy)基因进行克隆和测序,并和玉米Psy基因进行序列比对。结果表明,在高和低YP含量小麦品种中均扩增出一条长1192bp的Psy基因片段,该片段包含一条可编码78个氨基酸的小麦Psy基因的外显子,与玉米Psy基因第4外显子的核苷酸序列同源率为80.74,同源区域内有47个SNPs,但仅11个SNPs导致氨基酸编码序列的改变,二者氨基酸序列的同源率达85.89,推测Psy基因在不同物种中的表达具有较高的保守性。BLAST聚类分析表明,禾谷类植物Psy基因的分类与物种的亲缘关系存在明显的相关性,小麦Psy基因在系统进化中比禾谷类其他植物更为高级。     

How do food quality and larval crowding affect performance of the autumnal moth,Epirrita autumnata?

Outbreak densities of autumnal moth, Epirrita autumnata (Borkhausen) (Lepidoptera: Geometridae), lead to high larval crowding. Phenotypic responses of E. autumnata to larval crowding and to food quality were studied by measuring growth and consumption as well as pupal weight and fecundity. Crowding may trigger increased consumption and faster development to avoid impending food shortage on good quality food. This is suggested by the result that on a good‐quality diet, the growth of crowded larvae was better than that of solitary larvae, though they did not consume more food than solitary larvae. Crowded larvae also completed the last instar earlier than solitary larvae. The fecundity of crowded autumnal moths was not lower than the fecundity of solitarily grown autumnal moths. This may provide conditions for extra rapid population build‐up of E. autumnata. During the population increase phase the crowding effect may facilitate larval performance; however, at peak density the crowding starts to have negative effects on the performance of larvae. On a poor‐quality diet, the performance of crowded and solitary larvae did not differ. The growth of larvae was better on a good‐quality diet than on a poor‐quality diet, due to higher efficiency in food utilization. Larvae feeding on low‐quality diet did not prolong their development time, but pupated at smaller size; this resulted in lower fecundity. A decrease in food quality can be seen as a cue of oncoming food shortage and resource depletion; it may be advantageous to pupate at a smaller size and ensure survival till reproduction, rather than risk prolonging development to achieve larger size and higher fecundity.     

Localization of post-proline cleaving peptidases in Tenebrio molitor larval midgut

Two soluble post-proline cleaving peptidase activities, PPCP1 and PPCP2, were demonstrated in Tenebrio molitor larval midgut with the substrate benzyloxycarbonyl-L-alanyl-L-proline p-nitroanilide. Both activities were serine peptidases. PPCP1 was active in acidic buffers, with maximum activity at pH 5.3, and was located mainly in the more acidic anterior midgut lumen. The dynamics of PPCP1 activity and the total activity of soluble digestive peptidases in the course of food digestion were similar, suggesting that the enzyme participates in protein digestion. PPCP2 is a nondigestive soluble tissue enzyme evenly distributed along the midgut. An increase in the activity of PPCP2 was observed in buffers of pH 5.6-8.6 and was maximal at pH 7.4. The sensitivity of PPCP2 to inhibitors and the effect of pH are similar to prolyl oligopeptidases with a cysteine residue near the substrate binding site.     

Temperature and substrate controls on intra-annual variation in ecosystem respiration in two subarctic vegetation types

Arctic ecosystems are important in the context of climate change because they are expected to undergo the most rapid temperature increases, and could provide a globally significant release of CO₂ to the atmosphere from their extensive bulk soil organic carbon reserves. Understanding the relative contributions of bulk soil organic matter and plant‐associated carbon pools to ecosystem respiration is critical to predicting the response of arctic ecosystem net carbon balance to climate change. In this study, we determined the variation in ecosystem respiration rates from birch forest understory and heath tundra vegetation types in northern Sweden through a full annual cycle. We used a plant biomass removal treatment to differentiate bulk soil organic matter respiration from total ecosystem respiration in each vegetation type. Plant‐associated and bulk soil organic matter carbon pools each contributed significantly to ecosystem respiration during most phases of winter and summer in the two vegetation types. Ecosystem respiration rates through the year did not differ significantly between vegetation types despite substantial differences in biomass pools, soil depth and temperature regime. Most (76–92%) of the intra‐annual variation in ecosystem respiration rates from these two common mesic subarctic ecosystems was explained using a first‐order exponential equation relating respiration to substrate chemical quality and soil temperature. Removal of plants and their current year's litter significantly reduced the sensitivity of ecosystem respiration to intra‐annual variations in soil temperature for both vegetation types, indicating that respiration derived from recent plant carbon fixation was more temperature sensitive than respiration from bulk soil organic matter carbon stores. Accurate assessment of the potential for positive feedbacks from high‐latitude ecosystems to CO₂‐induced climate change will require the development of ecosystem‐level physiological models of net carbon exchange that differentiate the responses of major C pools, that account for effects of vegetation type, and that integrate over summer and winter seasons.     

Reproducibility of vegetation cover estimates in south‐central Alaska forests

Abstract. Reproducibility of vegetation measurements is critical for large‐scale or long‐term studies, where numerous observers collect data, but past studies have questioned repro‐ducibility of some techniques. Five methods of evaluating understory composition were appraised for reproducibility among six observers in two forest types in south‐central Alaska: ocular estimates in quadrats, overall community species rank and cover estimates, nested rooted frequency, horizontal‐vertical profiles, and pin drop (systematic points). One forest type was selected to represent structure of coastal communities, another to represent structure of interior Alaska communities. Three general methods of evaluating reproducibility were considered: standard deviations (precision among observers), components of variance (percentage of total variance attributable to observers), and analysis of variance (significance of observer variance). Observer variances were generally similar among techniques and significant in most cases. No technique stood out as being more reproducible than others. Features of techniques other than reproducibility may be more important when selecting a technique. Management decisions based on vegetation cover data should consider the observer errors involved as well as biological significance.     

新疆黄鹀冬季的生物学资料

调查资料表明,黄鹀(Emberiza citronella erythrogenys)在中国境内新疆北部越冬,并非是偶见冬候鸟或迷鸟。     

Gap Junctional Channels Regulate Acid Secretion in the Mammalian Gastric Gland

Gap junction channels are regarded as a primary pathway for intercellular message transfer, including calcium wave propagation. Our study identified two gap junctional proteins, connexin26 and connexin32, in rat gastric glands by RT-PCR, Western blot analysis, and immunofluorescence. We demonstrated a potential physiological role of the gap junctional channels in the acid secretory process using the calcium indicator fluo-3, and microinjection of Lucifer Yellow. Application of gastrin (10⁻⁷ m) to the basolateral membrane resulted in the induction of uniphasic calcium signals in adjacent parietal cells. In addition, single parietal cell microinjections in intact glands with the cell-impermeant dye Lucifer Yellow resulted in a transfer of dye from the injected cell to the adjacent parietal cell following gastrin stimulation, demonstrating gastrin-induced cell-to-cell communication. Both calcium wave propagation and Lucifer Yellow transfer were blocked by the gap junction inhibitor 18α-glycyrrhetinic acid. Our studies demonstrate that functional gap junction channels in gastric glands provide an effective means for rapid cell-to-cell communication and allow for the rapid onset of acid secretion. Received: 4 December 2000/Revised: 5 June 2001     

Analysis of a combined F1/F2 diallel cross in wheat

Analysis of a conventional diallel cross offers only perfect-fit estimates of the genetic components of variation, but no test for the goodness of fit of the model based on these estimates. When F₂ progenies are available, however, combining F₁ and F₂ diallels in a single experiment overcomes these problems. Least-squares estimates of these components can be calculated, errors attached to them and the goodness of fit of the resultant model tested. This analysis was applied to data on the severity of yellow rust infection in an F₁/F₂ half-diallel cross among eight bread wheat lines adapted to the East African highlands. After removing two interacting arrays, genetic analysis indicated that an additive/dominance model of gene action satisfactorily explained the variation observed among the remaining six parents and their progenies, in both the individual F₁ and F₂ diallels and the combined F₁/F₂ diallel. Resistance to yellow rust was dominant to susceptibility and genes for increased resistance were more frequent. Received: 25 May 2000 / Accepted: 31 July 2000