水面和水下长航对艇员肠道菌群影响的比较及意义探讨

比较研究和水下两种长期航行条件对航艇和核潜艇艇员肠道菌群的影响并对其意义进行初步探讨。结果显示两种长航条件均对人体肠道菌群产生显著影响,可打破肠道微生态平衡,但两者所致的肠道菌群构成变化的特点不同。提示不同长航条件可造成不同的微生态失调,需区别对待。     

辽西褐土施肥及养分循环再利用中长期试验Ⅳ.土壤肥力变化

经12年田间试验,各施肥处理耕层土壤的肥力变化表明,在保持农业系统养分循环再利用基础上,施用适量化肥以平衡土壤养分收支,不仅可实现作物高产,减少过剩养分进入环境,并可改善土壤肥力,表现为明显提高了耕层的有机C,N浓度,不过,在本例中欲保持较高的土壤有效P水平,恐需在平均土壤P收支基础上适当增加P肥施用量。     

Reproductive strategies in some arctic Saxifraga (Saxifragaceae), with emphasis on the narrow endemic S. svalbardensis and its parental species

Arctic saxifrages show conspicuous reproductive and chromosomal variation. We examined sexual and asexual traits in 43 phytotron-cultivated Svalbard populations of nine species, including the endemic, supposedly entirely asexual and aneupolyploid S. svalbardensis and its parental species, S. cernua and S. rivularis. All species were self-compatible hermaphrodites with low pollen/ovule ratios, including the strongly protandrous S. cernua , which previously has been reported as self-incompatible with an androdioecious mating system. Spontaneous selfing resulted in considerable seed set in several species and a few seeds in S. svalbardensis and S. cernua; hand-selfing and cross-pollination often increased seed set in the two latter species. Self-fertilized seeds of S. svalbardensis and S. cernua were viable and developed into normal, vigorous plants. Saxifraga rivularis and its close relative S. hyperborea were strongly autogamous. The bulbil-reproducing S. svalbardensis and S. cernua showed extreme variation in fertility, probably because of frequent aneuploidy. Many plants of S. cernua were fully fertile, suggesting that although natural seed set rarely has been observed, sexual reproduction is frequent enough to maintain its previously reported high levels of clonal diversity. Some plants of S. svalbardensis were also fairly fertile. This species may have considerable evolutionary potential; sexual events can lead to increasingly fertile genets with euploid chromosome numbers.     

Changes in soil phosphorus fractions following positive and negative phosphorus balances for long periods

The effect of phosphorus (P) balance (addition, in both fertilizers and farmyard manure (FYM), minus removal in crops) on eight soil P fractions determined by sequential extraction, was measured on archived soils from various long-term experiments run by Rothamsted Experimental Station in the United Kingdom. It has been established unequivocally that, for all the soils investigated, no one of the eight P fractions was increased or decreased during long periods of P addition or depletion, respectively. However, changes were mainly in the resin (24–30%) and the inorganic (P_i) component of the four fractions extracted sequentially by 0.5 M NaHCO₃, 0.1 M NaOH, 1.0 M NaOH, 0.5 M H₂SO₄ (41–60%). For the sandy loam there were also consistent changes in the organic (P_o) fraction (25%), especially that extracted by bicarbonate, presumably because the soil contained only a little clay and presumably had low sorption capacity. When the soils were cropped without P addition the largest proportional change was in the P extracted by resin, 0.5 M NaHCO₃ and 0.1 M NaOH, suggesting that the P in these fractions is readily available, or has the potential to become available, for crop growth. This was supported by changes in the overall P balance. On the heavier textured soils, 50–80% of the change in total soil P (P_T) was in these fractions; on the sandy soil this increased to more than 90%. The change in the sum of the first five fractions accounted, on average, for 90% of the P balance. However these changes in the P in the plough layer frequently left large amounts of P unaccounted for in some of the excessively P enriched soils. The amount of P_i extracted by resin and bicarbonate (P_i(r+b)) ranged between 14 and 50% of the sum of the P_i fractions. Soils with the lower percentages were those known to be most responsive to P fertilizers. P_i(r+b) accounted for an average of 70% of the P balance (negative) in P depleting soils where crop offtake was not offset or exceeded by annual P additions (positive balance). The ratio between P_i(r+b) and P_i(sum) could be a guide in defining soils deficient in P and those which are excessively enriched.     

Evaluation of a new culture method for mass-propagation of a photoperiod-temperature sensitive genic male sterile rice strain N19S

A newly established culture method was evaluated for application in mass-propagation of a photoperiod-temperature sensitive genic male sterile rice strain. It was found that the new culture method was very efficient for the regeneration of plants from callus of this strain, and a high concentration of 6-benzyladenine necessary for highly efficient plant regeneration culture did not seem to have negative effects on some agronomic traits investigated of the regenerated plants and their progenies. By the new culture method, a large number of plants could be regenerated in a relatively short time (approximately 8×10¹² plants within 300 days) from one naked seed-explant. Because of this, prominent drift of the PTGMS rice strain, which accumulates gradually during the course of propagation of the seeds through generations, in the response to photoperiod-temperature conditions could be avoided when this in vitro culture protocol is employed instead of seed propagation. Differences in rates of pollen fertility and seed setting were found between regenerated plants and seed-grown plants, and between their respective first and second progenies. These differences are also of important application value in two-line rice production: Higher pollen fertility of the regenerated plants can be applied with higher efficiency for the propagation of the strain seeds because they have much higher seed setting by self-fertilization; lower pollen fertility of the regenerated plant progenies will result in much lower seed setting by self-fertilization and is, therefore, conducive to the production of hybrid seeds of higher purity by natural crossing with the other line in the two-line system.     

Habitat and Fish Fauna Structure in a Subtropical Mountain Stream in Taiwan before and after a Catastrophic Typhoon

Habitats and fish populations of a subtropical mountain stream in Taiwan were surveyed before and after the hit of super-typhoon Herb in July 1996. There was a significant decrease in total pool area and an increase in total riffle area. Upper stream habitat was more susceptible to the disturbance. Relative abundance of the species was significantly correlated before and after the typhoon (rs=0.89, p<0.001). Morisita's index of similarity for the fish communities in June 1996 and October 1997 ranged between 0.82 and 1.02 for seven out of nine stations. Most common cyprinids decreased in densities after Herb, but recovered seventeen months after the typhoon. There were only minor changes in fish community fourteen months after the typhoon. Cyprinids that are smaller in size, such as Candidia barbata and Abottina brevirostris alticorpus were affected the most. Gobiid Rhinogobius nantaiensis that is well adapted to riffle habitat was unaffected throughout the surveys. The results of this study suggested that in subtropical mountain stream, severe typhoon may significantly alter the habitats, but the impact on fish populations could be relatively small due to features of these mountain species.     

江苏下扬子区寒武系-三叠系牙形刺色变指标(CAI)图及其意义

本文对多年来积累的江苏下扬子区寒武系－三叠系牙形刺CAI材料进行了系统收集和整理,并采用Anita Harris建立的统一标准,编制了本区寒武系－三叠系的5幅牙形刺CAI图;进而结合牙形刺CAI与镜质组反射率（Ro)的对应关系,对上述各系的有机质成熟度进行了评价,对本区海相中、古生界油气勘探具有十分重要的意义。     

Survival of extrapair and within-pair young in tree swallows

In monogamous species, it is generally accepted that males seekextrapair matings to increase their reproductive success withoutadditional parental investment; however, the benefits of extrapairmatings to females are much less clear. One possibility isthat females obtain genes for enhanced offspring viabilityfrom the extrapair sires. If this is the case, then the increasedviability of extrapair young may be evident throughout the periodof embryonic development as well as later in life. Tree swallows(Tachycineta bicolor) have one of the highest known levelsof extrapair mating in birds, and females have substantialcontrol over the paternity of their offspring. We used moleculartechniques to determine the parentage of nestlings and unhatchedembryos to examine the possibility that female tree swallowsgain viability benefits for their extrapair offspring. Althoughboth extrapair paternity and mortality of embryos and nestlingswere high (89% and 54% of broods respectively), we found nodifference in the viability of within-pair and extrapair youngprior to fledging. In addition, extrapair young were not morelikely to be male. There was no bias in the sex of young atfledging, but unhatched embryos were more likely to be male.Our results do not support the idea that female tree swallowsengage in extrapair mating to increase offspring viability,at least early in life.     

The effect of phosphite on the sexual reproduction of some annual species of the jarrah (Eucalyptus marginata) forest of southwest Western Australia

Phosphite is a cost-effective fungicide used to control the pathogen Phytophthora cinnamomi which is damaging the diverse flora of the southwest of Western Australia. Three annual species of the southwest jarrah (Eucalyptus marginata) forest of Western Australia (Pterocheata paniculata, Podotheca gnaphalioides and Hyalosperma cotula), were studied to determine the effect of the fungicide phosphite on the species’ reproduction. Phosphite at concentrations of 2.5, 5 and 10 g L^–1 reduced pollen fertility of Pt. paniculata when plants were sprayed at the vegetative stage. Pollen fertility of all three species was reduced when plants were sprayed at anthesis with 10 g L^–1 phosphite. Seed germination was reduced by phosphite in Pt. paniculata and H. cotula when plants were sprayed in the vegetative stage. Phosphite when sprayed at anthesis at a concentration of 5 g L^–1 reduced seed germination of H. cotula. Phosphite at concentrations of 5 and 10 g L^–1 killed a proportion of plants from all three species and up to 90% of Po. gnaphalioides plants. The frequent application of phosphite, therefore, may reduce the abundance of annual plants in this ecosystem. Received: 14 December 2000 / Revision accepted: 10 March 2001     

粘型小麦雄性不育系减数分裂特征及育性恢复研究

调查了粘型1B／1R和非1B／1R小麦雄性不育系,保持系及其F2的花粉母细胞减数分裂中期Ⅰ染色体联会情况、后期Ⅰ出现落后染色体的细胞频率以及末期Ⅱ含有微核的四分体的频率,结果表明：（1）粘果山羊细胞质对1B／1R型不育系减数分裂染色体配对水平具有特异性降低作用;（2）粘型1B／1R不育系减数分裂中期Ⅰ出现单价体细胞频率与后期Ⅰ出现落后染色体细胞的频率呈正相关,也与含微核的四分体频率呈正相关,而对应保持系则没有相关性;（3）粘果山羊草细胞质对非1B／1R不育系减数分裂过程影响不大,5个1B／1R不育系减数分裂过程中,3个时期染色体行为变异率的差异是特定的1B／1R核型与粘果山羊草细胞质互作的结果;（4）粘型1B／1R不育系杂交R2单株减数分裂3个时期染色体行为变异率与其恢复度成反比,这类不育系减数分裂中染色体行为不同步是其恢复不高且变异较大的一重要原因。