氮肥对风箱果幼苗形态和生理特性的影响

采用盆栽实验的方法,设置4种水平氮肥处理,研究不同氮肥处理对风箱果1年生幼苗的生长表现、生物量积累和分配、光合生理特征、非结构性碳（NSC）积累等的影响。结果表明：施用氮肥促进了风箱果幼苗的地径、分枝数和冠幅的生长,促进了茎、叶和总生物量的积累（P<0.05）,提高了茎的生物量分配比例,减少了根生物量的分配比例;施用氮肥显著提高了净光合速率、叶氮含量、茎中的可溶性糖和NSC的积累（P<0.05）,但减少了根中的可溶性糖和NSC含量（P<0.05）。不同水平氮肥处理间（N1、N2、N3）的大部分指标差异并不显著,说明风箱果幼苗对土壤养分的变化并不敏感。     

体外受精-胚胎移植中完全受精失败的原因分析

受精是生命起源至关重要的一个步骤。在辅助生殖的过程中,完全受精失败发生具有其复杂性和不可预见性。受精失败常伴随着一些胞间调控机制异常,其中,可能阻滞在与精子穿越卵冠丘复合体、精子-透明带结合/穿透、精子-卵膜结合、卵子激活、精子去浓缩或原核形成等任一阶段。通过卵胞浆内单精子注射可以避免大部分受精失败现象,但某些患者仍无法成功受精,即使采用辅助人工激活也无法完全避免其发生。对于在辅助生殖过程中完全受精失败患者,结合其卵子成熟情况、精子质量及相关检测结果,在后续周期调整临床方案可有效避免受精失败的再次发生。     

In vitro evidence for the participation of Drosophila melanogaster sperm β‐N‐acetylglucosaminidases in the interactions with glycans carrying terminal N‐acetylglucosamine residues on the egg's envelopes

Fertilization is a complex and multiphasic process, consisting of several steps, where egg‐coating envelope's glycoproteins and sperm surface receptors play a critical role. Sperm‐associated β‐N‐acetylglucosaminidases, also known as hexosaminidases, have been identified in a variety of organisms. Previously, two isoforms of hexosaminidases, named here DmHEXA and DmHEXB, were found as intrinsic proteins in the sperm plasma membrane of Drosophila melanogaster. In the present work, we carried out different approaches using solid‐phase assays in order to analyze the oligosaccharide recognition ability of D. melanogaster sperm hexosaminidases to interact with well‐defined carbohydrate chains that might functionally mimic egg glycoconjugates. Our results showed that Drosophila hexosaminidases prefer glycans carrying terminal β‐N‐acetylglucosamine, but not core β‐N‐acetylglucosamine residues. The capacity of sperm β‐N‐acetylhexosaminidases to bind micropylar chorion and vitelline envelope was examined in vitro assays. Binding was completely blocked when β‐N‐acetylhexosaminidases were preincubated with the glycoproteins ovalbumin and transferrin, and the monosaccharide β‐N‐acetylglucosamine. Overall, these data support the hypothesis of the potential role of these glycosidases in sperm–egg interactions in Drosophila.     

Joint evolution of differential seed dispersal and self‐fertilization

Differential seed dispersal, in which selfed and outcrossed seeds possess different dispersal propensities, represents a potentially important individual‐level association. A variety of traits can mediate differential seed dispersal, including inflorescence and seed size variation. However, how natural selection shapes such associations is poorly known. Here, we developed theoretical models for the evolution of mating system and differential seed dispersal in metapopulations, incorporating heterogeneous pollination, dispersal cost, cost of outcrossing and environment‐dependent inbreeding depression. We considered three models. In the ‘fixed dispersal model’, only selfing rate is allowed to evolve. In the ‘fixed selfing model’, in which selfing is fixed but differential seed dispersal can evolve, we showed that natural selection favours a higher, equal or lower dispersal rate for selfed seeds to that for outcrossed seeds. However, in the ‘joint evolution model’, in which selfing and dispersal can evolve together, evolution necessarily leads to higher or equal dispersal rate for selfed seeds compared to that for outcrossed. Further comparison revealed that outcrossed seed dispersal is selected against by the evolution of mixed mating or selfing, whereas the evolution of selfed seed dispersal undergoes independent processes. We discuss the adaptive significance and constraints for mating system/dispersal association.     

Light asymmetry explains the effect of nutrient enrichment on grassland diversity

One of the most ubiquitous patterns in plant ecology is species loss following nutrient enrichment. A common explanation for this universal pattern is an increase in the size asymmetry of light partitioning (the degree to which large plants receive more light per unit biomass than smaller plants), which accelerates the rates of competitive exclusions. This ‘light asymmetry hypothesis’ has been confirmed by mathematical models, but has never been tested in natural communities due to the lack of appropriate methodology for measuring the size asymmetry of light partitioning in natural communities. Here, we use a novel approach for quantifying the asymmetry of light competition which is based on measurements of the vertical distribution of light below the canopy. Using our approach, we demonstrate that an increase in light asymmetry is the main mechanism behind the negative effect of nutrient enrichment on species richness. Our results provide a possible explanation for one of the main sources of contemporary species loss in terrestrial plant communities.     

长期不同施肥下水稻产量及土壤有机质和氮素养分的变化特征

利用开始于1982年的湖南祁阳官山坪水稻长期(1982-2010年)定位试验,研究不同施肥条件下水稻产量及土壤有机质、氮素养分的动态变化特征,试验设置NPK、NPKM(M为牛粪)、 NPM、NKM、PKM、M和CK等7个处理.28年长期不同施肥处理结果表明：肥料的施用均能提高土壤有机质、全氮、碱解氮含量和水稻产量.氮、磷、钾化肥+有机肥(NPKM)处理的水稻产量一直保持最高水平,氮、磷、钾化肥(NPK)处理随着试验年限的延长呈下降趋势,其水稻产量逐渐低于其他施肥处理.单施有机肥或有机无机肥配施各处理土壤有机质含量在试验开始后的前16年有一个快速增加的过程,之后略有下降,然后仍保持增长趋势;NPK化肥处理土壤有机质含量仅在试验开始后的前8年增加较快,之后在一个相对稳定的范围内波动.各施肥处理在试验开始后的前8年内土壤全氮含量均呈快速积累趋势,以NPKM处理增幅最大.各施肥处理土壤碱解氮含量在试验开始后的前12年增加较慢,平均每年增加0.66～2.25 mg·kg^-1,1994-1998年增加较快,平均每年增加6.45～32.45 mg·kg^-1;1998年之后,各施肥处理土壤碱解氮含量均略有下降,其中,有机无机肥配施处理增加较快,单施化肥处理增加较慢.表明有机肥的施用是红壤性水稻土有机质和氮素营养水平稳定提升的关键措施,是红壤稻田土壤可持续利用的重要保障.     

硫素对不同大豆品种成熟期AM真菌群落多样性的影响

研究硫素对不同大豆品种成熟期丛枝菌根（arbuscular mycorrhizal,AM）真菌群落多样性的影响,探索有利于提高3个特定大豆品种根围土壤和根系AM真菌多样性的最佳施硫量,为提高大豆产量和改善大豆品质提供理论依据。试验采用盆栽,选用黑农44（HN44）、黑农48（HN48）、黑农37（HN37）3个大豆品种作为试验材料,设4个硫素处理S1（对照）,S2（0.02g/kg）,S3（0.04g/kg）和S4（0.06g/kg）。采用PCR-DGGE技术分析3个大豆品种根围土壤和根系中AM真菌群落多样性。结果表明：在S2处理下HN37和HN44根围土壤和根系AM真菌多样性最高,而在S3处理下HN48根围土壤和根系AM真菌多样性最高;DGGE图谱中各样品优势种群变化显著,球囊霉属Glomus和柄囊霉属Funneliformis真菌为3个大豆品种根围土壤和根系中AM真菌的优势菌群。由此可见,硫素对不同大豆品种根围土壤和根系AM真菌群落多样性有显著影响,适量施硫能够提高大豆根围土壤和根系中AM真菌的多样性,不施或过高施硫反而抑制AM真菌的多样性。     

施氮量和种植密度对东北特早熟棉区棉铃生物量和氮素累积的影响

以辽棉19号和美棉33B为材料,研究了不同施氮量(0、240、480 kg ·hm-2)和不同种植密度(75000、97500、120000 plants·hm-2)对东北特早熟棉区棉花棉铃生物量和氮素累积特征的影响.结果表明： 棉花单铃、棉籽和纤维的生物量及其氮素累积随棉花生育进程的动态变化均符合“S”型曲线,种植密度和施氮量可以显著影响棉铃各部分生物量和氮素累积的动态特征,以及棉花产量与品质;在施氮量240 kg·hm-2和种植密度97500 plants·hm-2处理下,单铃、棉籽和纤维的生物量均达到最大,生物量和氮素累积的快速累积起始时间和终止时间较早但持续时间较短,生物量快速累积速率最大,生物量和氮素在铃壳中的分配系数最低,在棉籽和纤维中分配系数最高.     

模拟放牧斑块与氮素添加对半干旱草原群落植物生长的影响

放牧时,动物采食及其排泄物会影响植物的生长,但动物彩食及其排泄物的空间异质性可能会影响这咱效应.在位于我国北方典型农牧交错区的内蒙古多伦县,我们研究了模拟入牧斑块和施氧肥对植物生长的影响,实验采用模拟放牧采食斑块(观割半径分别0、10、20、40和8cm)和土壤施氮(分别为0、5、20Gn\m2)两种处理,植物地上部收获后分为绿体和立柯两部分,并分析其含氮量.结果表明,刈割降低了植物的生物量(40.5%),而施氮可增加生物量(57.8%)刈割交通规则植物生长的抑制作用在面积最水又施肥的斑块上表现更明显.土壤施氮可以促进杜物生长并且影响刈割效应.同时植物的绿-枯比阻碍施氮水平的增回而增回,因此氮会延迟植物的衰老.以上结果表明,刈割(模拟动物采食)斑块的大小会影响草原植物的生长,土壤施氮(模拟动物尿氮)可以提高草原生态系统的初级生产力,并影响刈割效应.