Accelerated organic matter decomposition in thermokarst lakes upon carbon and phosphorus inputs

Mineralization of dissolved organic matter (DOM) in thermokarst lakes plays a non-negligible role in the permafrost carbon (C) cycle, but remains poorly understood due to its complex interactions with external C and nutrient inputs (i.e., aquatic priming and nutrient effects). Based on large-scale lake sampling and laboratory incubations, in combination with ¹³C-stable-isotope labeling, optical spectroscopy, and high-throughput sequencing, we examined large-scale patterns and dominant drivers of priming and nutrient effects of DOM biodegradation across 30 thermokarst lakes along a 1100-km transect on the Tibetan Plateau. We observed that labile C and phosphorus (P) rather than nitrogen (N) inputs stimulated DOM biodegradation, with the priming and P effects being 172% and 451% over unamended control, respectively. We also detected significant interactive effects of labile C and nutrient supply on DOM biodegradation, with the combined labile C and nutrient additions inducing stronger microbial mineralization than C or nutrient treatment alone, illustrating that microbial activity in alpine thermokarst lakes is co-limited by both C and nutrients. We further found that the aquatic priming was mainly driven by DOM quality, with the priming intensity increasing with DOM recalcitrance, reflecting the limitation of external C as energy sources for microbial activity. Greater priming intensity was also associated with higher community-level ribosomal RNA gene operon (rrn) copy number and bacterial diversity as well as increased background soluble reactive P concentration. In contrast, the P effect decreased with DOM recalcitrance as well as with background soluble reactive P and ammonium concentrations, revealing the declining importance of P availability in mediating DOM biodegradation with enhanced C limitation but reduced nutrient limitation. Overall, the stimulation of external C and P inputs on DOM biodegradation in thermokarst lakes would amplify C-climate feedback in this alpine permafrost region.     

四川缙云山森林群落林窗边缘效应的研究

 本文运用Shannon—Wiener物种多样性指数、Simpson生态优势度指标以及边缘效应强度指数,对缙云山亚热带森林群落林窗的边缘效应现象进行了初步研究。29个林窗样地不同部位上述指标的测定表明用物种多样性指数拟合边缘效应测度通式,缙云山亚热带森林群落林窗的边缘效应强度值为1—3左右;而用生态优势度值拟合边缘效应强度测式,则上述边缘效应强度值为0.1一1.2左右。研究表明林窗边缘区由于边缘效应的作用有增大物种多样性的趋势。而林窗面积、所处坡向以及林窗所在的森林群落类型,都对处于不同发育阶段的林窗的边缘效应强度具有影响。在此基础上,本文对林窗边缘效应强度的变化规律、效应性质、测定意义以及对森林营造和优化管理上的作用进行了一定探讨。     

用转移因子治疗159例奶牛乳房炎的效果观察

本文报道了在国内首次用转移因子制剂治疗奶牛隐性乳房炎的效果。我们采用的转移因子制剂是本单位从健康猪脾细胞提取的,经按人用转移因子制检规程检测达到要求后,用于本省西部、东部和郊区三个奶牛场计159头患隐性乳房炎的奶牛,每天一次肌注,连续用药5次,测定用药前后的客观指标(CMT、BTB、苛性钠及氯化物凝乳试验等),以痊愈、显效、好转及无效等判定标准,经统计学处理后看出,用药后与用药前比较,差异非常显著(P<0.01),治疗组的有效率为91.2％,看出了应用转移因子治疗奶牛隐性乳房炎具有明显的治疗效果。     

Soil legacy effects of plants and drought on aboveground insects in native and range-expanding plant communities

Soils contain biotic and abiotic legacies of previous conditions that may influence plant community biomass and associated aboveground biodiversity. However, little is known about the relative strengths and interactions of the various belowground legacies on aboveground plant–insect interactions. We used an outdoor mesocosm experiment to investigate the belowground legacy effects of range-expanding versus native plants, extreme drought and their interactions on plants, aphids and pollinators. We show that plant biomass was influenced more strongly by the previous plant community than by the previous summer drought. Plant communities consisted of four congeneric pairs of natives and range expanders, and their responses were not unanimous. Legacy effects affected the abundance of aphids more strongly than pollinators. We conclude that legacies can be contained as soil ‘memories’ that influence aboveground plant community interactions in the next growing season. These soil-borne ‘memories’ can be altered by climate warming-induced plant range shifts and extreme drought.     

Perception of heterochromatic flicker by honeybees: a behavioural study

Freely flying honeybees were trained to discriminate a stimulus consisting of two alternating chromatic lights (heterochromatic flicker) from a steady mixture of the same two lights, using 3 different pairs of lights: blue-UV, UV-green, and green-UV. With each light pair, training to the heterochromatic flicker was conducted at several flicker frequencies, using experimentally naive bees in each training. In subsequent tests, the trained bees were given a choice between the two lights that constituted the flicker, presented steady, as well as between either of them and the steady mixture. We find that bees trained to particular frequencies of heterochromatic flicker prefer one of the component lights over the other as well as over the steady mixture, suggesting that the colour they perceive in the heterochromatic flicker to which they have been trained is shifted in the direction of one of the lights contained in the flicker. The colour shift occurs at flicker frequencies that depend on the pair of lights used. We propose that the shift is generated by an effect similar to the Brücke-Bartley phenomenon known from human vision. This effect is based on the enhancement of the photoreceptors' response upon onset of stimulation, causing an intermittent light to appear brighter than a steady light of identical physical intensity. We propose that the degree of enhancement might differ among the 3 spectral classes of photoreceptor, causing the colour perceived in a heterochromatic flicker to differ from that perceived in a steady mixture of its two light components.     

Response of shoaling fish to the threat of aerial predation

Synopsis Many species of shoaling fish are preyed upon by aerial predators. However, to date there has been no analysis of the evasive response of a group of shoaling fish to an aerial threat or attack. The response of a shoal of fish encompasses a suite of behaviors starting with a startle response. Shoals of golden shiner, Notemigonus crysoleucas, responded to the threat of aerial predation from a kingfisher model with a startle response, an increase in shoal depth, an increase in polarity, swimming in the opposite direction under the model predator, shoal compression along the depth axis, and shoal expansion on the plane perpendicular to the depth axis. It was hypothesized that shoal compression along the depth axis serves to increase predator confusion by placing more fish in the predator's visual field. This compression was termed the ‘plane of confusion’.     

Crop responses to CO2 enrichment

Carbon dioxide is rising in the global atmosphere, and this increase can be expected to continue into the foreseeable future. This compound is an essential input to plant life. Crop function is affected across all scales from biochemical to agro-ecosystem. An array of methods (leaf cuvettes, field chambers, free-air release systems) are available for experimental studies of CO₂ effects. Carbon dioxide enrichment of the air in which crops grow usually stimulates their growth and yield. Plant structure and physiology are markedly altered. Interactions between CO₂ and environmental factors that influence plants are known to occur. Implications for crop growth and yield are enormous. Strategies designed to assure future global food security must include a consideration of crop responses to elevated atmospheric CO₂. Future research should include these targets: search for new insights, development of new techniques, construction of better simulation models, investigation of belowground processes, study of interactions, and the elimination of major discrepancies in the scientific knowledge base.     

Upper thermal limits predict herpetofaunal responses to forest edge and cover

Amphibians and reptiles are sensitive to changes in the thermal environment, which varies considerably in human-modified landscapes. Although it is known that thermal traits of species influence their distribution in modified landscapes, how herpetofauna respond specifically to shifts in ambient temperature along forest edges remains unclear. This may be because most studies focus on local-scale metrics of edge exposure, which only account for a single edge or habitat patch. We predicted that accounting for the combined effect of multiple habitat edges in a landscape would best explain herpetofaunal response to thermally mediated edge effects. We (1) surveyed herpetofauna at two lowland, fragmented forest sites in central Colombia, (2) measured the critical thermal maximum (CT_max) of the species sampled, (3) measured their edge exposure at both local and landscape scales, and (4) created a thermal profile of the landscape itself. We found that species with low CT_max occurred both further from forest edges and in areas of denser vegetation, but were unaffected by the landscape-scale configuration of habitat edges. Variation in the thermal landscape was driven primarily by changes in vegetation density. Our results suggest that amphibians and reptiles with low CT_max are limited by both canopy gaps and proximity to edge, making them especially vulnerable to human modification of tropical forest. Abstract in Spanish is available with online material.     

Rhizosphere effect of nanoscale zero-valent iron on mycorrhiza-dependent maize assimilation

Rhizosphere effect of nanoscale zero-valent iron (nZVI) is crucial but little reported. Maize seeds were dressed with four nZVI concentrations (0, 1.0, 1.5, 2 g kg⁻¹) and inoculated with arbuscular mycorrhizal fungus (AMF) (Funneliformis mosseae). The SEM images illuminated that excessive nZVI particles (2 g kg⁻¹) were agglomerated on the surface of hyphae and spore, causing severe deformation and inactivation of AMF symbionts and thereafter inhibiting water uptake in maize seedlings. This restrained the scavenging effects of enzymatic (superoxide dismutase, peroxidase) and non-enzymatic compounds (proline & malondialdehyde) on ROS, and leaf photoreduction activity and gas exchange ability (p < 0.05). Interestingly, the inoculation with AMF effectively alleviated above negative effects. In contrast, appropriate dose of nZVI, that is, ≤1.5 g kg⁻¹, can be evenly distributed on the hyphae surface and form the ordered symbionts with AMF. This help massively to enhance hyphae growth and water and nutrient uptake. The enhanced mycorrhizal infection turned to promote rhizosphere symbiont activity and leaf Rubisco and Rubisco activase activity. Light compensation point was massively lowered, which increased photosynthetic carbon supply for AMF symbionts. Particularly, such priming effects were evidently enhanced by drought stress. Our findings provided a novel insight into functional role of nZVI in agriculture and AMF-led green production.     

Matrix synthesis of chiral carboxy derivatives: Aldehyde chiral discrimination due to a two-point coordination of Mg2+

To control stereoselectivity in aldol-like reactions with chiral carbohydrate templates, we studied the interaction between completely protected dialdo compounds and magnesium enediolates of arylacetic acids. Diastereomeric mixtures of the highly functionalized acids obtained were esterified to isolate individual methyl uronates. It was found that all the diastereomeric esters exhibit Cotton effects of the same positive sign in the 220–230 nm region and so possess the same S configuration of the aryl chiral center C(6). Chiral center C(5) configurational assignments were performed using IR and ORD spectroscopy. We separated and specified four pairs of diastereomeric methyl uronates. It follows that the precursory acids have the same 5R*, 6S (major isomers) and 5S*, 6S (minor isomers) configurations. A tentative mechanism for complexation and possible models of Mg²⁺ -protected dialdose intermediate complexes has been proposed. We have concluded that a kind of orbital steering is realized, accompanied by some “tuning” of molecular assembly conditioned by two-point coordination between Mg²⁺ and potential cation-binding sites in the substrate molecules. Thus it has been demonstrated that reasonable diastereo-selectivity can be achieved even through the use of small matrix molecules using rather small functional groups, which do not impose any stringent steric requirements. © 1993 Wiley-Liss, Inc.