Effects of prolonged drought on the anatomy of sun and shade needles in young Norway spruce trees

Predicted increases in the frequency and duration of drought are expected to negatively affect tree vitality, but we know little about how water shortage will influence needle anatomy and thereby the trees’ photosynthetic and hydraulic capacity. In this study, we evaluated anatomical changes in sun and shade needles of 20‐year‐old Norway spruce trees exposed to artificial drought stress. Canopy position was found to be important for needle structure, as sun needles had significantly higher values than shade needles for all anatomical traits (i.e., cross‐sectional needle area, number of tracheids in needle, needle hydraulic conductivity, and tracheid lumen area), except proportion of xylem area per cross‐sectional needle area. In sun needles, drought reduced all trait values by 10–40%, whereas in shade needles, only tracheid maximum diameter was reduced by drought. Due to the relatively weaker response of shade needles than sun needles in drought‐stressed trees, the difference between the two needle types was reduced by 25% in the drought‐stressed trees compared to the control trees. The observed changes in needle anatomy provide new understanding of how Norway spruce adapts to drought stress and may improve predictions of how forests will respond to global climate change.     

江苏东山山地枇杷果实品质与果园土壤、叶片和果实矿质元素的关系

以江苏省苏州吴中区山地种植的24个枇杷果园的‘白玉’枇杷为研究对象,采用典型相关分析法研究土壤、叶片和果实矿质元素间及其与果实品质指标的相关性,应用多元线性回归分析法筛选影响枇杷果实品质的土壤、叶片和果实的主要矿质元素和影响叶片矿质元素的主要土壤矿质养分因子,为改善枇杷果实品质的果园营养管理技术提供理论参考依据。结果表明:(1)枇杷果实品质指标在不同果园间存在较大差异。(2)枇杷果实品质主要受其叶片和果实矿质元素含量影响,其中:枇杷单果质量与叶片中N含量呈显著正相关,与果实中N含量呈显著负相关;可溶性固形物含量与叶片中N和Mg元素含量呈极显著正相关,与果实中P、Mn元素含量呈极显著正相关,与果实中Ca、Mg元素含量呈极显著负相关;可滴定酸含量与叶片中N和Zn元素含量呈显著负相关,与果实中N、Mn元素含量呈显著负相关,与果实中Ca元素含量呈显著正相关。(3)果实品质指标与土壤矿质养分含量的相关性较弱,土壤矿质养分主要通过影响叶片矿质元素含量,进而间接影响果实品质,其中土壤中P、K、Ca、Mn、Cu元素对叶片中矿质元素含量影响较大。研究认为,提高土壤中P、K、Zn含量并减少土壤Ca含量是东山山地枇杷果园土壤管理的关键技术途径;提高叶片中N含量以及果实中N、P、Mn含量和减少果实中Ca、Mg含量是改善东山山地枇杷果实品质的关键措施。     

A biosensor for all D-amino acids using evolved D-amino acid oxidase

Determination of the D-amino acid content in foods and in biological samples is a very important task. In order to achieve this goal we developed a biosensor employing the flavoenzyme D-amino acid oxidase from the yeast Rhodotorula gracilis. To produce a device in which the D-amino acid composition does not alter the results, both the wild-type and a number of mutants obtained by rational design and directed evolution approaches were used. An analysis of D-amino acid oxidase mutants activity on D-amino acid mixtures containing various ratios of neutral, acidic, and basic substrates identified the Amberzyme-immobilized T60A/Q144R/K152E and M213G mutants as the best choice: their response shows an only limited dependence on the solution composition when at least 20% of the D-amino acid is made up of D-alanine (standard error is approximately 5-9%). This is the first report, to our knowledge, demonstrating that the entire D-amino acid content can be determined by using a screen-printed electrode amperometric biosensor, with a detection limit of 0.25 mM and a mean response time of 10-15 min. The D-amino acid assay based on R. gracilis DAAO-biosensor is inexpensive, simple to perform, and rapid: the D-amino acid concentration of a variety of biological samples can be investigated using this assay.     

Competitive ability of Daphnia under dominance of non-toxic filamentous cyanobacteria

It is generally assumed that Daphnia is more susceptible to the inhibitory effects of filamentous cyanobacteria than small cladocerans since daphnids have a larger gape size and filtrate the filaments, whereas small cladocerans do not. This study addresses the question whether food limitation has the potential to modify this scenario of cladoceran response to dominance of non-toxic filamentous cyanobacteria. Daphnia galeatawas grown under limited (0.1 mg C l^–1) and unlimited concentrations (1.0 mg C l^–1) of high-quality food algae both in the absence/presence of non-toxic filamentous Aphanizomenon flexuosum. As the effects of these cyanobacteria on D. galeatawere positive under food limiting conditions and negative at the high food density, it was concluded that D. galeatawas mainly affected by nutritional quality due to its ability to ingest the filaments, while mechanical interference with food collection was not important. In competition experiments between D. galeataand Bosmina longirostris, D. galeatawas the dominant species at regular additions of food (1.0 mg C l^–1) in the absence of Aphanizomenon. In the presence of these cyanobacteria, D. galeatawas inhibited during the first days of the experimental period. However, the negative effect at the initially high food density was outweighed by nutrition at food limiting conditions and the outcome in competitive dominance was not changed. The results demonstrate that the ability of D. galeata to ingest large-sized non-toxic cyanobacteria can be considered as advantageous under food limiting conditions.     

钙、硼对花生生长、产量和品质的影响

在土壤代换性钙和有效硼含量分别为0.84me/100g和0.163mg/kg的条件下,研究了施钙、施硼及钙、硼配施对花生生长、产量和品质的影响。结果表明,施用钙肥能提高花生的产量和品质;施用硼肥能改善品质,但在产量上却产生负效应;钙、硼配施也能提高产量,但主效应仍然是钙。施用钙硼肥料不但使花生成熟期植株中钙、硼含量提高,而且种植花生后土壤中的钙、硼残留量也明显增加。     

Asymmetric introgression between fishes in the Red River basin of Texas is associated with variation in water quality

When ecologically divergent taxa encounter one another, hybrid zones can form when reproductive isolation is incomplete. The location of such hybrid zones can be influenced by environmental variables, and an ecological context can provide unique insights into the mechanisms by which species diverge and are maintained. Two ecologically differentiated species of small benthic fishes, the endemic and imperiled prairie chub, Macrhybopsis australis, and the shoal chub, Macrhybopsis hyostoma, are locally sympatric within the upper Red River Basin of Texas. We integrated population genomic data and environmental data to investigate species divergence and the maintenance of species boundaries in these two species. We found evidence of advanced‐generation asymmetric hybridization and introgression, with shoal chub alleles introgressing more frequently into prairie chubs than the reciprocal. Using a Bayesian Genomic Cline framework, patterns of genomic introgression were revealed to be quite heterogeneous, yet shoal chub alleles were found to have likely selectively introgressed across species boundaries significantly more often than prairie chub alleles, potentially explaining some of the observed asymmetry in hybridization. These patterns were remarkably consistent across two sampled geographic regions of hybridization. Several environmental variables were found to significantly predict individual admixture, suggesting ecological isolation might maintain species boundaries.     

Assessing water scarcity by simultaneously considering environmental flow requirements,water quantity,and water quality

Water scarcity is a widespread problem in many parts of the world. Most previous methods of water scarcity assessment only considered water quantity, and ignored water quality. In addition, the environmental flow requirement (EFR) was commonly not explicitly considered in the assessment. In this study, we developed an approach to assess water scarcity by considering both water quantity and quality, while at the same time explicitly considering EFR. We applied this quantity–quality-EFR (QQE) approach for the Huangqihai River Basin in Inner Mongolia, China. We found that to keep the river ecosystem health at a “good” level (i.e., suitable for swimming, fishing, and aquaculture), 26% of the total blue water resources should be allocated to meet the EFR. When such a “good” level is maintained, the quantity- and quality-based water scarcity indicators were 1.3 and 14.2, respectively; both were above the threshold of 1.0. The QQE water scarcity indicator thus can be expressed as 1.3(26%)|14.2, indicating that the basin was suffering from scarcity problems related to both water quantity and water quality for a given rate of EFR. The current water consumption has resulted in degradation of the basin's river ecosystems, and the EFR cannot be met in 3 months of a year. To reverse this situation, future policies should aim to reduce water use and pollution discharge, meet the EFR for maintaining healthy river ecosystems, and substantially improve pollution treatment.     

Fish community response to the longitudinal environmental gradient in Czech deep-valley reservoirs: Implications for ecological monitoring and management

Ecological quality assessment of non-natural water bodies is, in contrast to natural systems, less developed and requires determining biological indicators that reliably reflect environmental conditions and anthropogenic pressures. This study was motivated to propose fish indicators appropriate for assessment of reservoir ecosystems in central Europe. We analysed changes in water quality, total biomass and the taxonomic, trophic and size composition of fish communities along the longitudinal axes of four elongated, deep-valley reservoirs. Due to high nutrient inputs from their catchments, the reservoirs exhibited pronounced within-system gradients in primary productivity and water transparency. Although fish communities were similar among the reservoirs and dominated by few native species, the community structure and biomass systematically changed along the longitudinal axes of the reservoirs. The biomass and proportion of planktivores/benthivores in the fish community were highest at eutrophic sites near the river inflow and declined substantially towards deep, more oligotrophic sites close to the dam. The biomass and proportion of piscivores significantly increased downstream within the reservoirs alongside improving water quality. At species level, perch Perca fluviatilis and bream Abramis brama responded most sensitively, although in opposite directions, to the longitudinal environmental gradient. The major longitudinal changes in fish community characteristics were found to be consistent between pelagic and benthic habitats. The results of this study suggest that fish communities are appropriate indicators of eutrophication and can be used for ecological quality assessment of non-natural lentic water bodies, such as reservoirs. Moreover, our results underline the necessity to consider within-system gradients in water quality and the fish community when planning sampling programmes for deep-valley reservoirs.     

流溪河流域景观空间特征与河流水质的关联分析

人类活动影响或改变流域景观空间结构,并有可能对河流水质产生不同程度的影响,以流溪河流域为研究区,分析流域景观空间格局特征与水质指数之间的相关关系。将流域划分为27个子流域,采集水样分析水质状况,所选用的水质指标有氨氮(NH3-N)、硝态氮-亚硝态氮(NO3-N+NO2-N)、总磷(TP)、化学需氧量(CODCr)。结果表明:1)该流域土地利用结构与水质具有显著相关性,其中居住用地对水质的影响作用最强,林地对河流水质具有净化功能,与水质指标之间的关系表现为负相关,园地与水质指标关系具有不确定性;2)流域景观特征从上游到下游之间表现为城市化增强的梯度,水质状况响应这个梯度变化表现为上游优于下游,人类活动及城市化发展引起的土地利用变化及土地管理方式对水质变化有显著影响;(3)景观破碎度与水质呈现显著正相关性,是影响水质的重要指标,景观聚集程度和斑块形状复杂程度与水质有负相关关系;子流域尺度和河岸带尺度景观空间特征对水质的影响差异不明显。