Nitrous oxide emissions from grass–clover swards as influenced by sward age and biological nitrogen fixation

Grassland renovation by cultivation and reseeding has been shown to increase short-term emissions of N₂O, but there is uncertainty about long-term effects, despite the potential impacts of reseeding on sward composition and soil functions. A field experiment was therefore carried out to determine how N₂O emissions from previously renovated grasslands varied in the intermediate to long-term, compared with an undisturbed permanent grassland (PG). Plots on the PG site were renovated, either two (G2) or five (G5) years prior to the two experimental years. In each sward age and experimental year, annual N₂O-measurements were conducted on a weekly basis and compared with the undisturbed PG. Plots were either unfertilized or were fertilized with slurry (240 kg N ha⁻¹ year⁻¹). On average, annual N₂O emissions were 0.39 kg N/ha for the unfertilized swards, and 0.91 kg N/ha for slurry-fertilized swards. Sward age had no effect on N₂O emissions. With increasing sward age the proportion of legumes in the sward was reduced, but a minimum biological nitrogen fixation (BNF) of 88 kg N/ha was maintained even in the fertilized PG. Both sward age and BNF were of limited importance for the annual N₂O emissions compared with the effects of soil carbon content and nitrogen surplus levels. However, measured N₂O emissions were low in all sward age treatments, with a low risk of additional N₂O emissions when BNF is taken into account in fertilizer planning.     

Cuticular calcium penetration is directly related to the area covered by calcium within droplet spread area

Calcium penetration from salt solutions of calcium chloride and calcium acetate was measured through isolated tomato fruit (Solanum lycopersicum L., cultivar ‘Panovy’) cuticles after 4, 24, and 48 h. Droplet spread area (volume = 1 μL) and the area ultimately covered with calcium were determined with a scanning electron microscope which has an integrated energy dispersive X-ray microanalysis system. An ethoxylated rapeseed oil surfactant (RSO 5) was used for inducing different degrees of droplet spread and together with different calcium concentrations of the solutions to vary the concentration gradient in the penetration experiments. As a rule, penetration of calcium from CaCl₂ was higher than that of Ca(CH₃COO)₂. The addition of RSO 5 to salt solutions resulted in enhanced calcium penetration in comparison to unformulated solutions. However, extending penetration time from 4 to 48 h predominantly did not enhance the penetrated calcium amount significantly. Droplet spread area was enhanced up to 4-fold after adding RSO 5, whereas the area ultimately covered with calcium did not exceed twice as much. This resulted in lower percentage area covered by calcium in droplet footprints from formulated solutions in comparison to solutions without addition of RSO 5. Correlation analyses showed that penetration was not related to droplet spread area but significantly correlated with the area covered by calcium. These observations were true for unformulated calcium salts as well as for calcium solutions with addition of RSO 5. Therefore, the area ultimately covered with calcium or even other xenobiotics within a droplet footprint should be considered in developing mathematical models to simulate active ingredient (a.i.) penetration.     

基于机载LiDAR数据的农作物叶面积指数估算方法研究

叶面积指数(LAI)是农作物长势监测及估产的重要参数,激光雷达能够提供精确的农作物冠层结构信息,可弥补光学遥感在提取冠层结构信息方面的不足。因此,本文旨在挖掘激光雷达所能提取的农作物垂直结构信息,并研究冠层结构参数与农作物叶面积指数之间的关系,从而估算整个研究区的叶面积指数。首先,基于机载激光雷达数据提取平均高度(Hmean)、最大高度(H_(max))、最小高度(H_(min))、高度百分位数(H_(25th)、H_(50th)、H_(75th)、H_(90th))、激光穿透力指数(LPI)、回波点云密度、孔隙率(fgap)、叶倾角(MTA)等结构参数;然后,利用Pearson相关性分析法对以上参数与地面实测LAI进行相关性分析,并选择与LAI相关性高的参数;最后,对选择的敏感性参数进行回归分析,构建激光雷达参数与实测LAI的LiDAR-LAI估算模型,估算整个研究区的农作物冠层LAI。精度评价结果表明:预测LAI与实测LAI之间的相关系数为0.79,均方根误差为0.47,说明激光雷达所提取的农作物冠层结构参数可用于估算空间上连续、大面积的农作物LAI。     

苹果叶盘法基因转化中抗生素种类和浓度的筛选

以苹果品种嘠拉试管苗为试材，研究了卡那霉素（Km）、潮霉素（Hm）对继代苗生长和离体叶片再生的影响，以确定叶盘法基因转化的选择压和转化体的筛选浓度以确定苹果叶盘法基因转化中的选择压和抗性芽的筛选浓度；同时研究了不同浓度的头孢霉素（Cef）和羧苄青霉素（Carb）对苹果离体叶片再生的影响及对农杆菌EHA105和LBA4404的抑菌效果，以确定苹果叶盘法基因转化中合适的抑菌抗生素种类和浓度；以确定侵菌共培养后合适的抑菌抗生素种类和浓度。。结果证明表明：Km卡那霉素10mg/L、Hm4.0 mg/L完全抑制了叶片不定芽的分化，可作为苹果叶盘法转化时抗性芽的选择压； 在Km 50mg/L、Hm5.0 mg/L达到继代苗的半致死浓度，可作为基因转化后抗性芽苗的筛选浓度，10mg/L时完全抑制供试叶片不定芽的分化。；由于抗性芽再生的选择压与抗性苗筛选浓度相差较小，Hm相对于Km更适合作为苹果基因转化的选择标记；培养基中附加潮霉素的浓度为5mg/l继代苗不再分化生长，作为基因转化后抗性芽的筛选浓度，2.0mg/L时完全抑制供试叶片不定芽的再生，作为基因转化后抗性芽的筛选浓度。头孢青霉素在Cef 300mg/L时就能完全抑制农杆菌生长，对叶片不定芽的再生影响不大；而附加Carb羧苄青霉素则需400mg/L以上时才能抑制农杆菌LBA4404的生长，同时严重抑制了叶片再生。因此，宜选用Cef作为苹果基因转化的抑菌抗生素。     

用紫外分光光度法直接测定蔬菜中维生素C的含量

根据Ｃｕ（Ⅱ）在室温下催化氧化Ｖ－Ｃ的原理［１］，在ｐＨ６，测定吸收波长为２６７ｎｍ处，用紫外分光光度法直接测定蔬菜中的Ｖ－Ｃ含量，与常规方法比较，结果基本一致．而且这一方法具有快速、稳定、试剂易得、易保存等特点．     

A serologic assessment of exposure to viral pathogens and Leptospira in an urban raccoon (Procyon lotor) population inhabiting a large zoological park.

In urban environments, raccoons (Procyon lotor) may act as reservoirs for an array of pathogenic organisms, presenting spillover risks for human, domestic animal, and captive (zoo) animal populations. Over 5 yr, 159 raccoons from a high-density raccoon population in St. Louis, Missouri (USA), were surveyed for exposure to canine distemper virus (CDV), canine adenovirus 1 (CAV-1); feline parvovirus (FPV; =feline panleukopenia), and several serovars of Leptospira interrogans. Exposure to each of the viruses and two Leptospira serovars (grippotyphosa and icterohemorrhagiae) was detected (prevalence of CDV = 54.1%; FPV = 49.7%; CAV-1 = 6.9%; L. interrogans icterohemorrhagiae = 8.9%; L. interrogans grippotyphosa = 6.3%). Eighty percent of raccoons showed evidence of exposure to at least one of the five primary pathogens, and 39% were positive for multiple species. Among the viruses, there was a significant co-occurrence of CDV and CAV-1. Longitudinal data on a subset of animals revealed that among individuals who were diagnosed as seropositive on first capture, 33-100% became seronegative for the pathogen of interest when reexamined at a later date. Thus, free-ranging urban raccoons have been exposed to multiple infectious agents, some of which may pose risks to humans and to nonvaccinated domestic and captive animal populations.     

A recent growth increase of European beech (Fagus sylvatica L.) at its Mediterranean distribution limit contradicts drought stress

Future changes in tree growth, associated with a warmer and drier climate, are predicted for many species and locations across the European Mediterranean Basin. However, quantification of the intensity and severity of related consequences for forest ecosystem functioning and productivity remains challenging. Species-specific distribution limits that are particularly sensitive to small changes in the ambient climate may provide an ideal test bed to assess the nature of past growth trends and extremes and their responsible controls. Here, we seek to understand how twentieth century climate change affected the growth of European beech (Fagus sylvatica L.) nearby its south-eastern distribution limit in Albania and Macedonia on the Balkan Peninsula. We sampled 93 living trees from undisturbed mixed forest stands at ~1,450 m a.s.l. and 29 timbers from nearby historical buildings. Application of different tree-ring detrending techniques allowed robust composite chronologies with varying degrees of high- to low-frequency variability to be developed back to 1648 ad. Comparison with local meteorological station measurements and continental grid-box climate indices revealed spatiotemporal instability in growth–climate response patterns. Nevertheless, year-to-year and decadal-long fluctuations in radial beech growth were significantly (P < 0.001) negatively correlated at ?0.61 with June–September temperature over the 1951–1995 period. This (inverse) relationship between increased beech growth and decreased summer temperature is somewhat indicative for the importance of plant-available soil moisture, which likely controls ring width formation near the species-specific south-eastern distribution limit. Significant positive correlations between beech growth and drought (scPDSI; r = 0.57) confirm metabolistic drought constraints. However, an unexpected late twentieth century growth increase not only contradicts the previously observed growth dependency to summer soil moisture, but also denies any putative drought-induced forest ecosystem suppression in this part of the Mediterranean Basin.     

Evaluating the effect of plant water availability on inner alpine coniferous trees based on sap flow measurements

Climate simulations anticipate an increase in mean summer temperature with synchronous decrease in summer precipitation during the course of the current century in Central Europe. As a consequence, transpiration of forest trees and stands may be altered along with soil water availability. In this study, the effect of reduced plant water availability to conifers was investigated into an open Pinus sylvestris forest (Erico-Pinetum typicum; P. sylvestris 60 %, Picea abies 20 %; and Larix decidua 20 %) within the inner alpine dry valley of the Inn River in Tyrol, Austria. For reducing plant water availability, we installed a transparent roof construction above the forest floor to prevent precipitation to reach the soil. The roofed area covered 240 m² and included 10 trees. A respective number of 11 trees served as controls in the absence of any manipulation. Roofing significantly reduced plant water availability as indicated in lower predawn needle water potentials. Sap flow density (Q _s) was 63, 47, and 24 % lower in roofed P. sylvestris, P. abies, and L. decidua trees, respectively, as compared to control trees. Our findings suggest that P. sylvestris and P. abies behaves “isohydric” as they close their stomata relatively early under conditions of reduced plant water availability and thus stabilize their water relations, whereas L. decidua behaves “anisohydric” and maintains high transpiration rates.