Relationships between soil bulk electrical conductivity and the principal component analysis of topography and soil fertility values

Measures of soil electrical conductivity (EC) and elevation are relatively inexpensive to collect and result in dense data sets which allow for mapping with limited interpolation. Conversely, soil fertility information is expensive to collect so that relatively few samples are taken and mapping requires extensive interpolation with large estimation errors, resulting in limited usefulness for site-specific applications in precision agriculture. Principal component (PC) analysis and cokriging can be applied to create meaningful field scale summaries of groups of attributes and to decrease the estimation error of maps of the summarized attributes. Deep (0–90 cm) and shallow (0–30 cm) EC, elevation, and soil fertility attributes were measured in fields under corn (Zea mays L.) and soybean (Glycine max L.) rotations, at two sites in Illinois (IL) and two sites in Missouri (MO). Soil fertility and topography attributes were summarized by PC analysis. The first topography PC (TopoPC1) contrasted flow accumulation against elevation and curvature, to describe the main topographic pattern of the fields. The first soil fertility PC (SoilPC1) consistently grouped together cation exchange capacity (CEC), Ca, Mg, and organic matter (OM). SoilPC1 was well correlated to soil EC for all sites and cokriging with EC had higher r ² in the crossvariogram models compared to ordinary kriging. The second and third soil fertility PCs (SoilPC2 and SoilPC3) were concerned with soil pH and P, and reflected historic land use patterns. Maps of SoilPC2 and SoilPC3 had little relationship to soil EC or topography and so could not be improved by cokriging.     

Integrated responses of hydraulic architecture, water and carbon relations of western hemlock to dwarf mistletoe infection

Dwarf mistletoe (Arceuthobium spp.) is a hemiparasite that is said to be the single‐most destructive pathogen of commercially valuable coniferous trees in many regions of the world. Although its destructive nature is well documented in many respects, its effects on the physiology of its host are poorly understood. In the present study, water and carbon relations were characterized over a range of scale from leaf to whole tree in large (40‐ to 50‐m‐tall) individuals of western hemlock (Tsuga heterophylla (Raf.) Sarg.) that were either heavily infected, or uninfected with hemlock dwarf mistletoe (Arceuthobium tsugense). Specific hydraulic conductivity (k_s) of infected branches was approximately half that of uninfected branches, yet leaf‐specific conductivity (k_L) was similar because leaf area : sapwood area ratios (A_L : A_S) of infected branches were lower. Pre‐dawn and minimum leaf water potential and stomatal conductance (g_s) were similar among infected and uninfected trees because adjustments in hydraulic architecture of infected trees maintained k_L despite reduced k_s. Maximum whole‐tree water use was substantially lower in infected trees (approximately 55 kg d^?1) than in uninfected trees (approximately 90 kg d^?1) because reduced numbers of live branches in infected trees reduced whole‐tree A_L : A_S in a manner consistent with that observed in infected branches. Maximum photosynthetic rates of heavily infected trees were approximately half those of uninfected trees. Correspondingly, leaf nitrogen content was 35% lower in infected trees. Foliar δ¹³C values were 2.8‰ more negative in infected than in uninfected individuals, consistent with the absence of stomatal adjustment to diminished photosynthetic capacity. Adjustments in hydraulic architecture of infected trees thus contributed to homeostasis of water transport efficiency and transpiration on a leaf area basis, whereas both carbon accumulation and photosynthetic water use efficiency were sharply reduced at both the leaf and whole‐tree scale.     

Aquaporins account for variations in hydraulic conductance for metabolically active root regions of Agave deserti in wet, dry, and rewetted soil

The importance of aquaporins for root hydraulic conductance (L_P) was investigated along roots of the desert succulent Agave deserti in wet, dry and rewetted soil. Water channel activity was inferred from HgCl₂‐induced reductions of L_P that were reversible by 2‐mercaptoethanol. Under wet conditions, HgCl₂ reduced L_P for the distal root region by 50% and for the root region near the shoot base by 36% but did not affect L_P for the mid‐root region. For all root regions, L_P decreased by 30–60% during 10 d in drying soil and was not further reduced by HgCl₂. After soil rewetting, L_P increased to pre‐drying values and was again reduced by HgCl₂ for the distal and the basal root regions but not the mid‐root region. For the distal region, water channels in the epidermis/exodermis made a disproportionately large contribution to radial hydraulic conductance of the intact segment; for the basal region, water channel activity was highest in the cortex and endodermis. The role of water channels was greatest in tissues in which cells were metabolically active both in the distal root region, where new apical growth occurs in wet soil, and in the basal region, which is the most likely root region to intercept light rainfall.     

柠檬形克勒克酵母对温州蜜柑“国庆一号”采后贮藏的防腐效果

Citrus unshiu “Guoqing No.1” was used as material for elucidating the effect of Kloeckera apiculata suspension post-harvest treatment on preventing fruit decay during storage period. The result showed that K. apiculata preparation of 2×106CFU/mL (CFU, cloning forming unit) significantly reduced the development of decay caused by green mold, blue mold and stem rot, showing the same effect of carbendazim treatment after storage period of 100 days, and the disease incidence was controlled under 1%. The antagonist population was between 3.5×105CFU/mL and 1.7×107CFU/mL in citrus fruit, and increased 1.7×107CFU/mL after 40 days storage, and then stabilized for the remaining storage period. After storage at 5℃ for 100 days, K. apiculata strain 34-9 did not alter any quality parameters of fruit. During storage, the change of relative electrical conductivity (REC) showed a coordinate tendency with malondlaldehyde (MDA) content, which kept continuously growing from the beginning to the end of the storage. In the storage period of 25 days, the REC value and MDA content of the treatments were all significantly lower than those of water treatment, but had no obvious difference from those of carbendazim treatment. K. apiculata strain 34-9 had no effect on the enzyme activity of super oxide dismutase (SOD), but significantly improved peroxidase (POD) activity after 100 day storage.     

硝酸镧对香蕉幼苗两个抗寒生理指标的影响

在人工气候箱中进行人工模拟寒潮对香蕉的冷害 ,研究硝酸镧对改善香蕉抗寒性的生理作用。结果表明 :香蕉幼苗叶面喷施 0 .2 5～ 0 .2 8mmol/L浓度硝酸镧后 ,可提高香蕉叶片过氧化物酶的活性 44.2 %～61 .5 %及降低相对电导率 1 7.6%～ 2 7.7%。     

Biogeography of copepods in lakes and ponds of subarctic Québec,Canada

We aimed to determine whether the copepod assemblages in lakes and ponds of northern Québec, Canada, were closer in composition to those found in southern Québec, or to those reported from the subarctic and arctic. Six calanoid and five cyclopoid species were identified from 37 ponds and lakes located in the region between 55° N and 59° N. Species diversity was generally low, ranging from 0 to 4 species per lake. Dominant species were Leptodiaptomus minutus and Acanthocyclops vernalis. The species assemblages showed high affinity with those found in forested regions of southern Québec. Exceptions were Leptodiaptomus tyrrelli, previously only recorded west of Hudson Bay, and Hesperodiaptomus arcticus, hitherto recorded north of 58° N. Relationships between the lakes, species, and environmental variables were explored using multivariate analysis. Lakes situated along the coast and on two offshore islands clustered together and were characterised by higher conductivity and pH than those lakes located further inland. Leptodiaptomus tyrrelli was common in these coastal lakes. Canonical correspondence analysis revealed statistically significant relationships between copepod distributions and conductivity, dissolved organic carbon and pH. These three variables accounted for 70% of the variation in the species' distribution.     

负压状态下压力变化导致鲫鱼身体组织的损伤

通过试验研究负压状态下压力变化过程对鲫（Carassius auratus auratus)的损伤,试验采用真空泵和空气压缩机在试验容器内形成不同的压力变化过程,统计不同体长的鲫经历压力变化过程后的损伤情况,并对部分受损伤的鲫进行解剖和组织观察。研究发现负压状态下压力时变导数较大的变化过程会对鲫的生存构成直接威胁,主要损伤是鱼鳔部分或全部受损,在肝胰脏、肾脏等处有明显出血点。综合分析不同试验条件对鲫损伤的情况,得到了对鲫尽可能安全的压力时变导数极限值,从而为新型环保水力设施的设计提供参考依据,起到保护渔业资源的作用。     

激光对玉米陈种子萌发的生物效应

用不同剂量的He-Ne激光辐照贮存三年的玉米种子。结果表明,适宜的激光可有效地提高玉米陈种子的发芽势、发芽率和降低种子浸出液的电导率。