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51.
52.
Understanding and quantification of phosphorus (P) fluxes are key requirements for predictions of future forest ecosystems changes as well as for transferring lessons learned from natural ecosystems to croplands and plantations. This review summarizes and evaluates the recent knowledge on mechanisms, magnitude, and relevance by which dissolved and colloidal inorganic and organic P forms can be translocated within or exported from forest ecosystems. Attention is paid to hydrological pathways of P losses at the soil profile and landscape scales, and the subsequent influence of P on aquatic ecosystems. New (unpublished) data from the German Priority Program 1685 “Ecosystem Nutrition: Forest Strategies for limited Phosphorus Resources” were added to provide up‐to‐date flux‐based information. Nitrogen (N) additions increase the release of water‐transportable P forms. Most P found in percolates and pore waters belongs to the so‐called dissolved organic P (DOP) fractions, rich in orthophosphate‐monoesters and also containing some orthophosphate‐diesters. Total solution P concentrations range from ca. 1 to 400 µg P L?1, with large variations among forest stands. Recent sophisticated analyses revealed that large portions of the DOP in forest stream water can comprise natural nanoparticles and fine colloids which under extreme conditions may account for 40–100% of the P losses. Their translocation within preferential flow passes may be rapid, mediated by storm events. The potential total P loss through leaching into subsoils and with streams was found to be less than 50 mg P m?2 a?1, suggesting effects on ecosystems at centennial to millennium scale. All current data are based on selected snapshots only. Quantitative measurements of P fluxes in temperate forest systems are nearly absent in the literature, probably due to main research focus on the C and N cycles. Therefore, we lack complete ecosystem‐based assessments of dissolved and colloidal P fluxes within and from temperate forest systems.  相似文献   
53.
The impact of ectomycorrhizal fungi or rhizosphere bacteria on tree seedling growth and nutrient uptake is well known. However, few studies have combined those microorganisms in one experiment to clarify their relative contribution and interactions in nutrient acquisition. Here, we monitored the respective contributions of pine roots, two ubiquitous forest ectomycorrhizal fungi Scleroderma citrinum and Laccaria bicolor, and two S. citrinum-mycorrhizosphere bacterial strains of Burkholderia glathei and Collimonas sp., on mineral weathering, nutrient uptake, and plant growth. Pinus sylvestris plants were grown on quartz–biotite substrate and inoculated or not with combinations of mycorrhizal fungi and/or bacterial strains. Magnesium and potassium fluxes were measured and nutrient budgets were calculated. Both ectomycorrhizal fungi significantly increased Mg plant uptake. No significant effects of the two bacterial strains were detected on the K and Mg budgets, but co-inoculating the mycorrhizal fungus S. citrinum and the efficient mineral-weathering B. glathei bacterial strain significantly improved the Mg budget. Similarly, co-inoculating S. citrinum with the Collimonas sp. bacterial strain significantly improved the pine biomass compared to non-inoculated pine plants. In order to better understand this process, we monitored the survival of the inoculated bacterial strains in the quartz–biotite substrate, the pine rhizosphere, and the mycorrhizal niche. The results showed that the two bacterial strains harboured different colonization behaviours both of which depended on the presence of the ectomycorrhizal partner. The populations of the Burkholderia strain were maintained in all these environments with a significantly higher density in the mycorrhizal niche, especially of S. citrinum. In contrast the population of the Collimonas strain reached the detection level except in the treatment inoculated with S. citrinum. These results highlight the need for taking into account the ecology of the microorganisms, and more specifically the fungal–bacterial interactions, when studying mineral weathering and plant nutrition.  相似文献   
54.
Fine earth accumulated within the weathering fissures of the coarse‐soil fraction (particles > 2 mm), so called “stone‐protected fine earth”, can provide a high short‐term nutrient release by cation exchange. It is thus hypothesized that unweathered gneiss particles cannot provide plants with exchangeable‐cation nutrients and that biological weathering is needed to include silicate‐bound nutrients into biochemical cycles. In a microcosm experiment, ectomycorrhizal Norway spruce (Picea abies) seedlings were grown on either weathered or unweathered paragneiss coarse‐soil fragments under natural hydraulic and climatic boundary conditions. A nutrient solution containing N, P, and K was added, however Mg and Ca could only be taken up from the coarse‐soil substrate. Solutes in drainage were analyzed during the experiment; plant nutrient uptake was determined after the experiment ended. Solute dynamics depended on the weathering state of the substrates: unweathered gneiss showed high initial Mg and Ca fluxes that diminished strongly afterwards, whereas weathered gneiss showed a much more gradual and sustainable release of these cations. Patterns in dissolved organic C and sulfate drainage indicated that the internal pores of weathered gneiss fragments contained organic material most likely as a result of living spaces from microorganisms. Plant biomass did not differ between treatments, however Mg content was higher in seedlings grown on weathered gneiss. Nutrient budgets demonstrated that the “stonesphere” of weathered gneiss can act as a quasi‐constant nutrient source whereas unweathered gneiss only provided high initial nutrients fluxes. In nutrient‐depleted, acidified fine‐earth environments, the coarse‐soil fraction may therefore act as a retreat for nutrient‐adsorbing tissues and as a buffer for nutrient shortages.  相似文献   
55.
We investigated the cellular responses of stem tissues of mature Scots pine (Pinus sylvestris L.) trees to inoculations with two fungal pathogens. The bark beetle vectored fungus, Leptographium wingfieldii Morelet, induced longer lesions in the bark, stronger swelling of polyphenolic parenchyma cells, more polyphenol accumulation and increased ray parenchyma activity compared with the root rot fungus, Heterobasidion annosum (Fr.) Bref., or mechanical wounding. Axial resin ducts in the xylem are a general feature of the preformed defenses of Scots pine, but there was no clear induction of additional traumatic axial resin ducts in response to wounding or fungal infection. The anatomical responses of Scots pine to pathogen infection were localized to the infection site and were attenuated away from bark lesions. The responses observed in Scots pine were compared with published studies on Norway spruce (Picea abies (L.) Karst.) for which anatomically based defense responses have been well characterized.  相似文献   
56.
Five isonitrogenous and isoenergetic diets with soybean oil (SO), linseed oil (LO), algae oil from Schizochytrium sp. (AO), mixed oil (MO, SO:LO:AO = 1:1:1) and fish oil (FO; control group) were selected to feed juvenile Onychostoma macrolepis (initial weight 1.86 ± 0.07 g) for eight weeks. The results showed that in the LO and FO groups fish grew best. There was no significant difference in specific growth rate (SGR) and feed efficiency (FE) between the MO and FO groups (p > .05). The highest contents of 18:2n‐6, 18:3n‐3 and 22:6n‐3 in liver and muscle were found with the SO, LO and AO groups, respectively (p < .05). There appeared the highest malondialdehyde (MDA) content and the lowest superoxide dismutase (SOD) activity in the fish liver of the AO group. There appeared the highest concentrations of serum glucose (GLU), cholesterol (CHOL) and triglycerides (TG) in the SO group. The expressions of lipid anabolism genes were significantly up‐regulated by dietary SO and LO (p < .05). The expressions of lipid catabolism genes were significantly higher with the AO, MO and FO groups (p < .05). This study recommended that LO or MO as a better vegetable oil source for juvenile O. macrolepis.  相似文献   
57.
The mechanical properties and responses of cells to external stimuli (including drugs) are closely connected to important phenomena such as cell spreading, motility, activity, and potentially even differentiation. Here, reversible changes in the viscoelastic properties of surface-attached fibroblasts were induced by the cytoskeleton-perturbing agent cytochalasin D, and studied in real-time by the quartz crystal microbalance with dissipation (QCM-D) technique. QCM-D is a surface sensitive technique that measures changes in (dynamically coupled) mass and viscoelastic properties close to the sensor surface, within a distance into the cell that is usually only a fraction of its size. In this work, QCM-D was combined with light microscopy to study in situ cell attachment and spreading. Overtone-dependent changes of the QCM-D responses (frequency and dissipation shifts) were first recorded, as fibroblast cells attached to protein-coated sensors in a window equipped flow module. Then, as the cell layer had stabilised, morphological changes were induced in the cells by injecting cytochalasin D. This caused changes in the QCM-D signals that were reversible in the sense that they disappeared upon removal of cytochalasin D. These results are compared to other cell QCM-D studies. Our results stress the combination of QCM-D and light microscopy to help interpret QCM-D results obtained in cell assays and thus suggests a direction to develop the QCM-D technique as an even more useful tool for real-time cell studies.  相似文献   
58.
原有插秧机的插秧株距调节为挡位调节式,田间作业过程中操作不便且为有级调节。为此,设计了一种插秧机株距无级调节系统,该系统可以根据插秧机行进速度和插植传动轴转速无级调节插秧株距。采用液压系统取代原有插秧机株距调节的挡位调节方式,单片机作为CPU,结合接近开关、编码器以及直流电机,设计了插秧机株距无级调节系统。试验表明,该系统可实现插秧机株距无级调节,作业质量符合农艺要求,且性能稳定,可用于后续的插秧机全自动控制研究中。  相似文献   
59.
60.

Purpose

In spite of equal lithology, the local climate can affect soils’ geochemical characteristics. We investigated the dependence of heavy metal content on climatic factors according to a hierarchical nested analysis of variance design (ANOVA).

Materials and methods

We examined the heavy metal content in soils developed on the Upper Triassic dolomite at six locations situated at increasing distances from the Adriatic Sea towards inland. We tested the influence of the locations’ position, i.e. climate, vegetation cover, small-scale variability and analytical error. Co, Cr, Cu, Ni, Pb and Zn contents were determined by emission spectrometry.

Results and discussion

An initial increase in annual precipitation towards inland is followed by a steady decrease. Very high small-scale variability prevented statistically significant differences from being established at the location level due to the high variance components exhibited. However, the simpler one-way and non-parametric varieties of ANOVA confirmed significant differences in Co, Cr and Ni among locations. The differences are more pronounced in grassland soils where the Cu and Pb contents also differ between locations. There is a positive correlation among annual precipitation, Co, Cr and Ni, and it seems that the prevailing winds can also influence their content in soils.

Conclusions

The Co, Cr, Cu and Ni values are readily the highest in those locations with the greatest precipitation, possibly due to their resistance to leaching. The soils could be additionally enriched by an eolian contribution from the SW located outcropping flysch rocks. The established variability could be due to somewhat different dolomite composition. The reasons for the observed geochemical variability are complex and only partly due to climate.
  相似文献   
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