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31.
Patrick A.W. van Hees David L. Jones Douglas L. Godbold 《Soil biology & biochemistry》2005,37(4):771-776
Organic acids may play a key role in rhizosphere and pedogenic processes. The effects of young trees and ectomycorrhizas on the soil solution concentrations of low molecular weight organic acids (LMWOAs) were studied in soil columns (E horizon) in the presence or absence of Pinus sylvestris and Picea abies with or without three ectomycorrhizal fungi. Several LMWOAs were identified at concentrations ranging from <0.1 to 11 μM. Compared to soil columns without tree seedlings, the presence of non-mycorrhizal or mycorrhizal tree seedlings sometimes resulted in small but statistically significant increases in citrate, formate, malonate and oxalate concentration. The general nutrient concentration and low P had little short-term effect on soil solution organic acid concentrations. The results suggest that biodegradation rather than production may be the major factor regulating soil solution organic acid concentrations. 相似文献
32.
Lisa Bjørnlund Søren Mørk Mette Vestergård Regin Rønn 《Biology and Fertility of Soils》2006,43(1):1-11
The aim was to study the effects of P fertilization and leaf aphid attack on the trophic interactions of bacteria and bacterial feeders in the rhizospheres of barley plants. The density of protozoa peaked in the rhizospheres of plants fertilized with N and P, whereas nematodes peaked in the rhizospheres of plants to which only N had been added. Fingerprinting of bacterial communities by length heterogeneity polymerase chain reaction revealed differences in community structure between NP rhizospheres and N rhizospheres as well as aphid-related differences within N rhizospheres. Specifically, α-proteobacteria increased with P addition. To evaluate if differences in bacteria in terms of their quality as food could partly explain the observed differences in protozoan and nematode abundances, growth of the flagellate Cercomonas sp. was assessed with 935 bacteria isolated from the different treatments. This assay indicated that bacterial isolates were of higher food quality to Cercomonas sp. in NP than in N rhizospheres when plants were subjected to aphid attack. Bacteria of high and low food quality for Cercomonas sp., respectively, were fed to the nematode Caenorhabditis elegans and larval production examined. α-Proteobacteria supported the growth of Cercomonas sp. well, whereas Actinobacteria did not. In contrast, C. elegans reproduced poorly on most α-proteobacteria but were able to reproduce well on some Actinobacteria. These results suggest that the different response of protozoa and nematodes to P addition could be mediated through a food quality-related change in community composition of bacteria and that leaf aphid attack may interfere with nutrient effects on bacterial assemblages of rhizospheres. 相似文献
33.
Rice fields are an important source for atmospheric CH4, but the effects of fertilization are not well known. We studied the turnover of CH4 in rice soil microcosms without and with addition of potassium phosphate. Height and tiller number of rice plants were higher in the fertilized than in the unfertilized microcosms. Emission rates of CH4 were also higher, but porewater concentrations of CH4 were lower. The δ13C values of the emitted CH4 and of the CH4 in the porewater were both 2-6% higher in the fertilized microcosms than in the control. Potassium phosphate did not affect rate and isotopic signature of CH4 production in anoxic soil slurries. On the other hand, roots retrieved from fertilized microcosms at the end of incubation exhibited slightly higher CH4 production rates and slightly higher CH4-δ13C values compared to roots from unfertilized plants. Addition of potassium phosphate to excised rice roots generally inhibited CH4 production and resulted in increasingly lower δ13C values of the produced CH4. Fractionation of 13C during plant ventilation (i.e. δ13C in pore water CH4 versus CH4 emitted) was larger in the fertilized microcosms than in the control. Besides plant ventilation, this difference may also have been caused by CH4 oxidation in the rhizosphere. However, calculation from the isotopic data showed that less than 27% of the produced CH4 was oxidized. Collectively, our results indicate that potassium phosphate fertilization stimulated CH4 emission by enhancing root methanogenesis, plant ventilation and/or CH4 oxidation, resulting in residence times of CH4 in the porewater in the order of hours. 相似文献
34.
J. F. Dormaar 《Biology and Fertility of Soils》1990,10(2):121-126
Summary The effect of one form of soil organic matter, such as living roots or root exudates on another form of soil organic matter, such as dead roots or incorporated litter and litter leachates, has been studied from various perspectives over the last 25 years. The effect seems to be either positive (priming) or negative (conserving). The present review concentrates on the conserving effect, measured as a decrease in 14CO2 released, in both field and greenhouse/growth chamber studies. The field experiments suggested that certain physical conditions in the soil, such as less available moisture or restricted aeration which led to lower microbial activity, explained the conserving effect of living roots on soil organic matter. Although more detailed greenhouse/growth chamber studies confirmed the conserving effect per se, it appears that biological rather than physical factors could better explain the reduction in the rate of decomposition of 14C-labelled plant residues in the presence of roots. However, a complex picture has emerged through a variety of postulates, all proposed in attempts to explain the conserving effect. Finally, the most recent studies have argued that the decrease in decomposition of labelled organic matter in planted soil is probably more apparent than real. A decrease in respired 14CO2 could be explained by an incorporation of 14C derived from old roots into the rhizosphere microbial populations of the living roots. To make any further progress on the fundamental question of how soil organic matter moves along its continuum from a living to a refractory state, the microenvironment needs to be examined at periodic intervals. New developments in improved histochemical and electron-probe microanalyses look promising.LRS Contribution no. 3878970 相似文献
35.
Emile Benizri Christophe Nguyen Sophie Slezack-Deschaumes 《Soil biology & biochemistry》2007,39(5):1230-1233
The organic compounds released from roots (rhizodeposits) stimulate the growth of the rhizosphere microbial community. They may be responsible for the differences in the structure of the microbial communities commonly observed between the rhizosphere and the bulk soil. Rhizodeposits consists of a broad range of compounds including root mucilage. The aim of this study was to investigate if additions of maize root mucilage, at a rate of 70 μg C g−1 day−1 for 15 days, to an agricultural soil could affect the structure of the bacterial community. Mucilage additions moderately increased microbial C (+23% increase relative to control), which suggests that the turnover rate of microorganisms consuming this substrate was high. Consistent with this, the number of cultivable bacteria was enhanced by +450%. Catabolic (Biolog® GN2) and 16S-23S intergenic spacer fingerprints exhibited significant differences between control and mucilage treatments. These data indicate that mucilage can affect both the metabolic and genetic structure of the bacterial community as shown by a greater catabolic potential for carbohydrates. We concluded that mucilage is likely to significantly contribute to differences in the structure of the bacterial communities present in the rhizosphere compared to the bulk soil. 相似文献
36.
Increased root exudation and a related stimulation of rhizosphere-microbial growth have been hypothesised as possible explanations for a lower nitrogen- (N-) nutritional status of plants grown under elevated atmospheric CO2 concentrations, due to enhanced plant-microbial N competition in the rhizosphere. Leguminous plants may be able to counterbalance the enhanced N requirement by increased symbiotic N2 fixation. Only limited information is available about the factors determining the stimulation of symbiotic N2 fixation in response to elevated CO2.In this study, short-term effects of elevated CO2 on quality and quantity of root exudation, and on carbon supply to the nodules were assessed in Phaseolus vulgaris, grown in soil culture with limited (30 mg N kg−1 soil) and sufficient N supply (200 mg N kg−1 soil), at ambient (400 μmol mol−1) and elevated (800 μmol mol−1) atmospheric CO2 concentrations.Elevated CO2 reduced N tissue concentrations in both N treatments, accelerated the expression of N deficiency symptoms in the N-limited variant, but did not affect plant biomass production. 14CO2 pulse-chase labelling revealed no indication for a general increase in root exudation with subsequent stimulation of rhizosphere microbial growth, resulting in increased N-competition in the rhizosphere at elevated CO2. However, a CO2-induced stimulation in root exudation of sugars and malate as a chemo-attractant for rhizobia was detected in 0.5-1.5 cm apical root zones as potential infection sites. Particularly in nodules, elevated CO2 increased the accumulation of malate as a major carbon source for the microsymbiont and of malonate with essential functions for nodule development. Nodule number, biomass and the proportion of leghaemoglobin-producing nodules were also enhanced. The release of nod-gene-inducing flavonoids (genistein, daidzein and coumestrol) was stimulated under elevated CO2, independent of the N supply, and was already detectable at early stages of seedling development at 6 days after sowing. 相似文献
37.
The effect of elevated pCO2 (60 Pa) on the frequency of nitrate-dissimilating Pseudomonas (NDP) was investigated in the rhizosphere of fertilised Lolium perenne swards in the Swiss Free Air Carbon dioxide Enrichment (FACE) experiment. Numbers of cultivable root-associated Pseudomonas were greater under elevated (60 Pa) than under ambient (36 Pa) pCO2 in both high and low N-fertilised swards. For both pCO2 conditions, the NDP frequency decreased with closer root proximity to L. perenne roots in low fertilised swards. Anyway, in high N swards the NDP frequency was similar in root and soil fractions. Thus, N availability may be a major factor influencing NDP populations under elevated pCO2, most likely due to increased competition for N between plant and nitrate-dissimilating bacteria. 相似文献
38.
39.
樱桃根际土壤酶活性与土壤养分动态变化及其关系研究 总被引:6,自引:0,他引:6
通过盆栽试验研究了樱桃根际脲酶、磷酸酶活性与氮、磷、钾动态变化及其相互关系。结果表明,生长季前期樱桃根际脲酶、磷酸酶活性明显提高,根际酶活性显著高于根外,随物候期进展土壤酶活性及R/S值逐渐降低。氮、磷、钾元素在年生长周期内整体上呈下降趋势,生长季前期根际全氮、碱解氮及全磷亏缺明显,而根际有效磷、速效钾明显富集,这种作用亦随物候期进展逐渐减弱。土壤脲酶、磷酸酶活性与氮磷钾土壤营养元素含量间存在着一定的相关性,以春梢停长期相关程度最高。 相似文献
40.