Can the arbuscular mycorrhizal fungus Glomus intraradices actively mobilize P from rock phosphates?

Plants colonized by arbuscular mycorrhizal (AM) fungi have been shown to respond positively to the application of insoluble forms of inorganic phosphorus (P) such as rock phosphates (RPs). The mechanism(s) underlying such responses remain(s) unknown and although it has been hypothesized, there is no experimental support for the production of chelating agents by AM fungal hyphae. Here we investigate whether AM fungi can solubilize P from RPs and transfer it to plant roots. Using root-organ cultures of Daucus carrota L. inoculated or not with Glomus intraradices Schenk & Smith and containing P from different RP sources, we predicted that: (1) roots inoculated with G. intraradices would take up more P than those uninoculated; that (2) the amount of P taken up by roots through G. intraradices would be positively correlated with the RP reactivity; and that (3) G. intraradices would have access to RP through localized alterations of pH and/or by the production of organic acid anions that may act as chelating agents. The RP reactivity was positively correlated with P uptake. However, mycorrhizal roots grew initially slower and did not respond differently to any P treatment than those uninoculated. There was no evidence of localized changes in pH in proximity of G. intraradices hyphae, indicating that responses to RP by mycorrhizal plants observed in previous studies do not appear to result from the release of H⁺ ions alone or in combination with organic acid anions.     

低分子量有机酸对不同合成磷源的释磷效应

采用化学浸提方法,研究了5种低分子量有机酸(草酸、柠檬酸、酒石酸、苹果酸、乙酸)对不同合成磷源的释磷效应。结果表明:供试有机酸(低浓度乙酸除外)均能促进不同合成磷源(DCP、OCP、FA、Fe-P、A l-P)中磷素的释放;其释磷效果与有机酸的种类和浓度有关,强弱顺序依次为柠檬酸、草酸、酒石酸、苹果酸、乙酸,有机酸浓度越高其释磷效果越好;有机酸与氟磷灰石(FA)反应后,溶液pH值升高。低浓度条件下pH值变化较大,而高浓度条件下pH值变化较小。     

Utilization of Sparingly Soluble Phosphate by Red Clover in Association with Glomus mosseae and Bacillus megaterium

A pot experiment was conducted to investigate the mobilization of sparingly soluble inorganic and organic sources of phosphorus (P) by red clover (Trifolium pratense L.) whose roots were colonized by the arbuscular mycorrhizal (AM) fungus Glomus mosseae and in association with the phosphate-solubilizing (PS) bacterium Bacillus megaterium ACCC10010. Phosphate-solubilizing bacteria and rock phosphate had a synergistic effect on the colonization of plant roots by the AM fungus. There was a positive interaction between the PS bacterium and the AM fungus in mobilization of rock phosphate, leading to improved plant P nutrition. In dual inoculation with the AM fungus and the PS bacterium, the main contribution to plant P nutrition was made by the AM fungus. Application of P to the low P soil increased phosphatase activity in the rhizosphere. Alkaline phosphatase activity was significantly promoted by inoculation with either the PS bacterium or the AM fungus.     

Recycled iron phosphate as a fertilizer raw material for tree stands on drained boreal peatlands

Fertilization of drained peatland forests with easily soluble or slow-release apatite fertilizers can increase phosphorus (P) export to water courses, especially when the soil is low in aluminum (Al) and iron (Fe) hydroxides and oxides. Application of Al and Fe together with P increases P adsorption to the soil and decreases the risk of leaching. The aim of this study was to investigate the use of recycled iron phosphate (rFePO₄) as forest fertilizer raw material from environmental and forest production perspectives. Trial fertilizers with different mixtures of rFePO₄ and Russian Kola apatite (Kap) were applied on 15 mini-catchments (area 100 m²), where the discharge at the outlet was collected, sampled and analyzed throughout the about 4-year measurement period. The foliage P content and height growth of the trees on the mini-catchments were measured. The biomass growth of the extramatrical mycorrhizal mycelia (EMM) was studied with a separate in-growth mesh bag experiment conducted on the same site. The results indicated no increase in phosphorus export to surface waters after application of rFePO₄ and 25/75 and 50/50 mixtures of rFePO₄ and Kap. In contrast to earlier studies showing a relatively high P export with different types of apatite fertilizers, the Kap fertilizer showed only minor phosphorus export. The height growth measurements and needle analyses of the juvenile Scots pine stands indicated poor P availability from pure rFePO₄, but the P availability from the 50/50 and 25/75 mixtures of rFePO₄ and Kap was similar to pure Kap. The mixtures of Kap and rFePO₄ enhanced the EMM biomass by 2- to 3-fold, whereas Kap and rFePO₄ alone, and high P availability (superphosphate) had no significant effect compared to non-P controls. The increase in EMM biomass as induced by concurrent application of Kap and rFePO₄ was not clearly reflected in tree growth and P acquisition. However, longer follow-up studies than in this one may be needed in order to verify the effect of increased EMM biomass on mycorrhizal mycelia mediated nutrient uptake and tree growth.     

Soil organic carbon and phosphorus availability regulate abundance of culturable phosphate-solubilizing bacteria in paddy fields

Low availability of phosphorus(P) is a major constraint for optimal crop production, as P is mostly present in its insoluble form in soil. Therefore,phosphate-solubilizing bacteria(PSB) from paddy field soils of the Indo-Gangetic Plain, India were isolated, and their abundance was attempted to be correlated with the physicochemical characteristics of the soils. Ninety-four PSB were isolated on Pikovskaya's agar medium, and quantitative phosphate solubilization was evaluated using NBRIP medium. The isolates solubilized P up to a concentration of 1 006 μg mL~(-1) from tricalcium phosphate with the secretion of organic acids. These isolates were identified by 16 S rRNA gene sequence comparison, and they belonged to Gammaproteobacteria(56 isolates),Firmicutes(28 isolates), Actinobacteria(8 isolates), and Alphaproteobacteria(2 isolates). Phylogenetic analysis confirmed the identification by clustering the isolates in the clade of the respective reference organisms. The correlation analysis between PSB abundance and physicochemical characteristics revealed that the PSB population increased with increasing levels of soil organic carbon, insoluble P, K~+, and Mg~(2+). The promising PSB explored in this study can be further evaluated for their biofertilizer potential in the field and for their use as potent bio-inoculants.     

Application of low‐phosphorus‐containing legume residues reduces extractable phosphorus in a tropical Ultisol

Application of legume green manure (GM) is suggested to be effective in increasing the availability of native soil phosphorus (P) and the dissolution and utilization of phosphate rock (PR)‐P by food crops. Experiments were conducted to study the dynamics of extractable P (P extracted by Bray‐1‐extracting solution) of an Ultisol amended with or without GM residues of contrasting P concentrations in the absence of growing plants. In two separate experiments, GM residues of Aschynomene afraspera (a flood‐tolerant legume) and of Crotalaria micans (upland) with varying P concentrations were added to an acidic soil amended with PR‐P or triple superphosphate (TSP) in plastic bottles. Soil moisture was brought to field capacity of the soil in the upland experiment and saturated with distilled water in the lowland setup. This was done to simulate aerobic upland and anaerobic lowland soil conditions in the relevant plastic bottles. Only P concentration of the residues added varied, while lignin and C : N ratios were similar. A temperature of 25°C was maintained throughout the experiment. Changes in soil extractable Bray‐1‐P were measured at the end of the incubation period (60 or 80 d). In the aerobic soils, extractable P in the combined PR+GM or TSP+GM treatments was significantly lower than in the PR‐ or TSP‐ treated soils. The amendment with GM residues alone significantly increased Bray‐1‐P over the unamended control in the case of the inorganic P‐fertilized GM residues. The trend in extractable P was similar in the soils incubated under anaerobic conditions. However, in the case of PR, concentrations of P extracted by Bray‐1 solution did not significantly change in the presence or absence of GM. The results suggest that the incorporation of GM residues with low P concentration does not lead to a net P release in upland or lowland soils. These results have implications for nutrient cycling in farming systems in W Africa as most of the soils are poor and very low in available P.     

Making modern agriculture sustainable: Fam research network on agroecosystems

All forms of agriculture cause changes in the balances and fluxes of preexisting ecosystems, thereby limiting self-regulatory ecosystem (resiliency) functions. The intensive agriculture of the past, with its strong reduction of landscape structures and vast decoupling of energy and matter cycles, has caused stress and degradation of the production base; massive influence has also been exerted on neighboring compartments. This has resulted in the well known problems of pesticide loads, high phosphate loads to surface waters via over-fertilized soils or erosion as such. To overcome the economic, social and political inadequacies leading to ecological degradation, the demand for sustainable agricultural management needs to be transposed into knowledge-based practical instructions and political regulations on a regional scale. Thus, applied research for a sustainable and ecologically compatible land use aimed at sufficient food production is ever so important. In the FAM, thirty German research institutes have merged to perform research on this topic.     

黑糯玉米面粉磷酸单酯制备及性质的研究

研究了制备黑糯玉米面粉磷酸单酯的最佳工艺条件，并测试了其主要特性。试验结果表明：在pH值6．5、NaH2PO4与面粉配比为0．19、反应温度为130℃，反应时间为1h的工艺条件下制备的产品效果最好，粘度最高。糊粘度和冻融稳定性达到了黑糯玉米淀粉的水平。     

土壤磷素Langmuir等温吸附特性与磷肥效果的关系

应用Langmuir等温式解释土壤磷吸收附等温线,具有良好的适合性。在24个供试土壤中,有21个土壤的相关系数达到极显著水准,3个达显著水准。通过Langmuir等温式可获得土壤吸磷参数——最大吸磷量(Xm)和吸附平衡常数(K)。Xm值可以衡量土壤磷库的大小,K值反映了土壤吸磷反应自由能下降的程度。Xm和K与磷肥利用率呈极显著负相关,其相关系数分别为-0.7146、～0.6233。不同性质的土壤,适宜作物生长的土壤平衡溶液磷浓度差异不大。当土壤平衡溶液磷浓度为0.1ppm P时,水稻产量可达最高产量的95％以上。因此,可根据Langmuir方程计算出满足水稻正常生长所需要的磷肥施用量。     

活化磷矿粉在砖红壤上的施用效果

砖红壤酸性强和活性铁、铝含量高，对磷固定强烈，磷肥有效性低．为了提高磷肥利用率，将高分子有机化合物与磷矿粉混合加工制成活化磷矿粉，分别施用于种植甘蔗的新垦砖红壤和种植大白菜的严重侵蚀砖红壤以及种植花生的水旱轮作熟化砖红壤，结果表明：施用活化磷矿粉的肥效至少与过磷酸钙相当，甚至优于过磷酸钙．因此，为了节省生产成本和改良土壤，活化磷矿粉值得在砖红壤区推广应用。