Impact of legume versus cereal root residues on biological properties of West African soils

Many microbial turnover processes in acidic sandy subtropical soils are still poorly understood. In a 59-day pot and a 189-day laboratory incubation experiment with two West African continuous cereal soils, the effects of 2 mg g^?1 root residues were investigated on growth of sorghum seedlings, soil microbial biomass and activity indices, using cowpea, groundnut, pearl millet, maize and sorghum. The effects of root residues were compared with mineral P or mineral P + N treatments and with a non-fertilized control treatment. On the Alfisol (Fada, Burkina Faso), shoot dry mass was always significantly higher than on the Ultisol (Koukombo, Togo). Highest shoot dry mass was observed after application of mineral P + N on the Alfisol and after mineral P alone on the Ultisol. The application of legume root residues led to small and non-significant increases in dry mass production compared to the non-amended control, whereas the application of cereal root residues led to a decline, regardless of their origin (millet, maize or sorghum). Contents of microbial biomass C, microbial biomass N and ergosterol were 75 to 100% higher in the Alfisol than in the Ultisol, while ATP was only 36% higher. Organic amendments increased ergosterol concentrations by up to 145% compared to the control and mineral P application. Microbial biomass C and microbial biomass N increased by up to 50% after application of root residues, but ATP only up to 20%. After application of legume root residues, cumulative CO₂ production was similar in both soils with an average of 370?µg CO₂-C g^?1 over 189 days. After application of cereal root residues, cumulative CO₂ production was higher in the Alfisol (530?µg g^?1) than in the Ultisol (445?µg g) over 189 days.     

解钾促生菌的筛选鉴定及对东北黑土区玉米的促生效应

[背景]东北地区作为全国玉米的主产区,土壤缺钾严重限制了玉米的高产.解钾促生菌可活化土壤中难溶的钾,提高土壤钾的有效性,进而促进植物生长.[目的]从中国东北黑土区的玉米根际土壤中筛选鉴定高效解钾菌,研究其在缺钾条件下对玉米生长的促生效果,为开发适应当地环境的微生物钾肥提供优良的菌种资源.[方法]采用选择性培养基从玉米根...     

Effects of Manure Compost Application on Soil Microbial Community Diversity and Soil Microenvironments in a Temperate Cropland in China

The long-term application of excessive chemical fertilizers has resulted in the degeneration of soil quality parameters such as soil microbial biomass, communities, and nutrient content, which in turn affects crop health, productivity, and soil sustainable productivity. The objective of this study was to develop a rapid and efficient solution for rehabilitating degraded cropland soils by precisely quantifying soil quality parameters through the application of manure compost and bacteria fertilizers or its combination during maize growth. We investigated dynamic impacts on soil microbial count, biomass, basal respiration, community structure diversity, and enzyme activity using six different treatments [no fertilizer (CK), N fertilizer (N), N fertilizer + bacterial fertilizer (NB), manure compost (M), manure compost + bacterial fertilizer (MB), and bacterial fertilizer (B)] in the plowed layer (0–20 cm) of potted soil during various maize growth stages in a temperate cropland of eastern China. Denaturing gradient electrophoresis (DGGE) fingerprinting analysis showed that the structure and composition of bacterial and fungi communities in the six fertilizer treatments varied at different levels. The Shannon index of bacterial and fungi communities displayed the highest value in the MB treatments and the lowest in the N treatment at the maize mature stage. Changes in soil microorganism community structure and diversity after different fertilizer treatments resulted in different microbial properties. Adding manure compost significantly increased the amount of cultivable microorganisms and microbial biomass, thus enhancing soil respiration and enzyme activities (p<0.01), whereas N treatment showed the opposite results (p<0.01). However, B and NB treatments minimally increased the amount of cultivable microorganisms and microbial biomass, with no obvious influence on community structure and soil enzymes. Our findings indicate that the application of manure compost plus bacterial fertilizers can immediately improve the microbial community structure and diversity of degraded cropland soils.     

内蒙古温带草原土壤微生物生物量碳的空间分布及驱动因素

【目的】探索内蒙古温带草原土壤微生物生物量碳的空间分布特征以及驱动因素。【方法】在内蒙古自治区境内沿着年均温、年降水梯度选择17个草原样点,在土壤剖面上分0-10 cm、10-20 cm、20-40 cm、40-60 cm、60-100 cm五层,分别采集土壤样品,测定土壤微生物生物量碳以及主要的环境和生物影响因子,分析不同草地类型以及不同土壤深度土壤微生物生物量碳的差异,探索非生物因子和生物因子对土壤微生物量碳的影响。【结果】草甸草原土壤微生物量碳最高,典型草原次之,荒漠草原最低。在0-10 cm土壤中,草地类型间的微生物量碳变异系数高于草甸草原和典型草原,低于荒漠草原;在0-100 cm土壤中,草甸草原样点间的微生物量碳的变异系数低于典型草原和荒漠草原。土壤微生物量碳与年降水、土壤含水量、粘粒含量、土壤养分元素、地上生物量、地下生物量呈显著正相关,与年均温和土壤p H值呈显著负相关关系。随着土壤深度的增加,土壤微生物量碳显著减少,非生物因子与微生物量碳的相关性减弱,草地类型间以及同一草地类型不同样点间的变异系数增加。0-10 cm土壤微生物量碳与10-40 cm土壤微生物量碳的相关指数高于0.5,与40-100 cm的土壤微生物量碳的相关指数小于0.3。【结论】内蒙古温带草原土壤微生物量碳的垂直分布呈现一定的规律性,且非生物因子对微生物量碳的影响也呈现垂直减弱的规律。     

改变碳输入对亚热带人工林土壤微生物生物量和群落组成的影响

通过在亚热带杉木(Cunninghamia lanceolata)和米老排(Mytilaria laosensis)人工林中设置互换凋落物、去除凋落物、去除凋落物+去除根系和对照处理来分析改变地上、地下碳输入对人工林土壤微生物生物量和群落组成的影响。结果显示,改变地上、地下碳输入对土壤微生物生物量碳、氮的影响因树种而异。在米老排林中,土壤微生物生物量不受碳源的限制。而在杉木林中,加入米老排凋落物、去除凋落物和去除凋落物+去除根系3种处理中土壤微生物生物量碳、氮具有明显增加的趋势。磷脂脂肪酸分析结果显示,杉木林中,添加高质量的米老排凋落物后,革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了24%、24%、53%、25%、28%,革兰氏阴性细菌和丛枝菌根真菌的相对丰度均有显著增加。与对照相比,杉木林中去除凋落物后革兰氏阳性细菌、阴性细菌、丛枝菌根真菌、放线菌和真菌群落生物量分别显著增加了22%、29%、44%、25%、52%,真菌与细菌比值显著增加了21%。但是,去除凋落物+去除根系处理对两个树种人工林土壤微生物群落组成均无显著影响。米老排和杉木林土壤微生物生物量碳、氮的季节变化格局不同,土壤养分有效性可能是驱动土壤微生物生物量季节变化的主要因子。未来研究需要关注凋落物和根系在不同树种人工林中对土壤微生物群落的相对贡献。     

Photosynthesis, productivity, and yield of maize are not affected by open-air elevation of CO2 concentration in the absence of drought

While increasing temperatures and altered soil moisture arising from climate change in the next 50 years are projected to decrease yield of food crops, elevated CO2 concentration ([CO2]) is predicted to enhance yield and offset these detrimental factors. However, C4 photosynthesis is usually saturated at current [CO2] and theoretically should not be stimulated under elevated [CO2]. Nevertheless, some controlled environment studies have reported direct stimulation of C4 photosynthesis and productivity, as well as physiological acclimation, under elevated [CO2]. To test if these effects occur in the open air and within the Corn Belt, maize (Zea mays) was grown in ambient [CO2] (376 micromol mol(-1)) and elevated [CO2] (550 micromol mol(-1)) using Free-Air Concentration Enrichment technology. The 2004 season had ideal growing conditions in which the crop did not experience water stress. In the absence of water stress, growth at elevated [CO2] did not stimulate photosynthesis, biomass, or yield. Nor was there any CO2 effect on the activity of key photosynthetic enzymes, or metabolic markers of carbon and nitrogen status. Stomatal conductance was lower (-34%) and soil moisture was higher (up to 31%), consistent with reduced crop water use. The results provide unique field evidence that photosynthesis and production of maize may be unaffected by rising [CO2] in the absence of drought. This suggests that rising [CO2] may not provide the full dividend to North American maize production anticipated in projections of future global food supply.     

The impact of cover crop shoot decomposition on soil microorganisms in an apple orchard in northeast China

Mowing can facilitate the incorporation of cover crop shoots into soil and improve the properties of soils in apple orchards. This article evaluated how apple orchard soil responds to the decomposition of the shoot residues of three cover crops[native mixed herbs (NMS), red clover (RCS), and ryegrass (RES)] in terms of microbial metabolism and biomass, and discussed the relationships between microbial responses and shoot chemistry. The chemical composition of shoots was analysed and a buried bag experiment was carried out to simulate shoot decomposition in an apple orchard. The results revealed significant differences in the chemical compositions and shoot C:N ratios (NMS: 10.9, RCS: 19.1, and RES: 12.9) of the three cover crops. The decomposition of the cover crop shoots promoted microbial metabolism and boosted soil bacterial reproduction (increase in the biomass indicator muramic acid: 19.44, 124.15, and 14.83 mg kg⁻¹, respectively. But there are different types of effects on soil fungal reproduction (change in the biomass indicator glucosamine: 712.51, 887.45, and 103.97 mg kg⁻¹), and they are obviously negative, significantly positive, and non-significant respectively. Thus, the native mixed herbs and red clover are preferable swards for better shoot enhancement in apple orchard.     

Enhanced biodegradation of methoxychlor in soil under sequential environmental conditions.

Ring-U-[14C]methoxychlor [1,1-bis(p-methoxyphenyl)-2,2,2-trichloroethane] was incubated in soil under aerobic and anaerobic conditions. Primary degradation of methoxychlor occurred under anaerobic conditions, but not under aerobic conditions, after 3 months of incubation. Analysis of soil extracts, using gas chromatography, demonstrated that only 10% of the compound remained at initial concentrations of 10 and 100 ppm (wt/wt) of methoxychlor. Evidence is presented that a dechlorination reaction was responsible for primary degradation of methoxychlor. Analysis of soils treated with 100 ppm of methoxychlor in the presence of 2% HgCl2 showed that 100% of the compound remained after 3 months, indicating that degradation in the unpoisoned flasks was biologically mediated. Methanogenic organisms, however, are probably not involved, as strong inhibition of methane production was observed in all soils treated with methoxychlor. During the 3-month incubation period, little or no evaluation of 14CO2 or 14CH4 occurred under either aerobic or anaerobic conditions. Cometabolic processes may be responsible for the extensive molecular changes which occurred with methoxychlor because the rate of its disappearance from soil was observed to level off after exhaustion of soil organic matter. After this incubation period, soils previously incubated under anaerobic conditions were converted to aerobic conditions. The rates of 14CO2 evolution from soils exposed to anaerobic and aerobic sequences of environments ranged from 10- to 70-fold greater than that observed for soils exposed solely to an aerobic environment.     

土壤pH对玉米与微生物竞争吸收氨基酸的影响

化学合成肥料的大量使用导致土壤pH发生显著变化,但其对植物与根际微生物竞争吸收氨基酸的影响机制尚不明确.本试验通过电解法调节杭州红壤和铁岭棕壤两种土壤pH, 采用外源添加¹⁵N标记甘氨酸短期吸收4 h的方法,研究了pH对玉米及根际微生物竞争吸收氨基酸的影响.结果表明:土壤pH对玉米根和地上部生物量有显著影响,对于红壤,pH为6.48最适宜玉米生长,且玉米地上部¹⁵N丰度和¹⁵N-甘氨酸吸收量也显著高于其他处理;对于棕壤,pH为7.65最适宜玉米生长,其玉米地上部和根系¹⁵N丰度显著低于pH为5.78处理,但¹⁵N-甘氨酸吸收量显著高于其他处理.红壤pH为6.48条件下,其微生物生物量碳相对较高,而棕壤pH为7.65条件下,其微生物生物量碳相对较低.综合根系吸收、转运及微生物竞争吸收的结果,推断红壤在pH为6.48条件下虽然面临着微生物的竞争吸收,但生长于其上的玉米通过提高吸收速率和转移比率提高了氨基酸的吸收量;在pH为7.65的棕壤中,微生物活性较低,降低了与玉米竞争吸收氨基酸的能力,从而增加了玉米对氨基酸的吸收量.     

有机物添加下太岳山油松林土壤微生物元素组成的稳态分析

在山西太岳山地区,向油松林土壤中分别添加生物炭、玉米秸秆、蒙古栎叶、油松叶、木屑等5种有机物,测定各处理的土壤养分、酶及微生物生物量等指标,研究外源有机物添加下土壤酶化学计量特征及微生物元素组成的内稳性。结果表明: 添加木屑显著增加了土壤N(17.1%)、P(37.6%)含量,显著增加了微生物生物量碳(118.0%)、氮(41.0%)、磷(176.6%)。C、N、P获取酶(β-1,4-葡萄糖苷酶、β-1,4-N-乙酰氨基葡萄糖苷酶、亮氨酸氨基肽酶、酸性磷酸酶)活性总体上随添加有机物C/N值(生物炭<蒙古栎叶<油松叶<玉米秸秆<木屑)的增加而增加,其化学计量变化受土壤养分状态及微生物生物量的调控。酶活性相对比例及矢量特性表明,研究区微生物生长受到P的限制,且添加有机物没有缓解P的制约作用。微生物生物量碳、氮及化学计量比C∶N、C:P、N∶P属于绝对稳态型,而微生物生物量磷处于非稳态。微生物通过改变酶的分配策略保持微生物体元素及比例的相对稳定,仅有微生物生物量磷对土壤养分变化表现出不稳定性,可能因为P是研究区微生物生长的限制性元素。     

Effects of Zn and P addition on the microbial biomass in a Zn deficient calcareous soil amended with glucose

A 35-day laboratory incubation experiment at 25°C was carried out to investigate the effects of Zn and P addition on microbial biomass C, N, and P in a Zn deficient calcareous soil, sampled at 15–40 cm depth in Central Anatolia, Turkey, amended with glucose. The underlying hypothesis was that P, but also Zn addition leads to a decrease in the microbial biomass C/N ratio. In the glucose-amended soil, the microbial biomass C/N ratio was not affected by the addition of P at day 5. At day 35 in this treatment, the significant P addition × day interaction revealed a significant decrease in the microbial biomass C/N ratio from 11.3 to 8.9. In the glucose-amended soil, Zn addition also had generally significant negative effects on microbial biomass C in comparison with the pure glucose treatment. A similar tendency was observed for microbial biomass N and consequently the microbial biomass C/N ratio remained unaffected. No evidence was found in the present incubation experiment that the microbial community suffered from Zn deficiency.     

Elevated ozone decreases the multifunctionality of belowground ecosystems

Elevated tropospheric ozone (O₃) affects the allocation of biomass aboveground and belowground and influences terrestrial ecosystem functions. However, how belowground functions respond to elevated O₃ concentrations ([O₃]) remains unclear at the global scale. Here, we conducted a detailed synthesis of belowground functioning responses to elevated [O₃] by performing a meta-analysis of 2395 paired observations from 222 publications. We found that elevated [O₃] significantly reduced the primary productivity of roots by 19.8%, 16.3%, and 26.9% for crops, trees and grasses, respectively. Elevated [O₃] strongly decreased the root/shoot ratio by 11.3% for crops and by 4.9% for trees, which indicated that roots were highly sensitive to O₃. Elevated [O₃] impacted carbon and nitrogen cycling in croplands, as evidenced by decreased dissolved organic carbon, microbial biomass carbon, total soil nitrogen, ammonium nitrogen, microbial biomass nitrogen, and nitrification rates in association with increased nitrate nitrogen and denitrification rates. Elevated [O₃] significantly decreased fungal phospholipid fatty acids in croplands, which suggested that O₃ altered the microbial community and composition. The responses of belowground functions to elevated [O₃] were modified by experimental methods, root environments, and additional global change factors. Therefore, these factors should be considered to avoid the underestimation or overestimation of the impacts of elevated [O₃] on belowground functioning. The significant negative relationships between O₃-treated intensity and the multifunctionality index for croplands, forests, and grasslands implied that elevated [O₃] decreases belowground ecosystem multifunctionality.     

玉米根茬留田对土壤微生物量碳和酶活性动态变化特征的影响

通过田间试验分析了玉米根茬留田对土壤生物活性动态变化的影响,结果表明,玉米根茬留田对提高土壤微生物量碳含量和土壤脲酶、磷酸酶、纤维素酶以及转化酶活性效果显著。动态变化特征表明,各处理的土壤微生物量碳和4种酶活性均在播种后60d左右出现高峰。此时正值作物生育旺盛时期,利于作物生长发育,说明玉米根茬留田配施化肥的培肥土壤效果显著,而且可以保持玉米持续高产稳产。     

Resistance and resilience of Cu-polluted soil after Cu perturbation, tested by a wide range of soil microbial parameters

Copper (Cu)-polluted and unpolluted soils were used to study the effect of initial pollution on soil biological resistance and resilience by measuring the responses to perturbation using different parameters. Microbial biomass carbon, substrate-induced respiration and copy numbers of 16S rRNA gene were grouped as general parameters, while potential ammonia oxidation rate and copy numbers of amo A gene were grouped as specific functions. In addition, to illustrate how initial pollution affects soil biological resistance and resilience following secondary perturbation, the microbial community structure, together with free Cu²⁺ activities ([Cu²⁺]) in soil pore water and soil pH were also measured after secondary perturbation. Results showed that general parameters were more stable than specific ones. High [Cu²⁺] and low pH in soil pore water induced by Cu addition may lead to apparently low resistance and resilience, whereas the formation of a tolerant community after Cu pollution, secondary perturbation and Cu aging may contribute to resistance and resilience. Analysis of the phospholipid fatty acids profile showed that microbial community structure shifted along with the [Cu²⁺] gradient. The microbial community structure of the control soil was both resistant and resilient to 400 mg kg⁻¹ Cu perturbation, whereas other treatments were neither resistant nor resilient.     

The influence of waterlogging at different temperatures on penetration depth and porosity of roots and on stomatal diffusive resistance of pea and maize seedlings

The 8 days old seedlings of pea (cv. Ilowiecki) and maize (cv. Alma F1) were subjected to differentiated aeration conditions (control — with pore water tension about 15 kPa and flooded treatment) for 12 days at three soil temperatures (7, 15 and 25 °C). The shoots were grown at 25 °C while the soil temperature was differentiated by keeping the cylinders with the soil in thermostated water bath of the appropriate temperature. Lowering the root temperature with respect to the shoot temperature caused under control (oxic) conditions a decrease of the root penetration depth, their mass and porosity as well as a decrease of shoot height, their mass and chlorophyll content; the changes being more pronounced in maize as compared to the pea plants. Flooding the soil diminished the effect of temperature on the investigated parameters; the temperature effect remaining significant only in the case of shoot biomass and root porosity of pea plants. Root porosity of pea plants ranged from 2 to 4 % and that of maize plants — from 4 to 6 % of the root volume. Flooding the soil caused an increase in the root porosity of the pea plants in the entire temperature range and in maize roots at lower temperatures by about 1 % of the root volume. Flooding the soil caused a decrease of root mass and penetration depth as well as a decrease of plant height, biomass and leaf chlorophyll content.     

玉米生长期间土壤微生物量与土壤酶变化及其相关性研究

研究了玉米生长期间土壤微生物量碳、氮与土壤过氧化氢酶、蔗糖酶、脲酶、蛋白酶活性变化及其相关性．结果表明，玉米生长前期和中期，土壤微生物量碳、氮及酶活性迅速上升，并逐渐达到最大值；玉米生长后期，土壤微生物量碳、氮、酶活性下降至某一值后并逐渐趋于平稳．几种处理相比较，以秸秆＋尿素处理的土壤微生物量碳、氮及酶活性为最大．除玉米生长后期，土壤微生物量碳、氮与碱解氮、活性腐殖质、土壤ｐＨ不相关外，土壤微生物量碳、氮与土壤过氧化氢酶、蔗糖酶、脲酶、蛋白酶活性及速效养分在玉米生长期间均相关或极相关     

Mineral nutrition and growth of tropical maize as affected by soil acidity

Soil constraints linked to low pH reduce grain yield in about 10% of the maize growing area in tropical developing countries. The aim of this research was to elucidate the reasons for this maize yield reduction on an oxisol of Guadeloupe. The field experiment had two treatments: the native non-limed soil (NLI, pH 4.5, 2.1 cmol Al kg^–1, corresponding to 20% Al saturation), and the same soil limed 6 years prior to the experiment (LI, pH 5.3, 0 cmol Al kg^–1). The soils were fertilized with P and N. The above-ground biomass, root biomass at flowering, grain yield and yield components, leaf area index (LAI), light interception, radiation-use-efficiency (RUE), P and N uptake, soil water storage, and soil mineral N were measured during the maize cycle. The allometric relationships between shoot N concentration, LAI and above-ground biomass in LI were similar to those reported for maize cropped in temperate regions, indicating that these relationships are also useful to describe maize growth on tropical soils without Al toxicity. In NLI, soil acidity severely affected leaf appearance, leaf size and consequently the LAI, which was reduced by 60% at flowering, although the RUE was not affected. Therefore, the reduction in the above-ground biomass (30% at flowering) and grain yield (47%) were due to the lower LAI and light interception. At flowering, the root/shoot ratio was 0.25 in NLI and 0.17 in LI, and the root biomass in NLI was reduced by 64% compared to LI. Nitrogen uptake was also reduced in NLI in spite of high soil N availability. Nevertheless, shoot N concentration vs aboveground biomass showed a typical decline in both treatments. In NLI, the shoot P concentration vs above-ground biomass relationship showed an increase in the early stages, indicating that P uptake and root-shoot competition for the absorbed P in the early plant stages controlled the establishment and the development of the leaf area.     

Manganese reduction in the rhizosphere of mycorrhizal and nonmycorrhizal maize

The influence of rhizosphere microorganisms and vesicular-arbuscular (VA) mycorrhiza on manganese (Mn) uptake in maize (Zea mays L. cv. Tau) plants was studied in pot experiments under controlled environmental conditions. The plants were grown for 7 weeks in sterilized calcareous soil in pots having separate compartments for growth of roots and of VA mycorrhizal fungal hyphae. The soil was left either uninoculated (control) or prior to planting was inoculated with rhizosphere microorganisms only (MO-VA) or with rhizosphere microorganisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol and Gerd.) Gerdemann and Trappe] (MO+VA). Mycorrhiza treatment did not affect shoot dry weight, but root dry weight was slightly inhibited in the MO+VA and MO-VA treatments compared with the uninoculated control. Concentrations of Mn in shoots decreased in the order MO-VA > MO+VA > control. In the rhizosphere soil, the total microbial population was higher in mycorrhizal (MO+VA) than nonmycorrhizal (MO-VA) treatments, but the proportion of Mn-reducing microbial populations was fivefold higher in the nonmycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbial populations upon root infection with the mycorrhizal fungi. The most important microbial group taking part in the reduction of Mn was fluorescent Pseudomonas. Mycorrhizal treatment decreased not only the number of Mn reducers but also the release of Mn-solubilizing root exudates, which were collected by percolation from maize plants cultivated in plastic tubes filled with gravel quartz sand. Compared with mycorrhizal plants, the root exudates of nonmycorrhizal plants had two fold higher capacity for reduction of Mn. Therefore, changes in both rhizosphere microbial population and root exudation are probably responsible for the lower acquisition of Mn in mycorrhizal plants.     

选择性抑菌剂对添加稻草红壤旱土团聚体磷素微生物转化的影响

为了进一步探明红壤旱土磷素微生物固持的机理,采用室内模拟培养试验研究了微生物类群对红壤旱土团聚体(0.2～2mm)磷素转化的作用.结果表明:在培养90d期间,添加稻草处理能显著提高红壤旱土团聚体的微生物生物量碳、生物量磷、提取磷(Olsen法)和有机磷的含量.在培养前期(5～30d),与添加稻草处理比较,稻草+真菌抑制剂(放线菌酮)、稻草+细菌抑制剂(四环素+链霉素硫酸盐)处理团聚体微生物生物量碳含量分别降低10.5%～31.8%和6.8%～11.6%,前者的降低幅度显著大于后者(P0.01),此后加入抑菌剂处理团聚体微生物生物量碳基本保持稳定.添加细菌抑制剂处理团聚体微生物生物量磷含量在培养5～20d期间比加真菌抑制剂处理高10.0%～28.8%,差异显著(P0.01).表明真菌和细菌均参与红壤旱土团聚体磷素的固持,但真菌的作用明显大于细菌.     

Effects of slow-release urea fertilizers on urease activity,microbial biomass, and nematode communities in an aquic brown soil

A field experiment was carried out at the Shenyang Experimental Station of Ecology (CAS) in order to study the effects of slow-release urea fertilizers high polymer-coated urea (SRU1), SRU1 mixed with dicyandiamide DCD (SRU2), and SRU1 mixed with calcium carbide CaC2 (SRU3) on urease activity, microbial biomass C and N, and nematode communities in an aquic brown soil during the maize growth period. The results demonstrated that the application of slow-release urea fertilizers inhibits soil urease activity and increases the soil NH4+-N content. Soil available N increment could promote its immobilization by microorganisms. Determination of soil microbial biomass N indicated that a combined application of coated urea and nitrification inhibitors increased the soil active N pool. The population of predators/omnivores indicated that treatment with SRU2 could provide enough soil NH4+-N to promote maize growth and increased the food resource for the soil fauna compared with the other treatments.