三峡库区中低产土壤重金属含量及其与小麦吸收的关系

三峡库区中低产土壤的Hg、As、Cr、Pb、Cu五个重金属含量(除渝北区外),均在国家土壤环境质量标准内,属自然背景值一级标准。Cd和Zn高于全国土壤中的平均含量和背景值含量,属二级标准。土壤的重金属含量与土壤母质类型、pH值、阳离子交换量、有机质、无定形铁和物理性粘粒有关,同时存在一定的地域分布。重庆近郊的土壤所有重金属含量相对较高。土壤重金属的可给态或有效性含量极低,锌和铜不是过量,而是不足。小麦籽粒中As、Cr、Pb、Zn、Cu含量低于国家食品对重金属限量标准和小麦籽粒的背景值标准,Hg、Cd含量高于国家规定标准。籽粒中的Cu、Zn含量是小麦茎叶中的2.0～2.2倍,而茎叶中的Hg、Pb、As、Cr、Cd含量明显高于籽粒。

脲酶/硝化抑制剂对土壤有效态氮、微生物量氮和小麦氮吸收的影响

研究了脲酶抑制剂 (NBPT)、硝化抑制剂 (DCD)及二者组合在草甸棕壤上施用对尿素态N转化及土壤总有效态N、微生物量N的影响 .结果表明 ,尿素配施NBPT、DCD及抑制剂组合能够增加尿素水解后土壤NH+ 4 含量 2 %～ 5 3% ,显著降低了氧化态N的浓度 ,抑制了土壤中铵态N的氧化 ,增加土壤总有效N 34%～ 4 4 % ,小麦吸N量增加 0 2 6 %～ 6 79% ,其中以脲酶抑制剂与硝化抑制剂组合的效果最明显 .抑制剂施用增加了微生物在小麦生长初期对有效态N固持 ,有利于后期土壤有效态N的矿化 .

长期定位施肥对潮土微生物活性和小麦养分吸收的影响

利用中国科学院封丘农业生态实验站农田生态系统养分平衡长期定位试验地,研究长期不同施肥对土壤微生物区系、土壤呼吸强度以及小麦养分吸收的影响。结果表明,施有机肥或无机肥均有利于提高土壤细菌和放线菌数量,且有机肥优于无机肥、平衡施肥优于缺素施肥,但只有施有机肥处理显著提高土壤真菌数量。此外,施有机肥也显著提高土壤呼吸强度,有机无机配施、NPK平衡施肥、NP、PK等处理效果次之,缺P施肥(NK处理)效果最差,但施有机肥或有机无机配施均会显著降低微生物个体的CO2呼吸强度。不同施肥处理小麦幼苗对养分N、P、K的吸收累积存在显著差异,其中施有机肥处理小麦对N、P、K的吸收较为均衡,而无机肥因为所供化学养分的速效性而更易于被小麦幼苗高水平吸收;与NPK平衡施肥处理相比,缺素(N、P或K)施肥均直接导致小麦植株体内相应养分的明显亏缺,且缺N施肥(PK处理)还同时制约了小麦对K素的吸收。

Effects of Continuous Nitrogen Application on Grain Yield and Nitrogen Uptake and Utilization in Winter Wheat-Summer Maize Rotation System

[Objective] This study aimed to achieve high yield and stable yield of win- ter wheat-summer maize rotation system and provide basis for rational application of nitrogen fertilizer. [Method] Effects of continuous nitrogen application on grain yield, economic profit, nitrogen uptake and utilization efficiency, and soil inorganic nitrogen accumulation in winter wheat-summer maize rotation system were investigated. [Re- sult] Nitrogen application could significantly increase the y（eld of the winter wheat- summer maize rotation system, which increased by 17.76%-30.32% and 22.24%- 46.63% in two rotation cycles, respectively. The yield of the winter wheat-summer maize rotation system was the maximum in two rotation cycles with nitrogen appli- cation amount of 660.0 kg/hm2, which reached respectively 23 391.19 and 23 444.35 kg/hm2, the yield and economic benefit were the highest, the nitrogen fertilizer use efficiency was 22.2% and 30.7%, the agronomic efficiency was 8.3 and 11.3 kg/kg. However, the nitrogen fertilizer use efficiency and agronomic efficiency between ni- trogen application amount of 540.0 and 660.0 kg/hm2 showed no significant differ- ence. After two rotation cycles, inorganic nitrogen accumulation in 0-40 cm soil with nitrogen application amount of 540.0 kg/hm2 was almost equal to that before experi- ment. [Conclusion] Under the experimental conditions, comprehensively considering the grain yield, economic profit, nitrogen fertilizer efficiency and soil inorganic nitro- gen balance, the optimal nitrogen application amount was 625.3-660.0 kg/hm2 in high-yield winter wheat-summer maize rotation system.

The Influence of Surfactants on Chlorophyll Binding Status and Excitation Energy Transfer in Photosystem Ⅰ of Wheat

Surfactants are widely used in the purification and research of structure and function of the protein complexes in photosynthetic membrane. To elucidate the mechanism of interaction between surfactants and photosystem Ⅰ (PSⅠ), effects of two typical surfactants, Triton X_100 and sodium dodecyl sulfate (SDS) on PSⅠ, were studied at different concentrations. The results were: SDS led to the reduction of apparent absorption intensity and blue shift of absorption peaks; while Triton X_100 led to the decrease of apparent absorption intensity in red region and blue shift of the peak, but to the increase of apparent absorption intensity in blue region. The fourth derivative spectra show that the longwavelength (669 nm and 683 nm) absorbing chlorophyll a was affected greatly and their relative changes of absorbance were axially symmetrical. The presence of surfactant could make the long wavelength fluorescence emission decrease greatly and a new fluorescence peak appeared around 680 nm, it was obvious that the surfactant interceded the transfer of excitation energy from antenna pigments to reaction center. The surfactants might affect the microenvironment of proteins, even the structure of PSⅠ protein subunits and hence changed the binding status of pigments with protein subunits, or the pigments might be released from the subunits. All of these might affect the absorption and the transfer of excitation energy.

Phosphorus Uptake from Rhizosphere Soil by Two Wheat Cultivars

Inorganic soil phosphorus extractable with sodium bicarbonate (NaHCO3-Pi), soil pH and root hairs length and density in the rhizosphere of two winter wheat cultivars (Triticum aestivum L. cv. Shichun,Sleipner) grown on a high pH Chinese silt loam (52.7 mg NaHCO3-Pi kg-1) and a Danish sandy loam (43.4mg NaHCO3-Pi kg-1) were studied to assess how these wheat cultivars differed in phoephorus uptake.The rhizosphere soil pH of two wheat cultivars grown on the two soils were fairly unchanged with increasing distance from the root surface. However the root hairs of Shichun were 2.1 times longer than those of Sleipner. Root surface area (RSA) of Shichun increased by 192% due to root hairs whereas root hairs of Sleipner increased RSA by 68% only. Hence the root system of Shichun was in contact with more soil than that of Sleipner, even though Sleipner had a longer root. Grown at the lower pH and level of NaHCO3-Pi in the Danish soil Shichun absorbed more inorganic phosphorus than Sleipner whereas at the higher pH and level of NaHCO3-Pi in the Chinese soil there was no phosphorus uptake difference between the two wheat cultivars.

Effect of Bacterial-Feeding Nematode Inoculation on Wheat Growth and N and P Uptake

A 40-day gnotobiotic microcosm experiment was carried out to quantify the effect of hastenal-feeding nematode on plant growth and nutrient absorption. The results showed that inoculation of bacterial-feeding nematode Protorhabditis sp. stimulated the growth of wheat (Triticum aestivum) and the uptake of N. By the end of the 40-day incubation wheat biomass and N uptake in the treatment with nematode and bacteria (Pseudomonas sp.) increased by 6.5% and 5.9%, respectively, compared with bacteria alone treatment. The presence of nematode mainly accelerated the growth of aboveground of wheat, while it slightly inhibited the root development. There was little difference in plant tissue N concentration between treatments. P concentration and uptake of wheat, however, were generally reduced by nematode. It appears that the enhancement of plant growth and nitrogen uptake is attributed to the enhancement of nitrogen mineralization induced by nematode feeding on bacteria, and the reduction of phosphorous uptake is the result of weak root status and competition by bacteria immobilization.

Kinetic Characteristics of Nitrate Uptake by Wheat and Rape and Their Determination

15-day old seedlings of wheat and rape were grown in a series of solutions with different concentrations of KNO3 for a definite period of time. The changes in NO3- concentration of the solutions were determined by the double ion-selective electrode method, and then the amount of NO3- taken up by the plants was estimated and values of Km and Imax of the Michealis-Menten equation were calculated. Results show that both the method and conditions of determination affected the values of Km and Imax. For example, the Km value was appreciably reduced when the volume of culture solution was increased or when the duration of nutrient uptake was shortened; the Km value obtained with short-term depletion method was higher than that obtained with long-term one. Similar Variations were found for the values of Imax. There was a considerable difference in the characteristics of uptake kinetics between wheat and rape when determined under the same conditions of determination. The isotherm of NO3- uptake by wheat could be separated into saturated and unsaturated parts, and when the concentration of NO3- exceeded 180 uuuuuuuuuuuuM, the relationship between the rate of NO3- uptake and NO3- concentration tended to be linear. However, the isotherm of NO3- uptake by rape was found to fit the Michealis-Menten equation and no linear relationship could be found.

Use of Cation Exchange Membrane in Soil Potassium Release and Wheat Response to Potassinm

A pot experiment was conducted in the growth chamber on Saskatchewan soils with dfferent texture todeterniine the K release status and wheat K demand. The relationship between K uptake and soil availableK extracted by cation exchange membrane (CEM-K) and the effect of K fertilizer on wheat growth and soilavailable K was also evaluated. Theatments of 0, 60 and 120 mg K/kg were applied to sandy, low and highK loamy and clay soils. The highest yields were achieved with the application of 120 mg K/kg in sandysoil and 60 mg K/kg in other soils. On the whole, the clay soil contributed K more than other soils fromslowly available fraction. Regression revealed a linear relationship between the soil available K extractedby NH_4OAc(Ka) and CEM-K in suspensions (r=0.93). Results also showed that CEM-K in burial and insuspensions were different not only in the amount but also in correlation with Ka or K uptake.

Effects of Atmospheric CO_2 Enrichment, Applied Nitrogen and Soil Moisture on Dry Matter Accumulation and Nitrogen Uptake in Spring Wheat

Spring wheat (Triticum aestivum L. cv. Dingxi No. 8654) was treated with twoconcentrations of atmospheric CO_2 (350 and 700 μmol mol^(-1)), two levels of soil moisture(well-watered and drought) and five rates of nitrogen fertilizer (0, 50, 100, 150, and 200 mgkg^(-1) soil) to study the atmospheric CO_2 concentration effect on dry matter accumulation and Nuptake of spring wheat. The effects of CO_2 enrichment on the shoot and total mass depended largelyon soil nitrogen level, and the shoot and total mass increased significantly in the moderate to highN treatments but did not increase significantly in the low N treatment. Enriched CO_2 concentrationdid not increase more shoot and total mass in the drought treatment than in the well-wateredtreatment. Thus, elevated CO_2 did not ameliorate the depressive effects of drought and nitrogenstress. In addition, root mass decreased slightly and root/shoot ratio decreased significantly dueto CO_2 enrichment in no N treatment under well-watered condition. Enriched CO_2 decreased shoot Ncontent and shoot and total N uptake; but it reduced root N content and uptake slightly. Shootcritical N concentration was lower for spring wheat grown at 700 μmol mol^(-1) CO_2 than at 350μmol mol^(-1) CO_2 in both well-watered and drought treatments. The critical N concentrations were16 and 19 g kg^(-1) for the well-watered treatment and drought treatment at elevated CO_2 and 21 and26 g kg^(-1) at ambient CO_2, respectively. The reductions in the movement of nutrients to theplant roots through mass flow due to the enhancement in WUE (water use efficiency) and the increasein N use efficiency at elevated CO_2 could elucidate the reduction of shoot and root Nconcentrations.

Vesicular Arbuscular Mycorrhizae-Mediated Uptake and Thanslocation of P and Zn by Wheat in Calcareous Soil

Vesicular-arbuscular mycorrhizal (VAM) fungi have been credited with improving the groWth and mineral nutrition of many host plants but these effects are moderated by soil factors and nutrient balance. The combined effects of VAM, Zn and P application on the growth and translocation of nutrients in wheat were investigated using a calcareous soil marginal in P and Zn concentrations. Wheat was grown in a growth chamber under various combinations of VAM, P and Zn with measurements done at heading stage and maturity.Vegetative dry matter accumulation was increased by P application and reduced by VAM treatments. Both P and VAM increased grain yield. Zinc concentration and uptake were generally reduced by P addition and VAM infection. There were no antagonistic effects of Zn on P acquisition in the plant. The role of VAM in enhancing the translocation of Zn and P from root to grain would be beneficial to seed setting and yield.

大气对流层臭氧浓度升高下AM真菌对小麦生长的影响

利用中国唯一的开放式空气组分增高(free-air component enrichment,FACE)稻麦轮作试验平台,研究大气对流层O3浓度升高条件下接种外源AM真菌对小麦生长及土壤微生物生物量的影响.结果发现,O3浓度升高处理小麦苗期AM真菌侵染率有升高趋势,而从孕穗期起逐渐显示出对小麦生长的不利影响,收获时植株地上部生物量、株产与千粒重均显著下降(p<0.05),分别降低22%、29%和9%,土壤微生物生物量N也下降了37%,但籽粒全N含量从2.2%显著提高到2.6%(p<0.05).O3浓度升高条件下接种外源AM菌剂对小麦根系AM真菌侵染具有促进作用,孕穗期AM真菌侵染率与植株地上部生物量均显著高于不接种对照(p<0.05),收获时植株受灾程度降低了50%,土壤微生物生物量N也显著升高(p<0.05),虽然小麦产量没有提高,但籽粒全N含量下降到与当前O3浓度处理没有显著差异的水平上.结果表明,O3胁迫下小麦通过提高苗期AM真菌侵染来增强其抗胁迫能力,接种外源AM真菌可以促进小麦营养生长,并可通过改善根系分泌物等来提高土壤微生物生物量.

The role of maize root size in phosphorus uptake and productivity of maize/faba bean and maize/wheat intercropping systems

Interspecific root/rhizosphere interactions affect phosphorus (P) uptake and the productivity of maize/faba bean and maize/wheat intercropping systems. The aim of these experiments was to determine whether manipulation of maize root growth could improve the productivity of the two intercropping systems. Two near isogenic maize hybrids (the larger-rooted T149 and smaller-rooted T222) were intercropped with faba bean and wheat, under conditions of high- and low-P availability. The larger-rooted T149 showed greater competitive ability than the smaller-rooted T222 in both maize/faba bean and maize/wheat intercropping systems. The higher competitive ability of T149 improved the productivity of the maize/faba bean intercropping system in P-sufficient conditions. In maize/wheat intercropping systems, root growth, shoot biomass, and P uptake of maize were inhibited by wheat, regardless of the P-supply. Compared with T222, the larger-rooted T149 suffered less in the intercropping systems. The total biomass of the maize/wheat intercropping system was higher for wheat/T149 than for wheat/T222 under low-P conditions. These data suggested that genetic improvement of maize root size could enhance maize growth and its ability to compete for P resources in maize/faba bean and maize/wheat intercropping systems. In addition, depending on the P availability, larger maize roots could increase the productivity of intercropping systems.

Magnesium Uptake and Palygorskite Transformation Abilities of Wheat and Oat

Weathering of clay minerals is a source of nutrients to plants. Palygorskite is a Mg-rich fibrous clay mineral that commonly occurs in the soils and sediments of arid regions. Although many studies have examined the environmental conditions required for the formation and stability of palygorskite, information on the transformation of this mineral in the root zone （or rhizosphere） of agricultural crops is limited. This study explored the possibility of palygorskite transformation in the rhizosphere of wheat and oat and compared the ability of these crops to extract structural Mg from palygorskite. The crops were cultivated in pots consisting of a mixture of sand from Hamadan region, Iran and Florida palygorskite, irrigated with distilled water, and treated with either complete or Mg-free nutrient solutions. After 100 d, Mg uptake by the crops was measured. Clay-sized particles in each pot were also separated from the sand and were analyzed through X-ray diffraction （XRD）. The X-ray pattern of the particles was compared with that of the pure palygorskite particles （before cultivation）. The results showed that palygorskite could provide sufficient Mg for the growth of wheat in the pots supplied with Mg-free nutrient solution. In spite of the magnesium uptake by both plants from the palygorskite structure, no detectable peaks indicating the transformation of pMygorskite were recognized by XRD. A decrease of 1.05 nm in peak intensity was more obvious for the pots containing palygorskite and irrigated with Mg-free nutrient solution than for the pots irrigated with complete nutrient solution. Although the decrease in peak intensity was greater for oat than wheat, indicating greater palygorskite weathering by oat, Mg uptake by oat was low, as evidenced by the deficiency symptoms observed.