水稻生育期对稻水象甲成虫种群空间格局影响及抽样技术

[目的] 明确四川省西南浅丘稻区稻水象甲成虫种群在水稻不同生育期的空间格局及抽样技术，为获取准确稻水象甲虫情调查资料和制定有效的综合防控措施提供理论依据。[方法] 调整水稻播栽时间，错开2组试验田水稻的生育期，用聚集度指标法、回归模型法和频次卡方检验法分析稻水象甲成虫种群的空间格局及水稻生育期对空间聚集特性的影响，并对田间序贯抽样技术和抽样方法进行研究。[结果] 不同田块稻水象甲成虫平均密度为0.48~5.83头·丛^-1，分蘖期水稻田虫口密度显著高于抽穗期。稻水象甲成虫在不同水稻生育期稻田间呈负二项聚集分布，基本成分为个体群，个体间相互吸引，聚集强度随种群密度的升高而增加。当种群密度较低时，其聚集由环境因素引起；种群密度较高时，其聚集为其自身的聚集习性与环境因素共同引起。双对角线抽样法是稻水象甲成虫田间抽样的最佳方法，当稻水象甲成虫防治指标为1头·丛^-1时，Iwao序贯抽样模型为T_1（n），T_0（n）=n±1.96√2.286n，结合Kuno序贯抽样模型建立了用于田间抽样的复序贯抽样图。[结论] 稻水象甲成虫在不同水稻生育期稻田间呈负二项聚集分布，分蘖期水稻田虫口密度显著高于抽穗期，双对角线抽样法是稻水象甲成虫田间抽样的最佳方法。     

Soil N and C trace gas fluxes and microbial soil N turnover in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary

During two intensive field campaigns in summer and autumn 2004 nitrogen (N₂O, NO/NO₂) and carbon (CO₂, CH₄) trace gas exchange between soil and the atmosphere was measured in a sessile oak (Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N₂O emission rates were 1.5 μg N m⁻² h⁻¹ in summer and 3.4 μg N m⁻² h⁻¹ in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 μg N m⁻² h⁻¹) as compared to summer (6.0 μg N m⁻² h⁻¹). However, as NO₂ deposition rates continuously exceeded NO emission rates (−9.7 μg N m⁻² h⁻¹ in summer and −18.3 μg N m⁻² h⁻¹ in autumn), the forest soil always acted as a net NO _x sink. The mean value of CO₂ fluxes showed only little seasonal differences between summer (81.1 mg C m⁻² h⁻¹) and autumn (74.2 mg C m⁻² h⁻¹) measurements, likewise CH₄uptake (summer: −52.6 μg C m⁻² h⁻¹; autumn: −56.5 μg C m⁻² h⁻¹). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N₂O/CH₄ soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO_{2 resp} ΔO_{2 resp}⁻¹) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 μg N kg⁻¹ SDW d⁻¹) and autumn measurements (0.89 μg N kg⁻¹ SDW d⁻¹). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 μg N kg⁻¹ SDW d⁻¹) and significantly lower in the uppermost mineral layer (1.3–2.9 μg N kg⁻¹ SDW d⁻¹). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N₂O emissions and negatively correlated with CH₄ uptake, whereas soil CO₂ emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn.     

氮素形态对杉木幼苗侧根生长和叶片光合特性的影响

以3月龄的杉木实生苗为试验材料,分析了不同氮素形态——硝态氮(NO₃^- N)、铵态氮(NH4⁺ N)和硝酸铵(NH₄NO₃)(氮素浓度均为3 mmol·L^-1)对杉木幼苗侧根生长、叶片光合气体交换参数和叶绿素荧光参数的影响,以揭示杉木幼苗对不同形态氮的偏好性,以及不同形态氮肥下杉木幼苗侧根生长和光合生理的响应特征,为杉木苗期氮肥管理提供理论依据。结果显示：(1)不同氮素形态对杉木幼苗地上部和侧根生物量具有显著影响,其中NH₄⁺ N处理下幼苗地上部和侧根生物量最大,NO₃^- N处理次之,而NH₄NO₃处理最小。(2)NH₄⁺ N和NO₃^- N处理下杉木幼苗总根长、根系总表面积和根系总体积均显著高于NH₄NO₃处理(P＜0.05),且NH₄⁺ N处理又显著高于NO₃^- N处理,但不同氮形态处理间侧根数量差异不显著。(3)NH₄⁺ N处理下杉木幼苗叶片净光合速率、气孔导度和蒸腾速率明显高于NO₃^- N和NH₄NO₃处理,但NO₃^- N和NH₄NO₃处理之间无明显差异。(4)NH₄⁺ N处理下杉木叶片初始荧光强度低于NO₃^- N处理,而最大荧光强度、可变荧光强度和PSⅡ潜在活性却高于全硝氮和硝铵氮处理。上述结果表明,NH₄⁺ N处理不仅有利于杉木幼苗侧根生长发育,且其叶片具有较强的光合能力,较高的PSⅡ中心稳定性、光化学活性以及电子传递效率,从而更有利于植株生长。因此,从根系生长和光合特性来看,杉木幼苗对铵态氮具有偏好性。     

川西平原小流域不同水体N2O排放特征及驱动因素

氧化亚氮（N₂O）是一种潜在的、强大的温室气体,应该根据京都议定书规定开展监测和削减。河流、水库、鱼塘和沟渠等受人类影响的小流域水生生态系统是氮素生物地球化学循环的活跃区域,更是N₂O重要的源和汇。然而,同一流域不同水体N₂O的排放特征差异及其驱动因素尚不清楚。因此,选择川西平原西河流域作为研究区,于2016年6月到2017年5月连续监测不同水体水气界面的N₂O排放强度,并结合聚类分析解析N₂O排放特征的驱动因素。结果显示,不同水体的N₂O年排放通量差异显著,沟渠的N₂O年排放通量最高（（52.68±36.09）μg m^-2 h^-1）,城市段河流和鱼塘次之（（34.16±23.97）μg m^-2 h^-1和（29.03±31.41）μg m^-2 h^-1）,乡镇段和农区段河流再次（（8.32±28.60）μg m^-2 h^-1和（8.52±9.43）μg m^-2 h^-1）,水库最低（（-16.45±29.76）μg m^-2 h^-1）。除水库表现为N₂O的汇,其他水体均表现为N₂O的排放源。另外,不同水体N₂O排放的季节特征差异显著,农区段河流和农业沟渠表现为夏天最高,冬春最低（P<0.05）,而其他水体均表现为冬春显著高于夏秋（P<0.05）。根据N₂O排放季节特征及其驱动因素可将西河流域水体分为四类：第一类农业类水体的N₂O排放季节特征受气象因素和农业活动的联合驱动;第二类城乡类河流和第三类鱼塘分别受控于人类活动和养殖活动,与降雨温度等气象指标关系较弱;第四类水库主要受控于气象因素。并且,第一类农业类水体已成为大气N₂O排放的重要源,农业氮素管控是区域控制N₂O排放的重点。     

Biodegradation of monohalogenated alkanes by soil NH(3)-oxidizing bacteria

Although cooxidative biodegradation of monohalogenated hydrocarbons has been well studied in the model NH₃-oxidizing bacterium, Nitrosomonas europaea, virtually no information exists about cooxidation of these compounds by native populations of NH₃-oxidizing bacteria. To address this subject, nitrifying activity was stimulated to 125–400 nmol NO₃ ^– produced g^–1 soil h^–1 by first incubating a Ca(OH)₂-amended, silt loam soil (pH 7.0±0.2) at field capacity (270 g H₂O kg^–1 soil) with 10 μmol NH₄ ⁺ g^–1 soil for 14 days, followed by another 10 days of incubation in a shaken slurry (2:1 water:soil, v/w) with periodic pH adjustment and maintenance of 10 mM NH₄ ⁺. These slurries actively degraded both methyl bromide (MeBr) and ethyl chloride (EtCl) at maximum rates of 20–30 nmol ml^–1 h^–1 that could be sustained for approximately 12 h. Although the MeBr degradation rates were linear for the first 10–12 h of incubation, they could not be sustained regardless of NH₄ ⁺ level and declined to zero over 20 h of incubation. The transformation capacity of the slurry enrichments (~1 μmol MeBr ml^–1 soil slurry) was similar to the value measured previously in cell suspensions of N. europaea with similar NH₃-oxidizing activity. Several MeBr-degrading characteristics of the nitrifying enrichments were found to be similar to those documented in the literature for MeBr-degrading methanotrophs and facultatively methylotrophic bacteria. Electronic Publication     

The mycotoxin fumonisin B1 inhibits eukaryotic protein synthesis: in vitro and in vivo studies

Inhibitory action of Fumonisin B₁ (FB₁) on eukaryotic protein synthesis was investigated, both in animal and plant system, and was compared with cycloheximide. Inhibitory effect of FB₁ was monitored in the TCA precipitable proteins of rabbit reticulocyte lysates exposed to various concentrations of the mycotoxin (0.0013–2.76 mM), using ³⁵ S-methionine as a tracer. FB₁ inhibited the protein synthesis by 6%, at 0.0013 mM and by 88%, at a higher concentration of 2.76 mM. Cycloheximide at a concentration of 0.355 mM was found to inhibit protein synthesis by 88%. Inhibitory action of FB₁ (1 mg kg⁻¹ body mass and a higher dose of 10 mg kg⁻¹ body mass) or cycloheximide (10 mg kg⁻¹ body mass; positive controls), injected intra-peritoneally into BALB/c mice was studied using ¹⁴C-l-Leucine as a tracer. FB₁ at lower dose of 1 mg kg⁻¹ body mass inhibited protein synthesis in liver by 8% and at a higher dose of 10 mg kg⁻¹ body mass by 38% in the BALB/c mice, when compared to cycloheximide which inhibited protein synthesis by 61%. The effects of FB₁ on protein synthesis in plant system was studied in germinated maize seedlings exposed to FB₁ at 0.9 μM, 0.009 mM and 0.09 mM concentrations, using ¹⁴C-l-Leucine as a tracer. Fumonisin B₁ at low, middle, and higher concentrations (0.9 μM, 0.009 mM, and 0.09 mM) inhibited protein synthesis in the seedlings by 4%, 12% and 22%, respectively. The inhibitory effects of FB₁ on the protein synthesis in the animal system in vitro and in vivo conditions, and in the plant system were found to be dose-dependent, though it was less potent compared to cycloheximide.     

不同恢复方式下大兴安岭重度火烧迹地林地土壤温室气体通量

为研究大兴安岭重度火烧迹地在不同恢复方式下林地土壤CO₂、CH₄和N₂O排放特征及其影响因素,采用静态箱/气相色谱法,在2017年生长季（6月-9月）对3种恢复方式（人工更新、天然更新和人工促进天然更新）林地土壤温室气体CO₂、CH₄、N₂O通量进行了原位观测。研究结果表明：（1）3种恢复方式林地土壤在生长季均为大气CO₂、N₂O的源,CH₄的汇;生长季林地土壤CO₂排放通量大小关系为人工促进天然更新（（634.40±246.52）mg m^-2 h^-1） > 人工更新（（603.63±213.22）mg m^-2 h^-1） > 天然更新（（575.81±244.12）mg m^-2 h^-1）,3种恢复方式间无显著差异;人工更新林地土壤CH₄吸收通量显著高于人工促进天然更新;天然更新林地土壤N₂O排放通量显著高于其他两种恢复方式。（2）土壤温度是影响3种恢复方式林地土壤温室气体通量的关键因素;土壤水分仅对人工更新林地土壤N₂O通量有极显著影响（P < 0.01）;3种恢复方式林地土壤CO₂通量与大气湿度具有极显著的响应（P < 0.01）;土壤pH仅与天然更新林地土壤CO₂通量显著相关（P < 0.05）;土壤全氮含量仅与人工促进天然更新林地土壤CH₄通量显著相关（P < 0.05）。（3）基于100年尺度,由3种温室气体计算全球增温潜势得出,人工促进天然更新（1.83×10⁴ kg CO₂/hm²） > 人工更新（1.74×10⁴ kg CO₂/hm²） > 天然更新（1.67×10⁴ kg CO₂/hm²）。（4）阿木尔地区林地土壤年生长季CO₂和N₂O排放量为8.85×10⁶ t和1.88×10² t,CH₄吸收量为1.05×10³ t。     

代谢工程强化脱氮副球菌DYTN-1去除氮素污染物

【目的】脱氮副球菌(Paracoccus denitrificans)是一种环境友好的α-变形菌纲菌株,在有氧条件下也可进行反硝化过程,具有较好的脱氮能力。本研究以脱氮副球菌DYTN-1为底盘细胞,筛选氮素诱导型启动子用于强化硝化和反硝化途径,进而达到代谢工程强化脱氮副球菌DYTN-1去除氮素污染物的目的。【方法】通过接合转移的方法分别将过表达amoA、amoB、hao和nirS基因的重组质粒导入脱氮副球菌DYTN-1细胞中。经过荧光定量检测和氮素定量检测对脱氮副球菌DYTN-1的基因元件和氮去除能力进行表征。【结果】从基因组中挖掘了6个受NO₂^‒、NO₃^‒和NH₄⁺诱导的启动子,诱导差异为2‒26倍;且过表达nirS的菌株用2 g/L KNO₃处理24 h后培养基中NO₃^‒的残余量为野生型菌株的67%。同时过表达hao和nirS基因的菌株在用1 g/L NH₄Cl和2 g/L KNO₃处理12 h后,其NO₃^‒的剩余量仅为野生型菌株的50%,且最终总氮的降解效率达79.5%,剩余总氮仅为野生型菌株的一半。【结论】上述研究表明,利用筛选获得的启动子工具在P. denitrificans DYTN-1中进行代谢工程改造强化氮素污染物的去除具有可行性。     

Phytoplankton primary production in a mesotrophic pond in sub-tropical Bangladesh

Annual gross primary productivity in mesotrophic Shahidullah Hall pond (Dhaka, Bangladesh) was 1383.35 g C m⁻² y⁻¹ (arithmetic mean). Daily primary productivity (between 1.6 and 6.8 g C m⁻² d⁻¹ was correlated with chlorophylla, day length and dissolved silica. Chlorophylla related significantly withk, incident light, SRP, alkalinity and conductivity. A negative correlation existed between biomass and rainfall. Productivity, biomass, conductivity, alkalinity, and SRP increased after mid-winter.k, I _k andZ _eu varied according seasonally.P _max related directly with temperature. Seasonal variation of ∝ ^B was 0.0049–0.0258 mg C (mg chla mmol PAR)⁻¹ m⁻². Q₁₀ was 2.12, community respiration 1334.99 g C m⁻² y⁻¹, and the underwater light climate 186.43μE m⁻² s⁻¹.     

城市化地区典型水体的N2O排放通量特征——以南京市为例

内陆淡水水体是大气中N₂O的重要排放源,然而目前对于内陆典型城市水体N₂O排放通量的监测数据依然匮乏,典型城市水体的N₂O排放特征及驱动因素尚不清楚。本研究选取了南京市江北新区的典型水体,包括湖库、河流、养殖池塘和景观池塘,在2020年5月-2021年4月利用漂浮箱法连续监测了不同水体类型的水-气界面N₂O排放特征,并通过测定水环境特征,探究驱动水体N₂O排放通量的关键因素。研究结果表明,典型城市水体整体均表现为N₂O排放源,河流和养殖池塘的日平均排放通量最大,分别为（503±1236）μg m^-2 d^-1和（508±797）μg m^-2 d^-1,其次为景观池塘（（179±989）μg m^-2 d^-1）,而湖库的N₂O排放通量最小,仅表现为微弱的N₂O排放源（（54±212）μg m^-2 d^-1）。水体的N₂O排放呈现季节性差异,河流和养殖池塘夏季的N₂O排放通量显著高于其他季节（P<0.01）。水体全年N₂O排放数据与水体温度和溶解氧含量（DO）呈显著相关。而在温度较高的5月份-9月份（>20℃）,氮输入成为影响N₂O排放通量的关键因素（P<0.01）,因此控制城市水体的氮输入尤其是在水温较高的夏季是减少N₂O排放的有利措施。此外,由于水文化学条件差异等因素,小型封闭水体包括养殖池塘和景观池塘的N₂O排放通量差异较大,未来应加强监测不同水体的水文化学特征和N₂O的时空排放特征,探讨影响小型封闭水体水-气界面N₂O排放通量的具体驱动因素。此研究为城市区域N₂O排放的精准核算提供了数据支撑,为N₂O排放模型的修正提供了科学依据。     

棒叶落地生根对干旱与复水的生理响应

为探讨棒叶落地生根(Kalanchoe tubiflora)耐旱的机制,在干旱与复水条件下,对其叶片的一些生理生化指标进行了测定。结果表明,随干旱时间延长,棒叶落地生根叶片中O2-·生成速率增大,H2O2含量升高,导致脂质过氧化产物MDA含量增高;同时SOD活性升高,CAT活性降低;可溶性糖与脯氨酸含量增加,但复水后这些指标均恢复到干旱前的水平。这说明棒叶落地生根能够耐受干旱环境是通过积累渗透调节物质,提高活性氧的清除能力,从而减少氧化胁迫造成的伤害。     

Relationship between fresh leaf traits and leaf litter decomposition of 20 plant species in Kerqin sandy land, China

20 plant species (10 monocots and 10 dicots) grown in Kerqin sandy grassland were incubated under indoor conditions to monitor the amount and rate of CO₂ release from the leaf litter. 11 traits of mature fresh leaves including caloric value, contents of Mg, P, N, K, C, C/N, N/P, specific leaf area, dry matter content and leaf surface area were measured to determine the relationship between CO₂ release and leaf characteristics. All those traits have great variation among the 20 species with over 3 fold differences between the maximum and minimum values, and a few traits such as leaf Mg content reached as high as 9 folds. After 28 d's incubation, the average CO₂ release amount from all the species was (4121 ± 1713) μg kg^?1 dry soil. The highest level from Chenopodium acuminatum was (8767 ± 177) μg kg^?1 dry soil, which was 5 folds higher than the lowest level ((1669 ± 47)μg kg^?1 dry soil) from Digitaria sanguinalis. However, CO₂ release rate showed the same trend in all the 20 species, i.e., the leaf litter decomposed faster initially (0–4 d), and gradually slowed down during extended cultural periods. Comparison between monocots and dicots showed that these two taxonomic groups had significant differences in terms of the amount and rate of CO₂ released from leaf litter, and N and C contents, leaf C/N, and dry matter content of mature leaves. Contents of N, C and dry matter, and C/N of mature leaves are significantly correlated with CO₂ release from leaf litter decomposition, which has been revealed by the Pearson correlation test. It can be concluded that these three traits of mature leaves can be used indirectly to predict decomposition rate of the leaf litter.     

Acid soil damage in sorghum genotypes: Role of magnesium deficiency and root impairment

The effects of liming and Mg fertilization on growth, specific root length (root length per unit of root dry weight; SRL) and nutrient uptake of twelve sorghum genotypes (Sorghum bicolor (L.) Moench) were studied in two pot experiments. Liming increased the pH of the sandy loam from pH 4.3 (unlimed) to 4.7 (with 0.5 g Ca(OH)₂ kg^-1 soil) and to 6.1 (with 2.5 g Ca(OH)₂ kg^-1 soil). Liming increased the dry matter yield of the genotypes by factors of 1.2 to 6.0 (between pH 4.3 and 4.7) and by 1.1 to 2.4 (between pH 4.7 and 6.1). In absence of Mg at soil pH of 4.3 and 4.7, all genotypes suffered from Mg deficiency, as indicated by low Mg concentrations in the shoots (26–94 mmol Mg kg^-1 DM) and visible Mg deficiency symptoms. At pH 4.7 several of the genotypes responded to Mg application and produced significantly more dry matter. At pH 4.3, however, none of the genotypes responded to Mg, even though the internal Mg concentrations were increased by applied Mg. The relative increase in dry matter yield between pH 4.3 and 4.7 was closely correlated to the relative change in specific root length in the same soil pH interval, especially when the soil was fertilized with Mg (r²=0.91^**). The group of genotypes where SRL and dry matter yield were reduced by soil acidity was not the same as the group that responded positively to Mg application at pH 4.7.It is concluded that the growth of sorghum genotypes on acid soils is determined by two independent characteristics: the sensitivity of root development to soil acidity and the efficiency of the uptake and utilization of Mg. The first characteristic is predminant at high soil acidity whilst the latter is dominant at moderate soil acidity.     

Measurement and modelling of photosynthetic response of pearl millet to soil phosphorus addition

There have been no studies of the effects of soil P deficiency on pearl millet (Pennisetum glaucum (L.) R. Br.) photosynthesis, despite the fact that P deficiency is the major constraint to pearl millet production in most regions of West Africa. Because current photosynthesis-based crop simulation models do not explicitly take into account P deficiency effects on leaf photosynthesis, they cannot predict millet growth without extensive calibration. We studied the effects of soil addition on leaf P content, photosynthetic rate (A), and whole-plant dry matter production (DM) of non-water-stressed, 28 d pearl millet plants grown in pots containing 6.00 kg of a P-deficient soil. As soil P addition increased from 0 to 155.2 mg P kg^–1 soil, leaf P content increased from 0.65 to 7.0 g kg^–1. Both A and DM had maximal values near 51.7 mg P kg^–1 soil, which corresponded to a leaf P content of 3.2 g kg^–1. Within this range of soil P addition, the slope of A plotted against stomatal conductance (g_s) tripled, and mean leaf internal CO₂ concentration ([CO₂]_i) decreased from 260 to 92 L L^–1, thus indicating that P deficiency limited A through metabolic dysfunction rather than stomatal regulation. Light response curves of A, which changed markedly with P leaf content, were modelled as a single substrate, Michaelis-Menten reaction, using quantum flux as the substrate for each level of soil P addition. An Eadie-Hofstee plot of light response data revealed that both K_M, which is mathematically equivalent to quantum efficiency, and V_max, which is the light-saturated rate of photosynthesis, increased sharply from leaf P contents of 0.6 to 3 g kg^–1, with peak values between 4 and 5 g P kg^–1. Polynomial equations relating K_M and V_max, to leaf P content offered a simple and attractive way of modelling photosynthetic light response for plants of different P status, but this approach is somewhat complicated by the decrease of leaf P content with ontogeny.     

镍离子对尖叶莴苣氮素吸收和生长生理的影响

以‘全年油麦菜’尖叶莴苣为试验材料,采用水培方式,研究3个浓度(0 mg·L^-1、0.1 mg·L^-1、1 mg·L^-1)Ni²⁺在22.4 mg·L^-1 N处理下对尖叶莴苣氮素吸收的生长及生理影响。结果显示：(1)尖叶莴苣根系和地上部生物量随处理时间的增加呈上升趋势。与对照T₁(0 mg·L^-1 Ni²⁺、112 mg·L^-1 N)相比,T₂处理(0 mg·L^-1 Ni²⁺、22.4 mg·L^-1 N)对尖叶莴苣根系及叶片生长具有一定抑制作用,植株鲜重、干重、根冠比、根系长度、平均直径、表面积、体积、根尖数、分根数、叶片表面积和体积在T3处理(0.1 mg·L^-1 Ni²⁺、22.4 mg·L^-1 N)下显著高于对照,T₄处理(1 mg·L^-1 Ni²⁺、22.4 mg·L^-1 N)对尖叶莴苣根系及其叶片生长具有一定促进作用,但对其根尖数和分根数表现出一定抑制性。(2)随着Ni²⁺浓度的增加,尖叶莴苣叶片叶绿素a、叶绿素b和总叶绿素含量呈先升后降的变化规律,且均在T₃处理下显著提高。(3)随着处理时间的增加,尖叶莴苣叶片的净光合速率(P_n)、气孔导度(G_s)和蒸腾速率(T_r)逐渐上升,胞间CO₂浓度(C_i)逐渐下降,且T₃处理叶片的G_s显著高于对照,其C_i最低,P_n最大。(4)施加Ni²⁺对尖叶莴苣有机酸、可溶性蛋白和可溶性糖含量以及SOD和POD活性有显著影响,在T₃处理下有机酸含量降低,可溶性糖和可溶性蛋白含量显著增加,SOD和POD活性显著提高。(5)T₃处理尖叶莴苣根系中N及叶片中B和Ca含量较高;根系中Ni含量高于叶片,T₃处理叶片中的Ni含量较低,Mg含量较高;植株体内Cu含量随Ni²⁺浓度增加而下降。研究表明,外源Ni²⁺处理能影响低氮条件下(22.4 mg·L^-1 N)尖叶莴苣幼苗生长及生理状况,适宜浓度(0.1 mg·L^-1)Ni²⁺可有效提高尖叶莴苣根系对氮素的吸收利用效率,减少氮素施用量,促进尖叶莴苣根系和地上部叶片生长,增加光合色素含量,并提高净光合速率,进而改善植株的产量和营养品质。     

柠檬酸和EDTA-Na2对黑麦草吸收Pb及营养元素特性的影响

为探究柠檬酸或EDTA-Na_2对Pb污染下黑麦草(Lolium perenne L.)吸收Pb和营养元素特性的影响,对水培黑麦草进行不同处理,研究黑麦草一些生理生化指标的变化。结果表明,与对照相比,Pb处理降低黑麦草干重,增加质膜透性和根系脱氢酶活性,且在叶和根中积累Pb,而叶和根中6种营养元素含量的变化不尽相同。与Pb处理同时加入低浓度的柠檬酸或EDTA-Na_2对其生长影响较小,且叶片的Pb积累量较低;而同时加入高浓度的柠檬酸或EDTA-Na_2,虽然强化Pb在叶片中的积累,但是加重了生长的抑制作用和营养元素的稳态失衡;1 mmol L~(–1)的柠檬酸强化叶片积累Pb的效应强于同浓度的EDTA-Na_2,而5和10 mmol L~(–1)柠檬酸的强化作用则弱于同浓度的EDTA-Na_2。因此,适当浓度的柠檬酸或EDTA-Na_2在治理Pb污染环境中具有一定作用。     

Depletion of soil mineral N by roots of Cucumis sativus L. colonized or not by arbuscular mycorrhizal fungi

Two experiments were conducted where Cucumis sativus were grown in uncompartmented pots either alone or in symbiosis with Glomus intraradices Schenck and Smith (Experiment 1) or Glomus sp. (Experiment 2) in order to investigate if root colonization by arbuscular mycorrhizal (AM) fungi has an effect on depletion of the soil mineral N pool. All pots were gradually supplied with 31 mg NH₄NO₃-N kg^-1 dry soil from 12–19 days after planting and an additional 50 mg (NH₄)₂SO₄-N kg^-1 dry soil (¹⁵N-labelled in Experiment 1) was supplied at 21 or 22 days after planting in Experiments 1 and 2, respectively. Dry weight of plant parts, total root length, mycorrhizal colonization rate and soil concentration of NH ₄ ⁺ and NO ₃ ^- were recorded at five sequential harvest events: 21, 24, 30, 35 and 42 days (Experiment 1) and 22, 25, 28, 31 and 35 days (Experiment 2) after planting. In Experiment 1, plants were also analysed for total content of N and ¹⁵N. The mycorrhizal colonization rate increased during time: from 25 to 40% in Experiment 1 and from 50 to 60% in Experiment 2. Plant dry matter accumulation was unaffected by mycorrhizal colonization, except in Experiment 1 where shoot dry weights were slightly increased and in Experiment 2 where root dry weights were slightly decreased compared to non-mycorrhizal control plants. The total root length was similar in the control and mycorrhizal treatments in Experiment 1, while it was decreased (20–30%) by mycorrhizal colonization in the last two harvest in Experiment 2. Mycorrhizal colonization affected the rate of depletion of soil mineral N in Experiment 1, where both NH ₄ ⁺ and NO ₃ ^- concentrations were markedly lower in the first two harvests, when plants were mycorrhizal. As the root length was similar in mycorrhizal and control treatments, this may indicate that the external AM hyphae contributed to the depletion of the soil mineral N pool. A similar pattern was observed in Experiment 2, although the effect was less pronounced. The ¹⁵N enrichment in mycorrhizal plants (Experiment 1) also indicated a faster NH ₄ ⁺ uptake than in the non-mycorrhizal controls in the first two harvests after application of the ¹⁵N-labelled N source. However, the external hyphae and roots seemed to have access to the same N sources as the ¹⁵N enrichment and total N content were similar in mycorrhizal and control plants at the end of the experiment. This revised version was published online in June 2006 with corrections to the Cover Date.     

Top and root growth and nutrient absorption of Prunus avium L. at two soil pH and P levels

One-year-old Prunus avium L. were grown under greenhouse conditions in a Countesswells soil in all combinations of 2 pH and 2 P levels. The soil, obtained from a long-term liming and fertilizer experiment, provided pH values throughout the experiment of 3.75–3.99 (pH 1) and 4.81–5.41 (pH 2). The P treatments had 0.43% acetic acid extractable P of 31–44 g g^-1 (P1) and 145–173 g g^-1 (P2). The trees were harvested 92 (H1), 134 (H2), and 168 (H3) days after initiation of growth.Top (leaf+new stem) dry weight was significantly increased for pH 2 and P2 at H2 and H3. P2 also increased leaf weight (H1), the weight of the original stem-root (H2 and H3), and root length but decreased root diameter at both soil pHs (H2 and H3). Total tree uptake of N, P, K, Ca, and Mg was also increased by pH-P combinations which had significantly greater dry matter production and root length. Total Mn uptake decreased at pH2. Root nutrient inflows (uM m^-1 day^-1) were increased for Ca at pH2 and for P at P2. Mn inflow decreased at pH2 and at pH1 P2 although the increased root length associated with the latter treatmen resulted in increased total tree Mn uptake. In general, high nutrient inflows occurred in all trees at H1 and in severely stunted trees at pH1 P1; both had larger than average root diameters.     

Maize and pigweed response to nitrogen supply and form

As nitrogen management practices change to achieve economic and environmental goals, effects on weed-crop competition must be examined. Two greenhouse experiments investigated the influence of N amount and form on growth of maize and redroot pigweed (Amaranthus retroflexus L.). In Experiment 1, maize and pigweed were grown together in a replacement series (maize: pigweed ratios of 0:4, 1:3, 2:2, 3:1, 4:0) under three NH₄NO₃-N supplies (0, 110, and 220 mg N kg^-1 soil). Maize was planted into established pigweed and plants were harvested 24 days after maize germination. Pigweed responded more to supplemental N than maize and accumulated 2.5 times as much N in shoots at the high N supply. Competition effects were not significant. Maize and pigweed were grown separately in Experiment 2 and supplied 220 mg N kg^-1 as either Ca(NO₃)₂ or (NH₄)₂SO₄ plus a nitrification inhibitor (enhanced ammonium supply, EAS). In maize, EAS treatment did not affect shoot growth and reduced root growth 25% relative to the NO₃-N treatment. In pigweed, shoot and root growth were restricted 23 and 86% by EAS treatment, respectively. Total plant N accumulation under EAS treatment was higher in maize, less in pigweed. Under EAS treatment, pigweed leaves were crinkled and chlorotic; leaf disks extracted in 70% ethanol, pH 3, contained less malate and oxalate but more NH₄ ⁺ compared to the NO₃-N treatment. Maize leaf disk malate levels were generally higher compared to pigweed but were less due to EAS treatment. Ammonium level in maize leaf disks was unaffected by N form and EAS treatment increased oxalate levels. Final bulk soil pH was generally lower in pots where pigweed were grown and tended to be lower due to EAS. Leaf disk malate levels and soil pH were positively associated. Results indicate that pigweed is more likely to compete with maize when high levels of NO₃-N are provided. Enhancing the proportion of N supplied as NH₄ ⁺ should restrict the growth of NH₄ ⁺-sensitive pigweed.     

Macronutrient content in leaves of bean plants (Phaseolus vulgaris,L.) grown with differents rates of N/S as fertilizers

Summary The effect of increasing rates of nitrogen (N) and sulphur (S) as fertilizers on the yield, leaf area and N, P, S, Ca, Mg, NO₃ ⁻ and SO₄ ⁼ content in leaves of bean (Phaseolus vulgaris, L.) were studied in a hydroponic culture experiment under greenhouse conditions. Bean plants responded significantly to all treatments with differents N/S ratios. When plants grew with high N/S ratios, the leaf content of N, Ca and NO₃ ⁻ increased while the content of K, P and SO₄ ⁼ decreased. However, optimal yield and leaf area were not obtained. Optimal leaf and fruit dry matter was obtained at N/S ratio value of 1.41. When lower N/S rates were used, optimal leaf and fruit dry matter was only observed when the leaf N/S ratio was between 15 and 16. At high sulphate levels in the nutrient solution there is no interaction with nitrate which is easily observed, resulting in an increase in yield. An interaction between nitrate and sulphate in the nutrient solution was found at a N/S ratio of 0.81 which produced in leaves a synergic effect between P-K, an antagonistic effect between N-P and N-K and a lower yield. This research was supported by Fundacion ‘Ramon Areces’.