Short-term partitioning of <Superscript>14</Superscript>C-[U]-glucose in the soil microbial pool under varied aeration status

The effect of soil aeration status on carbon partitioning of a labelled organic substrate (¹⁴C-[U]-glucose) into CO₂, microbial biomass, and extra-cellular metabolites is described. The soil was incubated in a continuous flow incubation apparatus under four different aeration conditions: (1) permanently aerobic, (2) permanently anaerobic, (3) shifted from anaerobic to aerobic, and (4) shifted from aerobic to anaerobic. The soil was pre-incubated for 10 days either under aerobic or under anaerobic conditions. Afterwards, glucose was added (315 g C g^–1) and the soils were incubated for 72 h according to four treatments: aerobic or anaerobic conditions maintained, aerobic conditions shifted to anaerobic conditions and anaerobic conditions shifted to aerobic conditions. Carbon partitioning was measured 0, 8, 16, 24, 48 and 72 h after the glucose addition. In permanently aerobic conditions, the largest part of the consumed glucose was built into microbial biomass (72%), much less was mineralised to CO₂ (27%), and only a negligible portion was transformed to soluble extra-cellular metabolites. Microbial metabolism was strongly inhibited when aeration conditions were changed from aerobic to anaerobic, with only about 35% of the added glucose consumed during the incubation. The consumed glucose was transformed proportionally to microbial biomass and CO₂. In permanently anaerobic conditions, 42% of the consumed glucose was transformed into microbial biomass, 30% to CO₂, and 28% to extra-cellular metabolites. After a shift of anaerobic to aerobic conditions, microbial metabolism was not suppressed and the consumed glucose was transformed mainly to microbial biomass (75%) and CO₂ (23%). Concomitant mineralisation of soil organic carbon was always lower in anaerobic than in aerobic conditions.     

不同生育期缺水和补充灌水对冬小麦氮磷钾吸收及分配影响

采用盆栽试验研究了不同生育期缺水和补充灌水对冬小麦N、P、K吸收及在体内分配的影响。结果表明 ,水分缺乏不仅抑制作物生长 ,还降低养分吸收。分蘖、拔节和灌浆期是作物需水关键期 ,这些时期缺水 ,生长量降低36.1%～72.3% ;N吸收降低 40.6%～72.0% ,P降低 40.5%～72.4% ,K降低 25.9%～69.5% ;而越冬期缺水 ,生长和养分吸收降低较少。不同生育期补充灌水也不一定能使小麦生长和养分吸收增加。拔节期补水生长量增加幅度最高 ,达 18.2% ;N、P、K吸收量增幅也最大 ,分别为 14.5% ,15.6%和 38.2%。其次是越冬和灌浆期补水。分蘖期补水 ,生长量和养分吸收量却显著降低。越冬、拔节、灌浆期补充灌水 ,虽能促进小麦整株生长 ,增强养分吸收 ,但养分向子粒的转移和分配并不相应增强。越冬和灌浆期补水 ,子粒吸N量分别提高 5.5%和 20.9% ,吸P量提高 9.1%和 6.2% ;拔节期补水 ,N、P吸收量反而分别降低 19.6%和 13.5%。 3个时期补水 ,子粒吸K量均降低3.0%～26.7%。     

Ammonia Nitrogen Removal in Step-Feed Rotating Biological Contactors

The effect of step-feed on biological ammonia nitrogen (NH₃-N) removal in a rotating biological contactor (RBC) system consisting of two three-stage units (one control and one step-feed) treating synthetic wastewater was examined. The performance of the step-feedRBC was evaluated in comparison to a regularly fed RBC in terms of NH₃-N removals and stage-dissolved oxygen (DO) conditions over a range of hydraulic and organic loading rates (HLR = 0.032 to 0.125 m³ m^-2. d^-1 and OLR = 11.03 to 111.6 g COD m^-2. d^-1). The results indicate that the step-feed unit showed better removal efficiency (%) at high HLR and ORL than the regularly fed control unit. Increasing the HLR and the OLR resulted in a decrease in DO in all the stages of the two units. However, DO values in the step-feed system were higher than those recorded for the control system. In addition, O₂ limiting conditions (DO ≤ 2 mg l^-1) and heavy growth of Beggiatoa were detected in stage 1 of the control unit at high loading rates.     

微孔曝气流量与曝气管长度对水体增氧性能的影响

为了探究曝气流量与曝气管长度对增氧性能的影响,在不同曝气流量、不同曝气管长度条件下进行了室内水体底部微孔曝气增氧试验。分析了曝气流量与曝气管长度对氧体积传质系数、增氧量和氧利用率的影响。研究结果表明,当曝气流量为0.27~0.55 m3/s、曝气管长为0.9~1.5 m时,所对应的氧体积传质系数在0.63~1.1 h-1变化,增氧量在6.8~12.9 g/h变化,氧利用率在6.87%~9.28%变化,且在一定的曝气管长度下,氧体积传质系数、增氧量均与曝气流量成正比,而氧利用率则与其成反比关系;在一定的曝气流量下,曝气管长度对氧体积传质系数产生的影响表现为先高后低再高的趋势;氧体积传质系数与修正的饱和溶解氧浓度是否作为增氧量的主要影响因子取决于曝气管长度;曝气流量对氧利用率较曝气管长度更为敏感。研究还发现,微孔曝气系统中存在着最优曝气管长度,使得增氧性能最佳,并建立了最优曝气管长度与曝气流量、水深、输入压力、最优初始气泡直径的相关关系式,为低碳经济下微孔曝气系统的设计和运行提供了理论依据。     

加气灌溉改善大棚番茄光合特性及干物质积累

为揭示不同加气灌溉参数对作物光合特性及干物质积累的影响规律,以番茄为研究对象,研究了不同土壤加气量与加气深度组合对番茄光合作用、叶绿素含量、干物质积累及产量的影响。结果表明,对番茄根区土壤加气可显著提高叶片叶绿素含量和气孔导度,增强光合作用,增加干物质积累及产量。随加气量的升高,大棚番茄净光合速率总体上呈先升高后降低的趋势。15和40 cm滴管带埋深下,标准加气量（49.4 L/m2）下2次测定净光合速率平均较不加气处理升高21.4%和65.0%。滴灌带埋深为15 cm时,叶绿素含量、干物质积累量及产量随加气量的升高呈先升高后降低趋势,标准加气量下较不加气处理分别提升38.0%、55.4%和59.0%,滴灌带埋深为40 cm时随加气量的升高呈持续升高趋势,1.5倍标准加气量（74.2 L/m2）处理较不加气处理分别提升33.7%、36.2%和105.4%。综合考虑,当滴灌带埋深为15 cm时,宜采用标准加气量作为加气标准,而埋深为40 cm时,最佳加气量为1.5倍标准加气量。     

Composting Hog Manure/Sawdust Mixtures Using Intermittent and Continuous Aeration: Ammonia Emissions

Odorous emissions from manures have become a significant problem. Preliminary work on composting hog manure with sawdust had indicated that intermittent aeration could reduce ammonia emissions during this process. This paper presents results from four additional runs with a total of 22 pilot-scale vessels that have confirmed that ammonia emissions are affected by aeration. The pilot-scale vessels consisted of insulated, stainless steel, 205 L drums that either received continuous (high/low rate, thermostatically controlled blowers) or intermittent (5 min on high rate, 55 min off) aeration. Ammonia emissions, air flow rates, carbon dioxide production, oxygen utilization, and temperatures at four locations in each vessel were monitored. Ammonia emissions under intermittent aeration were roughly 50% less than those from the continuously aerated vessels. However, this appeared to result more from total air flow than from the aeration technique used. A linear regression of emissions versus total air flow data for all vessels yielded a fit of y = 0.1309x + 29.385 (y being total ammonia emitted [in g of N] and x being total air flow [in kg]) with an R² = 0.6808. Since air flow termination was relatively arbitrary, this only means basically, that ammonia emissions were doubled for a quadrupling of air flow. Under intermittent aeration, the minimum oxygen level in the exhaust air occasionally dropped to as low as 1%. So the aeration pattern used probably represents the lowest one suitable for maintaining aerobic conditions. Within this constraint, however, lower air flow appears to be suitable for reducing odorous ammonia emissions.     

Microbial responses to fluctuation of soil aeration status and redox conditions

 The response of the microbial community to changes in aeration status, from oxic to anoxic and from anoxic to oxic, was determined in arable soil incubated in a continuous flow incubation apparatus. Soil incubated in permanently oxic (air) and/or anoxic (O₂-free N₂) conditions was used as the control. Before experiments soil was preincubated for 6 days, then aeration status was changed and glucose added. Glucose concentration, extractable C, CO₂ production, microbial biomass, pH and redox potential were determined 0, 4, 8, 12, 16, 24, 36 and 48 h after change of aeration status. If oxic conditions were changed to anoxic, the amount of glucose consumed was reduced by about 60%, and CO₂ production was 10 times lower at the end of incubation compared to the control (permanently oxic conditions). Microbial biomass increased by 114% in glucose-amended soil but did not change in unamended soil. C immobilization prevailed over C mineralization. Redox potential decreased from +627 mV to –306 mV. If anoxic conditions were changed to oxic, consumption of glucose and CO₂ evolution significantly increased, compared to permanently anoxic conditions. Microbial biomass did not change in glucose-amended soil, but decreased by 78% in unamended soil. C mineralization was accelerated. Redox potential increased from +238 to +541 mV. The rate of glucose consumption was low in anoxic conditions if soil was incubated in pure N₂ but increased significantly when incubation was carried out in a CO₂/N₂ mixture. Received: 6 January 1999     

基于作物生长模型参数调整动态估测夏玉米生物量

针对如何利用作物生长模型定量解析区域夏玉米生物量动态变化的热点问题,该文在沿东海岸的江苏省盐城市大丰区设置大田夏玉米生物量估测试验,在构建夏玉米生物量过程模拟模型的基础上,对夏玉米多个生育阶段的生物量(指地上部生物量)及其变化特征进行分析,并结合试验实测数据探讨利用实测叶面积指数和生物量数据调整生物量模拟模型参数的可行性。结果表明:夏玉米生物量过程模拟模型可以对夏玉米从出苗到灌浆期间的多个生育阶段生物量动态变化进行估测。出苗到拔节前的生长阶段,生物量积累主要来源于叶片形成,模拟模型可以对生物量进行有效预测,预测值与实测值之间的均方根差(root mean square error,RMSE)为18.31 kg/hm~2,相对误差为3.35%。拔节到抽雄前的生长阶段,由于茎节伸长与节数增加,生物量积累加快,预测值与实测值之间的差异较大。拔节初期生物量预测值为535.5 kg/hm~2,实测值为480 kg/hm~2,相对误差11.56%。抽雄前生物量预测值为7 036.46 kg/hm~2,实测值为5 794 kg/hm~2,相对误差21.44%。拔节到抽雄前生长阶段预测值与实测值之间的RMSE为825.94 kg/hm~2。经过模型参数调整,抽雄前生物量预测值为6 036 kg/hm~2,与实测值较为接近,RMSE为219.43 kg/hm~2,相对误差4.18%。利用参数调整后的模拟模型继续对抽雄到灌浆前生长期间生物量进行预测,预测值与实测值较为一致,灌浆期生物量预测值为11 156 kg/hm~2,实测值为10 785 kg/hm~2,相对误差3.44%,而参数调整前预测值为12 492 kg/hm~2,相对误差15.83%。在玉米拔节期进行模型参数调整,对拔节到抽雄和抽雄到灌浆2生长阶段的生物量预测效果较好。该研究可为县域夏玉米不同生长阶段生物量及其动态变化预测提供参考,可辅助县域农业管理部门进行适时生产措施调整。     

Sewage Treatment in a Rotating Biological Contactor (RBC) System

The treatment of domestic wastewater at a temperature of 12–24°C was investigated in an RBC system. The RBC consists of a two stage system connected in series. The system was operated at different organic loading rates (OLR's) and hydraulic retntion times (HRT's) in order to optimize the RBC performance. The overall removal efficiencies for chemical oxygen demand (COD_total, COD_suspended and COD_colloidal) significantly decreased when decreasing the total HRT from 10 to 2.5 h and increasing the OLR from 11 to 47 g COD/m².d. However, the effluent quality of COD_soluble remained unaffected. Most of the COD was removed in the 1^st stage and nitrification took place in the 2^nd stage of the two stage system.The overall nitrification efficiency was 49% at total OLR of 11 gCOD/m².d. At total HRT's of 10, 5 and 2.5 h, the Escherchia coli (E. coli) concentration was reduced by a value of 1.6, 1.5 and 0.8 log₁₀ respectively. The sludge volume index (SVI) decreased as the OLR increased. However, the SVI of the excess sludge produced in the RBC under different OLR's was always <74 ml/gTS, which indicates vadjust a good settleability. The performance of the single versus two stage RBC operated at the same total OLR of 22 g COD/m².d and the same HRT of 5.0 h was examined. The results obtained showed that the COD concentration and the E. coli content in the final effluent of a two stage were lower than in the effluent of the single stage RBC. Moreover, the nitrification efficiency in the two stage system was higher comapred to one stage system.     

四川单季稻区主栽水稻品种的生长模拟*4

利用四川单季稻区7个农业气象观测站5个主栽品种的田间观测数据,结合当地栽培管理措施、土壤条件及逐日气象资料对ORYZA2000模型进行参数调试,并确定四川单季稻区5个主栽品种的作物参数值;利用4～5a各主栽品种的观测数据对单季稻生育期、叶面积指数、生物量和产量等指标的模拟结果进行验证和评价。结果表明,合系39营养生长期发育速率最大,而生殖生长期发育速率最小,Ⅱ优838营养生长期发育速率最小,而D优63和汕优2生殖生长期发育速率最大;模型对5个单季稻主栽品种的生育期模拟效果较好,各品种开花期与成熟期的相对模拟误差均在1～2d,归一化均方根误差（NRMSE）均小于1%;各品种产量的NRMSE在5.26%～10.01%,叶面积指数的NRMSE为10.37%～19.19%,地上部总生物量、茎生物量、绿叶生物量及穗生物量的 NRMSE 分别为13.17%～18.69%、14.31%～20.41%、18.95%～24.74%和20.85%～25.39%。由此可见,ORYZA2000模型能够较为准确地模拟四川单季稻区5个主栽品种的发育及产量形成过程,适应能力较强,可以应用于四川单季稻生产。     

叶轮式增氧机的研究

本文对叶轮式增氧机工作时的池塘溶氧分布作了试验研究;对氧气在气—水界面上的传递与增氧机的功耗作了分析探讨。提出了通过增大气流速度,采用阶递形池底、局部增氧来提高增氧机效率的新论点;为增氧机的研制与应用提供了新的方法和依据。     

微孔扩散器形状对曝气增氧性能影响的试验

为了探究不同形状(直线型、C型、S型和圆盘型)的微孔曝气扩散器对增氧性能的影响,在3个水深和5个曝气流量下进行了一系列的室内曝气增氧试验.结果表明:相同水深和流量下,直线型的氧体积传质系数、充氧能力、动力效率和氧利用率均最大,例如在0.7 rn水深时4个技术指标的范围值分别为0.853～1.762 h-1、8.701～17.432 g/h、4.146～6.869 kg/(kW·h)、3.257％～4.912％;而S型是最低的,其范围值分别为0.798～1.504 h-1、6.850～12.627 g/h、2.630～4.444 kg/(kW·h)、3.823％～2.339％;其次是C型和圆盘型微孔曝气扩散器,其他水深试验条件下也得到了类似的规律.由此说明直线型的增氧效果最好.为了仅探究扩散器形状对增氧性能的影响,在试验水池表面铺设薄膜阻隔了空气-自由水表面氧传质后,4种扩散器的氧体积传质系数均下降,最大的下降率分别为12.29％、8.73％、12.26％和6.74％,空气-自由水表面氧传质对不同形状的扩散器的影响程度不同.但下降后的氧体积传质系数值最高的仍是直线型,其次是C型和圆盘型,S型仍然最低;直线型、C型、圆盘型、S型在0.7 m水深下分别为1.693、1.470、1.438和1.227 h-1,在其他工况下也得到了类似的规律.因此,增氧性能最好的是直线型微孔曝气扩散器.此研究结果可为微孔曝气技术的绿色环保应用以及实际工程中对微孔扩散器形状的选取提供一定的参考价值.     

Biofilm Communities and Operational Monitoring of a Rotating Biological Contactor System

A full scale rotating biologicalcontactor (RBC) system has been studied for a year.The main objective was to determine the distributionof protozoan and metazoan communities inhabiting theRBC biofilms, and to relate them to the BOD₅content along RBC train. RBC system operatedefficiently as showed the removal of TBOD₅ and TSSalong the plant. A weak nitrification process tookplace at last stages of the system. Orthophosphatesand pH average values were maintained quite similarthroughout the RBC stages. Microscopical countingindicated that communities were mainly made up ofciliated protozoa, although the abundance anddiversity of species varied widely along the differentRBC stages. A careful characterisation of ciliatespecies was carried out, with Vorticellaconvallaria, Epistylis entzii and Carchesiumpolypinum being the most abundant species in the wholesystem. Metazoa only reached a noticeable proportionin the last stages of the system. Spatial distributionof biofilm communities reflected the environmentalchanges observed as waste purification progresses.Associations between microorganisms and BOD₅concentrations were studied by correlation analysis.Results chiefly revealed the importance of ciliatedprotozoa in this biological system. They showed a highabundance on the biofilms and some groups– cyrtophorids, hypotrichs, scuticociliates andpleurostomatids ciliates – were closely related to adecrease of BOD₅ content.     

四川单季稻区主栽水稻品种的生长模拟

利用四川单季稻区7个农业气象观测站5个主栽品种的田间观测数据,结合当地栽培管理措施、土壤条件及逐日气象资料对ORYZA2000模型进行参数调试,并确定四川单季稻区5个主栽品种的作物参数值;利用4～5a各主栽品种的观测数据对单季稻生育期、叶面积指数、生物量和产量等指标的模拟结果进行验证和评价。结果表明,合系39营养生长期发育速率最大,而生殖生长期发育速率最小,Ⅱ优838营养生长期发育速率最小,而D优63和汕优2生殖生长期发育速率最大;模型对5个单季稻主栽品种的生育期模拟效果较好,各品种开花期与成熟期的相对模拟误差均在1～2d,归一化均方根误差（NRMSE）均小于1%;各品种产量的NRMSE在5.26%～10.01%,叶面积指数的NRMSE为10.37%～19.19%,地上部总生物量、茎生物量、绿叶生物量及穗生物量的NRMSE分别为13.17%～18.69%、14.31%～20.41%、18.95%～24.74%和20.85%～25.39%。由此可见,ORYZA2000模型能够较为准确地模拟四川单季稻区5个主栽品种的发育及产量形成过程,适应能力较强,可以应用于四川单季稻生产。     

Comparative Study of Static Pile Composting Using Natural,Forced and Passive Aeration Methods

Poultry manure slurry amended with sphagnum peat was composted by natural aeration (NA), forced aeration (FA) and passive aeration (PA). Compost piles were built in trapezoidal shape with a volume of 5 m³. A total of nine replicates, three for each treatment method, were built. A total of 231 thermocouples were used to establish a three-dimensional temperature regime in each pile.

The results showed that, for the selected configuration of aeration pipes and aeration schedule, temperature drop occurred almost two weeks sooner in PA and FA process than NA process. Also, temperature inside PA and NA processes stayed above 55°C for a longer time than FA process. Both FA and PA methods were effective in providing more oxygen. Low O₂ concentrations were measured at the bottom and middle of NA pile and middle of PA pile during the early stages of the process which is an indication of anaerobic conditions. A total mass reduction of 32 percent and volumetric reduction of 16 to 22 percent were observed. The mass reduction was mainly due to water evaporation, around 550 liters of water per each pile. C/N ratio dropped from the initial value of 21.9 to 18.9, 19.8 and 20.9 for NA, PA and FA, respectively.

The influence zone of aeration pipes in FA and PA composting was determined using a statistical procedure involving the verage of absolute differences (AAD) of temperature readings and two-way ANOVA. By comparing analogous thermocouple locations between PA with NA as well as FA with NA piles, it could be established whether inclusion of the aeration pipes affected the temperature at that location. A three-dimensional influence zone was mapped for PA and FA composting. Results indicate that for the selected configuration of aeration pipes and aeration schedule, PA pipes influenced temperatures in the bottom half of the PA pile while FA pipes affected the interior part of the pile. Near the pile surface, aeration was predominantly by diffusion, as these positions were not influenced by the aeration pipes. The results obtained were also verified by Cluster analysis.     

Improving Performance of Treatment Wetlands: Evaluation of Supplemental Aeration,Varying Flow Direction,and Phosphorus Removing Filters

Pollutant removal was compared among subsurface flow constructed wetland (CW) mesocosms used for dairy farm wastewater treatment. Supplemental aeration, flow direction, and the use of phosphorus-reducing filters (PRFs) were varied among the CWs. The following were compared: (1) vertical flow CWs with and without supplemental aeration, (2) aerated CWs with horizontal and vertical flow directions, (3) single-cell and two-cell treatment systems, and (4) wetland-wetland systems (two CWs in series) and wetland-PRF systems (a CW followed by a PRF). The results from this investigation showed that, first, nearly all treatment strategies, either singly or in pairs, substantially reduced almost all the contaminants we tested. Second, supplemental aeration resulted in higher ammonium-nitrogen (NH₄-N) removal efficiencies in aerated vertical flow CWs, compared to unaerated CWs. However, it caused no further improvement in dissolved reactive phosphorus (DRP), total suspended solids (TSS), E. coli, or BOD₅ removal. Third, there was no difference between aerated horizontal and aerated vertical flow CWs in removal of any of the tested contaminants. Fourth, adding a second stage of treatment significantly improved DRP, TSS, E. coli, and NH₄-N removal, but not BOD₅. Finally, treatment systems with PRFs showed superior performance in DRP and E. coli removal.     

Interactions of oxygen‐nitrogen‐salinity stresses on plant growth and mineral content of sunflower (Helianthus annuus L.) in sand culture

Reports relating the separate and combined influences of soil aeration, nitrogen and saline stresses on the germination, growth and ion accumulation in sunflowers are lacking in the literature. The sunflowers of this report were grown in sand culture in the greenhouse. Separate and combined treatments of two levels of aeration, three levels of nitrogen and three levels of NaCl were applied to plants which were harvested at 40 and 56 days. Seed germination was excellent in all treatments. Plant height and dry weight decreased with each type of stress. Low oxygen (0.20 μg O₂ cm^‐2 min^‐1) and nitrogen (10 ppm) combined with 70 meq/1 NaCl caused the greatest reduction of plant growth. Leaf number was reduced by low nitrogen and excess salt. Low oxygen reduced the accumulation of K, Ca and Mg and increased the Na and N‐NO₃ content of sunflower leaves. Potassium to sodium ratios in plant on sunflower growth could be partially ameliorated with the tissue were decreased by greater EC values of the nutrient solution and low soil ODR. The adverse effects of salt and oxygen stresses addition of nitrogen. Ion accumulation was an earlier indicator of plant stress than plant growth and both parameters provided excellent methods for assessing plant tolerance to soil aeration, nitrogen and saline stresses.     

基于卫星光谱尺度反射率的冬小麦生物量估算

为探索基于光学卫星遥感数据的冬小麦地上生物量估算方法,本研究通过3年田间试验,获取冬小麦4个关键生育期（拔节期、抽穗期、开花期和灌浆期）和3种施氮水平下的地上生物量以及对应的近地冠层高光谱反射率数据。通过将高光谱数据重采样为具有红边波段的RapidEye、Sentinel-2和WorldView-2卫星波段反射率数据,构建任意两波段归一化植被指数。同时,将卫星波段反射率数据与6种机器学习和深度学习算法相结合,构建冬小麦生物量估算模型。研究结果表明：任意两波段构建的最佳植被指数在冬小麦开花期对生物量的敏感性最强（决定系数R2为0.50～0.56）。在不同施氮水平条件下,高施氮水平增强了植被指数对生物量的敏感性。Sentinel-2波段数据所构建的植被指数优于其他两颗卫星波段数据。对6种机器学习和深度学习算法,总的来说,基于深度神经网络（Deep Neural Networks,DNN）算法所构建的模型要优于其他算法。在单一生育期中,在拔节期（R2为0.69～0.78,归一化均方根误差为26%～31%）和开花期（R2为0.69～0.70,归一化均方根误差为24%～25%）的估算精度最高。Sentinel-2波段数据与DNN算法结合的估算精度最高,在全生育期中预测精度R2为0.70。施氮水平的提高同样增强了DNN模型的估算精度,3颗卫星波段数据在300 kg/hm2施氮条件下的预测精度R2都在0.71以上,均方根误差小于219 g/m2。研究结果揭示了光学卫星遥感数据在不同生育期和施氮条件下估算冬小麦生物量的潜力。     

Redistribution of crop residues during row cultivation creates a biologically enhanced environment for soil microorganisms

Formation of ridges during row cultivation creates microsites that could enhance spatial heterogeneity of soil properties, such as organic C, and thereby influence soil microbial communities. A study was conducted during 2003 near Shelton, NE, on a corn (Zea mays L.) field mapped using apparent electrical conductivity (ECa). New ridges were built each year with a row cultivator when corn reached the V3–V4 growth stage. Cultivation increased labile C fractions and soil microbial biomass in the row position for all ECa classes. Canonical discrimination analysis showed no clear differences in relative abundance of specific microbial groups among ECa classes or between row and furrow position, except for enhanced mycorrhizal biomass in the row. Microbial biomass responded strongly to changes in C redistribution, but was not accompanied by a significant change in the abundance of specific microbial groups. Labile C fractions (coarse and fine particulate organic matter) and crop residues in diverse stages of decomposition are associated with diverse microbial groups. Thus, row cultivation for weed control creates a biologically enhanced root zone that may improve early season performance of corn.     

自然条件下半干旱雨养春小麦生育后期旗叶光合的气孔和非气孔限制

为探究半干旱地区雨养春小麦旗叶的光合作用限制因素、不同生育期差异及其适应策略,分析了大田条件下春小麦旗叶在抽穗期和灌浆期光合生理特征的动态变化规律,探讨了自然条件下光合作用的气孔与非气孔限制特征。结果表明:净光合速率日变化趋势在抽穗期和灌浆期分别为单峰型和双峰型,峰值相当,为18.5μmol(CO2)·m-2·s-1左右。气孔导度具有与净光合作用几乎相似的日变化规律,胞间CO2浓度大致为上午下降、下午回升。胞间CO2浓度变化除受光合作用消耗和气孔限制共同作用外,下午时段叶肉导度增大,也影响胞间CO2浓度变化。在抽穗期和灌浆期,春小麦旗叶光合作用速率与气孔导度相关性十分显著,相关系数分别达0.916(P=0.000)和0.945(P=0.000)。并且2个生育期均出现明显的光合气孔限制,抽穗期达0.64,灌浆期为0.53。其中,抽穗期气孔导度对饱和水汽压差响应十分敏感,下午出现较为明显的气孔限制;灌浆期中午出现较为明显的光合"午休"现象,其主要原因是半干旱区较大饱和水汽压差和强烈辐射致使气孔关闭,气孔限制达到极大值,并且非气孔限制因素也较为突出。抽穗期至灌浆期,由于气孔对饱和水汽压差敏感性的下降以及"午休"策略,光合气孔限制逐渐减小,是春小麦在半干旱地区维持较高光合速率和保证产量的重要自适应机制。