Effects of deep placement of fertilizer on periphytic biofilm development and nitrogen cycling in paddy systems

Periphytic biofilms are commonly presented at the water-soil interface in paddy fields. Different fertilization methods can affect the concentration and distribution of nutrients in paddy fields and thus affect the development of periphytic biofilms. In this study, the roles of periphytic biofilms in nitrogen(N) cycling in paddy systems and how they are affected by different fertilization methods were studied using microcosm experiments. Microcosms were prepared using soil samples from a paddy field and treated with surface and deep fertilization under light and dark conditions. Surface fertilization under light condition promoted the development of periphytic biofilms, while deep fertilization under dark condition inhibited their development. The development of periphytic biofilms increased the pH and dissolved oxygen levels in the overlying water. Surface fertilization resulted in high N concentrations in the overlying water and the topsoil layers, which enhanced NH3 volatilization and nitrification-denitrification but inhibited N fixation. The development of periphytic biofilms reduced NH3 volatilization loss but increased nitrification-denitrification loss and the overall N loss in the paddy system. The results from this work suggest that the presence of periphytic biofilms in paddy fields could increase N loss by 3.10%–7.11%. Deep fertilization is an effective method to retard the development of periphytic biofilms in the paddy system and can potentially increase the overall N use efficiency.     

Impacts of silver nanoparticles on enzymatic activities, nitrifying bacteria, and nitrogen transformation in soil amended with ammonium and nitrate

Silver nanoparticles (AgNPs) are effective antimicrobial compounds that are used in a myriad of applications. Soil microorganisms play crucial roles in nitrogen cycling, but there is a lack of comprehensive understanding of the effects of AgNPs on enzymatic activity in the nitrogen cycle, nitrifying bacteria, and nitrogen transformation in soil. Herein, enzyme activities were determined following the addition of different forms of nitrogen, ammonium nitrogen ((NH₄)₂SO₄), nitrate nitrogen (KNO₃), and amide nitrogen (urea, CO(NH₂)₂) at 200 mg N kg^-1, into the soil amended with AgNPs at 0, 10, 50, and 100 mg kg^-1. After 7 d of incubation with 10 mg kg^-1 AgNPs, the activities of urease, nitrite reductase (NiR), nitrate reductase (NaR), and hydroxylamine reductase (HyR) were reduced by 12.5%, 25.0%, 12.2%, and 24.2%, respectively. Of particular note, more than 53.5%, 61.7%, and 34.7% of NaR, NiR, and HyR activities, respectively, were inhibited at 100 mg kg^-1AgNPs. The abundance (most probable number) of ammonia- and nitrite-oxidizing bacteria (AOB and NOB, respectively) was measured using real-time quantitative polymerase chain reaction (qPCR) and the Cochran method. The abundance of AOB and NOB decreased when AgNPs were present in the soil. The NH₄NO₃ amendment increased copy numbers of bacterial and archaeal amoA nitrification functional genes, by 38.3% and 12.4%, respectively, but AgNPs at 50 mg kg^-1 decreased these values by 70% and 56.4%, respectively. The results of ¹⁵N enrichment (atom% excess) of NH₄⁺ and NO₃^- experiments illustrated the influence of AgNPs on soil nitrogen transformation. According to the ¹⁵N atom% excess detected, the conversion of ¹⁵N-labeled NH₄⁺ to NO₃^- was significantly inhibited by the different levels of AgNPs in soil. The reduced gross nitrification rate further confirmed this finding. Overall, this study revealed considerable evidence that AgNPs inhibited nitrogen cycle enzyme activity, the number of nitrifying bacteria, the abundance of the amoA gene, and the gross nitrification rate. Silver nanoparticles inhibited nitrogen transformation, and the rate of nitrification was also negatively correlated with AgNP levels.     

Main environmental drivers of abundance, diversity and community structure of comammox Nitrospira in paddy soils

The recently discovered complete ammonia oxidizers comammox Nitrospira contain clades A and B that can establish an independent one-step nitrification process; however, little is known about their environmental drivers or habitat distributions in agricultural soils. Previous studies on comammox Nitrospira in paddy soils have mainly focused on small-scale samples, and there is a lack of multisite research on comammox Nitrospira in paddy soils. In this study, we conducted a survey of 36 paddy soils to understand the community structure, abundance, and diversity of comammox Nitrospira and the degree to which they are affected by environmental factors at a large scale. Comammox Nitrospira were found to be widely distributed among the paddy soils. The abundance of comammox Nitrospira clade A was mostly lower than that of clade B, whereas its diversity was mostly higher than that of clade B. Correlation analysis showed that multiple factors affected (P < 0.05) the abundance of comammox Nitrospira, including soil pH, organic matter, total carbon, and total nitrogen, latitude, mean annual temperature, and mean annual precipitation. Moreover, there was a clear relationship between the comammox Nitrospira community and habitat, indicating that some amplicon sequence variants (ASVs) had a unique dominant position in specific habitats. Phylogenetic analysis showed that the ASVs of comammox Nitrospira clade A clustered with the known sequences in the paddy soils and were significantly different from the known sequences in other habitats, which may be related to the unique paddy field habitat. In contrast, comammox Nitrospira clade B showed no clear habitat dependence. These results support the wide distribution and high abundance of comammox Nitrospira in paddy soils and provide novel insights into nitrogen cycling and nutrient management in agricultural ecosystems.     

不同生物硝化抑制剂对红壤性水稻土N2O排放的影响及其机制

为揭示不同生物硝化抑制剂(BNIs)对红壤性水稻土N₂O排放的影响差异及作用机制,通过21 d的土柱淹水培养试验,比较了三种BNIs 1,9-癸二醇(1,9-D)、亚麻酸(LN)和3-(4-羟基苯基)丙酸甲酯(MHPP)与化学合成硝化抑制剂双氰胺(DCD)对土壤N₂O排放及相关硝化、反硝化功能基因的影响。结果表明:不同BNIs(1,9-D、LN、MHPP)可以显著平均降低土壤N₂O日排放峰值40.1%;1,9-D和MHPP可分别抑制N₂O排放总量44.5%和43.9%,而DCD和LN对N₂O排放总量没有显著影响。1,9-D和MHPP对AOA(氨氧化古菌)、AOB(氨氧化细菌)硝化菌和nirS、nirK型反硝化菌的调控均有所不同,1,9-D可以同时抑制AOA、AOB和nirS微生物的生长;MHPP仅可以抑制AOA的生长;其中,AOA-amoA和nirS基因丰度与土壤N₂O的排放呈显著正相关关系。同时,1,9-D和MHPP均增加了nosZ基因丰度及其与AOA-...     

脲酶抑制剂与硝化抑制剂对稻田土壤硝化、反硝化功能菌的影响

[目的]在农业生产中,脲酶抑制剂(urease inhibitor,UI)与硝化抑制剂(nitrification inhibitor,NI)常作为氮肥增效剂来提高肥料利用率。本文研究了在我国南方红壤稻田施用脲酶抑制剂与硝化抑制剂后,土壤中氨氧化细菌(ammonia oxidizing bacteria,AOB)、氨氧化古菌(ammonia-oxidizing archaea,AOA)以及反硝化细菌的丰度以及群落结构的变化特征,旨在揭示抑制剂的作用机理及其对土壤环境的影响。[方法]试验在我国南方红壤稻田进行,共设5个处理:1)不施氮肥(CK);2)尿素(U);3)尿素+脲酶抑制剂(U+UI);4)尿素+硝化抑制剂(U+NI);5)尿素+脲酶抑制剂+硝化抑制剂(U+UI+NI),3次重复。脲酶抑制剂与硝化抑制剂分别为NBPT[N-(n-butyl)thiophosphrictriamide,N-丁基硫代磷酰三胺]和DMPP(3,4-dimethylpyrazole phosphate,3,4-二甲基吡唑磷酸盐)。通过荧光定量PCR(Real-time PCR)研究水稻分蘖期与孕穗期抑制剂对三类微生物标记基因拷贝数的影响,并分析土壤铵态氮、硝态氮与三种菌群丰度的相关性;利用变性梯度凝胶电泳(DenaturingGradient Gel Electrophoresis,DGGE)分析抑制剂对土壤AOB、AOA以及反硝化细菌群落结构的影响,并对优势菌群进行系统发育分析。[结果]1)荧光定量PCR结果表明,施用氮肥对两个时期土壤中AOB的amoA基因与反硝化细菌nirK基因的拷贝数均有显著提高,而对AOA的amoA基因始终没有明显影响;AOB与nirK反硝化细菌的丰度与两个时期的铵态氮含量、分蘖期的硝态氮含量呈极显著正相关,与孕穗期的硝态氮含量相关性不显著;DMPP仅在分蘖期显著减少了AOB的amoA基因拷贝数,表明DMPP主要通过限制AOB的生长来抑制稻田土壤硝化过程;NBPT对三类微生物的丰度无明显影响;2)DGGE图谱表明,在分蘖期与孕穗期,施用氮肥均明显增加了图谱中AOB的条带数,而对AOA却没有明显影响;氮肥明显增加了孕穗期反硝化细菌的条带数;与氮肥的影响相比,抑制剂NBPT与DMPP对AOA、AOB以及反硝化菌的群落结构影响甚微;系统发育分析结果表明,与土壤中AOB的优势菌群序列较为接近的有亚硝化单胞菌和亚硝化螺菌。[结论]在南方红壤稻田中,施入氮肥可显著提高AOB与反硝化细菌的丰度,明显影响两种菌群的群落结构,而AOA较为稳定;NBPT对三类微生物的群落结构丰度无明显影响;硝化抑制剂DMPP可抑制AOB的生长但仅表现在分蘖期,这可能是其缓解硝化反应的主要途径;这也说明二者对土壤生态环境均安全可靠。     

农肥和化肥对黑土农田生态系统氮素循环与平衡影响的研究

在不同施肥处理条件下,分别定量测定了玉米田土壤氮素自生固氮作用、氨化作用、硝化作用、反硝化损失、氨挥发、NO3--N淋溶损失等氮素循环转化途径。研究结果表明,不施肥的土壤生态系统每年土壤全氮将减少-110.5kg/hm2。施肥能够有效地提高土壤氮素转化能力,农肥的氮素转化作用明显高于化肥的氮素转化作用。各处理反硝化损失的氮量为7.26～21.66kg/hm2,淋溶损失量为0.09～0.21kg/hm2,氨挥发损失的氮量为0～15.23kg/hm2。玉米田施肥处理总的氮素平衡处于盈余状态,不施肥处理的氮素平衡处于亏缺状态。单施农肥的盈余量高于单施化肥及农肥化肥配比处理的盈余量,低量施肥模式土壤中氮素的输入和输出基本处于平衡状态,高量施肥模式土壤中氮素处于盈余状态,虽有利于培肥地力,但却造成了肥料的浪费。     

不同施氮量下双季稻连作体系土壤氨挥发损失研究

采用密闭室间歇通气法研究双季稻连作体系不同施氮量下土壤氨挥发损失。结果表明,早稻氨挥发损失主要发生在施肥后的15d内,第3～5d出现峰值,损失总量为N 22.60～162.0 kg /hm2,损失率为 29.29%～52.32%;晚稻氨挥发主要发生在施肥后的11d内,第3 d出现峰值,损失总量为N 22.35～141.4 kg /hm2,损失率为35.75%～46.82%。早、晚稻各生育期连作周期的氨挥发量均与施氮量呈显著线性关系。     

优化施氮对旺长期和成熟期烤烟地上部氮素挥发的影响

通过盆栽试验,采用地上部氮挥发研究装置研究施氮量和基追比[对照处理:不施氮;传统施氮处理:施氮量为0.30 g(N).kg 1(土),基追肥比为7︰3;优化施氮处理:施氮量为0.15 g(N).kg 1(土),基追肥比为3︰7]对烤烟"粤烟97"在旺长期和成熟期地上部氮素挥发的影响。结果表明,与不施氮处理和传统施氮处理相比,优化施氮处理显著提高了成熟期烤烟地上部NO的挥发速率;但是3种施氮处理下成熟期烤烟对NO2表现为净吸收,且平均吸收速率差异不显著。3种施氮处理中,传统施氮处理无论是旺长期还是成熟期烤烟地上部平均N2O挥发损失量最高,其次是优化施氮处理,对照处理最小;传统施氮处理和优化施氮处理成熟期烤烟地上部平均N2O挥发损失量分别是旺长期的3.06倍和6.12倍。旺长期3种施氮处理之间烤烟地上部NH3挥发没有显著差异;但成熟期时,与传统施氮处理相比,优化施氮处理显著提高了烤烟地上部NH3挥发速率。减少施氮量和优化基追比例可减少旺长期和成熟期烤烟地上部N2O挥发,但增加成熟期NH3挥发。上述结果表明,优化施氮(氮肥后移)尽管促进烤烟中后期氮素吸收,但也促进了烤烟内源N2O形成、排放。因此,优化施氮(氮肥后移)对抑制烤烟氮素挥发的调控作用不明显。     

不同水氮条件下双氰胺(DCD)对温室黄瓜土壤氮素损失的影响

【目的】设施蔬菜习惯"大水大肥"的传统管理模式,不仅影响蔬菜的品质和产量,造成严重的资源浪费,而且引起的环境污染问题日益受到人们的关注。本研究针对设施蔬菜生产中过量施用氮肥以及不合理的灌溉所导致的氮肥利用率低、氮素损失等资源浪费和环境的负效应问题,重点研究双氰胺(DCD)在设施蔬菜生产体系中的硝化抑制效果及其影响机制,并筛选出了适用于设施黄瓜生产的最优水氮管理方案。【方法】采用田间原位跟踪法,对温室黄瓜追肥期间土壤N2O排放量、氨挥发损失量、无机氮含量等指标进行了测定。N2O气体样品用密闭式静态箱法采集,用Agilent GC6820气相色谱仪进行测定。氨挥发样品用密闭室法采集,硼酸溶液吸收,标准硫酸滴定法测定。新鲜土样用1.0 mol/L KCl浸提,滤液用TRACCS 2000型流动分析仪测定土壤的NH+4-N和NO-3-N含量。【结果】在不同水氮条件下[传统水氮(T)的施氮量为N 988.6 kg/hm2、灌溉量为758.8 t/hm2;推荐水氮Ⅰ(R1)的施氮量为N 709.4 kg/hm2,推荐水氮Ⅱ(R2)的施氮量为N 746.9 kg/hm2,灌溉量均为531.2 t/hm2]。加施DCD后,推荐水氮Ⅰ、推荐水氮Ⅱ处理N2O的排放通量分别显著减少了42.1%和64.1%,但氨挥发损失分别显著增加了34.3%和40.4%;0—10 cm土层土壤硝态氮与N2O排放通量呈极显著的正相关,铵态氮与氨挥发损失呈极显著正相关。传统水氮处理在0—60 cm土壤剖面均检测到大量的硝态氮,前两次追肥后尤为明显。在减氮基础上加施DCD有助于减少硝态氮的累积,对0—30 cm根区硝酸盐淋洗的抑制作用较为明显。在0—30 cm土壤-蔬菜体系中,传统水氮处理的氮素表观损失显著高于其他施氮处理。加施DCD后,推荐水氮Ⅰ、推荐水氮Ⅱ处理的氮素盈余和氮素损失率均有所降低。与传统水氮处理相比,推荐水氮Ⅱ+DCD的处理增产23.3%,经济效益增加25560yuan/hm2。【结论】在本试验条件下,适度减氮控水措施是切实可行的,不仅满足了作物生长所需要的氮素,而且减少了氮素的盈余,提高了氮素的利用率,且不影响作物产量。在控水灌溉条件下,推荐施氮Ⅱ+DCD(氮素用量的15%)不仅能减少土壤氮素的盈余量,而且可有效地增加经济效益和环境效益。     

不同氮磷浓度及氮磷比对龙须菜生长和琼胶含量的影响

本文研究了不同氮磷浓度及氮磷比对龙须菜生长和琼胶含量的影响。结果表明：污染环境中的两种不同化合态氮对龙须菜的生长和琼胶含量的影响没有差异,在试验范围内(氨氮0～50 μmol/L;硝氮0～100 μmol/L),随着氮浓度升高,龙须菜的生长速率增加而琼胶含量下降;环境中的磷对龙须菜生长的影响与氮相似,但对琼胶含量的影响却与氮相反;此外,不同的氮磷比对龙须菜的生长和琼胶含量也有很大影响,本试验中10∶1的氮磷比,龙须菜生长最好;而1∶1的氮磷比,藻体的琼胶含量最高。因此,在实际应用中,收获龙须菜前,要根据所作用环境的不同,对收获的海藻作适当的处理,如让海藻在有利于琼胶合成的环境中(低氮磷比、氮限制、富磷的环境)暂养2周,使得所收获龙须菜的琼胶产量高、质量好。     

Fluctuations in the abundance of ammonia oxidizers and the contents of inorganic nitrogen in solarized soil

Solarization makes a great impact on the abundance of ammonia oxidizers and nitrifying activity in soil. To elucidate fluctuations in the abundance of ammonia oxidizers and nitrification in solarized soil, copy numbers of amoA gene of ammonia-oxidizing bacteria (AOB) and archaea (AOA), viable number of ammonia oxidizers and inorganic nitrogen contents were investigated in greenhouse experiments. The copy number of amoA gene and the viable number of ammonia oxidizers were determined by the quantitative polymerase chain reaction and most probable number methods, respectively. Abundance of AOB based on the estimation of amoA gene copy numbers and viable counts of ammonia oxidizers was decreased by the solarization treatment and increased during the tomato (Solanum lycopersicum L.) cultivation period following the solarization. Effect of solarization on the copy number of amoA gene of AOA was less evident than that on AOB. The proportion of nitrate in inorganic nitrogen contents was declined by the solarization and increased during the tomato cultivation period following the solarization. Positive correlations were found between the proportion of nitrate in inorganic nitrogen content and the copy number of bacterial or archaeal amoA gene or the viable number of ammonia oxidizers; the copy number of bacterial amoA gene showed a strong correlation with the viable number of ammonia oxidizers. The present study revealed influences of solarization on the fluctuation in the abundance of ammonia oxidizers and dynamics of inorganic nitrogen contents in soil and the results indicate that the determination of amoA gene of AOB is possibly a quick and useful diagnostic technique for evaluating suppression and restoration of nitrification following solarization.     

有机肥部分替代化肥氮对叶菜产量和环境效应的影响

针对叶菜类蔬菜有机肥氮替代化肥氮的最佳替代比例及对经济效益和环境效应综合评价较缺乏等问题,本研究采用田间试验,对包心菜和小青菜进行等氮水平下不同比例有机肥替代化肥处理,包括:纯化肥氮(0M),25%、50%、75%和100%有机肥替代化肥(25%M、50%M、75%M和100%M),研究不同处理下蔬菜产量、经济效益、土壤氨挥发和氧化亚氮排放。结果表明, 25%M处理下包心菜和小青菜产量均达最高,且与0M处理相比包心菜和小青菜的产量分别增加15.0%(P0.05)和16.3%(P0.05)。25%M比0M处理经济效益分别增加11.7%和5.4%,但在50%M、75%M和100%M处理下经济效益为负增长。25%M处理下,氨挥发累积排放量在包心菜和小青菜季分别为42.1kg·hm~(-2)和12.9kg·hm~(-2),比0M处理分别降低23.4%(P0.05)和41.6%(P0.05); 0M和25%M处理间氧化亚氮累积排放量无显著差异, 25%M处理在包心菜和小青菜季的氧化亚氮累积排放量分别为0.74 kg·hm~(-2)和3.06 kg·hm~(-2);与25%M处理相比, 50%M、75%M和100%M处理下氧化亚氮排放分别增加33.7%～60.8%(P0.05)、50.0%～134.3%(P0.05)和56.8%～185.6%(P0.05)。基于此,提出叶菜类蔬菜有机肥氮替代化肥氮的适宜替代比例在25%左右时可实现最佳的增效减排效果。     

水体氮浓度对狐尾藻和金鱼藻片段萌发及生长的影响

为了厘清水体氮浓度对沉水植物片段萌发及生长的影响,通过模拟控制试验,设计了水体总氮浓度分别为0 (CK)、 0.5 mg/L (N1)、 2 mg/L (N2)、 8 mg/L (N3)和12 mg/L (N4）共5个处理,研究了水体不同氮浓度条件下狐尾藻 (Myriophyllum spicatum) 和金鱼藻 (Ceratophyllum demersum)片段(3节)萌芽数、 萌发位置、 芽长和生物量的差异。结果表明, 水体氮浓度对不同沉水植物片段萌发的影响存在差异,较高的水体氮浓度不利于狐尾藻片断萌发,而对金鱼藻片段却有一定程度的促进;氮浓度处理促进了狐尾藻顶端优势,却抑制了金鱼藻的顶端优势。狐尾藻以0.5 mg/L处理的芽长较长,生物量以2 mg/L处理最大;而金鱼藻以8 mg/L处理芽长最长,生物量以2 mg/L处理最大。由此可见,不同沉水植物对水体氮适应性存在差异,水体氮浓度较低时,沉水植物断枝可以进行萌发和生长, 而当氮浓度超过2 mg/L时,对沉水植物断枝萌发及生长反而有抑制作用;金鱼藻片段比狐尾藻对水体氮浓度的耐受性强。     

Effects of artificial drainage on soil mineral nitrogen dynamics in winter wheat on the southern piedmont

Abstract

Excess soil moisture is believed to cause reduced levels of soil mineral N and crop production in winter wheat on the Southern Piedmont. Artificial subsurface drainage was used to relieve excess soil moisture and soil mineral N levels, mineralization, nitrification, denitrification and a group of soil properties were analyzed in both drained and undrained treatments. Drainage increased rates of mineralization and nitrification and decreased rates of denitrification, leading to higher levels of soil mineral N in drained plots than in undrained plots. Wheat yields were not affected by drainage, probably because the rate of N applied in spring (80 kg‐N/ha) was high enough to counteract the effects of decreased soil mineral N levels in undrained treatments.     

水氮用量对设施栽培蔬菜地土壤氨挥发损失的影响

【目的】针对我国设施蔬菜生产中存在的水肥过量施用问题,研究不同水氮条件下黄瓜-番茄种植体系内的土壤氨挥发特征,探讨影响设施菜地土壤氨挥发的重要因子,为降低氮肥的氨挥发损失、 建立合理的灌溉和施肥制度提供参考。【方法】以华北平原设施黄瓜-番茄轮作菜地为研究对象,设常规灌溉(W1)和减量灌溉(W2)2个灌溉水平,每种灌溉水平下设不施氮(N0)、 减量施氮(N1)和常规施氮(N2)3个氮水平,共6个处理组合(W1N0、 W1N1、 W1N2、 W2N0、 W2N1、 W2N2)。采用通气法监测不同水氮条件下黄瓜-番茄轮作体系内的土壤氨挥发动态,分析与土壤氨挥发相关的主要影响因子。【结果】设施黄瓜-番茄种植体系内表层(0—10 cm)土壤铵态氮受施肥的影响波动较大,与常规施氮(N2)相比,相同灌水条件下减量施氮(N1)处理的0—10 cm土层铵态氮浓度最高值降低了25.1%~30.3%(P 0.05)。减量施氮可显著降低土壤氨挥发速率。与常规施氮(N2)相比,减量施氮处理(N1)在黄瓜季和番茄季内的氨挥发速率均值分别降低了21.1%~22.8%(P0.05)和16.5%~17.9%(P0.05)。整个黄瓜-番茄轮作周期内,土壤氨挥发损失量和氮肥的氨挥发损失率分别为17.8~48.1 kg/hm2和1.23%~1.44%。与常规施氮(N2)相比,减量施氮处理(N1)的土壤氨挥发损失量及氮肥的氨挥发损失率分别降低了19.3%~20.0%(P0.05)和0.85~0.92个百分点。各处理土壤氨挥发速率与0—10 cm土壤铵态氮浓度呈显著或极显著正相关,说明0—10 cm土壤铵态氮浓度是土壤氨挥发的重要驱动因子。与常规灌溉(W1)相比,减量灌溉(W2)条件下设施菜地土壤氨挥发速率及氨挥发损失量略有增加(P0.05)。适宜减少氮肥及灌溉量不仅能够维持较高的蔬菜产量,而且显著提高了灌溉水和氮肥的利用效率。其中减量施氮处理(N1)的氮肥农学效率比常规施氮(N2)提高了95.4%~146.4%; 减量灌溉(W2)的灌溉水农学效率比常规灌溉(W1)提高了27.7%~54.0%。【结论】通过合理的节水减氮措施可达到抑制氮肥氨挥发损失、 增加产量以及提高水氮利用效率的目的。在供试条件下,节水30%左右、 减施氮量25%的水氮组合(W2N1)具有较佳的经济效益与环境效应。     

Impacts of different N management regimes on nitrifier and denitrifier communities and N cycling in soil microenvironments

Real-time quantitative PCR assays, targeting part of the ammonia monooxygenase (amoA), nitrous oxide reductase (nosZ), and 16S rRNA genes were coupled with ¹⁵N pool dilution techniques to investigate the effects of long-term agricultural management practices on potential gross N mineralization and nitrification rates, as well as ammonia-oxidizing bacteria (AOB), denitrifier, and total bacterial community sizes within different soil microenvironments. Three soil microenvironments [coarse particulate organic matter (cPOM; >250 μm), microaggregate (53-250 μm), and silt-and-clay fraction (<53 μm)] were physically isolated from soil samples collected across the cropping season from conventional, low-input, and organic maize-tomato systems (Zea mays L.-Lycopersicum esculentum L.). We hypothesized that (i) the higher N inputs and soil N content of the organic system foster larger AOB and denitrifier communities than in the conventional and low-input systems, (ii) differences in potential gross N mineralization and nitrification rates across the systems correspond with AOB and denitrifier abundances, and (iii) amoA, nosZ, and 16S rRNA gene abundances are higher in the microaggregates than in the cPOM and silt-and-clay microenvironments. Despite 13 years of different soil management and greater soil C and N content in the organic compared to the conventional and low-input systems, total bacterial communities within the whole soil were similar in size across the three systems (∼5.15 × 10⁸ copies g⁻¹ soil). However, amoA gene densities were ∼2 times higher in the organic (1.75 × 10⁸ copies g⁻¹ soil) than the other systems at the start of the season and nosZ gene abundances were ∼2 times greater in the conventional (7.65 × 10⁷ copies g⁻¹ soil) than in the other systems by the end of the season. Because organic management did not consistently lead to larger AOB and denitrifier communities than the other two systems, our first hypothesis was not corroborated. Our second hypothesis was also not corroborated because canonical correspondence analyses revealed that AOB and denitrifier abundances were decoupled from potential gross N mineralization and nitrification rates and from inorganic N concentrations. Our third hypothesis was supported by the overall larger nitrifier, denitrifier, and total bacterial communities measured in the soil microaggregates compared to the cPOM and silt-and-clay. These results suggest that the microaggregates are microenvironments that preferentially stabilize C, and concomitantly promote the growth of nitrifier and denitrifier communities, thereby serving as potential hotspots for N₂O losses.     

我国茶园氮肥利用和损失现状分析

[目的]茶树是多年生叶用作物,对氮肥的需求量较大,施用氮肥是提高茶叶产量的主要措施之一.但过量施用氮肥不仅降低茶叶的氮肥利用率,还会带来环境风险.明确我国茶园氮肥施用状况和氮肥主要损失途径,为茶园合理施用氮肥,降低氮肥损失提供科学依据.[方法]以茶园、氮肥利用和损失为关键词,在中国知网和Web of Science筛选...     

稻虾共作对稻田土壤nirK反硝化微生物群落结构和多样性的影响

稻虾共作是水稻种植与克氏螯虾共作形成的互利共生的稻田种养复合生态模式。目前对稻虾共作模式稻田反硝化微生物多样性和群落结构的影响尚不清楚。本研究以江汉平原常规中稻模式(MR)为对照,设置连续3年(2014—2016年)稻虾共作模式(CR)为处理,通过特异引物提取中稻抽穗期稻田土壤nirK基因,采用Illumina Miseq高通量测序技术,探讨稻虾共作模式对稻田土壤nirK反硝化微生物多样性和群落结构的影响。结果表明:稻虾共作模式显著提升水稻抽穗期稻田土壤中硝态氮、全氮及全碳的含量,对土壤碳氮比、碱解氮和铵态氮含量没有显著影响。稻虾共作模式显著增加稻田土壤nirK基因微生物的丰富度指数,但对nirK基因微生物的多样性指数影响不显著。稻虾共作模式改变了nirK基因微生物在目、科、属、种水平的群落组成,较常规中稻模式,稻虾共作模式在各分类水平组成类群均减少;稻虾共作模式较常规中稻模式改变了目的种类,对共有目相对丰度没有显著性改变。RDA分析表明稻虾共作模式对土壤nirK基因菌群的群落结构有一定的改变,但稻虾共作模式与常规中稻模式在群落结构上仍保留着一定的相似性。硝态氮含量是影响nirK反硝化细菌群落结构的主效因子。可见,稻虾共作模式对微生物多样性指数没有显著影响,但显著增加了微生物丰富度指数,改变了稻田土壤nirK反硝化微生物在目、科、属、种的群落结构。     

常规灌溉条件下施氮对温室土壤氨挥发的影响

为明确温室土壤的氨挥发特征,探讨适宜的减量施氮措施对氨挥发损失量及黄瓜产量的影响,在常规灌溉条件下设置了3个施氮（尿素）处理,采用通气法测定了冬春季黄瓜地中的氨挥发速率。结果表明：温室土壤在氮肥基施后7 d出现氨挥发速率峰值,但在氮肥追施后,施肥带与非施肥带的氨挥发速率峰值分别在第1 d与第5 d出现,氨挥发速率的峰值比氮肥基施时下降了8.6%～46.3%,施肥带的累积氨挥发量是非施肥带的0.91～1.54倍。冬春季黄瓜地的氨挥发损失量为16.7～26.6 kg/hm2,其中减施氮25%处理N900（900 kg/hm2）与减施氮50%处理N600（600 kg/hm2）与习惯施氮处理N1200（1 200 kg/hm2）相比,氨挥发损失量分别降低了22.1%和37.2%。而2 a黄瓜产量的平均值以处理N600（600 kg/hm2）最高,比处理N1200（1 200 kg/hm2）增加了6.52%。综合考虑氨挥发损失量、黄瓜产量及施氮量,在河北省的温室冬春季黄瓜生产中,比农民习惯氮用量（1 200 kg/hm2）减少25%～50%的措施是可行的。