Lateral root elongation in maize is related to auxin synthesis and transportation mediated by N metabolism under a mixed NO_(3)^(–) and NH_(4)^(+) supply

A mixed nitrate (NO_(3)^(–)) and ammonium (NH_(4)^(+)) supply can promote root growth in maize (Zea mays),however,the changes in root morphology and the related physiological mechanism under different N forms are still unclear.Here,maize seedlings were grown hydroponically with three N supplied in three different forms (NO_(3)^(–)only,75/25 NO_(3)^(–)/NH_(4)^(+)and NH_(4)^(+)only).Compared with sole NO_(3)^(–)or NH_(4)^(+),the mixed N supply increased the total root length of maize but did not affect the number of axial roots.The main reason was the increased total lateral root length,while the average lateral root (LR) length in each axle was only slightly increased.In addition,the average LR density of 2nd whorl crown root under mixed N was also increased.Compared with sole nitrate,mixed N could improve the N metabolism of roots (such as the N influx rate,nitrate reductase (NR) and glutamine synthase (GS)enzyme activities and total amino content of the roots).Experiments with exogenously added NR and GS inhibitors suggested that the increase in the average LR length under mixed N was related to the process of N assimilation,and whether the NR mediated NO synthesis participates in this process needs further exploration.Meanwhile,an investigation of the changes in root-shoot ratio and carbon (C) concentration showed that C transportation from shoots to roots may not be the key factor in mediating lateral root elongation,and the changes in the sugar concentration in roots further proved this conclusion.Furthermore,the synthesis and transportation of auxin in axial roots may play a key role in lateral root elongation,in which the expression of ZmPIN1B and ZmPIN9 may be involved in this pathway.This study preliminarily clarified the changes in root morphology and explored the possible physiological mechanism under a mixed N supply in maize,which may provide some theoretical basis for the cultivation of crop varieties with high N efficiency.

Increasing nitrogen absorption and assimilation ability under mixed NO_(3)^(–)and NH_(4)^(+) supply is a driver to promote growth of maize seedlings

Compared with sole nitrate (NO_(3)^(-)) or sole ammonium (NH_(4)^(+)) supply,mixed nitrogen (N) supply may promote growth of maize seedlings.Previous study suggested that mixed N supply not only increased photosynthesis rate,but also enhanced leaf growth by increasing auxin synthesis to build a large sink for C and N utilization.However,whether this process depends on N absorption is unknown.Here,maize seedlings were grown hydroponically with three N forms (NO_(3)^(-)only,75/25 NO_(3)^(-)/NH_(4)^(+) and NH_(4)^(+) only).The study results suggested that maize growth rate and N content of shoots under mixed N supply was little different to that under sole NO_(3)^(-)supply at 0–3 d,but was higher than under sole NO_(3)^(-)supply at 6–9 d.^(15)N influx rate under mixed N supply was greater than under sole NO_(3)^(-) or NH_(4)^(+) supply at 6–9 d,although NO_(3)^(-) and NH_(4)^(+) influx under mixed N supply were reduced compared to sole NO_(3)^(-) and NH_(4)^(+) supply,respectively.qRT-PCR determination suggested that the increased N absorption under mixed N supply may be related to the higher expression of NO_(3)^(-) transporters in roots,such as ZmNRT1.1A,ZmNRT1.1B,ZmNRT1.1C,ZmNRT1.2 and ZmNRT1.3,or NH_(4)^(+) absorption transporters,such as Zm AMT1.1A,especially the latter.Furthermore,plants had higher nitrate reductase (NR)glutamine synthase (GS) activity and amino acid content under mixed N supply than when under sole NO_(3)^(-) supply.The experiments with inhibitors of NR reductase and GS synthase further confirmed that N assimilation ability under mixed N supply was necessary to promote maize growth,especially for the reduction of NO_(3)^(-) by NR reductase.This research suggested that the increased processes of NO_(3)^(-)and NH_(4)^(+) assimilation by improving N-absorption ability of roots under mixed N supply may be the main driving force to increase maize growth.

用(^(15)NH_(4))_(2)SO_(4)标记堆肥的研究

小型堆腐试验的结果表明：堆腐材料的Ｃ／Ｎ比和含Ｎ量，不影响堆肥有机Ｎ累积的比例，也不影响堆肥有机Ｎ组分的变化趋势。堆腐后，富含蛋白质的材料，氨基酸Ｎ和酸解铵态Ｎ的比例增加；富合纤维素和木质素的材料，提高未知态Ｎ和非酸解Ｎ的比例。加入的１５Ｎ主要构成有机组分中的氨基酸Ｎ。在降温阶段加入（１５ＮＨ４）２ＳＯ４，能使氨基酸Ｎ比例增加。用１５Ｎ直接标记堆肥，比用１５Ｎ标记有机物料制造的堆肥，减少了１５Ｎ损失，且提高了１５Ｎ的转化率。

NH_(4)^(+)浓度对N80钢在饱和CO_(2)的3%NaCl溶液中腐蚀行为的影响

利用失重法和电化学方法研究了N80钢在不同NH_(4)^(+)浓度下饱和CO_(2)的3%NaCl溶液中的腐蚀行为,通过SEM、3D轮廓仪、XRD和XPS对腐蚀形貌和腐蚀产物进行表征,阐释了腐蚀机理。结果表明,NH_(4)^(+)浓度对N80钢的腐蚀速率产生促进和抑制双重效果。当NH_(4)^(+)浓度为0~500 mg/L时,N80钢的均匀腐蚀速率随NH_(4)^(+)浓度增加而增加;当NH_(4)^(+)浓度增加至1000~2000 mg/L时,N80钢的均匀腐蚀速率随NH_(4)^(+)浓度增加而降低,且点蚀速率随NH_(4)^(+)浓度的变化规律与均匀腐蚀基本相同;当NH_(4)^(+)浓度为500 mg/L时,均匀腐蚀速率和小孔腐蚀速率最大。当NH_(4)^(+)浓度≤500 mg/L时,NH_(4)^(+)和Cl^(-)在金属表面发生了竞争吸附;当NH_(4)^(+)浓度大于500 mg/L时,NH_(4)^(+)在金属表面发生吸附对腐蚀起抑制作用。

生物炭用量对模拟土柱氮素淋失和田间土壤水分参数的影响

利用土柱模拟试验和田间试验，把由果树废枝干制备的生物炭以0，20，40，60 t·hm^-2和80 t·hm^-2的用量施入土壤，以探明不同用量的生物炭对土壤硝铵态氮素淋失和土壤水分的影响。结果表明，施用生物炭可降低土壤NH4＋-N和NO3--N累积淋溶量，其中用量为80 t·hm^-2处理较对照分别降低了41%和18.6%（P＜0.05）；NO3--N淋溶主要集中在前三次，其淋溶量占总量的97.3%～98.8%，生物炭能增加NO3--N在土壤中的滞留时间，延缓淋失；在整个淋洗过程中，氮素主要以NO3--N的形式淋失，其累积淋溶量占NO3--N、NH4＋-N淋溶总量的97.3%～98.14%；施用生物炭种植春玉米后，土壤含水率和总孔隙度增加不显著。

酸化沸石对尿素氮淋失和玉米籽粒氮素利用的影响

在尿素减量施用条件下,探究添加酸化沸石(SF)对氮素淋失及籽粒氮肥利用率的影响。通过等温吸附试验,结合土柱淋溶和玉米盆栽试验,研究酸化沸石对NH_4^(+)—N和NO_3^(-)—N的吸附性能,以及不同施氮梯度下,酸化沸石对氮素淋失和氮肥利用率的影响,试验分别设置农民习惯施肥(CN)、氮肥减量15%(CN1)、氮肥减量30%(CN2)3个施氮梯度并分别添加土重0.2%的酸化沸石(CN+SF、CN1+SF、CN2+SF)。结果表明,酸化沸石对NH_4^(+)—N和NO_3^(-)—N的最大吸附量分别为25.44,31.59 mg/g,吸附过程可用Langmuir模型较好拟合。在减氮15%和30%时,添加酸化沸石,使NH_4^(+)—N累计淋失量较CN1、CN2分别降低7.10%,8.76%。在减氮30%时,酸化沸石可有效降低NO_3^(-)—N累计淋失量,较CN2处理减少15.90%。酸化沸石可有效提高土壤氮素含量和玉米籽粒氮肥利用率,添加酸化沸石(CN+SF、CN1+SF、CN2+SF)较单施尿素(CN、CN1、CN2)籽粒氮肥利用率分别提高10.37%,20.79%,47.14%。综上,酸化沸石在减施尿素条件下可有效降低土壤氮素淋失,提高玉米籽粒氮肥利用率,具有一定的农艺价值。

氮素流失机制的定量化研究

氮素是维持高产和农业经济的关键因素。研究氮素流失定量化 ,假定整块农田的氮素来源、下渗流失机制具有一致性。氮素流失的主要途径有 :NH3 挥发 ;N2 O、NO、NO2 、N2 的损失 ,NO3 -的淋失 ;因风蚀和水蚀引起的有机氮和无机N0 3 -N和NO4-N的迁移。氮素具有很强的移动性 ,其在农业系统中的迁移受管理措施的影响很大 ,且具不可预见性。影响氮素来源的土壤特性的多变性使得提高氮素利用率 (EN)的氮素管理很困难 ,尤其在淋失和反硝化严重的灌溉农田中更是如此。全球的氮素利用率平均为 5 0 % ,禾谷类作物只有 33%。完善增加EN 的氮素管理措施 ,必须以氮素流失机制及其管理为依据研究氮素循环的内容 ,以能够减少环境中氮素流失为主要目标 。

C,N对厌氧氨氧化与反硝化耦合的影响

为解决实际废水中有机物对厌氧氨氧化的抑制作用,以硝态氮为直接电子受体成功启动厌氧氨氧化与反硝化耦合装置,并在回流比优化工艺的基础上,通过调节碳氮、硝态氮与氨氮的比,优化耦合系统的脱氮除碳效率。结果表明,C/N、NO_(3)^(-)-N与NH_(4)^(+)-N的比为1.5时,耦合系统表现出较好的活性,硝态氮、氨氮和COD去除率分别99.2%、63.5%、95.8%和95.8%、85.8%、94.5%,达到较好耦合脱氮效果。为厌氧氨氧化的广泛应用及推广提供参考和技术支持。