Belowground interactions between intercropped wheat and Brassicas in acidic and alkaline soils

Our previous studies showed that, under P-limiting conditions, growth and P uptake were lower in the wheat genotype Janz than in three Brassica genotypes when grown in monoculture. The present study was conducted to answer the question if P mobilised by the Brassicas is available to wheat; leading to improved growth of wheat when intercropped with Brassicas compared to monocropped wheat. To assess if the interactions between the crops depend on soil type, the wheat genotype Janz and three Brassica genotypes (two canolas and one mustard) were grown for 6 weeks in monoculture or wheat intercropped with each Brassica genotype in an acidic and an alkaline soil with low P availability (with two plants per pot). Wheat grew equally well in the two soils, but the Brassicas grew better in the acidic than in the alkaline soil. In the acidic soil, monocropped Brassicas had a 3 to 4 fold greater plant dry weight (dw) and P uptake than wheat; plant dw and P uptake in wheat were decreased or not affected by intercropping and increased in the Brassicas. In the alkaline soil, dw and P uptake of the Brassicas was twice as high as in wheat, with intercropping having no effect on these parameters. The contribution of wheat to the total shoot dw and P uptake per pot was 4-21% and 32-40% in acidic and alkaline soil, respectively. Mycorrhizal colonisation was low in all genotypes in the acidic soil (1-6%). In the alkaline soil, mycorrhizal colonisation of monocropped wheat was 62%, but only 43-47% in intercropped wheat. Intercropping decreased P availability in the rhizosphere of wheat in the acidic soil but had no effect on rhizosphere P availability in the alkaline soil. Intercropping had a variable effect on rhizosphere microbial community composition (assessed by fatty acid methylester analysis (FAME) and ribosomal intergenic spacer amplification (RISA)), ranging from intercropping having no effect on the rhizosphere communities to intercropping resulting in a new and similar rhizosphere community composition in both genotypes. The results of this study show that intercropping with Brassicas does not improve growth and P uptake of wheat; thus there is no indication that P mobilised by the Brassicas is available to wheat.     

再植枸杞根际真菌群落对长期连作的响应研究

受枸杞自身种植特点和道地产区土地资源限制,连作障碍已成为制约宁夏枸杞产业可持续发展的主要因素之一,导致严重的经济损失和生态问题。前期研究表明,连作能够显著影响再植枸杞根际土壤细菌的群落结构和多样性,但就连作对真菌群落结构和功能的影响目前仍不清楚。本文利用实时荧光定量PCR和高通量测序技术,研究连作对再植枸杞根际真菌群落丰度及多样性的影响。实时荧光定量PCR分析表明,与对照样地相比,连作显著促进再植枸杞根际及非根际土壤中细菌和真菌的丰度。但连作对真菌的促进作用明显高于细菌,导致细菌/真菌比例失衡,使再植枸杞根际及非根际土壤微生物环境偏向于真菌型。对测序结果的分析发现,所测定样地中枸杞根际及非根际土壤中的优势真菌门分别为子囊菌门、担子菌门、接合菌门、壶菌门及球囊菌门,其中连作地再植枸杞根际子囊菌门的相对丰度较对照样地显著降低,而接合菌门的相对丰度则显著增加(P0.05)。FUNGuild真菌功能预测也证实连作显著抑制再植枸杞根际土壤丛枝菌根真菌的相对丰度(P0.05)。基于距离的冗余分析(db-RDA)结果表明,土壤pH、电导率、硝态氮和有效磷含量是影响枸杞根际土壤真菌群落变化的主要因子(P0.05),而土壤硝态氮和有效磷含量则是解释非根际土壤真菌群落变化的主要因子(P0.05)。这些结果说明长期施用化肥可能是改变连作地再植枸杞根际土壤真菌群落结构及枸杞-真菌互作关系的主要因素之一。这一研究结果为理解枸杞连作障碍的形成机制提供理论基础。     

不同连作年限番茄根系淀积物的变化及其与根结线虫的关系

了解蔬菜连作与土传病虫害的关系有助于发展绿色农业。基于根系淀积物在植物-土壤之间功能反馈中的重要地位，选择野外定位试验中番茄第2、第6和第8茬的不同连作年限处理，研究根结线虫的变化及其与土壤性质特别是根系淀积物组成的关系。结果显示：与第2茬相比，连作茬数增加导致土壤pH显著降低（P< 0.05），而土壤有机碳和硝态氮含量显著升高；同时，根系淀积物的组分类别及其相对含量也有显著变化，其主要组分中有机酸类物质的数量和相对含量随连作茬数的增加而增加。土壤化学性质、根系淀积物和根结指数三者的网络结构分析表明，根结指数与网络中其他节点之间的联系伴随连作年限而增强。在第8茬中，根结指数与月桂酸含量呈负相关，与土壤NO₃^--N含量以及颠茄碱、麦角甾醇的含量呈正相关，说明连作番茄根结线虫病害加重与土壤化学性质尤其是根系淀积物的变化有密切联系。     

Synergic Effect of Flooding and Nitrogen Application on Alleviation of Soil Sickness Caused by Aerobic Rice Monocropping

Abstract

The “aerobic rice” system is the cultivation of high yielding rice cultivars under non-flooded conditions in non-puddled (aerobic) soil with supplemental irrigation. The major constraint in wide adoption of aerobic rice technology is soil sickness caused by continuous monocropping due to still unknown factors. The possible role of flooding and nitrogen application in alleviating the soil sickness caused by continuous monocropping of aerobic rice was examined by pot experiments. Plants were grown aerobically or anaerobically on the soil collected from a field grown with aerobic rice for 12 consecutive seasons. The results showed that flooding alleviated soil sickness, but not as much as soil oven-heating treatment (120ºC for 12 hr). Application of ammonium sulfate improved plant growth up to the level of oven-heating treatment, while ammonium sulfate application and flooding exceeded the soil oven-heating treatment significantly. The synergy of flooding with ammonium sulfate application was greater than that with urea. These results suggest that soil sickness caused by continuous aerobic monocropping can be alleviated by flooding and ammonium sulfate application.     

烤烟连作与轮作土壤养分差异研究

为探明影响烤烟连作障碍的土壤养分含量因素,对我国湖南、贵州、云南三大烟区烤烟连作与轮作土壤进行了样品采集与分析,并对植烟土壤养分含量及相关性进行了研究.结果表明,各烟区土壤养分共性特点是土壤有机质、土壤全氯、土壤碱解氮含量均比轮作土壤低(P＜0.05),而各烟区连作和轮作土壤全磷、Olsen磷、全钾、交换性钾的含量有所不同.相关性表明,土壤有机质、全氮和碱解氮极显著相关(P＜0.01),碱解氮与全磷、全钾负相关(P＜0.01),Olsen磷与土壤有机质、全氮、碱解氮极显著负相关(P＜0.01),交换性钾和其它养分不相关,仅与土壤pH相关.     

不同供水水平下间甲酚和间作对小麦、蚕豆耗水特性及产量的影响

通过盆栽试验,研究了3个供水水平(田间持水量的45%、60%和75%)和间甲酚对小麦间作蚕豆耗水量及产量的影响。结果表明:间作总耗水量较相应单作总耗水量的加权平均低12.87%～31.56%,间甲酚对不同作物全生育期总耗水量的作用不显著,但供水和种植模式与作物总耗水量间的相关性极显著。间甲酚对小麦、蚕豆的产量均具有负效应,提高供水量可弱化间甲酚对小麦产量的负效应,但不同供水水平下间甲酚对蚕豆经济产量的化感作用差异不显著。间作生物产量和经济产量较相应单作的加权平均分别高15.3%～37.41%和5.98%～31.27%,间作同时具有弱化间甲酚对蚕豆化感负效应的作用。     

马铃薯/玉米套作对玉米光合特性和产量的影响

以单作玉米为对照, 设置2︰2和3︰2两种马铃薯/玉米套作行数比, 研究大田套作条件下玉米光合特性的动态变化及对产量的影响。结果表明: 套作显著降低了玉米整个生育期叶面积指数(LAI); 比叶重(SLW)生育前期显著降低, 乳熟期与单作差异不显著; Chla、Chlb、Chla+Chlb套作3︰2行数比整个生育期显著低于单作, 套作2︰2行数比生育前期显著低于单作, 乳熟期差异不显著。2种行数比叶绿素a/b值拔节期套作低于单作, 吐丝期高于单作。与套作2︰2行数比相比, 套作3︰2行数比LAI苗期差异不显著, 生育后期显著低于套作2︰2行数比; Chla、Chlb、Chla+Chlb生育前期显著高于2︰2行数比, 乳熟期差异不显著; 叶绿素a/b值吐丝期和乳熟期显著低于套作2︰2行数比, 生育前期差异不显著; SLW整个生育期差异不显著。2种行数比玉米套作和单作PAR、Pn、Gs、Tr、WUE均随叶位的降低而降低。套作降低了玉米下位叶的Pn、Gs、Tr, 提高了下位叶的Ci, 上位叶Pn、Gs、Tr、Ci套作和单作差异不显著。上、下叶位的PAR套作均显著高于单作, 上、下叶位的WUE套作与单作差异均不显著。套作3︰2行数比上、下叶位PAR、Gs、Tr均显著低于2︰2行数比; 2种行数比上位叶Pn相近, 下位叶Pn套作3︰2行数比显著低于2︰2行数比。下位叶Pn的降低套作 3︰2行数比受气孔因素限制, 套作2︰2行数比受非气孔因素限制。总之, 马铃薯/玉米套作改变了玉米的光合特性, 并显著降低了玉米的籽粒产量。套作2︰2行数比和套作3︰2行数比土地当量比分别为0.88、1.24, 前者无套作优势, 在生产中不宜采用, 后者具有较强的套作优势, 宜在生产中推广。     

3种豆科作物与玉米间作对土壤硝态氮累积和分布的影响

为提高氮肥利用效率,减少过量施用氮肥对环境造成的污染,本文以甘肃省河西灌区为试验地点,在0和225kg（N）&#183;hm^-2氮水平下,探讨了蚕豆、豌豆、大豆3种豆科作物与玉米间作对土壤硝态氮累积和分布的影响。研究表明：蚕宜收获后,间作的蚕豆、大豆、豌豆和玉米土壤硝态氮累积量在两个氮水平下均低于相应的单作,蚕豆、大豆、豌豆的间作土壤剖面硝态氮含量也低于相应的单作,但表现的土层深度各异。玉米收获后,蚕豆和豌豆的间作土壤硝态氮累积量低于单作;不施氮条件下,大豆间作土壤硝态氮累积量低于单作,与蚕豆、豌豆和大豆间作的玉米土壤硝态氮累积量均高于单作玉米;在225kg（N）&#183;hm^-2氮水平下,与蚕豆和豌豆阔作的玉米土壤硝态氮累积量低于单作玉米,间作大豆和与大豆间作的玉米土壤硝态氮累积量高于相应的单作。玉米收获期,不施氮条件下3种豆科作物间作0～60cm土壤硝态氮含量均低于单作;225kg（N）&#183;hm^-2氮水平下,蚕豆、豌豆间作0～60cm土壤硝态氮含量低于单作,而间作大豆0～100cm土壤硝态氮含量高于单作。对不同深度土壤硝态氮相对累积量分析表明,蚕豆收获期间作0～60cm土层相对累积量高于单作,而100～180cm土层则低于单作。     

植烟土壤酶活性对连作的响应及其与土壤理化特性的相关性研究

[目的]研究植烟土壤酶活性对连作的响应及其与土壤理化特性的相关性,以期为烟叶基地土壤改良提供技术支撑。[方法]对我国主要烟叶产区(云南玉溪、贵州福泉、湖南浏阳)连作植烟土壤过氧化氢酶和脲酶2种酶活性特征进行了研究,并探讨2种酶活性与土壤理化指标的相关性。[结果]过氧化氢酶活性与有机质含量呈正相关,脲酶活性与全磷含量呈正相关,2种酶与交换性钾含量均呈负相关。[结论]长期连作使土壤酶活性降低。酶活性与土壤理化指标具有一定相关性。     

土壤强还原处理对三七连作障碍因子及再植三七生长的影响

为研究土壤强还原处理(Reductive soil disinfestation,RSD)对连作三七土壤中障碍因子及再植三七生长的影响,以云南省文山州连作三七土壤为研究对象,设置4个处理:对照(CK);分别添加高碳氮比有机物料(C/N 94,15 t·hm~(-2),SB),低碳氮比有机物料(C/N 19,15t·hm~(-2),BD),高、低碳氮比有机物料等质量混合(15 t·hm~(-2),SB+BD)的RSD处理。利用高效液相色谱测定土壤中皂苷类物质的含量,通过定量PCR和变性梯度凝胶电泳测定土壤微生物数量和群落结构,并统计再植三七的存苗率和发病率。结果表明,与CK相比,RSD能够显著消减土壤中皂苷类物质的含量,其中BD和SB+BD对Rb_1和Rh_1的降解率分别高达82.1%和85.8%～88.1%。RSD还能有效杀灭尖孢镰刀菌,显著降低其在真菌类群中的比例,其中杀菌率高达99.7%。同时,移栽5个月后,RSD处理再植三七的存苗率提高7.3倍～8.5倍,发病率由89.0%降低至12.9%～16.1%。因此,土壤强还原处理能够显著消减连作三七土壤中积累的障碍因子,改善土壤微生物群落结构,提高存苗率,降低发病率,是一种具有快速缓解三七连作障碍潜力的农业措施。