天水小陇山锐齿栎群落土壤全N分布特征及与生物多样性关系研究

对天水小陇山锐齿栎群落不同演替阶段土壤全N含量进行了分析 ,探讨了土壤全N与群落生物多样性之间的关系 ,结果表明 :随发育阶段土壤全N含量呈稳定的变化趋势。发育中期 ,随多样性指数、均匀度指数、优势度指数的增加 ,全N含量呈“V”型变化趋势 ,随丰富度指数增加 ,全N含量呈逐渐减小趋势 ;发育后期 ,随着多样性指数、丰富度指数、优势度指数的增加 ,全N呈逐渐增加趋势 ,随着均匀度的增加 ,全N变化不明显 ;发育末期 ,多样性指数、均匀度指数、优势度指数趋于稳定 ,土壤全N含量不稳定 ,随丰富度指数的升高 ,全N有先升高后降低的趋势。     

The effect of sowing date, stale seedbed, row width and mechanical weed control on weeds and yields of organic winter wheat

Three field experiments were carried out in organically grown winter wheat in Denmark. The treatments were sowing time (normal or late sowing) and false seedbed, row width (12 and 24 cm) and weed control method [untreated; mechanical weed control (weed harrowing at 12 cm supplemented with inter‐row hoeing at 24 cm); and herbicide weed control]. Weed biomass in midsummer was greatest on plots sown at the normal sowing time (compared with delayed sowing) and was reduced by mechanical or chemical weed control (compared with untreated plots). Row width alone had no influence on weed biomass, but in the experiment with high weed pressure, the more intensive mechanical weed control used at a row width of 24 cm reduced weed biomass. Normal sowing time tended to give higher yields, but this was only statistically significant in one of the three experiments. Wide rows gave a yield decrease in the experiment with low weed pressure. The effect of weed control on yield was dependent on the weed pressure. At low weed pressure, mechanical weed control caused a yield decrease compared with untreated or herbicide treated. At intermediate weed levels there were no differences, whereas at high weed pressure, mechanical weed control and herbicide treatment caused a yield increase compared with untreated. False seedbeds were shown to contribute to a decrease in the soil seed reserve.     

Comparison of kinetic properties of a hydrophilic form of acetylcholinesterase purified from strains susceptible and resistant to carbamate and organophosphorus insecticides of green rice leafhopper (Nephotettix cincticeps Uhler)

A hydrophilic form of acetylcholinesterase (AChE) was purified from N-methyl carbamate susceptible (SA) and highly N-methyl carbamate-resistant (N3D) strains of the green rice leafhopper (GRLH), Nephotettix cincticeps Uhler. Both of purified AChE from SA and N3D strains displayed the highest activities toward acetylthiocholine (ATCh) at pH 8.5. In the SA strain, the optimum concentrations for ATCh, propionylthiocholine (PTCh), and butyrylthiocholine (BTCh) were about 1 × 10⁻³, 2.5 × 10⁻³, and 1 × 10⁻³ M, respectively. However, in the N3D strain, substrate inhibition was not identified for ATCh, PTCh, and BTCh to 1 × 10⁻² M. The K_m value in the SA strain was 51.1, 39.1, and 41.6 μM and that in the N3D strain was 91.8, 88.1, and 85.2 μM for ATCh, PTCh, and BTCh, respectively. The K_m value in the N3D strain indicated about 1.80-, 2.25-, and 2.05-fold lower affinity than that of the SA strain for ATCh, PTCh, and BTCh, respectively. The V_max value in the SA strain was 70.2, 30.5, and 4.6 U/mg protein and that in the N3D strain was 123.0, 27.0, and 14.5 U/mg protein for ATCh, PTCh, and BTCh, respectively. The V_max value in the N3D strain was 1.75- and 3.15-fold higher for ATCh and BTCh than that in the N3D strain. However, it was 1.13-fold lower for PTCh. The increased activity of AChE in the N3D strain is due to the qualitatively modified enzyme with a higher catalytic efficiency. The bimolecular rate constant (k_i) for propoxur was 27.1 × 10⁴ and 0.51 × 10⁴ M⁻¹ min⁻¹ in the SA and N3D strain and that for monocrotophos was 0.031 × 10⁴ and 2.0 × 10⁴ M⁻¹ min⁻¹ in the SA and N3D strain. AChE from the N3D strain was 53-fold less sensitive than SA strain to inhibition by propoxur. In contrast, AChE from the N3D strain was 65-fold more sensitive to inhibition by monocrotophos than AChE from the SA strain. This indicated negatively correlated cross-insensitivity of AChE to propoxur and monocrotophos.     

贺兰山西坡不同海拔梯度草地土壤氮特征

以阿拉善左旗境内贺兰山中段(西坡)及山前地带不同海拔下的草地为研究对象,分析不同海拔梯度下草地土壤全氮的分布特征及其与气候因子、植被特征和土壤特性的关系.结果表明,土壤全氮含量随海拔的降低而逐渐降低,在典型草原中沿土壤垂直剖面依次降低,在高寒草甸、荒漠化草原和草原化荒漠0～20与20～40 cm土层中差异不显著,但高于40～60 cm土层.在海拔1 360～1 380 m草原化荒漠的5个样地上,由于放牧利用程度和植被类型的不同,0～20 cm土层土壤氮的含量变幅在0.022 8%～0.034 7%.0～20,20～40和40～60 cm土层土壤全氮含量与年降水量、植被盖度、草地生产力、土壤含水量、有机碳含量和<0.05 mm颗粒含量呈极显著正相关,与年均温、土壤pH值呈极显著负相关(P<0.001).偏相关分析显示,影响0～20 cm土层全氮(TN)含量最主要的因素是植被盖度(C)和年降水量(AP),相关方程是TN%=0.002 040 C 0.000 585 AP-0.076 800;而影响20～40 cm土层全氮含量的最主要因素是草地生产力(B),与土壤全氮回归方程为TN%=0.001 6 B 0.024 7.而各环境因素中影响土壤全氮含量最主要的因素,0～20 cm土层为土壤有机碳和年降水量,20～40 cm土层主要受土壤有机碳的影响.     

美系杜洛克种猪体尺、体重测定与体型评定研究

统计分析了2001年引进的新美系杜洛克种猪及繁殖后代在6月龄、12月龄、24月龄和36月龄四个阶段的体尺、体重数据，结合品种特征、体型外貌总结研究出杜洛克种猪的百分制评分及等级标准。     

光氮互作对草地早熟禾碳氮代谢的影响

以草地早熟禾的3个品种为试验材料,研究了高低光照下不同的施氮水平对植株体内碳氮代谢的影响。对可溶性糖和硝酸还原酶的含量测定结果显示:高低光强下早熟禾的氮素同化能力均随着氮水平的升高呈现先升高后降低的趋势,碳代谢的中间产物可溶性糖随着氮水平的升高呈现先降低后升高的趋势,高低光下糖的含量随着氮水平的升高其品种间差异逐渐减小;在低氮条件下,植物的氮素同化能力较弱,光合碳代谢相对较强,糖含量较高,随着氮水平的增大,光合产物逐渐流向氮素代谢,硝酸还原酶含量升高。     

光照和褪黑激素对内蒙古绒山羊氮分配的影响

从氮分配的角度研究了光照和褪黑激素对内蒙古白绒山羊营养分配的影响。结果表明:光照时间和埋植褪黑激素显著影响绒山羊体内氮物质分配,短光照或埋植褪黑激素显著提高绒山羊血液中的褪黑激素水平,并使其他相关激素如催乳素(PRL)、胰岛素(INS)、类胰岛素生长因子-I(IGF-I)、瘦素(LEP)的含量发生显著变化,结果使毛绒氮的沉积增加,体氮的沉积减少。短光照条件下毛绒氮和体氮的沉积分别为33.7%±0.64%和66.3%±0.64%;而长光照条件下则减少毛绒氮的分配量,增加体氮分配量,毛绒氮和体氮的沉积分别为23.6%±0.46%和76.4%±0.46%。短光照和褪黑激素之间有强烈的互作效应,短光照埋植褪黑激素组毛绒氮和体氮的分配比例分别为36.1%±0.79%和63.9%±0.79%。试验期绒山羊的产绒量平均增加(338.83±72)g,比普通绒山羊提高73.86%,新生羊绒的品质符合纺织工业标准的要求。     

耕作方式与长期定位施肥对雨养农田冬小麦产量的调控效应

为了明确西北黄土高原半湿润偏旱区耕作方式与长期定位施肥对冬小麦产量的调控效应,以设在半湿润偏旱区连续12年的耕作与肥料长期定位试验为平台,采用裂区设计,以传统耕作和免耕耕作为主处理,不施肥(CK)、单施无机氮肥(N)、单施无机磷肥(P)、单施有机肥(M)、无机氮磷肥配施(NP)、有机无机肥配施(NMP)为副处理,栽培制度为1年春玉米-3年冬小麦轮作,研究耕作及施肥措施对冬小麦产量的影响及其在生产年型间的变化关系。结果表明,不同年型及耕作方式均以有机无机配施冬小麦产量最高,有机肥单施高于化肥单施,磷肥单施高于氮肥单施。耕作方式间表现为传统耕作高于免耕耕作,年型间表现为丰水年>平水年>干旱年,耕作和施肥方式的增产效果以干旱年最好,平水年和丰水年差异不显著。有机无机配施与传统耕作结合优化了冬小麦冠层温度、叶绿素相对含量等生理指标,提高了光合速率、气孔导度及蒸腾速率,因而改善了有效穗、穗粒数和千粒重等产量性状而使冬小麦增产。在550 mm左右降水量的陇东旱塬雨养农业区,无论何种耕作方式及生产年型,长期采用有机无机或无机氮磷肥配施均表现出持续提高冬小麦产量的良好作用。因此,有机无机配施结合传统耕作是提高陇东半湿润偏旱区冬小麦产量的最佳耕作栽培模式。     

不同施肥模式对玉米各器官碳氮累积和分配的影响

以长期定位试验为依托,选取:1)不施肥(CK);2)农民习惯施肥(FP);3)推荐施肥(OP);4)有机肥氮替代100%化肥氮(OM);5)有机肥氮替代50%化肥氮(MF)5个处理,研究不同施肥模式对玉米植株及各器官碳氮含量、碳氮分配比例及C/N的影响,为西南紫色土地区合理施肥、作物增产提供科学依据。结果表明,与FP处理相比,MF处理显著增加了玉米植株生物量,达26.2%。相比OM和OP处理,MF处理显著增加玉米苞叶和根茬中碳浓度,分别增加5.4、4.2 g·kg^-1和7.4、21.3 g·kg^-1,同时增加玉米苞叶、根茬、穗轴和籽粒中的碳储量,玉米茎秆和籽粒中的氮储量也有增加。此外,相比FP处理,MF处理能显著增加玉米整株的碳储量和氮储量,达29.1%和16.9%。等氮水平下,MF、OP处理均能增加玉米苞叶和籽粒中碳同化物的分配比例,MF处理玉米籽粒中氮素的分配比例较OP和OM处理分别增加1.7%和3.6%,同时MF处理能使玉米维持较高的C/N。综上,有机肥氮替代50%化肥氮能增加玉米植株的生物量,同时提高玉米对氮素的吸收和碳素的累积,增加玉米籽粒中碳同化物和氮素的分配比例,同时,有机肥氮替代50%化肥氮能使玉米植株维持较高的C/N,有利于产量的形成,该施肥方式不仅能够促进氮素的高效利用,减少化肥的投入,还能够减少化肥损失,降低氮素损失引发的环境风险。     

不同轮作序列对旱地胡麻土壤有机碳稳定性的影响

为了探索陇中黄土高原半干旱丘陵沟壑区胡麻轮作序列对土壤碳库的影响,2012-2016年通过4年定位试验,以连作为对照,研究了不同胡麻频率下的轮作序列(F:休闲;PWFW:25%Flax、马铃薯-小麦-胡麻-小麦;WFWP:25%Flax、小麦-胡麻-小麦-马铃薯;FWPF:50%Flax、胡麻-小麦-马铃薯-胡麻;WPFF:50%Flax、小麦-马铃薯-胡麻-胡麻;FFFF:100%Flax、胡麻-胡麻-胡麻-胡麻)对土壤团聚体、总有机碳(TOC)、土壤颗粒有机碳(POC)、土壤微生物碳(MBC)和氮(MBN)的影响。结果表明,休闲、不同轮作序列和低胡麻频率显著增加了030 cm土层<0.25 mm粒级的土壤团聚体含量、TOC和POC含量,而随胡麻频率的增加三者的含量呈下降趋势。其中,25%Flax处理下土壤团聚体含量较播前和休闲处理分别显著增加了2.02%4.04%和9.56%11.73%;土壤有机碳(SOC)较连作显著增加5.95%7.48%。50%Flax处理下胡麻位置对土壤SOC影响显著,且轮作(FWPF)显著高于连作(WPFF)。060 cm土层土壤SOC含量表现为休闲>播前≈25%Flax>50%Flax>100%Flax。与连作相比,轮作显著提高了010 cm土层土壤TOC和POC含量,呈现表层富集现象。土壤POC含量表现为25%Flax≈休闲>50%Flax>100%Flax。此外,轮作换茬显著增加了土壤MBC含量,且随着胡麻频率的增加,030 cm土层土壤MBC含量逐渐降低。与播前、休闲、轮作相比,连作显著降低土壤微生物碳氮比,50%Flax(WPFF)轮作序列和土层深度对土壤有机碳和微生物量的互作效应显著。综合来看,休闲可以显著改善土壤理化性状,25%胡麻频率的轮作序列利于保持土壤团聚体稳定性,增加土壤TOC、SOC和POC含量,而50%Flax轮作序列(WPFF)能够提高土壤微生物量和微生物碳氮比。表明25%胡麻频率的轮作序列均可维持土壤有机碳的稳定性,是旱地胡麻比较理想的轮作序列。