外源激素对桑树组培无菌苗继代增殖及生根的影响

[目的]探讨外源激素因子对桑树组培无菌苗继代增殖及生根的影响。[方法]以桂桑优12号为材料,从外源激素的不同种类、浓度及组合对桑树组培无菌苗继代增殖和生根诱导进行比较试验。[结果]以IBA 0.1 mg/L＋6-BA 1.5 mg/L＋TDZ 0.03 mg/L激素组合对芽增殖效果最好,芽增殖倍数达到5.28。 NAA对生根诱导的效果优于 IBA和 IAA;以 NAA 2.0 mg/L＋PP331.0 mg/L的激素组合对生根诱导效果最佳,生根率达100%,根数为7.01条,根长为1.38 cm。[结论]该研究为桑树种苗的离体培养工厂化生产提供技术参考。     

NAA·IBA生根剂对圆叶福禄桐扦插效果的影响

[目的]研究NAA·IBA生根剂对圆叶福禄桐扦插效果的影响。[方法]选取不同部位的圆叶福禄桐2～3年生的健壮枝条作为扦插穗条,通过用不同浓度的N-I(NAA∶IAA=8∶2)生根剂进行浸蘸处理,探讨最佳的生根部位及生根剂浓度。[结果]N-I处理对圆叶福禄桐的扦插在成活率和须根期方面与单种生根剂处理相比有极显著差异。[结论]通过对试验结果进行多重分析和综合评价,当NI生根剂在浓度为200 mg/L时,圆叶福禄桐的扦插枝条的综合生长情况达到最优;通过与使用单种生根剂进行对比,发现混合生根剂的扦插效果明显好于单种生根剂。     

Plant pathogen protection by arbuscular mycorrhizas: A role for fungal diversity?

Arbuscular mycorrhizal (AM) fungi can confer protection to host plants against some root pathogens, and several mechanisms for these phenomena have been proposed. If AM fungal taxa vary in the ways that they limit the negative effects of pathogens on host plants, additive and/or synergistic interactions among members of diverse AM fungal assemblages and communities may result in a greater pathogen protection than is currently predicted. However, in a review of the literature on interactions between AM and pathogenic fungi, we found few examples that compared the effectiveness of single- and multi-species AM fungal assemblages. Here, we briefly recount the generally recognized mechanisms of pathogen protection by AM fungi and present evidence, where appropriate, for functional diversity among AM fungal taxa with regard to these mechanisms. We propose that functional complementarity of AM fungal taxa in interactions with pathogens could mimic, or even be the cause of, previously observed relationships between AM fungal diversity and plant productivity.     

Belowground carbon allocation patterns in a dry Mediterranean ecosystem: A comparison of two models

Total belowground C allocation (TBCA) accounts for a large fraction of gross primary production, it may overtake aboveground net primary production, and contributes to the primary source of detrital C in the mineral soil. Here, we measure soil respiration, water erosion, litterfall and estimate annual changes in C stored in mineral soil, litter and roots, in three representative land uses in a Mediterranean ecosystem (late-successional forest, abandoned agricultural field, rain-fed olive grove), and use two C balance approaches (steady-state and non-steady-state) to estimate TBCA. Both TBCA approaches are compared to assess how different C fluxes (outputs and inputs) affect our estimates of TBCA within each land use. In addition, annual net primary productivity is determined and C allocation patterns are examined for each land use. We hypothesized that changes in C stored in mineral soil, litter and roots will be slight compared to soil respiration, but will still have a significant effect on the estimates of TBCA. Annual net primary productivity was 648 ± 31.5, 541 ± 42.3 and 324 ± 22.3 g C m⁻² yr⁻¹ for forest, abandoned agricultural field and olive grove, respectively. Across land uses, more than 60% of the C was allocated belowground. Soil respiration (F_S) was the largest component in the TBCA approaches across all land uses. Annual C losses through water erosion were negligible compared to F_S (less than 1%) and had little effect on the estimates of TBCA. Annual changes in C stored in the soil, litter layer and roots were low compared to F_S (16, 24 and 10% for forest, abandoned agricultural field and olive grove, respectively), but had a significant effect on the estimates of TBCA. In our sites, an assumption that Δ[C_S + C_R + C_L]/Δt = 0 will underestimate TBCA, particularly in the abandoned agricultural field, where soil C storage may be increasing more rapidly. Therefore, the steady-state model is unsuited to these Mediterranean ecosystems and the full model is recommended.     

Evaluation of the intrinsic competitiveness and saprophytic competence of Rhizobium tropici IIB strains

Inoculation of beans (Phaseolus vulgaris L.) with strains of R. tropici IIB and R. etli resulted in the disappearance of the R. tropici IIB stains from the nodule population and their replacement by other (non R. tropici IIB) bean symbionts (Vlassak et al. 1996). Coinoculation studies in monoxenic conditions and in soil core microcosms with plants harvested at two different growth stages indicated that the inoculated R. tropici IIB strains CIAT899 and F98.5 possess a good intrinsic competitiveness which declines, however, at a later plant growth stage and in soil conditions. The poor saprophytic competence of R. tropici IIB strain CIAT899 was further demonstrated by its poor survival in soil core microcosms after bean harvest. Strains were isolated from the field plots with a 3-year bean-planting history, characterized and evaluated for their competitiveness against R. tropici IIB strain CIAT899. Isolates from field plots, which had been repeatedly inoculated with R. tropici IIB strain CIAT899, showed a higher nodule occupancy compared to R. tropici IIB strain CIAT899, and this higher competitiveness exhibited by the field isolates might be an additional reason for the poor performance of R. tropici IIB strain CIAT899 in the field study. Plots with and without a history of bean production revealed after 3-year bean cultivation an almost totally different population that also significantly differed in competitiveness. Received: 12 February 1996     

切根与不同形态氮素对板栗苗木根系构型及生长的影响

为探明不同调控技术对板栗根系构型的影响和对板栗生长发育的作用效果,以期为培育高质量板栗苗木提供科学依据,采用大田板栗苗木为对象进行切根(切根深度分别为12、8、4 cm、CK)及不同形态氮素(尿素、硝酸钠、CK)追肥试验。结果表明:苗高生长量最大的处理为X2N2,地径生长量最大的处理为X4N1,不同处理苗木地径生长量差异性不显著;在同样切根深度的处理下,施用尿素的苗木在根系总根长、总表面积、总体积上均大于施用硝酸钠的苗木,也即NH^+4较NO^-3对板栗苗木根系生长发育具有更好的促进效果;X1N1、X2N1、X2N3处理在不同径级侧根的根长、根表面积、根体积上分别达到最高,差异性显著(P<0.05)。综合考虑苗木根系指标和形态指标,X2N1即切根深度8 cm结合施用尿素为板栗苗木根系的最佳调控处理。     

不同种植密度对丹参根系形态学的影响

通过对不同种植密度的一年生丹参进行根系形态学研究,测定根系深度、根幅、根条数、根系总表面积、根干鲜重、根直径及根韧皮部与木质部之比等相关指标,并根据其综合指标来确定最适种植密度。结果表明,在株行距为20 cm×25 cm时,单株根系生物产量最高,干重、鲜重分别为57.48 g和174.76 g,根条数最多,根系总表面积最大(1 753.29 cm2),韧皮部与木质部之比最大,为1.28。     

条带深松对不同密度玉米群体根系空间分布的调节效应

为探究条带深松耕作(SS)对密植玉米群体根系空间分布与容纳量的调节效应,本试验设置3个种植密度(低密：4.50万株 hm^-2、中密：6.75万株 hm^-2、高密：9.00万株 hm^-2),以土壤免耕(NT)为对照,利用小立方原位根土取样器,通过“3D monolith”根系空间取样方法,比较研究玉米个体与群体根系的空间分布对种植密度与土壤耕作方式的响应。结果表明,单株根长受种植密度影响显著,在0~50 cm土层中(每10 cm为一土层),高密种植的单株根长较低密种植减少110.31、43.18、15.73、10.49和17.45 m;在高密种植条件下,与土壤免耕比,条带深松耕作增加20~30 cm、30~40 cm、40~50 cm土层中的单株根长13.32%、19.80%、47.20%;单株根干重与单株根长的变化一致。种植密度对群体总根长的影响不显著,却显著影响群体根系的空间分布。与低密种植比,高密种植的植株中心根长密度在0~10 cm、10~20 cm土层中分别降低3.82 cm cm^-3、0.62 cm cm^-3,但植株之间的根长密度在0~10 cm、10~20 cm、20~30 cm、30~40 cm土层中分别增加1.13 cm cm^-3、0.18 cm cm^-3、0.06 cm cm^-3、0.05 cm cm^-3;在高密种植条件下对土壤进行条带深松耕作,与土壤免耕比,植株中心的根长密度在0~10 cm土层中降低16.10%,在10~20 cm、20~30 cm土层中却分别增加47.45%和13.37%,植株之间的根长密度在20~30 cm、30~40 cm、40~50 cm土层中分别增加50.26%、30.72%和106.15%;条带深松耕作显著提高密植玉米群体下层根系的容纳量。高密条件下条带深松耕作增加了群体根干重、深层根系量、植株间根系分布及根表面积,进而增加了地上部群体叶面积指数及地上部干重,最终促进产量显著提高。说明密植群体通过条带深松耕作改善了群体的根系空间分布,减弱了上层根系的拥挤,通过增加深层土壤根系量及植株之间根系量增加了群体根系容纳量,发挥了密植群体根系功能,实现了密植群体的高产。     

生物炭土壤结皮覆盖垄沟集雨种植对红豆草根系和根瘤特征的影响

本试验为寻求垄沟集雨种植适宜覆盖材料,探究生物炭土壤结皮增产机理,以传统平作为对照,研究了不同垄覆盖材料和不同沟垄比对红豆草（Onobrychis viciifolia Scop）根系特征值（根干重、根长、根表面积、根体积）和根瘤特征值（根瘤数量和重量）的影响。结果表明,红豆草根系和根瘤集中分布于表层（0~20 cm）土壤,红豆草根系特征值和根瘤特征值随垄宽度增加而增加,随土壤深度增加而减少,沟边的根系和根瘤特征值明显大于沟中。与对照相比,土垄、玉米秸秆炭垄和牛粪炭垄的红豆草总根干重分别增加18%,113%和56%,总根瘤数分别增加180%,860%和313%,总根瘤重分别增加86%,489%和198%;但红豆草总根长分别减少37%,33%和27%,总根表面积分别减少53%,27%和44%,总根体积分别减少54%,14%和34%。适宜土壤湿度促进红豆草根干重、根瘤数量和根瘤重量提高;适宜土壤水分胁迫有利于红豆草根长、根表面积和根体积增加。     

黑豆根尖边缘细胞对盐胁迫的防护效应

采用振荡培养(移除根尖边缘细胞)和静置培养(保持边缘细胞附着在根尖)方法,对比研究盐胁迫对黑豆根系生长和根尖边缘细胞发育、根系Na+、K+含量的影响以及根系生理特性的变化。结果显示:100和200 mmol.L-1NaCl处理抑制边缘细胞发育,引起根系相对电导率和MDA含量增加。振荡培养去除根尖边缘细胞处理36 h,黑豆根相对伸长率、根尖K+含量明显低于对应NaCl浓度的静置培养处理,同时根尖Na+含量、相对电导率和MDA含量在去除边缘细胞后显著增加。说明包裹于根尖的边缘细胞通过调节Na+和K+的吸收和维持较高的细胞膜完整性,以适应盐害环境。