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  土壤学报  2018, Vol. 55 Issue (5): 1179-1189  DOI: 10.11766/trxb201802120407
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辜夕容, 倪亚兰, 江亚男, 等. 接种双色蜡蘑对马尾松根际土壤无机磷和活性铝含量的影响. 土壤学报, 2018, 55(5): 1179-1189.
GU Xirong, NI Yalan, JIANG Yanan, et al. Effect of Laccaria Bicolor Inoculation on Contents of Inorganic Phosphorus and Labile Aluminum in the Rhizosphere Soil of Pinus Massoniana Saplings. Acta Pedologica Sinica, 2018, 55(5): 1179-1189.

基金项目

国家自然科学基金项目(31570599,31100464)资助

作者简介

辜夕容(1973—),女,四川人,博士,副教授,主要从事林木营养、经济林培育和林业微生物研究。E-mail: gxr0956@163.com
接种双色蜡蘑对马尾松根际土壤无机磷和活性铝含量的影响
辜夕容 , 倪亚兰 , 江亚男 , 贾豪 , 何新华     
西南大学资源环境学院,土壤生物学研究中心,重庆 400716
摘要:将双色蜡蘑(Laccaria bicolor)的3个株系(Lb 270、Lb S238A和Lb S238N)分别与马尾松种子拌匀,培养在酸性土壤中,以检测根际土壤无机磷和活性铝含量,并分析外生菌根对磷有效性和铝活性的作用。结果发现,与非菌根苗相比,接种双色蜡蘑显著促进马尾松幼苗生长和对磷、铝的吸收,而对根际土壤无机磷和活性铝含量的影响因菌株而异:Lb 270和Lb S238N显著降低pH、有效磷、全铝、交换态铝含量,提高羟基态铝含量,且Lb 270还显著降低铁磷和钙磷含量; Lb S238A显著提高pH、有效磷含量,减少铝磷、全铝、活性铝、交换态铝和腐殖酸铝含量。即接种双色蜡蘑提高了磷的生物有效性,且Lb 270和Lb S238N增加、Lb S238A减少铝的活性。因此,接种供试双色蜡蘑都能提高马尾松的抗铝性,主要在于其增加磷的生物有效性,而是否降低铝的活性取决于菌株特性。
关键词活性铝    铝毒害    外生菌根    无机磷    马尾松    

磷是植物生长的重要营养元素,在大多数土壤里总量充足,但因其移动性差,易被铁、铝氧化物吸附和沉淀而导致生物有效性低[1]。在酸性土壤中,铝易溶出成为活性铝,常与HPO42-、H2PO4-或PO43-结合,转化成难溶性磷,使本就很低的有效磷更加匮乏,严重限制植物的生长和发育[2-3]。适生植物常有几种应对方式,其中之一即是与外生菌根(Ectomycorrhizal,EM)真菌共生[4]。研究发现,部分外生菌根植物在酸性铝胁迫下的生物量、磷吸收量都显著高于非菌根苗[5-6]。进一步检测发现,它们分泌的低分子量有机酸如草酸、柠檬酸、苹果酸、酒石酸、丙二酸等显著增加[5, 7]。由于这些有机酸可与Al3+、Fe3+等金属离子形成稳定的螯合物,因此研究者推测,EM增强植物抗酸性铝毒害的重要机理之一是低分子量有机酸与铝螯合,使铝失活并释放出磷,在解除铝毒的同时提高磷的有效性[5, 7-11]

然而,在Lactarius deliciosusLaccaria bicolorLactarius rufusSuillus luteusHebeloma crustuliniforme等EM真菌的纯培养试验中发现,菌丝体在酸性铝处理下不仅对磷的吸收增加,对铝的吸收也随铝水平增长[10, 12-13]。将EM真菌H. crustuliniforme接种欧洲云杉(Picea abies)、L. bicolor接种马尾松(Pinus massoniana Lamb.)后形成的菌根苗对磷和铝的吸收也有类似现象[4, 14]。此外,地球化学研究结果发现[15],植物根际常常出现酸化现象,这可能进一步导致酸性土壤中铝的活化,使土壤性质向不利于肥力提高的方向发展; 而且EM真菌在溶解土壤矿物颗粒获取磷等养分的同时,也会提高土壤溶液中活性铝的浓度[16-17]。推测EM真菌或EM植物在提高磷有效性的同时可能并未降低铝的活性,EM提高植物抗铝性的作用可能更多源于对磷有效性的提高,而非降低铝的活性。为验证此假设,试验以EM真菌L. bicolor接种马尾松,以未接种处理为对照,培养一段时间后取根际土壤,检测其中无机难溶性磷和活性铝的含量与分布,分析外生菌根真菌侵染对酸性土壤中难溶性磷和活性铝的作用,以探索外生菌根缓解铝毒性的机理。

1 材料与方法 1.1 研究区概况

试验地点位于西南大学农场(29°48′39″N,106°24′54″E,海拔255 m)。亚热带季风湿润气候,试验期间月平均最高气温29.4 ℃,月平均最低气温21.4 ℃,月平均降雨量157 mm。

1.2 供试材料

菌株:双色蜡蘑(L. bicolor)的3个株系,即Lb 270、Lb S238A和Lb S238N,由西南大学菌根研究室提供。其中,Lb 270来源于北美花旗松(Pseudotsuga menziesii)林下,Lb S238A和Lb S238N来源于法国火炬松(Pinus taeda)林下。

种子:马尾松(P. massoniana Lamb.)种子,由重庆市林木种苗站提供。

土壤:山地冷砂黄壤,采自重庆市北碚区鸡公山(N 29°48′54″,E 106°26′36″,海拔534 m)马尾松林下。去除石砾、草根、枯落物等,测其基本化学性质见表 1

表 1 供试土壤基本化学性质 Table 1 Chemical properties of the nursery soil before seeding
1.3 试验设计

取直径为3 mm的琼脂菌种4块,分别接种于含50 mL Pachlewski液体培养基[4]的250 mL三角瓶中,(25±2)℃、黑暗条件下静置培养21 d,制成液体菌种。将马尾松种子净种后先用0.3%甲醛溶液浸泡30 min,无菌水冲洗干净,然后在25 ℃左右水中浸种24 h,捞出沥干,25 ℃左右保湿催芽。土壤用2%甲醛水溶液消毒后装在1 m×1 m×0.5 m水泥池中备用。

每处理每菌株取5瓶液体菌种,分别过滤菌丝体,用灭菌的去离子水洗去附着的培养基,打浆机低速打散,与200粒经催芽露白后的马尾松种子拌匀后分别播种在1 m2的水泥池小区中,每天早晚两次浇水保湿,自然条件下培养。16周后分别获得3种马尾松菌根苗(即Lb S238A、Lb S238N和Lb 270)及其根际土壤。以不接菌的非菌根苗及其根际土壤作对照。试验小区随机排列,每处理3个重复,共12个小区。

1.4 测定项目与方法

连续培养16周后,在每小区近中心区域随机取25株幼苗,用显微镜检测菌根感染情况,发现菌根真菌处理后的苗木感染率达到100%,而对照苗木感染率为0。清水冲洗掉苗木上附着泥沙,80±2 ℃烘干至恒重后称重,25 000 r·min-1高速粉碎1 min后用浓HNO3-HClO4(V︰V=5︰1)混合酸消煮,分别用钼锑抗比色法和铝试剂比色法测定消化液中磷、铝浓度[18]。马尾松幼苗对磷、铝的吸收量分别为其磷、铝含量与生物量的乘积。

抖落法收集根际土壤,去除杂质,混合后风干、磨细、分别过0.85 mm筛和0.15 mm筛。按照文献[19]所示,土壤中pH用pHS-3C型精密酸度计测定(土水比为1︰2.5),全磷、全铝含量用HClO4-H2SO4(V︰V=1︰10)法消煮后测定,有效磷含量用0.05 mol·L-1 HCl-0.025 mol·L-1 (1/2 H2SO4)浸提法测定; 采用酸性土壤中无机磷分级方法,分别以1 mol·L-1 NH4Cl-0.5 mol·L-1 NH4F (pH 8.2)、0.1 mol·L-1 NaOH、0.3 mol·L-1柠檬酸钠+1.0 g Na2S2O4 + 0.5 mol·L-1 NaOH、0.5 mol·L-1(1/2 H2SO4)连续浸提土壤,分别得铝磷、铁磷、闭蓄态磷和钙磷浸提液。浸提液中磷含量用钼锑抗比色法测定。土壤中无机磷含量为铝磷、铁磷、闭蓄态磷和钙磷含量之和。

参照黄衍初和曲长菱[20]的方法,按以下步骤连续浸提土壤中的活性铝:取过0.15 mm筛土样1.000 0 g,置于离心管中,加入1 mol·L-1 KCl浸提液50 mL,在康氏振荡器上振摇30 min,5 000 r·min-1离心15 min,倾出上清液(1); 用去离子水洗涤残渣,加入1 mol·L-1 NH4OAc浸提液50 mL,振摇后离心分离,倾出上清液(2); 用去离子水洗涤残渣,加入1 mol·L-1 HCl浸提液50 mL,振摇后离心分离,倾出上清液(3); 用去离子水洗涤残渣,加入0.5 mol·L-1 NaOH 50 mL,振摇后离心分离,倾出上清液(4)。用铝试剂比色法[18]测定上述4种上清液中的铝含量。其中,上清液(1)中铝含量为交换态铝(Al3+)含量,上清液(2)中铝含量为羟基态铝[Al(OH)2+和Al(OH)2+]含量,上清液(3)中铝含量为酸溶无机铝(Al(OH)30)含量,上清液(4)中铝含量为腐殖酸铝(Al-HA)含量。土壤中活性铝含量为这4种形态铝含量之和。

1.5 数据处理

所得数据用IBM SPSS Statistics 21.0软件包作方差分析,LSD法进行各水平间的多重比较。采用GraphPad Prism 5制图,Microsoft Office Excel 2007制表。图和表中所有数据均为3次重复的平均值±标准差,显著性水平设为P < 0.05。

2 结果 2.1 接种双色蜡蘑对马尾松幼苗生长及磷、铝吸收的影响

接种双色蜡蘑的3个株系均显著促进马尾松幼苗的生长和对磷、铝的吸收(图 1)。与对照相比,接种Lb 270、Lb S238A、Lb S238N分别显著提高马尾松幼苗生物量74.4%、48.9%、74.6%(图 1a),磷吸收量107%、58.6%、129%(图 1b),铝吸收量145%、101%、145%(图 1c),3株真菌间的促进作用强弱依次为Lb S238N ≥ Lb 270>Lb S238A。

图 1 接种双色蜡蘑对马尾松幼苗生长(a)、磷(b)和铝吸收(c)的影响 Fig. 1 Effects of L. bicolor inoculation on the growth (a), uptake of P (b) and Al (c) of Pinus massoniana saplings 注:图中不同字母表示处理间差异显著(P < 0.05)。下同Note: Different letters indicate significant differences between treatments at P < 0.05. The same below
2.2 接种双色蜡蘑对根际土壤pH和有效磷含量的影响

接种双色蜡蘑对马尾松根际土壤pH的影响因菌株而异(图 2a)。与对照相比,Lb 270和Lb S238N的侵染均显著降低根际pH,且Lb 270的作用强于Lb S238N,两者分别降低0.11和0.07个单位; 而接种Lb S238A则相反,使pH显著增加0.11个单位。

图 2 接种双色蜡蘑对马尾松根际土壤中pH(a)和有效磷含量(b)的影响 Fig. 2 Effects of L. bicolor inoculation on the pH (a) and available P content (b) in the rhizosphere soil of Pinus massoniana saplings

马尾松根际土壤中有效磷含量仅3.40~5.08 mg·kg-1,仅占全磷含量的0.97%~1.50%,属全磷转化率低、有效磷容量和供给强度均较小的土壤。接种双色蜡蘑对有效磷含量的影响因菌株而异(图 2b)。与对照相比,接种Lb 270和Lb S238N使土壤中有效磷含量显著降低15.5%~15.9%,两菌株间无显著差异; 而接种Lb S238A则相反,使有效磷含量显著提高25.6%。

2.3 接种双色蜡蘑对根际土壤中无机磷含量及分布的影响

马尾松根际土壤中含全磷339.7~356.4 mg·kg-1,其中无机磷166.0~195.0 mg·kg-1,占全磷47.6%~57.4%。闭蓄态磷是无机磷的主要组成部分,占46.1%~50.1%;铁磷其次,占31.9%~35.9%;钙磷和铝磷含量均较低,分别只占9.44%~11.0%和6.96%~9.74%(表 2)。

表 2 接种双色蜡蘑对马尾松苗木根际土壤中无机磷分布的影响 Table 2 Effects of L. bicolor inoculation on distribution of inorganic P in the rhizosphere soil of Pinus massoniana saplings

与对照相比,接种双色蜡蘑对土壤全磷含量无显著改变,对无机磷含量虽有一定影响但未达显著程度(表 2)。在3个菌株中,Lb 270侵染后的土壤无机磷含量显著低于Lb S238A 17.4%,说明Lb 270菌根化幼苗对无机难溶性磷的转化利用能力强于Lb S238A。

双色蜡蘑侵染对马尾松根际土壤中4种无机磷组分含量及其在无机磷中分布的影响因菌株而异(图 3表 2)。与对照相比,接种Lb 270显著降低铁磷和钙磷含量,两者分别减少了12.3%和18.1%,显著提高铝磷在无机磷的分布; 接种Lb S238A显著降低铝磷含量,减少铝磷和铁磷、但增加闭蓄态磷在无机磷中的分布; 接种Lb S238N对铝磷和钙磷含量及其在无机磷中的分布均有一定减少,但未达显著程度。Lb 270菌根苗根际土壤中铝磷含量显著高于、但铁磷和钙磷含量显著低于Lb S238A和Lb S238N菌根苗根际,且闭蓄态磷含量显著低于Lb S238A菌根苗根际; Lb S238A菌根苗根际土壤中钙磷含量显著高于Lb S238N和Lb 270菌根苗根际。可见,接种双色蜡蘑显著促进马尾松幼苗对部分无机难溶性磷源的转化利用,且因菌株而异:Lb 270主要是铁磷和钙磷,Lb S238A主要是铝磷,而Lb S238N对铝磷和钙磷也有一定的转化利用。

图 3 接种双色蜡蘑对马尾松根际土壤中铝磷(a)、铁磷(b)、闭蓄态磷(c)和钙磷(d)含量的影响 Fig. 3 Effects of L. bicolor inoculation on the contents of Al-P (a), Fe-P (b), O-P (c), and Ca-P (d) in the rhizosphere soil of Pinus massoniana saplings
2.4 接种双色蜡蘑对根际土壤中活性铝含量及分布的影响

马尾松根际土壤中全铝含量40.7~48.2 g·kg-1,其中活性铝1.09~1.27 g·kg-1,占全铝的2.49%~2.77%。酸溶无机铝是活性铝的主要组成部分,含量为0.83~0.91 g·kg-1,占活性铝的71.6%~76.3%,腐殖酸铝其次,占22.6%~26.7%,这两种形态铝占活性铝的绝大部分,共占98.1%~99.0%。交换态铝和羟基态铝的含量均很低,仅占活性铝的0.23%~0.95%和0.70%~1.04%(表 3)。

表 3 接种双色蜡蘑对马尾松苗木根际土壤中活性铝分布的影响 Table 3 Effects of L. bicolor inoculation on the distribution of labile Al in the rhizosphere soil of Pinus massoniana saplings

接种双色蜡蘑显著降低土壤中全铝含量(表 3)。与对照相比,Lb S238A的侵染使全铝含量显著降低15.5%,明显高于Lb S238N和Lb 270的降幅(7.80%和5.06%)。而对活性铝含量的影响,则因菌株而异:Lb S238A显著降低,Lb 270显著增加,Lb S238N无显著影响,且Lb 270和Lb S238N的土壤活性铝含量显著高于Lb S238A。3种真菌均显著提高活性铝在全铝中的比例,增幅为7.14%~11.2%。

各形态铝的含量及在活性铝中的分布因菌株而异(图 4表 3)。与对照相比,接种Lb 270和Lb S238N分别显著降低交换态铝含量11.5%和11.0%、增加羟基态铝含量34.5%和50.2%,对酸溶无机铝和腐殖酸铝含量无显著影响; 接种Lb S238A显著减少交换态铝和腐殖酸铝含量,对前者的降幅高达77.7%,对后者的降幅为18.8%,对羟基态铝和酸溶无机铝含量则无显著影响。在3株真菌中,Lb 270和Lb S238N侵染后的土壤中4种形态铝含量均显著高于Lb S238A;Lb 270的腐殖酸铝含量显著高于Lb S238N。接种Lb 270显著降低交换态铝在活性铝中的比例,但增加羟基态铝比例; 接种Lb S238A显著降低交换态铝和腐殖酸铝比例,但增加羟基态铝和酸溶无机铝比例; 接种Lb S238N显著降低交换态铝和腐殖酸铝比例,但增加羟基态铝比例(表 3)。

图 4 接种双色蜡蘑对马尾松根际土壤中交换态铝(a)、羟基态铝(b)、酸溶无机铝(c)和腐殖酸铝(d)含量的影响 Fig. 4 Effects of L. bicolor inoculation on the contents of exchangeable Al (a), hydroxyl-Al (b), acid-soluble Al (c), and organic-complexed Al (d) in the rhizosphere soil of Pinus massoniana saplings
2.5 根际土壤中pH、有效磷、无机磷和活性铝含量间的相关性

表 4可见,土壤pH与有效磷、闭蓄态磷和钙磷含量间极显著正相关,与铝磷及4种形态的活性铝含量间极显著负相关; 有效磷含量与闭蓄态磷、钙磷含量间极显著正相关,与4种形态的活性铝含量间极显著负相关; 铝磷含量与交换态铝、腐殖酸铝含量间显著或极显著正相关; 闭蓄态磷和钙磷含量均与除羟基态铝之外的其他3种形态铝含量间显著或极显著负相关。因此,在酸性土壤中升高pH降低4种活性形态铝的产生,减少铝磷的形成,增加闭蓄态磷和钙磷含量,有利于提高磷的生物有效性。

表 4 马尾松根际土壤中pH值、有效磷、无机磷和活性铝含量间的相关性 Table 4 Pearson's correlation coefficients between pH, contents of available P, inorganic P, and labile Al in the rhizosphere soil of Pinus massoniana saplings
3 讨论

山地冷砂黄壤为酸性富铝化土壤,其中的铝活化程度高,易与PO43-、HPO42-、H2PO4-发生沉淀反应生成难溶性磷,降低磷的有效性,严重制约树木生长[3]。与辜夕容等[4]结果相同,接种双色蜡蘑的3个株系均显著促进该土壤上马尾松的生长和对磷的吸收。从土壤中各形态无机磷的含量和分布看,接种双色蜡蘑能促进根际土壤中难溶性磷的转化和利用。而所用EM真菌、寄主以及培养条件的不同,均可能引起外生菌根转化利用的难溶性磷源种类存在差异。如离体培养在含中性偏微酸性(pH 6.8)紫色土的培养基上时,Pisolithus tinctorius 715、Lactarius deliciosus 3、Cenococcum geophilum 4和Boletus badius 7偏向于对钙磷的转化利用[8];Lb S238N侵染北美花旗松后,菌根苗对铝磷的转化利用能力显著提高[21],浸染马尾松并培养于酸性的冷砂黄壤中时,对铝磷和钙磷均有较好的转化利用; 同样条件下的Lb 270对铁磷和钙磷、Lb S238A对铝磷有显著增强的转化利用能力。3株双色蜡蘑使马尾松幼苗对磷的吸收能力不仅显著提高,而且菌株间差异显著:Lb S238N和Lb 270的增幅均较Lb S238A的高约1倍,即Lb S238N和Lb 270菌根苗对土壤中磷的吸收利用程度显著高于Lb S238A。在都能促进土壤中难溶性磷转化条件下,Lb S238A根际土壤中有效磷含量显著高于Lb S238N和Lb 270。甚至与内生菌根真菌Glomus mosseae的作用相似[22],在Lb S238N和Lb 270菌根苗根际还出现有效磷的亏缺。因此,接种3株双色蜡蘑均能显著促进马尾松幼苗对酸性土壤中难溶性磷源向有效磷源的转化和利用,且Lb S238N和Lb 270强于Lb S238A。

在无机难溶性磷的转化利用过程中,多数研究认为低分子量有机酸中的有机酸根离子能与铝、铁、钙等金属离子螯合形成稳定的环状结构,将与其结合的磷释放出来,其中的H+也对无机难溶性磷起溶解作用[2, 7, 23-25]。在EM真菌离体培养过程中,同样发现酸性铝胁迫能促进草酸的分泌和培养液中的白色沉淀溶解[12],而且土壤中的无机难溶性磷等溶解量增加[8]。龚松贵[24]、周垂帆[17]等指出,H+对难溶性磷的溶解作用较有机酸更大,而且pH越低,越有利于土壤无机磷的活化,尤其是钙磷的活化对质子的酸效应非常明显。在Lb 270和Lb S238N菌根苗根际土壤中,pH显著低于非菌根苗根际,钙磷含量减少,说明两株双色蜡蘑促进了H+的分泌,并有助于钙磷的活化。同时,铁磷或铝磷含量的降低,说明有机酸根离子的络合作用可能促进了它们的转化。然而,3株真菌与马尾松形成的菌根苗对铝吸收量却并未减少,反而成倍高于非菌根苗,说明难溶性磷在活化的同时铝的释放量也在增加。同时,菌根苗对铝的大量吸收,使苗木为达到体内电荷平衡而分泌出大量的H+,而且Lb 270和Lb S238N菌根苗释放出的H+量应高于Lb S238A,这使前两者根际pH显著降低而后者相对提高。Lb S238A根际铝磷含量的显著降低和有效磷含量的显著增加,说明铝磷被大量转化为有效磷,过程中有机酸根离子的作用可能大于H+。因此,双色蜡蘑菌根苗对难溶性磷向有效磷源的转化,一方面可能源于有机酸根离子对铝、铁、钙的螯合作用,另一方面则是H+的溶解作用而释放出磷。相对而言,Lb 270和Lb S238N菌根苗更多地有赖于质子酸效应,而Lb S238A可能更多地源于有机酸根的络合效应,下一步工作中可对此探索。

许多研究认为[5, 9-11, 26-27],部分外生菌根能够缓解酸性土壤中铝活化引起的毒害,原因之一是使铝活性降低[7, 28]。试验所用的3种双色蜡蘑菌根苗根际土壤中交换态铝含量均显著低于非菌根苗,似乎证明了EM真菌侵染能减少铝活性。然而,其余3种形态活性铝含量的改变却因菌株而异:Lb 270和Lb S238N的羟基态铝含量分别较非菌根苗显著提高34.5%和50.2%,幅度明显高出交换态铝含量的降低程度; Lb S238A的活性铝总量显著降低,但除交换态铝外的其余3种活性形态的铝含量均未显著增加。土壤中交换态铝含量的下降可能来源于4个方面:(1)苗木的吸收; (2)交换态铝具有高移动性,易被雨水淋失或淋溶至土壤下层[29];(3)有机酸根离子等有机物对铝的络合作用使其失活[7, 28];(4)pH上升使铝溶解量下降[12]。3种双色蜡蘑菌根苗对铝的吸收均成倍高于非菌根苗,且Lb S270和Lb S238N吸收的铝量显著高于Lb S238A,说明土壤中减少的交换态铝可能主要由植株大量吸收所致。Lb S238A的全铝和活性铝含量均明显低于非菌根苗,加上交换性铝含量还显著低于Lb 270和Lb S238N,推测雨水淋失也是其中的重要原因。在4种形态的活性铝中,交换态铝和羟基态铝均属于高活性形态的铝,而酸溶无机铝和腐殖酸铝属于低活性形态的铝[29]Lb 270和Lb S238N菌根苗根际pH的显著下降,使低活性铝向高活性铝转化,促进了铝的活化[15, 30];而Lb S238A根际pH的显著上升,则有助于高活性铝向低活性铝转化,从而降低铝的活性[12]。因而,接种双色蜡蘑的3个株系对马尾松根际土壤中铝活性的改变因菌株而异:Lb 270和Lb S238N促进了铝的活化,而Lb S238A能降低铝的活性,它们对根际pH的改变在其中应起关键作用。

4 结论

接种双色蜡蘑有利于酸性土壤上马尾松幼苗的生长和对磷、铝的吸收,提高马尾松对铝的抗性。3株双色蜡蘑均能促进根际土壤中无机难溶性磷的活化,且活化的无机难溶性磷源种类因菌株而异:Lb 270活化铁磷和钙磷,Lb S238A活化铝磷,Lb S238N活化铝磷和钙磷。3个菌株中,Lb 270和Lb S238N对难溶性磷的转化利用能力强于Lb S238A,更适于酸性土壤上马尾松苗木的生长和对难溶性磷的利用; Lb 270和Lb S238N增加铝活性,Lb S238A降低铝活性。因此,接种双色蜡蘑能促进酸性土壤上马尾松幼苗的生长,提高其抗铝性,主要原因之一应是供试双色蜡蘑均促进了难溶性磷的转化和利用,而是否降低铝的活性取决于菌株特性。

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Effect of Laccaria Bicolor Inoculation on Contents of Inorganic Phosphorus and Labile Aluminum in the Rhizosphere Soil of Pinus Massoniana Saplings
GU Xirong , NI Yalan , JIANG Yanan , JIA Hao , HE Xinhua     
Centre of Excellence for Soil Biology, College of Natural Resources and Environment, Southwest University, Chongqing 400716, China
Abstract: 【Objective】 In most soils, TP (total phosphorus) is generally plenty, but its availability to plants is very low. When the soil is getting acidified, soil Al is liable to get activated and then bound with HPO42-, H2PO4-, and PO43-, turning them into hard-to-dissolve P, thus further lowering soil P availability. Some ectomycorrhizae (EM) are found to be able to deactivate soil Al, thus letting Al-complexes release bonded P in available form, for plants to take up. That is to say, some EMs could be introduced into acid soils to improve soil P availability and plant growth. In experiments of in vitro cultivation of EM fungi, some demonstrated their ability to raise P availability in soils neutral or slightly acidic, but little has been found in the literature validating such ability in the field. The present study aimed to assess effects of inoculation of EM fungi on inorganic P availability and Al activity in the rhizosphere soil of saplings planted in acid soil, and to explore mechanism of EM colonization improving host plants' resistance to Al toxicity.【Method】 Germinating Pinus massoniana seeds, inoculated with three strains of Laccaria bicolor, namely Lb 270, Lb S238A, and Lb S238N, separately, were imbedded into pots of cold sandy yellow soil collected from a P. massoniana stand, and irrigated twice a day to maintain a proper moisture regime for 16 weeks under the natural conditions. At the end, comparison was made of Pinus massoniana saplings inoculated with EM fungi with those in the control (without inoculation).【Result】 Results show that inoculation of L. bicolor significantly affected the contents of inorganic P and active Al in the rhizosphere soil of the saplings and the effects varied with the strain. Compared with the control, inoculation with any of the three L. bicolor strains significantly improved growth and P and Al, uptake of the saplings. In terms of the effect, the three strains exhibited an order of Lb S238N > = Lb 270 > Lb S238A. Inoculation with Lb 270 significantly decreased soil pH, the contents of available P, iron-bound P (Fe-P), calcium-bound P (Ca-P), total Al, and exchangeable Al, and the proportion of exchangeable Al in the fraction of labile Al, but increased the proportion of aluminum-bound P (Al-P) in the fraction of inorganic P, and the contents of labile Al or hydroxyl-Al and their proportions in total Al. Inoculation with Lb S238A significantly reduced Al-P, the proportion of Al-P or Fe-P in the fraction of inorganic P, total Al, labile Al, exchangeable Al, organic-complexed Al, and the proportion of exchangeable Al and organic-complexed Al in the fraction of labile Al, but raised soil pH, the content of available P, the proportion of occluded-P (O-P) in the fraction of inorganic P, the proportion of labile Al in total Al, and proportions of hydroxyl-Al or acid-soluble Al in the fraction of labile Al. Inoculation with Lb S238N significantly decreased soil pH, the contents of available P, total Al, exchangeable Al, and the proportions of exchangeable Al and organic-complexed Al in the fraction of labile Al, but increased the content of hydroxyl-Al, the proportion of labile Al in total Al and that of hydroxyl-Al in the fraction of active Al.【Conclusion】 All the findings in this experiment demonstrate that inoculation with L. bicolor can improve the resistance of P. massoniana saplings to Al toxicity, which may be attributed to the ability of the fungi to enhance bio-availability of soil P, but their abilities to lower Al activity vary with strain of the fungi.
Key words: Active aluminum    Aluminum toxicity    Ectomycorrhizae (EM)    Inorganic phosphate    Pinus massoniana Lamb