酸铝胁迫下外生菌根对难溶性磷的活化利用及机理研究

Increased sparingly soluble phosphates contents was one of the main toxic consequences brought from active aluminum (Al) in acidic soils. Although some ectomycorrhizae (ECM) could promote the uptake and utilization of P by the host under acid and Al stress, mechanisms on it remain unclear up to now. This research would mainly carry on the roles of special structures and special secretions of ECM on mobilization of sparingly soluble phosphates under acid and Al stress. In order to get the symbiont ECM, 4-6 strains of ECMF, which have been proved to be excellent in resisting aluminum toxicity and promoting the growth of hosts in preliminary trials, would be selected to inoculate seedlings of the host Pinus massoniana. After cultured in medium with active Al and sparingly soluble phosphates at pH 3.8, ECMF, ECM seedlings, non-ectomycorrihzal seedlings and the culture media would be detected. Species and contents of P in media and structures of cultures, absorption kinetics on P by cultures and their structures, the growth, nutrient and Al uptakes and distributions, fine roots dynamics and emanating hyphae dynamics, microbial communities and structures in soils surrounding fine roots and emanting hypae, contents of H+, organic acids, amino acids, polysaccharides, acid phosphatase activity in culture media and cultures et al, would be investigated by three-compartment boxes culturing, isotopic trace, minirhizotron, 31P-NMR, X-ray diffraction, scanning electron microscopy, transmission electron microscopy. All of the data would be used to analyse the roles of the structures (fine roots, emanating hyphae, mantle, hartig net and cells) and the secretions (proton, organic acids, amino acids, polysaccharides, acid phosphatase, et al) from ECM on the dissolution, desorption, chelation and mineralization of sparingly soluble phosphates. Therefore, the studies could provide new information on mechanisms on mobilization and utilization of sparingly soluble phosphates or other nutrients in acidic woodland by ECM. Also, it is beneficial to utilize ECMF broadly on forestation, restoration and reconstruction in degraded forest ecosystem thereby keeping forest healthy and increasing forest productivity.

难溶性磷含量增加是酸化土壤中铝活化后引起的主要毒害之一，部分外生菌根有利于植物对磷的吸收和利用，但有关其作用机理未有科学定论。研究重点围绕外生菌根的特定结构和特定分泌物对难溶性磷的活化作用展开，拟选取4-6种抗铝性能和促生效果优良的外生菌根真菌与马尾松合成外生菌根，采用“三室”培养、同位素示踪、微根管、核磁共振、X-衍射、扫描电镜、透射电镜等技术，结合磷的吸收动力学，考察酸铝胁迫下外生菌根的细根、外延菌丝、菌套、哈蒂氏网及细胞等结构和组分，以及H+、有机酸、氨基酸、多糖、酶等分泌物在难溶性磷的溶解、解吸、螯合、矿化等过程中的作用，对比研究和统计分析后，科学推断酸铝胁迫下外生菌根对难溶性磷的活化利用及机理。研究有望对外生菌根活化利用酸铝林地中难溶性养分的机理提出新的观点，积极推动外生菌根真菌在植树造林和生态修复上的应用，保障森林健康，提高森林生产力。

难溶性磷增加是酸化土壤中铝活化后引起的主要毒害之一，部分外生菌根(ECM)有利于植物对磷的吸收和利用，但其作用机理尚不明确。试验选取外生菌根真菌(ECMF)松乳菇和彩色豆马勃分别接种马尾松幼苗，研究酸铝胁迫下ECM对难溶性磷的活化利用及机理。结果发现，酸铝胁迫下，（1）ECM促进马尾松幼苗在含难溶性磷源土壤上的生长及对难溶性磷的吸收利用，并促进磷和生物资源的上行分配；对3种磷源的吸收利用能力为Fe-P > Al-P > Na-P，且松乳菇比彩色豆马勃的促进作用更强；（2）ECMF吸收的部分磷会与Al或Fe结合，成为难溶性的Al-P或Fe-P，且在无机磷中的占比为Al-P > 水溶性磷 > Fe-P；ECM促进马尾松幼苗吸收的磷转化成脂磷、酯磷、核酸磷、结合态磷等有机磷，减少无机磷和残渣磷的形成，增加磷在植物体内的有效性和利用程度；（3）ECMF对磷的吸收亲和力增加，吸收阈值降低且吸收速率加快，促进培养基中难溶性磷向有效磷转化；接种ECMF促进土壤中难溶性无机磷Al-P、Fe-P和O-P向有效磷转化；ECMF和ECM都对难溶性磷源Fe-P比Al-P的作用更强；（4）ECMF在利用难溶性磷源时分泌出更多的H+，分泌量增加的有机酸种类因菌种而异：Pt 715在利用Al-P时是甲酸，Ld 2在利用Al-P和Fe-P时是草酸和甲酸；ECM在利用难溶性磷源时向根际土壤中分泌的H+量增加，草酸和琥珀酸含量降低或不变，ACP活性降低，氨基酸含量增加；（5）ECM显著增加马尾松幼苗体内的有机酸、多糖和氨基酸含量，降低或不改变ACP活性；（6）ECM显著促进马尾松幼苗的根系加长、加粗以及分蘖生长，显著增加根长、根表面积、根体积、根尖数和根分枝数。因此，ECM促进酸铝胁迫下植物对难溶性磷的活化、吸收、利用和转运，主要通过（1）促进根系加长、加粗和分蘖生长，扩大根系长度与面积来增加与磷的接触和吸收能力；（2）增加与磷的亲和力、促进H+分泌溶解难溶性无机磷，以及氨基酸结合促进磷向植物体的转运；（3）促进植物体内有机酸溶解难溶性磷、多糖螯合铝、氨基酸转运磷等提高磷在生物体内的有效性。