供磷水平对玉米丛枝菌根侵染及其对异质养分吸收的影响

Influences of phosphorus application level on maize arbuscular mycorrhizal colonization and hyphal acquisition to heterogeneous phosphorus supply

【目的】探究酸性土壤玉米丛枝菌根侵染对植物磷素吸收的促进作用,以加深理解根外菌丝对局部磷养分的获取如何受丛枝真菌侵染和环境磷养分的影响。【方法】以玉米为宿主植物,进行盆栽试验。在低磷酸性土壤上设置供P 0、50、500 mg/kg 3个水平(P0、P50、P500),供试磷肥为磷酸二氢钾。每个处理再设置局部养分处理,即在每个重复中埋置两个各装有120 g灭菌土(提前加P 50 mg/kg)的塑料小管,分别用孔径为0.45μm(根系、菌丝均不能进入,以"–H"表示处理)和50μm(根系不能进入,菌丝可以进入,以"+H"表示处理)的尼龙膜封住管口。测定了玉米的生长与磷吸收、土著丛枝菌根真菌的侵染和根外菌丝密度以及菌丝对局部磷养分的获取。【结果】1)玉米株高、叶片SPAD值、全株干重、磷浓度及吸收量都随供磷水平升高而增加,以P50处理的根系干重最高,根冠比随供磷水平上升而降低。3个供磷水平下玉米根系均有不同程度的丛枝菌根真菌侵染。以P50处理的丛枝菌根侵染率、丛枝和孢囊结构发育最好;P0处理的丛枝菌根侵染率、丛枝丰度与P50处理没有显著差异,但孢囊丰度明显下降;P500处理虽然87.2%的根系具有侵染点,但整个根系形成的真菌结构、丛枝和孢囊比例远低于P0和P50处理,丛枝菌根的发育受到严重抑制。2)土体土(除塑料管之外的土)菌丝密度随供磷水平升高而降低,但P0和P50处理差异不显著。–H处理塑料管中的菌丝密度在3个供磷水平下基本不变,保持在极低水平,而+H处理塑料管中的菌丝密度随供磷水平升高而下降。在相同供磷水平下,土体土的菌丝密度最高,其次是+H处理,–H处理的菌丝密度最低。根外菌丝从+H处理塑料管中获取的磷随环境供磷水平的升高而减少。【结论】酸性土壤条件下,适当地供磷可以促进玉米根系生长和丛枝菌根真菌的侵染。根外菌丝对局部磷养分的获取受环境磷养分的调控,在环境磷养分较低而局部磷养分高于环境磷养分时,较多的菌丝会进入局部区域获取磷。

[Objectives] The objectives of this study are to investigate the arbuscular mycorrhizal infection on maize and their promotion to plant phosphorus uptake in acid soils, and to study the effects of arbuscular mycorrhizal fungi and environmental phosphorus nutrition on the acquisition of local phosphorus nutrition by root hyphae.[Methods] Using pot experiment and maize as host plant, three P levels of 0, 50 and 500 mg/kg （P0, P50 and P500, P was supplied by KH2PO4） were designed. Then two plastic chambers containing 120 g sterilized soil with P 50 mg/kg were installed in each pot. One chamber was enclosed with 0.45 μm mesh fabric to prevent hyphae and root from penetration （-H treatment）, and the other one was enclosed with 50 μm mesh fabric to allow hyphae penetration （＋H treatment）. Maize plant growth, P uptake, AM fungi colonization, hyphal density and P acquisition by hyphae from chambers were measured.[Results] The plant height, leaf SPAD value, total dry weight, P concentration and uptake were all increased with the increase of P supply level, with the highest root dry weight in P50 treatment, while root/shoot ratio was decreased with the increase of P level. The P50 treatment showed the best AM fungi colonization rate and development of arbuscule and vesicle. Compared with the P50 treatment, the P0 treatment had fewer vesicles although there was no significant difference in the AM colonization rate and arbuscule richness. Even with 87.22% colonization point existing in whole root system, plants of the P500 treatment showed the lowest AM fungi colonization rate and development of arbuscule and vesicle, indicating severe inhibition of high P supply on AM fungi. The bulk soil hyphal density was decreased with the increase of soil P level, with a little difference between the P0 and P50 treatments. The hyphal density kept stable and was very low in all -H chambers, while the hyphal density in the ＋H chambers was decreased with the increase of bulk soil P level. Under the same P application level, the hyphal density was highest in bulk soil, followed by ＋H chamber soil, and lowest in -H chamber soil. The P acquisition from the ＋H chamber by hyphae was decreased with increase of bulk soil P supply.[Conclusions] A moderate soil P supply could benefit root growth and AM fungi colonization in acid soil. The hyphae exploration for local P supply is influenced by bulk soil P status, with higher P acquisition from P-rich area when bulk soil P supply is low.