AMF colonization affects allelopathic effects of Zea mays L. root exudates and community structure of rhizosphere bacteria

Abstract

Arbuscular mycorrhizal fungi (AMF) widely exist in the soil ecosystem. It has been confirmed that AMF can affect the root exudates of the host, but the chain reaction effect of changes in the root exudates has not been reported much. The change of soil microorganisms and soil enzyme vigor is a direct response to the change in the soil environment. Root exudates are an important carbon source for soil microorganisms. AMF colonization affects root exudates, which is bound to have a certain impact on soil microorganisms. This manuscript measured and analyzed the changes in root exudates and allelopathic effects of root exudates of maize after AMF colonization, as well as the enzymatic vigor and bacterial diversity of maize rhizosphere soil. The results showed that after AMF colonization, the contents of 35 compounds in maize root exudates were significantly different. The root exudates of maize can inhibit the seed germination and seedling growth of recipient plants, and AMF colonization can alleviate this situation. After AMF colonization, the comprehensive allelopathy indexes of maize root exudates on the growth of radish, cucumber, lettuce, pepper, and ryegrass seedlings decreased by 60.99%, 70.19%, 80.83%, 36.26% and 57.15% respectively. The root exudates of maize inhibited the growth of the mycelia of the pathogens of soil-borne diseases, and AMF colonization can strengthen this situation. After AMF colonization, the activities of dehydrogenase, sucrase, cellulase, polyphenol oxidase and neutral protein in maize rhizosphere soil increased significantly, while the bacterial diversity decreased but the bacterial abundance increased. This research can provide a theoretical basis for AMF to improve the stubble of maize and the intercropping mode between maize and other plants, and can also provide a reference for AMF to prevent soil-borne diseases in maize.

Keywords: AMF; allelopathy; bacterial diversity; root exudates; soil enzyme vigor.

Figure 1

Classification map of differential compounds in maize root exudates after AMF colonization.

Figure 2

Molecular framework statistical map of differential compounds in maize root exudates after AMF colonization. The left side of the figure shows the classification of maize root exudates with significant differences after AMF colonization, and the right side shows the carbon skeleton corresponding to these root exudates.

Figure 3

Effect of CE and CK root exudates on seed germination rate in recipient plants. (A–E) shows the effects of CE and CK root exudates on the seed germination rate of radish, cucumber, lettuce, pepper, and ryegrass respectively, and (F) shows the difference of allelopathic effects of CE and CK root exudates on the germination rate of the above receptor plants; (A–E) represent radish, cucumber, lettuce, pepper, and ryegrass respectively.

Figure 4

Effect of CE and CK root exudates on seed germination potential of recipient plants. (A–E) shows the effects of CE and CK root exudates on seed germination potential and allelopathic effect index of radish, cucumber, lettuce, pepper, and ryegrass, respectively.

Figure 5

Effect of CE and CK root exudates on seed germination index in recipient plants. (A–E) shows the effects of CE and CK root exudates on seed germination index and allelopathic effect index of radish, cucumber, lettuce, pepper, and ryegrass respectively.

Figure 6

Effect of maize root exudates on the growth of recipient seedlings. (A–E) shows the effects of CE and CK root exudates on the growth of radish, cucumber, lettuce, pepper and ryegrass respectively. BP indicates the blank control without any treatment, CE indicates the effect of maize root exudates on recipient plant seedling growth after C.etunicum colonization, CK indicates the effect of maize root exudates without AMF colonization on recipient plant seedling growth.

Figure 7

Allelopathic effect index of root exudates of Maize on the growth of seedlings of recipient plants. (A–E) shows the allelopathic effect index of CE and CK root exudates on the growth of radish, cucumber, lettuce, pepper, and ryegrass respectively. (a–f) in the figure respectively represent the allelopathic effect index of maize root exudates on the hypocotyl length, bacon length, fresh weight of hypocotyl, fresh weight of mating root, dry matter accumulation of hypocotyl, and dry matter accumulation of radicle of the recipient plant.

Figure 8

Effect of root exudates of CE and CK on mycelial growth of soil-borne diseases. (A–C) shows the effect of root exudates on the mycelial growth of Fusarium graminearum, Fusarium oxysporum and Rhizoctonia solani, respectively. (a–f) in each figure shows the mycelial growth of mycelium after adding CE root exudates with concentrations of 0, 1, 2, 3, 4, and 5 mg/ml for 5 days, and figures (g–l) shows the mycelial growth of mycelium after adding CK root exudates with concentrations of 0, 1, 2, 3, 4 and 5 mg/ml for 5 days; 0 mg/ml is the blank control (BP).

Figure 9

Differences in bacterial phylum level distribution in maize rhizosphere soils.

Figure 10

Interaction of bacteria in maize rhizosphere soil. (A) shows the interaction between bacteria in CE rhizosphere soil and (B) shows the interaction between bacteria in CK rhizosphere soil.

Figure 11

Pearson correlation between soil bacteria and soil enzyme vigor in maize root system. SHAD, SSC, SCL, SPPO, and SNEP are the activities of dehydrogenase, sucrase, cellulase, polyphenol oxidase, and neutral protease in soil respectively * represents significant difference between CE and CK (p<0.05), ** represents extremely significant difference between CE and CK (p< 0.01), *** represents extremelysignificant difference between CE and CK (p<0.001).