内生真菌对花生残茬腐解及土壤酚酸含量的影响

土壤中花生残茬是导致连作障碍的原因之一。为了探讨施加内生真菌Phomopsis liquidambari(B3)对加速花生残茬腐解、改善连作花生土壤环境、缓解花生连作障碍的作用及其可能机理,通过向土壤中添加花生(Archis hypogaea)残体,利用盆栽试验探讨了施加B3对花生残茬腐解率、土壤部分酚酸物质和酶活性的影响。结果表明:与CK相比,在萌发期和苗期,添加B3处理显著加快残茬腐解,提高纤维素木质素降解率,增加土壤中对羟基苯甲酸、香草酸和香豆酸的含量;在花生整个生育期,施加B3显著调节了土壤中漆酶、锰过氧化物酶(Manganese peroxidase,Mn P)、木质素过氧化物酶(Lignin peroxidase,Li P)和多酚氧化酶(Polyphenol oxidase,PPO)活性的动态变化,这种变化有利于花生残茬快速腐解和酚酸类化感物质的及时转化。开花期之后施加B3处理土壤酚酸含量显著降低,花生荚果增产19.9%。实时定量PCR结果表明内生真菌B3在土壤中30 d内可以被检测,并对复杂多样的酚酸类物质具有广谱高效的降解能力。由此说明,施加内生真菌B3可以显著加快连作土壤中花生残茬腐解,进而通过减少土壤酚酸含量来缓解由残茬腐解引起的连作障碍。

Effects of an endophytic fungus on decay of peanut residues and phenolic acid concentrations in soil

Peanut residue in the soil is considered to be an obstacle to peanut replanting. We aimed to understand the effect of applying an endophytic fungus [Phomopsis liquidambari (B3)]on accelerating peanut residue decay, improving the micro-ecological environment in the soil, and alleviating an obstacle to peanut replanting as well as its possible mechanism. We investigated the dynamics of peanut residue decay, phenolic acid concentrations, and enzyme activities during peanut growth in a pot experiment, where peanut residues were added into soil. Results showed that applying endophytic fungus B3 (treatment B3+) significantly accelerated the decay of peanut residue at the peanut germination and seedling stages; the decay rate increased by 12.0%-14.7% and the degradation rate of cellulose and lignin increased by 13.7%-17.8% and 21.2%-26.0%, respectively, compared with controls (CK). From the flowering to maturation stages, the decay rate of peanut residues gradually decreased in treatment B3+, but remained higher than that in CK. In addition, the concentrations of p-hydroxybenzoic acid (4-HBA), vanillic acid (VA), and p-coumaric acid (p-CA) in treatment B3+ were significantly greater than those in CK at the germination and seedling stages. This indicated that application of endophytic fungus B3 significantly promoted the release of phenolic acids during decay of peanut residues before the seedling stage.The concentrations of the three kinds of phenolic acids in CK were much greater than those in treatment B3+ from flowering to maturation stages, which were critical stages for peanut formation and disease control; a high concentration of phenolic acids was harmful to peanut growth. In treatment B3+, the activities of laccase, manganese peroxidase, lignin peroxidase, and polyphenol oxidase were all significantly greater than those in CK at the corresponding peanut growth period, and peanut pod yield increased by 19.9%, compared with CK. Increases in activities of soil enzymes, which were associated with decay of peanut residues in treatment B3+, should be beneficial to decay of peanut residues and accelerate conversion of harmful phenolic acid allelochemicals. However, there was no significant difference in the decay rate of peanut residues, phenolic acids concentrations, enzyme activities, and peanut pod yield between treatment B3 (applying sterilized endophytic fungus B3) and CK, indicating that the availability of the endophytic fungus B3 in soils is important. To further demonstrate the availability of B3 and its role in degradation of phenolic acids, a real-time quantitative polymerase chain reaction technique was used to monitor dynamics of endophytic fungus B3 during peanut growth. The biodegradability of B3 was also investigated in pure culture. The results showed that endophytic fungus B3 could adapt to a non-host environment and survive for about 30 d in soil containing higher amounts of peanut residues under natural conditions after detaching from its host. With 200 mg/L VA and p-CA as the sole carbon source, the degradation rate of VA for 96 h and p-CA for 120 h reached 99% after inoculation with B3, and the biomass of B3 increased gradually with time after inoculation. The results suggested that promoting the rapid degradation of peanut residues and regulating dynamics of phenolic acids should be important mechanisms for B3 to alleviate obstacles in peanut replanting.