三种根系分泌脂肪酸对花生生长和土壤酶活性的影响

为了探讨花生连作后土壤中脂肪酸类物质的累积与花生连作障碍间的关系,为花生连作障碍机理的研究提供新的理论依据,以田间土壤为介质,采用盆栽试验的方法研究了花生根系分泌物中3种长链脂肪酸,即:豆蔻酸、软脂酸和硬脂酸的混合物,对花生植株生长、产量和土壤酶活性的影响。结果表明,当土壤中脂肪酸的初始含量较低时(80 mg/kg土),对花生植株的生长和产量有微弱的促进作用(P>0.05),当土壤中脂肪酸的初始含量较高时(160 mg/kg土和240 mg/kg土),显著抑制了花生植株的生长和产量(P<0.05)。叶片叶绿素含量、根系活力、土壤酶(蔗糖酶、脲酶、磷酸酶)活性在低脂肪酸含量处理下升高,在高脂肪酸含量处理下显著降低(P<0.001)。光合产物、根际有效养分的减少和根系养分吸收能力的降低,可能是导致花生植株生长和产量降低的原因之一。花生连作土壤中豆蔻酸、软脂酸和硬脂酸的累积与花生的连作障碍有着密切关系。

The effects of three root exudated fatty acids on peanut (Arachis hypogaea L.) growth and soil enzymes activities

Continuous cropping obstacle is a common problem in agriculture and autotoxicity of allelochemicals plays a major role in this problem of many crops. In field situations, allelochemicals (autotoxins) must accumulate and persist at phytotoxic levels and comes in contact with the target plant. The potential of plant allelopathy includes the combined effects of all allelochemicals released. Peanut (Arachis hypogaea L.) is a kind of oil crop and highly vulnerable to continuous cropping obstacle. In a previous study we showed the autotoxic potential of peanut root exudates. We have isolated and identified a number of compounds from the root exudates of peanut seedlings including long-chain fatty acids. Long-chain fatty acids are suggested as a group of potential allelopathic compounds. The object of this study was to discuss the relationship between the accumulation of fatty acids in field soil and peanut continuous cropping obstacle, and offer some new theoretical bases for the mechanism study of peanut continuous cropping obstacle. We investigated the synergetic effects of three long-chain fatty acids (Tetradecanoic, Hexadecanoic and Octadecanoic acids) in the root exudates of peanut (Arachis hypogaea L.) on peanut plant growth, production and soil enzyme activities. A simulation experiment in pot culture was carried out using the field soil as the growth medium. It was found that their low content (80 mg/kg soil) slightly stimulated the growth and production of peanut (P > 0.05), but their high contents (160 mg/kg soil and 240 mg/kg soil) significantly decreased the growth and production (P < 0.05). With increasing fatty acid content in the soil, growth of peanut plants was inhibited and the degree of inhibition increased in a dose-dependent manner. At flowering stage when fatty acids were at their highest content (240 mg/kg soil), plant height, shoot fresh weight, root fresh weight and total biomass were reduced by 14.4%, 22.0%, 30.9% and 23.7%, respectively. When the content of fatty acids was 160 mg/kg soil and 240 mg/kg soil, peanut pod production was significantly decreased by 15.4% (P = 0.021) and 22.4% (P = 0.005), respectively. Chlorophyll content in peanut leaves, root activity, soil enzymes (sucrase, urease and phosphatase) activities were slightly promoted at low content of fatty acids in soil but were suppressed at high conctents (P<0.001). At the highest fatty acid content (240 mg/kg soil), leaf chlorophyll content and root activity were reduced by 21.0% and 31.4% at the seedling stage and 22.7% and 33.3% at the flowering stage. At the flowering stage, sucrase, urease and phosphatase activities were reduced by 25.3, 25.4 and 26.1%, respectively, by fatty acids at their highest tested content (240 mg/kg soil). Decreases in photosynthates production, nutrients uptake and rhizosphere nutrients availability were one of the possible reasons which could decrease the peanut growth and production. The accumulation of three long-chain fatty acids, tetradecanoic, hexadecanoic and octadecanoic acids, in field soil has close relationship with peanut continuous cropping obstacle.