Retention, Fate And Allelopathy Variation Of Allelochemicals In Soil From Different Wheat (Triticum Aestivum L.) Varieties

Allelopathy or allelopathic effect, as typical natural phenomenon, implies that plants can produce secondary chemicals into the surrounding and subsequently affects the growth and development of other plants, including microorganisms, in the vicinity. Allelopathic effect is popular in agricultural ecosystem. At present, there is some information on wheat allelopathy. However, some details lack full explanation, such as the retention, fate and allelopathy variation of allelochemicals from wheat and wheat straw in soil depth.In this study four common winter wheat cultivars ("Bima No. 1","Fengchan No. 3","Ningdong No. 1"and"Xiaoyan No. 22") and their sraw were selected based on previous research results, using pot experiment and wheat straw mulching experiment under field condition, to research dynamics of allelopathic expression of wheat rhizosphere soil and 0-40 cm soil depth in the period of four consecutive growing seasons (seeding, returning-green, jointing, and tilling) and 10,25,45,60 days after wheat straw mulching . The regulation of allelopathic potential in the soil depth were studied, which can provide theoretical basis for making full use of allelopathic potential, reducing the relative effects of toxins and the influcence on the next crop. The results were displayed as the following:1. Spatial-temporal herterogeneity of allelopathic expression in wheat rhizosphere soil There is a significant difference on allelopathic expression in rhizosphere soil from different wheat varieties (P = 0.01). With growth and development process, allelopathic variation of rhizosphere soil closely depends on specific wheat cultivars. Soil allelopathic potential has an obvious stratification effect; generally 15 cm soil depth determines increase or decrease in key loci allelopathic trait. Based on normal distribution trait of allelopathic index, variation functions of four wheat varieties show that allelopathic expression in rhizosphere soils is independent, stochastic, and heterogeneous through mathematical modeling. It is concluded that four wheat varieties display four various functions :"Bima No. 1"for line model,"Fengchan No. 3"for spherical model,"Ningdong No. 1"for exponential model and"Xiaoyan No. 22"for Guass model. It shows that allelopathic expression of"Bima No.1"in rhizosphere soils increased gradually as the siol depth. Allelopathic dynamic of rhizosphere soil in"Ningdong No.1"exhibits significant topological trait adhering to scale level. Allelopathic expression indicats that"Ningdong No.1"displays enriched scattering fine roots, with efficient radii for cross radius as 5 cm and longitudinal radius as 14 cm. Allelopathic expression of"Fengchan No. 3"display spherical model, which ascended first and then descended with the level of soil. Allelopathic potential of"Xiaoyan No. 22"was Guass model with periodic changes and had a peak and trough, another its allelopathic background and spatial distribution is enhanced concerned with"Xiaoyan No. 22"during development process, which exhibits obvious spatial heterogeneity in surface soil (0-20 cm). From the present study, it is deduced that the spatial variability of topsoil quality index was stronger than subsurface soil and spatial variance of clay content increased with the distance of root, so the spatial and temporal heterogeneity of allelopathic expression of wheat rhizosphere soil is possibly related to surrounding soil environment.2. Spatial and temporal heterogeneity of allelopathic expression under the condition of wheat straw mulchingThe analysis of variance on dynamics of allelopathic expression of water extracts of soil with mulching wheat straw suggested that allelopathic index of four wheat straws were significantly higher than the control and had an obvious inhibitory action for the eceptor, it was proved that there were allelochemicals in wheat straw. The difference of allelopathic expression index between four wheats also reached a significant level and suggested that it had a significant relationship between allelopathic expression and wheat varieties. At the same time, the peak of allelopathic index most appearred at 15-25 d after wheat straw mulching and decreased to minimum at 60 d after wheat straw mulching, which indicated that allelopathic inhibition of wheat straw mulching disapreared after 60 d. The variances of allelopathic expression in the soil (0-40 cm) under the condition of wheat straw mulching were studied. During the whole mulching period, the peak of allelopathic index in"Bima No. 1"appeared in the soil depth of 5-15 cm, which indicated that allelochemicals of"Bima No. 1"mainly stranded in the surface soil; the peak of allelopathic index in"Fengchan No. 3"and"Ningdong No. 1"appeared in the soil depth of 15-25 cm, which indicated that allelochemicals of"Fengchan No. 3"and"Ningdong No. 1"migrate quicker than"Bima No. 1"; the allelopathic index of"Xiaoyan No. 22"is smaller and the peak appeared in the soil depth of 30-40 cm, which showed that allelochemicals of"Xiaoyan No. 22"was less and migratee faster...