黄土高原旱作小麦化感表达在根际土中的时空异质性研究

Spatio-temporal heterogeneity of allelopathic expression in rhizosphere soil under different winter-wheat cultivars on dryland Loess Plateau

采用盆栽试验基于统计学方法，对4种不同品种小麦在4个连续生长期根系表层土壤（0—20cm）化感潜势时空异质性进行了研究。结果表明：不同品种小麦之间根系土壤化感潜势差异极显著（P=0．01），随生育期变化。化感潜力的变异与品种有关，一般15cm为普通小麦耕层土壤化感潜力的转折位点。变异函数分析显示，4种小麦根系土壤化感潜势变化是独立、随机、异质性的。“碧玛1号”、“丰产3号”、“宁冬1号”、“小偃22号”变异函数理论模型分别为线形模型、球型模型、指数模型和高斯模型。其中“小偃22号”的化感背景值和化感潜力空间结构比随生育期增大，导致0～20cm表层土壤化感表达具有高度的空间异质性。4种普通小麦的化感表达均存在时空异质性，其中“宁冬1号”的表层土壤化感表达具有很好的分形特征，其空间分布格局的变异存在尺度依赖。“宁冬1号”化感潜势在表层土壤的空间分布趋于离散表达，化感潜力的有效纵向半径和有效延深半径分别为5cm和14cm。这种时空变异格局可能与根系发育特征、根系翻转运动及土壤环境有关，化感实施过程可能为熵增过程。根系表层土壤化感潜势时空异质性的研究可为监测化感作用实施，定位有效化感物质和合理利用土壤化感潜势提供理论依据，为根系分泌的化感物质可能存在迁移转化的机制奠定基础。

Using pot experiment, spatial and temporal heterogeneity of allelopathic potential of living-roots of four common winterwheat cultivars in amended soil of the Loess Plateau of China was investigated for four consecutive growing seasons through bioassay aqueous extraction from the top soil （0 -20 cm） in conjunction with typical statistics theory. There is a significant difference （P=0.01 ） in allelopathic expression in rhizosphere soil among different wheat cuhivars. With regard growth and development processes, rhizosphere soil allelopathic variability largely depends on specific wheat cuhivars. Interestingly though, 15 cm soil depth determines increase or decrease in key loci allelopathic trait. Based on normal distribution traits of allelopathic index, variability functions of the four wheat cultivars show that allelopathic expression in rhizosphere soil are independent, stochastic and heterogeneous. Through mathematical modeling, it is concluded that the four wheat cuhivars 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. Specifically, allelopathic background and spatial distribution are enhanced with regard ＂Xiaoyan No. 22＂ during development, which exhibits obvious spatial heterogeneity in the top-soil （0 -20 cm）. Among the spatial and temporal heterogeneity of the four wheat cultivars, allelopathic dynamics of rhizosphere soil in ＂Ningdong No. 1 ＂ exhibits significant topological trait, adhering to scale factor. Allelopathic expression indicates that ＂Ningdong No. 1＂ displays an enriched scatter of fine roots, with efficient radii （with average transverse radius of 5 cm and longitudinal radius of 14 cm）. From the present study, it is deduced and hypothesized that spatial and temporal heterogeneity of allelopathic expression of wheat rhizosphere soil is possibly related to root growth conformation, turnover movement and surrounding soil conditions. In fact allelopathic explosion leads to entropy enrichment. The study provides the theoretical base for monitoring the fate of allelochemicals, and the utilization of allelopathic potential in rhizosphere soils. Meanwhile, it also confirms the popular theory of shifting and transformation of root exudates, including allelochemicals with allelopathic evidence.