混播方式对豆禾混播草地植物根系构型特征的影响

为从地下根系方面阐明红豆草与无芒雀麦型混播草地高效生产机制,将种群空间距离(行距)、种群空间作用方式(同行/异行/异行阻隔)作为地下根系竞争环境的变化因素,从根系的几何形态、拓扑结构和分形特征分析和比较2种牧草在竞争生境中根系构型的变化。结果表明:1)异行混播和行距增大使2种牧草地上生物量增加,无芒雀麦的根系生物量和根冠比也增加,但红豆草的根系生物量和根冠比变化不明显。2)异行混播+行距增大使无芒雀麦≤0.16 mm的细根增加,红豆草0.16~0.50 mm的根系增加,从而增加了根长、根表面积和比根长;异行混播+阻隔使得2种牧草的根系直径增加,从而使得根系体积和比根面积增加。3)2种牧草在不同混播方式下拓扑指数(TI)均接近于1,修正拓扑指数(q_a)大于0.5,分支结构均为鱼尾状分支;随着种群空间距离的增加,2种牧草根系的拓扑结构有向叉状分支方向发展的趋势。4)2种牧草的根长、根表面积与根系生物量和地上生物量均呈线性的正相关关系,其他根系形态参数与根系生物量相关性显著,而与地上生物量、根冠比相关性不显著。因此,种群的空间距离、种群的空间作用方式改变了混播群体地下根系的竞争环境,其通过形态、拓扑结构和分形的可塑性来响应种间竞争关系变化,采取了拓展空间和高效利用水分养分的生态适应策略。

Effects plant spacing pattern on root morphological and architectural characteristics of legume-grass mixtures

In order to investigate the effect of root competition on production in mixtures of Onobrychis viciifolia and Bromus inermis,plant spacing and population density effects were varied so as to manipulate the underground competitive environment.The geometric morphology,topological structure and fractal characteristics of the root system were used to analyze and compare the changes in root structure of the two forage species in the competitive environment.The results showed that:1) Mixed species sowing in alternate rows or increasing row spacing increased aboveground biomass of both forage species,and the root biomass and root ∶ shoot ratio of B.inermis were also increased,while the root biomass and root ∶ shoot ratio of O.viciifolia were not obviously changed.2) Mixed species seeding within rows,and spacing increases resulted in increased formation of fine root (diameter≤0.16 mm) in B.inermis,and of roots in the category (diameter≤0.16-0.50 mm) of O.viciifolia.Thus the root length,root surface area and ratio of root length to root biomass increased for both species.Mixed species sowing within rows with a root barrier between,resulted in increased root diameter of both forage species,so that the root volume and ratio of root surface area to root biomass increased.3) Under different mixed seeding patterns,the topological index (TI) of both forages was close to 1,the fixed topological index (qa) was greater than 0.5,and the branching structures were of the fishtail shape.With increasing space between rows,there was a tendency for the topology of the roots of both forages to adopt the forked branch topology.4) Root length,root surface,root biomass and aboveground biomass had a linear positive correlation between the two forage species,and there were significant correlations between root biomass a nd other root morphology parameters,and no significant correlations between root biomass and root ∶ shoot ratios.Therefore,row spacing,planting pattern of species within rows,and population density effects changed the competitive interaction between the underground root systems of mixed B.inermis and O.viciifolia stands.Plasticity of root morphology was the ecological adaptation strategy that enabled effective utilization of water and nutrients,and more effective exploration of the root growth space.