西北黄土高原雨养农业区长期覆膜苹果树根系生长障碍的进程与机理

Roots were the foundation for growth and development of the apple tree,the results indicated that long-term film covering treatment In rainfed agricultural region of northwest loess plateau,film covering can improved the rhizosphere ecological environment, but roots in the number and physical activity declines,move concentrated distribution area up, phenolic accumulation were appeard.Imply that increasing of phenolic were closely related to the soil ecological changes by the long-term film covering,and react on secondary metabolism and expression of physiological activity of roots.In this project, we plan to uncover the relationship of film covering and rhizosphere ecological environment changes in long-term film covering orchards, by using the pure apple tree stand as control. We track apple-root physiological metabolism trends for a long-term; Analyze the secretion of phenolic by ASE-HPLC , reveal Secondary metabolic activity and behavior characteristics of phenolic; Test changes of soil Remainder decay, secreting characteristic and allelopathy of phenolic under different treatment, discuss concentration effects and threshold value of phenolic to apple roots. Indicate phenolic secretory characteristics have a role in processes and mechanisms of roots growth disorder in the ecological environment in long-term film covering orchard. Finally, our study is to mine the regulation mechanism of the seeondav metabolltes and mechanism of root growth by harmful phenolic acids in long-term film covering orchard in theory.Provides scientific basis for perfect reasonable implementation of the film covering dry farming technique in practice.

根系是苹果树生长发育的基础，西北黄土高原雨养农业区长期覆膜试验中发现，覆膜可改善根际生态环境，但出现细根大幅减少、生理活性下降、集中分布层上浮，并伴随酚酸大量累积的现象，暗示着根际酚酸含量的上升与长期覆膜土壤生态变化密不可分，并反作用于根系次生代谢及生理活性的表达。本项目对不同覆膜年限红富士苹果细根及土壤生态的监测，明确长期覆膜对根系生长动态、土壤生态环境的改变机制；运用ASE-HPLC技术对根区土壤累积酚酸进行测定，揭示根系次生代谢活性及酚酸环境行为的变化特征；对植物残体在不同覆膜年限下的腐解特性、酚酸的分解释放规律、化感作用进行分析，及不同种类酚酸对苹果根系的致害浓度效应与作用阈值进行研究，与大田试验结果相互验证。揭示酚酸分泌特性在长期覆膜下影响根系生长障碍的过程与机理。为丰富长期覆膜下根系次生代谢产生酚酸及有害酚酸对根系的作用机理，完善旱区苹果种植的保墒技术合理实施提供科学依据。

西北黄土高原雨养农业区长期覆膜试验中发现，覆膜可有效节水保墒，但长期实施苹果细根大幅减少、生理活性下降，并伴随酚酸大量累积的现象。本研究设置清耕 （CK）、覆膜2年、4年、6年四个处理，对苹果园根际土壤生态环境、根系生长特性、酚酸积累及其化感自毒效应进行研究。结果表明，2Y改善土壤理化特性，提高土壤稳定性，形成密集横向分枝细根提高原位土壤养分利用，促进深层细根延伸生长；6Y改变表层土壤质地与孔隙结构，呈“隐性”退化；淀积黏化破坏亚表层土壤质地、团聚体，呈“隐型”退化；POC、EOC和有机碳总量分别为CK的94.83%、46.88%和88.08%，有机碳储量为CK的83.41%。可见6Y土壤结构、肥力均受破坏，以促进根系延长、分支的方式提高表层土壤细根生物量积累、吸收功能表达；抑制亚表层细根生长，根系垂直分布中心相比CK提升7.11—18.11 cm，根长、表面积、体积、活力和根比导水率仅为CK的50.09%、61.86、68.82%、73.2%和37.12%；细根形成大管径、厚管壁、低密度导管结构，增加输水安全性。苹果园根际土壤苯甲酸含量最高，占比36.08—80.57%，酚酸总量与根系生长呈正相关，2Y>4Y>CK>6Y。6Y根系腐解产生苯甲酸含量、土壤滞留量均高于CK，因此6Y大田土壤苯甲酸为CK的388.81%。山定子种子和幼苗对苯甲酸的化感、自毒作用敏感于海棠，均表现为低浓度促进，高浓度抑制。山定子种子、幼苗抑制浓度为5 mg/kg和10 mg/kg，海棠种子、幼苗80 mg/kg和600 mg/kg。苯甲酸抑制根系数量、长度、表面积，促进根系增粗，增加栓塞脆弱性，降低根系活力。由此酚酸的自毒作用与亚表层土壤“隐型”退化共同危害苹果根系生长。本研究对长期覆膜苹果根系生长障碍的机理与进程开展深入探讨，有利于为优化西北旱区苹果栽培保墒技术的合理实施提供科学依据。

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