红壤穿透阻力对季节性干旱的影响机制及调控意义

Seasonal drought is an important factor that impairs the agriculture in red soil region of China. The poor physical properties of the red soil usually intensify the drought development and increase the danger. The red soil penetration resistances, which will increase rapidly with soil drying, usually restrict crop root dipping into and distributing in deep soil layer.This may reduce root water uptake from the soil, and then strengthen the crop water stress. On the other hand, the soil penetration resistances may help the plant to avoid severer drought, by the feedback of the resistance stress signal in the early drying stage to regulate the crop growth, and by the reduction of photosynthate and water consumption in root system. However, it is unclear how the red soil penetration resistances affect the seasonal drought. It is also questionable to relieve the seasonal drought by the soil penetration resistance regulation with proper soil tillages. In this research plan, we will first investigate the penetration resistance properties of red soils, and then study their effects on the seasonal drought. Using the red soil samples with different penetration resistance properties, several experiments are designed to regulate the soil penetration resistance, in lab by compaction and in field by tillage. During the crop growth in the experiments, both the soil water contents and soil penetrations are measured simultaneity and modeled in pots and in field plots. At the same time, the crop root and leaf morphologies, water physiologies, soil water uses, plant water stresses are also measured at a certain frequency. In this way, the effects of soil penetrations resistance on the crop will be distinguished from that of soil drought, and the effects on the soil-plant water relation will be revealed. This research project is designed to demonstrate the soil penetration resistance effects on the seasonal drought in red soil region, as well as to prove the effects of soil penetration resistance regulation methods on crop drought relief. The results are important in understanding the seasonal drought mechanism and drought-defense measures in red soil croplands.

季节性干旱是制约红壤区农业生产的重要因素，而红壤不良的物理性质对干旱的形成和发展起重要作用。红壤穿透阻力较大，在干旱过程中急剧增加，抑制根系下扎并降低吸水能力，这既可能加剧作物干旱，也可能通过减少根系本身对同化物和水分的消耗、早期阻力胁迫信号反馈调节作物生长而避免更严重干旱。红壤阻力对季节性干旱的影响和机制尚不清楚，通过耕作调控红壤阻力而减轻作物干旱的意义也存疑虑。本项目首先研究红壤的阻力特性和预报模型，然后采用不同阻力特性的红壤进行筒栽试验、设置耕作措施调控红壤阻力进行田间试验，现场监测并模拟干旱过程中土壤阻力和水分动态，同时测量作物根/叶的形态和水分生理指标、作物水分胁迫指数等，研究红壤阻力和土壤干旱对作物的胁迫和耦合作用，进而分析红壤阻力对田间作物水分关系的影响。研究结果可望探明红壤阻力对季节性干旱的影响大小和调控作用，对进一步揭示红壤季节性干旱机制和评价干旱防御措施具有重要意义。

红壤的物理性质对季节性干旱形成和发展起重要作用。本项目研究第四纪红色黏土发育的红壤穿透阻力对作物水分胁迫的影响，以揭示红壤季节性干旱形成机制和调控原理。在开展了室内土壤穿透阻力测试与模型模拟、室内筒栽玉米阻力和水分胁迫试验之后，主要在田间进行了5年的小区玉米试验，重点研究了不同穿透阻力（由4种耕作方式实现）、不同干旱程度（由灌溉量控制）及其共同作用下，玉米作物的水分关系和干旱致灾程度，取得了有新意的研究结果和进展：1）黏质红壤田间穿透阻力时空变化幅度大，旱季的20 cm根系层常常超过临界值2 MPa，土壤阻力大小与容重和含水量呈幂函数关系。2）土壤穿透阻力限制了玉米根系空间分布，显著降低了根系层特别是15 cm深度以下的根系质量分布密度，也降低了根系水平空间分布密度。3）土壤穿透阻力改变了玉米作物根系形态，包括降低根长、增大根径、减少细根比例，而干旱有相反的作用。4）从细胞尺度揭示了干旱和阻力胁迫下根尖形态变化特征，干旱促进了根尖皮层细胞分裂，而穿透阻力增大细胞尺寸，使作物单根消耗更多同化物、破坏根细胞形态而加剧干旱胁迫。研究结果解释了土壤干旱对作物根系影响表观上可能不一致的原因。5）穿透阻力提高了红壤萎蔫含水量、降低作物水势、增大作物水分胁迫指数、加剧干旱胁迫，显著降低玉米籽粒产量，高穿透阻力是黏质红壤季节性干旱严重的重要原因。6）常规耕作和深耕不仅能降低根系层土壤穿透阻力，同时也提高了干旱时的土壤含水量，显著减轻干旱胁迫，提高了干旱处理的玉米产量，一定程度上缓解了干旱胁迫。研究结果进一步揭示了红壤季节性干旱的形成机制，穿透阻力在作物干旱胁迫致灾中起到了重要的作用；研究结果揭示了耕作措施改善红壤作物受旱的机理，肯定了耕作措施在减缓红壤季节性干旱中的作用，为调控红壤季节性干旱提供了一条可能的途径。