压砂西瓜氯离子毒害临界值及氮、氯互作机制研究

The watermelon planting in gavel-sand-mulched field is one of the most important industry of Ningxia and is also the main way of money-making for farmers on dry land. The bottleneck problem of drought and lack of water in gravel-sand-mulched watermelon industry was greatly alleviated by using the underground brackish water resources. However, long-term brackish irrigation can lead to the accumulation of chlorine ions in the soil, which can seriously affect the growth and fruit quality of "chlorination crops" watermelon, and even cause chloride toxicity. By hydroponics experiment, soil-culture experiment and field experiment, this project is to study the response of gravel-sand-mulched watermelon to chlorine ion concentration, define the demand and toxicity characteristics of watermelon to chlorine ion, and then establish the diagnostic criteria of chloride toxicity. Also, the accumulation, distribution and migration of chlorine ions in soil- plant system of watermelon in gravel-sand-mulched land and its response to the growth and fruit quality of watermelon will be discussed to determine the critical value of chloride toxicity both in soil and plant when the growth of watermelon is inhibited. In addition, the relationship between nitrogen and chloride ions in watermelon plant will be analyzed to clarify the interaction mechanism between nitrogen and chlorine. The results can provide theoretical basis for safe and reasonable utilization of brackish water in gravel-sand-mulched land, preventing and controlling the chloride toxicity of watermelon, thus providing guarantee for high yield and quality production and sustainable utilization of gravel-sand-mulched land.

压砂西瓜是宁夏的特色优势产业和干旱地区农民脱贫致富的主要途径。利用地下微咸水资源有效缓解了压砂西瓜产业干旱缺水的瓶颈问题，然而，长期的微咸水灌溉会导致土壤中累积大量的氯离子，严重影响“忌氯作物”-西瓜的生长和果实品质，甚至产生氯离子毒害现象。本项目拟通过水培实验、土培试验和田间试验相结合的方法，探讨压砂西瓜对氯离子浓度的响应，明确西瓜对氯离子的需求程度和毒害特征，制定西瓜氯离子毒害诊断标准；阐明氯离子在压砂地土壤-西瓜植株系统的累积、分布、迁移规律，及其对西瓜生长和果实品质的响应，提出压砂西瓜生长受抑制时的土壤和植株氯离子临界值；探索氮素与氯离子在西瓜植株体内的消长关系，明确氮、氯之间的相互作用机制。研究结果可为压砂地安全合理利用微咸水，防止和调控西瓜氯离子毒害供理论依据，从而为压砂西瓜高产优质生产和压砂地的可持续利用提供保障。

针对压砂地西瓜种植过程中长期使用含氯地下微咸水灌溉引起的土壤次生盐渍化和氯离子毒害问题，通过模拟培养试验和田间定位试验，探讨了压砂西瓜对氯离子浓度的响应、需求程度和毒害特征；阐明氯离子在压砂地土壤-西瓜植株系统的累积、分布、迁移规律，提出压砂西瓜生长受抑制时的土壤和植株氯离子临界值，并探索了氮和氯的相互作用机制，阐明氮素缓解西瓜氯毒害的生理机制。取得的主要结果如下：（1）从浓度来看，0~40 mmol·L-1氯对西瓜植株生长发育有促进作用，当外源氯浓度超过85.34 mmol·L-1，西瓜植株氯浓度为121.12 mmol·L-1时，西瓜幼苗的生长发育受到抑制，并产生毒害现象；从施用量来看，氯水平在0~120 kg·hm-2时对西瓜植株的生长无明显抑制作用，氯水平超过120 kg·hm-2时会抑制土壤酶活性，降低氮、磷、钾的供应能力，并促进氯离子在植株体内大量累积，从而抑制茎叶生长，影响叶绿素合成并降低光合速率，降低西瓜产量和糖酸比。西瓜植株的耐氯临界值为86.55~89.60 g·kg-1，土壤氯临界浓度为128.80~141.0 mg·kg-1，临界施氯量为120 kg·hm-2。（2）氮、氯之间具有相互抑制作用，适量施氮可促进土壤酶活性，改善微生物群落结构，促进氮、磷、钾养分供应能力，从而缓解氯对西瓜的毒害作用，进而促进西瓜生长和养分吸收，提高产量并改善品质。（3）氯盐胁迫下，适量施氮有助于西瓜建立良好的根系构型，提高根系渗透物质含量，降低细胞渗透势，减少根系丙二醛含量，维持较强的根系活力，增加根系生物量和干物质，从而缓解高浓度氯盐对西瓜生长的抑制作用。同时，可促进植株对氮素的吸收利用率，并通过提高离子稳态、渗透调节物质、抗氧化酶活性及降低氧化损伤等增强西瓜植株的苗生理抗性，缓解了氯盐胁迫对西瓜的生长抑制，氯盐胁迫下综合氮吸收利用与生理抗性，本研究的推荐氮肥施用量为0.16~0.18 g/kg。.该成果可为压砂地安全合理利用微咸水和合理施用氮肥，防治和调控西瓜氯离子毒害供理论依据，从而为压砂西瓜高产优质生产和压砂地的可持续利用提供保障。项目执行期间，培养研究生8名，发表论文20篇，授权发明专利1项。