多重土壤逆境下长白落叶松根系分泌的有机酸及其生态适应意义

本项目是在国家自然科学基金项目（30901145）资助下完成的，属于林学、土壤学和生态学交叉领域。揭示了贫瘠、干旱、重金属污染等不同土壤逆境（即胁迫，尤其多重胁迫）下，我国东北林区 先锋造林树种——长白落叶松（Larix olgensis）根系分泌有机酸的种类和数量动态，研究了不同胁迫条件下长白落叶松根系分泌的胁迫诱增性有机酸对苗木生态适应性的意义，并构建了土壤胁迫下苗木根 系有机酸分泌行为与生态适应关系的概念模式。 一定程度Pb、Cd污染增加长白落叶松人工林根系有机酸的分泌总量，但污染较重时降低。养分、Cd和Pb胁迫均促进长白落叶松幼苗根系有机酸种类增多，并增加有机酸分泌量，增加程度均因胁迫时间和胁迫程度而异。水分处理也影响有机酸分泌种类和数量，一般处理时间越长、胁迫较重时分泌种类越多。不同水分处理下，根系分泌的有机酸数量因水分处理水平和时间而异。草酸和柠檬酸等有机酸显著影响养分胁迫下长白落叶松幼苗的多种生理生化特性，细胞膜透性和MDA含量降低，SOD、POD活性提高，脯氨酸、可溶性蛋白、叶绿素含量增加，生长指标、存活率、根系形态指标、叶绿素 荧光参数、根系和叶片磷累积量和磷吸收效率，以及Fe的吸收运输均提高，因此，有机酸提高了苗木对养分胁迫土壤的耐性和适应力。一般在20d效果最好，最佳浓度为5.0或10.0mmol/L，柠檬酸效果强于草酸。外源有机酸对Cd/Pb胁迫下苗木生理生化特性、生长指标的影响与养分胁迫类似，大多数处理降低了细根和叶片 Cd 含量、提高了Pb量，但均促进苗木生长，说明外源草酸和柠檬酸等有机酸对长白落叶松抵御 Cd/Pb 胁迫具有积极作用。

This study was supported by the National Natural Science Foundation of China (Grant No. 30901145), and falls within the interdisciplinary field of forestry, pedology and ecology. It revealed the dynamics of types and quantities of organic acids secreted by the roots of Larix olgensis, a pioneer afforestation tree species in the northeastern forest region of China, under different soil stresses including infertility, drought, heavy metal pollution and other soil adversities (especially multiple stresses). The study investigated the ecological adaptability significance of stress-induced organic acids secreted by the roots of Larix olgensis under different stress conditions, and established a conceptual model of the relationship between root organic acid secretion behavior and ecological adaptation of seedlings under soil stresses.

To a certain extent, moderate Pb and Cd pollution increased the total amount of organic acids secreted by the roots of Larix olgensis plantations, but decreased when the pollution was severe. Nutrient, Cd and Pb stresses all increased the types and quantities of organic acids secreted by the roots of Larix olgensis seedlings, and the degree of increase varied with stress duration and intensity. Water treatment also affected the types and quantities of secreted organic acids. Generally, the longer the treatment time and the more severe the stress, the more types of secreted organic acids. Under different water treatments, the quantity of root-secreted organic acids varied with water treatment level and time.

Organic acids such as oxalic acid and citric acid significantly affected multiple physiological and biochemical characteristics of Larix olgensis seedlings under nutrient stress: they reduced cell membrane permeability and malondialdehyde (MDA) content, increased superoxide dismutase (SOD) and peroxidase (POD) activities, and increased proline, soluble protein and chlorophyll contents. Additionally, growth indicators, survival rate, root morphological indicators, chlorophyll fluorescence parameters, phosphorus accumulation and phosphorus uptake efficiency in roots and leaves, as well as Fe absorption and transport, were all improved. Therefore, organic acids improved the tolerance and adaptability of seedlings to nutrient-stressed soil. The optimal effect was generally observed at 20 days, with the optimal concentration of 5.0 or 10.0 mmol/L, and citric acid had a stronger effect than oxalic acid.

The effects of exogenous organic acids on the physiological and biochemical characteristics and growth indicators of seedlings under Cd/Pb stress were similar to those under nutrient stress. Most treatments reduced the Cd content in fine roots and leaves and increased Pb content, but promoted seedling growth, indicating that exogenous organic acids such as oxalic acid and citric acid had positive effects on Larix olgensis’s resistance to Cd/Pb stress.