摘要
选取10—40a不同代际的长期集约连栽杨树土壤为对象,从自毒作用的角度探讨人工林连栽障碍的原因与机理。实施了不同连栽代际的杨树人工林土壤对莴苣种子发芽和扦插杨树枝条生长的抑制活性的系统生物测定试验。结果表明,连栽杨树林的根际土壤比非根际土壤能够显著抑制莴苣种子萌发率。对Ⅰ、Ⅱ、Ⅲ代林根际土壤的浓度梯度试验都表明浸提液的质量浓度越大,对种子萌发的抑制性越强,其中Ⅲ代林处理液的浓度效应最明显。将Ⅰ、Ⅱ、Ⅲ代杨树林根际土壤配置成加营养液组与无营养液组两组对照水培溶液测定扦插杨树枝条的胚芽生长长度和根伸长长度。结果表明,III代林根际土壤处理液的胚芽生长长度和根伸长长度显著小于Ⅱ代林根际土壤处理液,Ⅱ代林处理又显著小于Ⅰ代林处理,Ⅰ代林处理液与对照组无显著差别,这种随林代增大、根际土壤对植株生长的抑制活性增大的趋势在加营养液组更为显著。本文确定了连栽土壤抑制活性的根际效应与浓度效应,为连栽杨树人工林的自毒作用研究提供了重要的实验依据,并推断连栽杨树人工林通过根系分泌物的方式在根际部分逐代积累自毒物质,由于自毒物质的浓度效应,Ⅰ代林阶段自毒效应不显著甚至促进林木生长;随着集约时间增长,到Ⅲ代林阶段自毒效应显著抑制杨树生长和更新。在集约抚育中,对土壤实施人工添加营养液的方式无法缓解其抑制性自毒作用,有可能加剧连栽障碍的产生。
Populus is one of the most important tree species in the economic plantations in China. However, poplar plantations are vulnerable to the continuous monocuhure problems. Previous studies have focused on low availability of soil nutrients and poor management as the possible causes for such decline. With the progress of chemical ecology, allelopathy and autotoxicity in forest plantations have been increasingly regarded as key triggers of the problems associated with continuous monoculture. To the best of our knowledge, few studies on poplar autotoxicity have been based on long-term samples, even though poplar monocuhure is common in planting practice. Moreover, experiments to compare the effects of low availability of soil nutrients and autotoxicity have not been attempted. In this study, we selected soil samples from three generations of poplar plantations, which included monoculture plantation as old as 40 years, and carried out systemic germination bioassays of lactuca sativaseeds and seedling growth tests on branch cuttings of poplar trees grown on soils in which successive generations of the plant had been grown. We identified the inhibitory activity of rhizosphere soil and the effects of concentration dependence and independence on nutrient inhibitory activity, which provided basic experimental evidence for further study on autotoxicity in continuously cropped poplar plantations. In a laboratory experiment, we contrasted the inhibitory activities of rhizosphere soil and non-rhizosphere soil on continuously cropped poplar plantations by determining lettuce seed germination in the soil extracts. The results showed that rhizosphere soil significantly inhibited lettuce seed germination compared to the non-rhizosphere soil. Concentration-controlled assays of rhizosphere soil extracts of generations I, II, and III（ GenI, Genii, and GenIII） poplar plantations were used to investigate the inhibitory dose attribution effect. The results showed that greater the soil extract concentration, stronger was the inhibitory effect on seed germination, suggesting that soil extracts inhibited seed germination in a concentration-dependent manner. The results also showed that concentration dependence was strongest in GenIII poplar plantations. The rhizosphere soil extracts of GenI, Genii, and GenIII poplar plantations were divided into two groups （an added-nutrition group and a non-nutrition group） of culture solutions, which determined the length of shoot and root in the poplar branch cuttings. The results showed that the length of shoot and root in the GenIII treatments were significantly lower than in the Genii treatments, whereas those in the Genii treatments were significantly lower than in the GenI treatments. There were no significant differences between the GenI treatments and the control group. This tendency toward inhibitory activity on plant growth increased with time （with the successive poplar generations） and was more prominent in the added-nutrition group. Our results, therefore, suggest that autotoxins accumulated through root exudates in the rhizosphere soil of continuously monocuhured poplar plantations. As a result of concentration dependence, autotoxins did not significantly inhibit the plant growth at GenI stage. With increasing years of monoculture, the autotoxic effects significantly inhibited the plant growth by GenIII stage and were especially significant in the soils that received artificial nutrition. Therefore, long-term monoculture practice and inhibitory autotoxicity of rhizosphere soil are likely to cause the continuous planting problems seen in poplar plantations.
出处
《生态学报》
CAS
CSCD
北大核心
2017年第12期4053-4060,共8页
Acta Ecologica Sinica
基金
国家自然科学基金资助项目(31470709)
国家林业公益行业专项资助项目(201504406)
江苏省优势学科资助项目(PAPD)
关键词
化感作用
连栽障碍
扦插
莴苣
单一种植
种子萌发
allelopathy
continuous planting obstacle
cutting branch
Lactuca sativa
long-term monoculture
seed germination
