蚕豆增加直径为0.3～0.7mm的中等根系根长适应土壤异质养分供应

Increment of root length of 0.3–0.7 mm in diameter in fababean contributes to the adaptation to heterogeneous soil nutrients supply

【目的】土壤养分通常呈异质分布。蚕豆根系具有很强的养分活化能力,苗期蚕豆的生物量积累对土壤养分供应不敏感,研究蚕豆根系形态对异质养分供应的响应,为挖掘作物高效利用土壤养分的生物学潜力提供理论依据。【方法】采用盆栽试验,设四个处理:均质供应低量氮磷钾养分;异质供应低量氮磷钾养分;均质供应高量氮磷钾养分;异质供应高量氮磷钾养分。测定蚕豆生物量、根系形态特征、根际过程和地上部养分吸收。【结果】蚕豆地上部生物量在3.0~4.0 g/pot之间,根系生物量是地上部生物量的20%左右,四个处理间没有显著差异。在低养分土上,异质养分供应处理的蚕豆总根系长度比均质养分供应高46.0%。异质养分供应诱导了中等根系(0.3~0.7 mm)的增生,增加了根系总长度。在高养分土上,未供应养分一侧的蚕豆根系长度为1.7 m/pot,明显高于供应养分的一侧54.5%,后者与均质养分供应的根系长度无明显差异。无论低养分还是高养分土处理,直径为0.3~0.7 mm的中等根系都是蚕豆根系的主体,分别占总根长的67.5%和73.1%。蚕豆比根长在40.0~65.0 m/g之间。在低养分土上,异质养分供应蚕豆两侧的比根长显著高于均质养分供应处理41.4%和43.8%,但两侧比根长并无明显差异,说明异质养分供应能够减少根系的直径,增加根系的表面积。蚕豆根际酸性磷酸酶活性在PNP 0.22~0.53μmol/(g·h)(干土)之间。在低养分土中,均质与异质供应养分两侧的根际磷酸酶活性并无显著性差异。蚕豆根系分泌的有机酸阴离子种类有苹果酸阴离子、柠檬酸阴离子和琥珀酸阴离子,每种有机酸阴离子浓度在处理间无明显差异。所有处理蚕豆地上部养分浓度均在养分亏缺临界浓度之上。养分供应方式和强度对蚕豆地上部的氮磷钾浓度和吸收量没有显著影响。【结论】蚕豆根系能够感知土壤养分供应的状况,改变不同直径根系的比例和0.3~0.7 mm直径根系的长度,增强吸收土壤养分的能力。

【Objectives】Soil nutrients are distributed heterogeneously along soil profile. Fababean has been found a strong capacity to mobilize soil nutrients, and fababean seedlings are insensitive to soil nutrients supply.Studying the responses of fababean root morphology to heterogeneous and low nutrients supply will help exploring biological potential of crops to use soil nutrients efficiently. 【Methods】A pot experiment was carried out inside greenhouse with four treatments including homogenous and heterogeneous nutrients supply in low and high fertility soils. Biomass, root properties, rhizosphere processes and nutrients uptakes were determined.【Results】The shoot biomass ranged from 3.0 to 4.0 g/pot in all the treatments, and the root biomass were only about 20% of the shoot biomass. There were no significant differences on biomass accumulation among treatments. Fababean grown in the low fertility soil had a higher total root length, and the total root length with heterogeneous nutrients supply was 46.0% higher than that with the homogeneous nutrients supply. The heterogeneous nutrients supply significantly stimulated proliferation of roots with middle root diameter（0.3–0.7 mm）, which was the main contribution to the increment of the total root length. In the high fertility soil, the root length of the no nutrient supply side was 1.7 m/pot, which was higher than that in the nutrients supply side by 54.5%. The latter was similar with the root length in the treatments of homogeneous nutrients supply. The proportions of root length with middle diameter（0.3–0.7 mm） were 67.5% and 73.1% of the total root length in the low and high fertility soils, respectively. The specific root length of fababean was between40.0–65.0 m/g in all the treatments. In the low fertility soil, the specific root lengths in both sides of the treatments with heterogeneous nutrients supply were higher than that in the treatments with homogenous nutrients supply by 41.4% and 43.8%, respectively. There were no significant differences on the specific root length between two sides of the treatments with heterogeneous nutrients supply. The results indicated the heterogeneous nutrients supply reduced the diameter of roots and increased root surface. The activity of acid phosphatase（APase） in rhizosphere ranged from PNP 0.22 to 0.53 μmol/（g·h）, dry soil. There were no significant differences on the activity of APase between two sides of the treatments with heterogeneous nutrients supply in low fertility soil. Malate, citrate and succinate were found in rhizosphere of fababean. The types of nutrients supply did not affect the concentrations of carboxylates in rhizosphere. The nutrients concentrations of shoot were higher than the critical levels for maximal growth in all the treatments. The nutrients concentration in shoots had no response to the nutrients supply. 【Conclusions】Roots of fababean without nutrients deficiency can modify the proportion of roots with different diameters based on soil nutrients status to improve absorption of soil nutrients.