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

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 between 40.0-65.0 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.