The spatial and seasonal variation characteristics of fine roots in different plant configuration modes in new reclamation saline soil of humid climate in China

• More than 60% of FRB were concentrated in the soil depth range between 0 and 20 cm.
• The salinity should be below 1.5 mS/cm, which was conducive the growth of plant roots.
• Tree-shrub stand model may be the best configuration mode for ecological restoration in saline soil.

In order to study the spatial and seasonal variation characteristics of fine roots in a salinization area, we examined three configuration modes through soil samples collected via soil drilling. Fine roots biomass (FRB) showed significant differences among the different modes. Significant differences of FRB were observed at a soil depth of 0–60 cm in the three modes (p < 0.05). More than 60% of FRB were concentrated in the soil depth range between 0 and 20 cm, and decreased exponentially as soil depth increased. Specific root length (SRL) and fine root length density (FRLD) showed a similar vertical distribution pattern to the FRB. In all three modes, FRB showed significant seasonal differences (p < 0.05). FRB was highest in July, and showed the bimodal variation, while monthly variation of FRB in the root diameter range of Φ ≤ 2 mm and 2 mm < Φ ≤ 5 mm showed significant positive correlations (p < 0.05). Total FRB was highest in the tree-shrub stand model (TSSM). Due to the effect of salinity, FRB showed significant differences in different soil depths and resulted in FRB spatial niche separation. We found that high salt content salt had an obvious inhibitory effect on the distribution of FRB. Therefore, salinity should be below 1.5 mS/cm, which was conducive the growth of plant roots. The results indicated that TSSM had the highest FRB, SRL, and FRLD, and may have the strongest effect on salt suppression and salt control in saline-alkali land.