Moss Biochar Facilitates Root Colonization of Halotolerant Halomonas salifodinae for Promoting Plant Growth Under Saline–Alkali Stress

Abstract

The utilization of the widely distributed saline–alkali lands by planting forage grasses is a hot topic. However, the promotion of plant growth remains a great challenge during the exploration of this stressful soil. While halotolerant bacteria are beneficial for plants against saline–alkali stress, their stable colonization on plant roots should be further strengthened. In this study, we investigated the effect of moss biochar on the root colonization of the exogenous halotolerant Halomonas salifodinae isolated from saline lake sediments. During the incubation with the bacteria, the biochar strongly bound the bacterium and induced biofilm formation on the biochar surface. When the biochar and the bacterium were added into the culturing soil of the forage grass Medicago sativa, the biochar remarkably assisted the root binding and biofilm formation of this bacterium on the plant roots. Under the biochar–bacterium combined treatment, the numbers of total bacteria, halotolerant bacteria, and nitrogen-fixing bacteria increased from 105.5 CFU/g soil to 107.2 CFU/g soil, from 104.5 CFU/g soil to 106.1 CFU/g soil, and from 104.7 CFU/g soil to 106.3 CFU/g soil, respectively. After 30 days of culturing, the biochar and the bacterium in combination increased the plant height from 10.3 cm to 36 cm, and enhanced the accumulation of chlorophyll a, reducing sugars, soluble proteins, and superoxide dismutase in the leaves. Moreover, the combined treatment increased the activity of soil enzymes, including peroxidase, alkaline phosphatase, and urease. Meanwhile, the levels of various cations in the rhizosphere soil were reduced by the combined treatment, e.g., Na+, Cu2+, Fe2+, Mg2+, Mn2+, etc., indicating an improvement in the soil quality. This study developed the biochar–halotolerant bacterium joint strategy to improve the yield of forage grasses in saline–alkali soil.