Roles of endophytic bacteria in Suaeda salsa grown in coastal wetlands: Plant growth characteristics and salt tolerance mechanisms.

Salinity is a limiting factor in the growth of plants in coastal wetlands. The interaction of halophytes with salt-tolerant endophytes has been one of the major concerns in this area. However, the mechanism by which endophytes promote halophyte growth remains unclear. The growth and physiological responses of Suaeda salsa inoculated with endophytic bacteria (Sphingomonas prati and Sphingomonas zeicaulis) at 0 ‰ and 20 ‰ NaCl were studied. The results showed that Sphingomonas zeicaulis had stronger positive effects on the growth of Suaeda salsa under 0 ‰ NaCl, and Sphingomonas prati performed better under 20 ‰ NaCl. Sphingomonas prati inoculation increased the mean height, root length, fresh weight and dry weight by 45.43%, 9.91%, 82.00% and 102.25%, respectively, compared with the uninoculated treatment at 20 ‰ NaCl. Sphingomonas prati inoculation decreased MDA content by 23.78%, while the soluble sugar and soluble protein contents increased by 15.08% and 12.57%, respectively, compared to the control, at 20 ‰ NaCl. Increases in SOD and CAT in the Sphingomonas prati inoculation were 1.03 and 1.47-fold greater, respectively, than in the Sphingomonas zeicaulis inoculation, under 20 ‰ NaCl. Moreover, Sphingomonas prati and Sphingomonas zeicaulis had antagonistic interactions in Suaeda salsa according to the results of the "interaction equation" (most G values were negative). PCA, clustering analysis and the PLS model revealed two mechanisms for regulating plant salt tolerance by which Sphingomonas prati enhanced Suaeda salsa growth: (1) Sphingomonas prati improved intracellular osmotic metabolism and (2) Sphingomonas prati promoted the production of CAT in the antioxidant enzyme system and retained permeability. This study provides new insight into the comprehensive understanding and evaluation of endophytic bacteria as biological inoculants in plants under salt stress.

[Effect and Approach of Enteromorpha prolifera Biochar to Improve Coastal Saline Soil].

The use of biochar to improve adversity of soil has received increasing attention. Enteromorpha prolifera biochar is used to repair coastal saline-alkali soil, which can not only utilize Enteromorpha prolifera but can also increase the scale of the coastal land reserve. In this study, the method of soil culture experiments was used to explore the effect and pathway of 0%-3% addition of Enteromorpha prolifera on the improvement of saline-alkali soil. The results showed that the optimum preparation temperature of Enteromorpha prolifera biochar suitable for saline-alkali soil improvement was 400℃, and the optimum addition amount was 1.5%. At the optimum level, although the biochar had a negative effect, such as increasing soil salinity (0.12%) and pH (1.49%), it also produced positive effects, such as reducing soil Na+/K+ by 55.73%, increasing mineral content, and improving water conductivity. Enteromorpha prolifera biochar improved soil physicochemical and biological properties, increased nutrient content, enhanced microbial activity, improved soil nutrient availability, and produced positive effects. These positive effects were characterized by reducing soil bulk density by 11.35%, increasing organic matter by 42.64%, increasing the proportion of organic carbon in total carbon by 3.84 times, increasing the proportion of available phosphorus in total phosphorus by 4.15 times, and increasing soil invertase activity by 2.39 times, urease activity by 1.18 times, and catalase activity 1.50 times. Therefore, the positive effect of Enteromorpha prolifera biochar on saline-alkali soil is more than negative, and it can be used for the improvement of coastal saline-alkali soil. This study provides a new path for the resource utilization of Enteromorpha prolifera and the improvement of the ecological environment of coastal saline-alkali soil.