Silicon (Si) has been known to enhance salt resistance in plants. In this experiment, 4-weeks-old alfalfa seedlings were exposed to different NaCl concentrations (0–200 mM) with or without 2 mM Si for two weeks. The results showed that NaCl-stressed alfalfa seedlings showed a decrease in growth performance, such as stem extension rate, predawn leaf water potential (LWP) and the chlorophyll content, potassium (K + ) concentration, as well as the ratio of potassium/sodium ion (K + /Na + ). In contrast, NaCl-stressed alfalfa seedlings increased leaf Na + concentration and the malondialdehyde (MDA) level, as well as the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in alfalfa leaves. Besides, exogenous Si application enhanced photosynthetic parameters of NaCl-stressed alfalfa seedlings, which was accompanied by the improvement in predawn LWP, level of chlorophyll content, and water use efficiency (WUE). The Si-treated plants enhanced salinity tolerance by limiting Na + accumulation while maintaining K + concentration in leaves. It also established K + /Na + homeostasis by increasing K + /Na + radio to protect the leaves from Na + toxicity and thereby maintained higher chlorophyll retention. Simultaneously, Si-treated plants showed higher antioxidant activities and decreased MDA content under NaCl stress. Our study concluded that Si application enhanced salt tolerance of alfalfa through improving the leaves photosynthesis, enhancing antioxidant performance and maintaining K + /Na + homeostasis in leaves. Our data further indicated exogenous Si application could be effectively manipulated for improving salt resistance of alfalfa grown in saline soil.

A set of four experiments was conducted to develop methods for screening oat tolerance to salt and alkali and the following results were obtained. (1) In experiment 1, 68.5 mmol L-1 salt and 22.5 mmol L-1 alkali were identified as appropriate concentrations for determining oat tolerance to salinity and alkalinity during germination. (2) These concentrations were used in experiment 2 to screen 248 oat genotypes and 21 were identified to be tolerant to salinity and alkalinity in germination. (3) In experiment 3, one salt treatment, 40 L of Na2SO4:NaCl (1:1), 150 mmol L-1, was found to be optimal for screening oat tolerance to salinity during growth and development. For alkalinity tolerance, the optimal treatment was 40 L of Na2CO3:NaHCO3 (1:1) at 75 mmol L-1. (4) No significant correlation was found between tolerances at the germination and adult stages or between tolerances to salt and alkali. Three lines were found to be tolerant to both salt and alkali in both germination and adult stages. (5) In experiment 4, 25 out of 262 oat genotypes were found to be tolerant to both salinity and alkalinity. (6) GGE biplot analysis was found to be effective in interpreting the multivariate data and the plastic cone-container system was found to be cost-effective system for screening adult plant tolerance to salt and alkali. (7) The symptoms of salt stress and alkali stress were found to be different; alkali stress mainly reduces the chlorophyll content, while salinity mainly disrupts water absorption.

Desertification is a worldwide problem caused by climate change and human activity in dryland regions. In China, approximately 27% of the land surface is desertified. In these desertified ecosystems, aboveground interactions are known to greatly affect ecological succession, but belowground soil microbial communities are relatively unstudied. It is not yet clear how these communities change with different vegetation patch types (e.g., shrub vs. grass) across successional stages in dryland ecosystems. In this study, we assessed the effects of shrub patches (dominated by Artemisia ordosica) and grass patches on soil microbial community diversity, soil environment, and soil substrates across three successional stages (mobile, semi‐mobile, and fixed dunes) in a sand dune ecosystem in the Kubuqi Desert, China. Microbial alpha diversity, as indicated by the Shannon index or operational taxonomic unit (OTU) richness, was not affected by patch type but increased with successional stages. Patch type‐ or successional stage‐induced changes in soil bacterial and fungal alpha diversity were mainly associated with soil organic carbon. Unlike alpha diversity, soil microbial beta diversity was greatly affected by successional stage and patch type. The Mantel test revealed that changes in soil bacterial beta diversity were mainly associated with soil organic carbon, and changes in soil fungal beta diversity were mainly associated with soil organic carbon and soil pH. Microbial OTU richness responded more strongly to the successional stage than the microbial Shannon index, indicating that microbial OTU richness can be used as an indicator of successional status in desert ecosystems. The consistent differences in microbial beta diversity between shrub and grass patches across the three successional stages indicate that shrubs significantly influence soil microbial communities in desert ecosystems.