Planting Elymus nutans artificial grassland to replace degraded Artemisia baimaensis grassland on the Qinghai Tibetan plateau (QTP) can effectively alleviate local grass-livestock imbalance. However, it is unknown whether the allelopathy of natural grassland plant A. baimaensis on E. nutans affects grassland establishment. Accordingly, we examined the effects of varying concentrations of aqueous extracts of A. baimaensis litter on the seed germination and early seedling growth of E. nutans , and the effects of A. baimaensis volatile organic compounds (VOCs) on the growth parameters and physiological characteristics of E. nutans . The results indicate that the aqueous extract inhibited the force, percentage, and index of germination of E. nutans and affected early seedling growth, particularly at high concentrations. Further, the VOCs significantly reduced the aboveground and root biomass of E. nutans and increased malondialdehyde concentrations. Additionally, these VOCs altered the antioxidant enzyme activities and increased the superoxide dismutase, peroxidase, ascorbic acid peroxidase, soluble sugar, and proline content but significantly decreased glutathione reductase levels. Our results indicate that the allelopathy of A. baimaensis significantly inhibited the germination and seedling growth of E. nutans . Thus, the leaching of A. baimaensis may produce allelochemicals in the soil that inhibit the germination of E. nutans seeds. Moreover, the VOCs of A. baimaensis may disrupt the growth process, resulting in a decrease in biomass and a disruption of the physiological metabolism of seedlings under field conditions.

Medicago ruthenica (L.) Trautv., a wild grass species, is commonly grown as a forage crop in arid and semi-arid areas of China. Herein, we explored mulch patterns and planting methods for optimizing M. ruthenica seed production in the loess plateau of the Gansu Province, China from 2017 to 2019. The experiments comprised of six treatments including (1) flat ground without mulch (F0, control); (2) flat ground with a transparent white 0.008 mm thick plastic film mulch (FP); (3) flat ground with 4500 kg/hm 2 straw mulch (FS); (4) furrow with 10 cm ridges (R0); (5) furrow with plastic film mulch (RP); and (6) furrow with straw mulch (RS). Results showed that the harvested seed yield of M. ruthenica was the highest under RP treatment, followed by FP and FS treatments. Soil moisture content from mid-May to mid-August in 2017 was the highest under RP and FP treatments, followed by RS and FS treatments. In 2018, soil moisture content was the highest under RS and FS treatments. In 2017 and 2018, soil temperature was the highest under FP and RP treatments, followed by F0 and R0 treatments. Total and available nitrogen, phosphorus, and potassium contents were the highest under RS and FS treatments, followed by RP and FP treatments. Comprehensive analysis result showed that surface mulch improved soil microenvironment and increased seed yield of M. ruthenica. Straw mulch also effectively recycled excess crop straw, thereby encouraging the sustainable development of agriculture in this area. In conclusion, FS treatment was considered the best mode for M. ruthenica seed production in this area.

Low temperatures in the seedling stage during early spring limit Medicago ruthenica germination and seedling growth. Elucidating the physiological mechanism of γ-aminobutyric acid (GABA)-regulated cold tolerance in M. ruthenica could provide a reference for alleviating the harmful effects of low temperatures on legumes in alpine meadows. The regulatory effects of GABA on M. ruthenica physiological parameters were explored by simulating the ground temperatures in the alpine meadow area of Tianzhu, China, in early May (2 h at 7°C; 6 h at 15°C; 4 h at 12°C; 2 h at 7°C; 10 h at 3°C). Our results showed that 15 mmol/l GABA was the optimal spray concentration to promote growth in the aboveground and belowground parts and increase the fresh and dry weights of seedlings. At this concentration, GABA enhanced the activities of catalase, peroxidase, superoxide dismutase, and ascorbate peroxidase; increased the osmotic balance; and inhibited the production of harmful substances in the cells under low-temperature conditions. GABA also regulated the tissue structure of leaves, increased the cell tense ratio, maintained photochemical activity, increased the amount of light energy to the photochemical reaction center, and improved the photosynthetic rate. Furthermore, exogenous GABA application increased the endogenous GABA content by promoting GABA synthesis in the early stages of low-temperature stress but mainly participated in low-temperature stress mitigation via GABA degradation in the late stages. Our results show that GABA can improve the cold tolerance of M. ruthenica by promoting endogenous GABA metabolism, protecting the membrane system, and improving the leaf structure.

Elucidating the effect of γ-aminobutyric acid (GABA) on seed germination and seedling growth of Medicago ruthenica under low-temperature could provide a reference for alleviating the harmful effects of low temperatures on legumes in alpine meadows. We set up different temperatures to screen three low temperatures that inhibit seed germination of Medicago ruthenica, and six aqueous concentrations of GABA (0, 0.1, 0.5, 1, 5, 10 mM) were set up to screen out the best GABA seed soaking concentration that can promote the seed germination at low-temperature.The three temperatures of 10 C, 20/5 C and 15/5 C inhibited seed germination of Medicago ruthenica. Soaking seeds with 1 mM GABA could significantly increase seed germination rate of Medicago ruthenica at low-temperature (10 C). Soaking seeds only with 0.1 mM GABA could promote germination of Medicago ruthenica at 20/5 C, but there is no significant difference compared with distilled water soaking.Whereas, all GABA seed soaking concentrations delayed seed germination time and inhibited seed germination at 15/5 C. Pre-spraying seedlings with 1 mM GABA at 10 C reduced the production of superoxide anion, hydrogen peroxide and malondialdehyde content, and increased the activities of catalase, peroxidase, superoxide dismutase and ascorbate peroxidase in leaves of Medicago ruthenica on days 7. Simultaneously, Pre-spraying seedlings with 1 mM GABA at 10 C significantly increased the net photosynthetic rate and decreased intercellular CO 2 concentration. These data suggest that GABA could enhance the cold tolerance of Medicago ruthenica by promoting seed germination, regulating the antioxidant system, and increasing photosynthetic efficiency. However, the mitigation effect of GABA on low-temperature is only applicable to a certain temperature. The mitigation effect of GABA on low temperature will be weakened as the low temperature of plants is less than 10 C