Physiological, biochemical and phytohormone responses of Elymus nutans to α-pinene-induced allelopathy

Artemisia baimaensis allelopathy has a negative effect on the establishment of Elymus nutans artificial grassland in natural grassland

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.

Vapor and Liquid Phase Profiles of Essential Oils from Abies, Picea and Pinus Species and Their Phytotoxic Interactions with Weed Growth in Pre- and Post-Emergence Conditions

The chemical content of essential oils (EO) obtained from the leaves of four Pinaceae (Abies alba, Picea abies, Pinus cembra and Pinus mugo) was investigated by SPME-GC-MS technique. The vapor phase was characterized by the monoterpenes with values higher than 95.0%. Among them, α-pinene (24.7-48.5%), limonene (17.2-33.1%) and β-myrcene (9.2-27.8%) were the most abundant. The monoterpenic fraction prevailed over the sesquiterpenic one (≥74.7%) in the EO liquid phase. Limonene was the major compound in A. alba (30.4%), P. abies (20.3%) and P. mugo (78.5%), while α-pinene in P. cembra (36.2%). Regarding the phytotoxic properties, EOs were studied at different doses (2-100 μL) and concentrations (2-20/100 μL/mL). All EOs were found to be significantly active (p-value ˂ 0.05) against the two recipient species in a dose-dependent way. In pre-emergence tests, germination of Lolium multiflorum and Sinapis alba was reduced by up to 62-66% and 65-82%, respectively, as well as their growth by up to 60-74% and 65-67%, due to the effects of compounds in both the vapor and liquid phases. In post-emergence conditions, at the highest concentration, the phytotoxicity of EOs caused heavy symptoms and, in the case of S. alba, A. alba EO completely destroyed (100%) the treated seedlings.