FIGURE 6 Comprehensive allelopathic effect index of Elymus nutans extracts on highland grasses
4 DISCUSSION
Plant allelopathy is a traditional subject and numerous studies have demonstrated that weeds can exhibit allelopathic effects on economic crops (Nichols et al., 2015). Some perennial grass, such as quackgrass (Agropyron repens ), ryegrass (Lolium perenne ), red fescue (Festuca rubra ) and Kentucky bluegrass have also been proved to be allelopathic to other plants (Grummer 1961, Fales and Wakefield 1981). Recently, interest has developed in the allelopathic on agroecosystems, like cultivated land and commercial forest (Kural, 2020; Mushtaq, 2020). However, the role of allelopathic effects of perennial grass on the seeds and seedlings of crops and other grass species remain largely unknown. Our results indicated that the extracts from drooping wildryegrass plant materials and root zone soil did impact the germination and seedling growth of commonly cultivated crops on plateau area and perennial grasses of mix-seeded for vegetation restoration.
The effects of different extract treatments on germination varied with crops and extract types. The annual monocots were more susceptible to inhibition of the extracts, while the annual dicots tended to be more tolerant or be promoted. The effects of drooping wildryegrass plant materials and root zone soil extract on the growth of seedlings were mainly manifested in inhibiting the growth of roots and shoots, and the impact on monocot crops is greater than the impact on dicot crops. Out results suggested that the three type extracts had no significant inhibition or promotion on the seedlings growth of quinoa.
All tested grasses in this study were perennial, different from the aforementioned crops. The highest germination force of control was 67.8% and the lowest was only 26.2%, reflecting the disuniformity of germination. The germination rates of control of the five grasses ranged from 63.8% to 81.8%. Except for Siberian wildryegrass which was greater than 80%, the germination rate of other four species were all less than 70%. The control germination index of the five grasses were all less than 35%, reflecting the lower vitality of tested perennial grass seeds.
Except that the root zone soil extract did not have a significant effect on the two bluegrasses, other extract treatments caused significant decrease in the germination force, germination rate and germination index of the five grasses. The strongest inhibitory effect was the pieces extract. Among the five grass species, the least affected was Siberian wildryegrass, and the most affected was Chinese fescue, which was consistent with previous reports (Liang et al., 2020). The effects of the extracts on the growth of grass seedlings were mainly manifested in the inhibition of the growth of roots, especially the growth of drooping wildryegrass and Siberian wildryegrass. The three kinds of extracts had no significant effect on the seedling growth ofKentucky bluegrass , but other extracts had inhibitive effects on the growth of roots and shoots, as well as the dry weight. Particularly, the effects of the pieces extract were more apparent. From allelopathic perspective, these maybe reasonable explanations of the degradation of mix-seeded pasture in alpine area.
Previous studies on autotoxicity of forage were mainly focused on alfalfa and less reports of autotoxicity about Gramineae (Ghimire, 2019). The present study clearly demonstrated that drooping wildryegrass had autotoxicity during its germination and seedling growth. This may help to explain rapid decline of seed yield and above ground biomass of drooping wildryegrass monoculture after 3 years.
The differences in the same index for the same crop and forage should be attributed to different extracts. The composition of the whole plant extract was analogous to that of rain leaching under natural conditions. The plant pieces extract contained more components than whole plant extract because sample ground destroyed the internal tissues of plants and some enzymes, amino acids, inorganic salts, and nitrogen-containing substances could solve in the extracts. The soil extract from the root zone of drooping wildryegrass contained root exudates, leachate from above-ground parts, as well as residues from the decomposition of dead roots in the soil, and soil microorganisms related substances, although the amount may be a little. The composition differences of extracts might contribute to the indicator differences of the same crop or forage.
5 CONCLUSIONS
Drooping wildryegrass does have allelopathic potential on germination and seedling growth of highland crops or perennial grasses and the overall effect is inhibition. Different crops or perennial grasses respond differently, and some are sensitive and some are tolerant. The germination force (>80%) and germination rate (>85%) of the control of five crops were relatively higher, reflecting their good germination uniformity. Of the five crops, hulless barley and oat are susceptible and quinoa is tolerant. Of the five perennial grasses, Sibiricus wildryegrass is the least affected, and Chinese fescue is the most affected. The responses of seed germination and seedling growth of the same crop or grasses varies with the extracts from different sources. The pieces extract has stronger inhibition than others.
Drooping wildryegrass has less allelopathic effects on Kentucky bluegrass and crymophylla bluegrass than on Chinese fescue. It is recommended that the species combination of mixture for restoration should consider allopathic effects of the co-seeding and decrease the seeding rate of drooping wildryegrass in mixture. The subsequent crop or grass followed seed production of drooping wildryegrass monoculture should take planting annual dicots into consideration.