Effects of whole-plant extracts of four species dominant in the Qinghai-Tibetan plateau on their germination and growth patterns

Allelopathy plays an important role in driving plant interactions. Effects of allelopathy on seed germination and plant growth have been extensively investigated, while the impacts of whole-plant water extracts of different plants on their seed germination, and growth of shoots and roots are still unclear. Therefore, a manipulation experiment was conducted to explore such effects of whole-plant extract of four dominant species of the Qinghai-Tibetan Plateau (Elymus nutans, Festuca sinensis, Poa pratensis and Vicia unijuga). Four extract concentrations (0, 0.025, 0.05, and 0.1 g/ml) of each species were applied on the seeds of the four species. Results showed that water extract significantly affected their seed germination rate, and shoot length and root length. Specifically, the seed germination rate and seed germination index decreased with increasing extract concentrations, while the mean germination time increased. Further, the medium time of germination (the peak value of the germination period) had postponed with increasing extract concentrations. Moreover, the root length decreased with increasing extract concentration, yet the shoot length was only inhibited by the highest extract concentration. A stronger effect of the extracts on the roots than on the shoots was also inferred since (1) extract concentration was negatively correlated with the root length (not shoot length), and (2) root length contributed more than shoot length to the synthetical allelopathic effect index. Thus, root length could be a better bio-indicator in allelopathy assays than shoot length. Also, the plant species composition should be considered for obtaining significant effects of allelochemicals on seed germination and plant growth.