ORIGINAL ARTICLE Shiting Zhang • Junpeng Liu • Xiaohui Bao Kechang Niu Seed-to-seed potential allelopathic effects between Ligularia virgaurea and native grass species of Tibetan alpine grasslands Received: 25 March 2010 / Accepted: 6 July 2010 / Published online: 4 August 2010 Ó The Ecological Society of Japan 2010 Abstract Allelopathy is an important process in plant communities, but the role of seed allelopathy in natural ecosystems remains poorly understood. In the present study, we examined the potential allelopathic effects of Ligularia virgaurea (a dominant species in degraded Tibetan grasslands) seeds on the germination of four native grass species (Festuca sinensis, Agrostis gigantean, Bromus inermis, and Elymus nutans). The results showed that L. virgaurea seeds can have potential allelopathic effects on seed germination, mean time to germination and root growth rates of native grass species. We further demon- strate that these effects are driven by a water-soluble seed leachate. Species with smaller seeds were generally more sensitive than larger seeded species. The results suggest that seed-to-seed allelopathic potential may be an important mechanism driving the dominance of L. virgaurea in de- graded alpine grasslands on the Tibetan Plateau. Further studies are required to demonstrate effects of seed-to-seed potential allelopathy in a field setting. Keywords Allelopathy Æ Seed leachate Æ Seed germination Æ Root growth Æ Ligularia virgaurea Æ Alpine meadow Introduction Allelopathy is defined as the influence of one plant on another through the release of chemical compounds under natural conditions (Rice 1984). The main sources of allelopathic compounds are live and dead plant tis- sues, including roots (Javaid et al. 2006; Mutlu and Atici 2009), stems (Farooq et al. 2008; Han et al. 2008), rhizomes (Yoko et al. 2001; Vrchotova´ and S ˇ era´ 2008), leaves (Macı´as et al. 1993; Chaves and Escudero 1997; Jefferson and Pennacchio 2003), and flowers and inflo- rescences (Ballester et al. 1982; Wakjira et al. 2005). Recently, interest has developed in the allelopathic effects of seeds on the seeds and seedlings of other spe- cies (Suman et al. 2002; Qaderi et al. 2003; Rashid et al. 2005). However, the majority of seed allelopathy studies have focused on agroecosystems. The role of allelopathic seeds on natural vegetation process remains largely unknown. L. virgaurea is often a dominant species in degraded alpine meadows, replacing communities dominated by Kobresia capillifolia or Elymus nutans. Grass abun- dance declines in degraded grasslands, but the under- lying mechanisms driving this decline remain unclear (Xing 2009). Recent research has focused on the reproductive strategies and potential allelopathy of L. virgaurea as explanations for that species’ domi- nance. L. virgaurea exhibits aggressive sexual (Ma et al. 2006a) and asexual (Wang et al. 2008) reproduction, but there is also evidence for allelopathic effects from volatile and aqueous leaf and root extracts on the germination and growth of native forb species (Ma et al. 2005, 2006b). In the present study, we examine the potential of L. virgaurea for seed allelopathy. L. virgaurea germi- nates between mid- to late May, similar to the timing of most native grass species in Tibetan grasslands (Jia, unpublished data). Thus an allelopathic effect of L. virgaurea seeds on seed germination and seedling growth rates of other species may place L. virgaurea seedlings at a significant advantage. In this study we test whether the presence of L. virgaurea seeds or seed leachate negatively influence seed germination and root growth rates of common Tibetan native grass species. S. Zhang Æ J. Liu Æ X. Bao Institute of Ecology, Key Laboratory of Arid and Grassland Agroecology of the Ministry of Education, Lanzhou University, Lanzhou 730000, China K. Niu (&) Department of Ecology, College of Urban and Environmental Sciences and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China E-mail: kechangniu@pku.edu.cn Tel.: +86-931-8912891 Fax: +86-931-8912922 Ecol Res (2011) 26: 47–52 DOI 10.1007/s11284-010-0751-x