Competition And Allelopathy Among Three Bryophytes In Hani Peatland Of The Changbai Mountains

Plant-pant interactions may be classified as two aspects, positive (facilitation) and negative (competition). It is pointed out that competition is recognized as a key process in constructing plant communities, even though facilitation has attracted more and more attention recently. With the application of chemical methods, allelopathy including both positive and negative effects is also considered as an important element in the research on plant-plant interactions. Nevertheless, resource competition and allelopathy are so closely related that it is difficult to separate them to discover the mechanism of plant-plant interactions. In additon, it is not clear how the two above-mentioned interactions influence bryophytes in peatlands and what role they play in bryophyte communities.In this study, three common bryophytes, Sphagnum palustre L., S. magellanicum Brid. and Polytrichum strictum Menz. ex Brid. in Hani Peatland of the Changbai Mountains, northeastern China, were selected as study species to separate allelopathy from resource competition both in the laboratory and in the field. In that way, we aim to figure out the effect of resource competition and allelopathy on both morphological and physiological performance of the three bryophytes, and to clarify the significance of competition and allelopathy on coverage change of various bryophyte species in Hani Peatland of the Changbai Mountains. The main results and conclusions are as follows:(1) No significant competitive effect was found between S. palustre and S. magellanicum in the field or in the laboratory. On the contrary, mutual promotion existed in their soluble sugar content, height increment and biomass production, which confirmed the stress gradient hypothesis, namely plant-plant interactions give first place to facilitation rather than competition under adverse conditions. Besides, P. strictum increased its own proline content to balance the inhibitory effect of S. magellanicum on its side-shoot production, and decreased side-shoot production and proline content of S. palustre, suggesting that P. strictum acquire its competitive advantage via physiological adjustment.(2) Allelopathy enhanced height increment of S. magellanicum, soluble sugar content of S. palustre and proline content of P. strictum, but had no influence on either soluble sugar or proline content of S. magellanicum, which indicated the sensibility of S. palustre and P. strictum to allelopathy. However, compared to the experiment in the field, S. magellanicum had different responses to allelopathy in the laboratory, which probably resulted from the differences of allelochemicals.(3) At normal water table (-25cm), neighbours increased soluble sugar content of S. palustre and decreased proline content of S. palustre and S. magellanicum, but no influences were found on physiological traits of P. strictum with water table drawing down to -40cm while its C content and soluble sugar content were elevated and reduced by neighbours respectively, indicating stronger drought tolerance of P. strictum when with neighbours than that of Sphagnum. In addition, allelopathy increased N content of P. strictum, but lessened N content of S. palustre at low water table (-40cm), which could be one of the reasons for P. strictum to expand in peatlands of the Changbai Mountains in recent half a century.(4) Competition should be included into life history strategies of bryophytes, and different species have their own preferences:Sphagnum palustre, a competition inferior, is likely to prefer allelopathy to resource competition, while S. magellanicum and P. strictum, the competition superior, probably prefer resource competition. In addition, allelopathy of S. palustre decreased the biomass production of S. magellanicum in the laboratory, but promoted its height increment in the field, indicating that allelopathy among different bryophyte species is not only a form of competition, but also a valid method to accelerate species coexistence.