Effects Of Soil Heterogeneity On Spatial Expansion In Two Clonal Grass Populations: Hierochloe Glabra And Leymus Chinensis

The ability of rhizomatous plants to expand spatially by ramet production and rhizome growth may expose the clone to habitat heterogeneity. Many previous studies document physiological or morphological responses of clonal plants in heterogeneous environment with two or more separated patches, few allow nutrients and water in different patches communicate with each other when grown in multi-gradient patches.In order to discuss the spatial expansion strategies, we investigated by two rhizomatous plants Hierochloe glabra and Leymus chinensis in four different levels of soil nutrient in both heterogeneous and homogeneous habitats. We brought about the following questions: (1) Is expansion direction of clonal plants growing in heterogeneous habitats directed or random? (2) Dose ability of spatial expansion reduce in nutrient rich patch and enhance in nutrient poor patch?We conducted an open-end greenhouse experiment with two treatments: homogeneous and heterogeneous (including four different nutrient patches, A1–A4). We defined patch types A1–A4 progressively, from the poorest nutrient grade to the richest nutrient. At the end of the experiment, the number of ramets, buds and primary rhizomes, the ramet height, the length of internode, spacer and primary rhizome, the aboveground and belowground biomass were all measured and two species were compared.Results showed that both rhizomatous species are able to select their own favourable habitats significantly through preferential placement of offspring ramets. The number of buds and primary rhizomes in different patches were significantly for H. glabra but not significantly for L. chinensis. The aboveground biomass of both species showed significant differences among patches. Spacer length of both species didn't respond significantly in heterogeneous habitats. The response of primary rhizome length and internode length to heterogeneity in both species were the same, both lengths were significantly high in A3 patch, they decreased when the nutrient was too rich or too poor.In conclusion, we confirmed that both rhizomatous species are able to select favorable habitats actively and that these suitable habitats are different for each of the two species. However, distinctions were found in the ability of the two species to expand spatially. The expansion ability of H. glabra is more than that of L. chinensis because nutrient level, which is considered an important factor in the ability of clonal plants to expand spatially, is too low for L. chinensis. The abilities of spatial expansion shown by these two species sufficiently explain that rhizomatous plants growing in an environment with multigradient patches have significant responses.