| Clonal integration is one of the most significant functional traits that distinguish clonal plants from non-clonal plants.It is also an important adaptive feature of clonal plants to cope with heterogeneous and stressed environments,which has a profound impact on the growth and reproduction of clonal plants.Because most of the dominant species in aquatic plant community are clonal plants,clonal integration improves and optimizes the structure and function of aquatic plant community.At present,there are few studies on the mechanism of clonal integration of aquatic plants on the rhizosphere physiology and ecology of aquatic plants and the impact of clonal integration on aquatic plant community.In addition,the effects of clonal integration on aquatic plant community are still unknown.In this paper,controlled experiments were conducted to explore the effects and mechanisms of clonal integration on population growth and community characteristics of aquatic plants in homogeneous and heterogeneous environments.The main research results of this paper are as follows:1.Through the research on change of clonal integration between ramet pairs of submerged macrophyte Vallisneria natans with growth time,we found that the anatomical structure of stolons changed significantly with time;in the early growth stage of daughter ramets,clonal integration significantly increased the leaf nitrogen content of mother ramets,the total biomass of daughter ramets and the biomass of offspring ramets,but had no significant effect on these in the middle and late growth stage,indicating that the resource dependence of daughter ramets on mother ramets decreased with the growth of daughter ramets;during the growth of daughter ramets,the biomass of mother ramets was not affected by the connection or not.The root behavior induced by clonal integration and the effect of clonal integration on rhizosphere exudates were investigated from the perspectives of root traits,root growth dynamics and rhizosphere exudates under homogeneous conditions.The results showed that clonal integration did not lead to root separation between ramet pairs under high and low nutrient conditions.However,clonal integration increased the growth of ramet pairs under high nutrient conditions and decreased the growth of ramet pairs under low nutrient conditions.The main components of rhizosphere exudates in different treatments corresponded with the biomass of intersecting roots and total roots.In the presence of neighboring species,clonal integration did not alter the growth of the ramet pairs under high nutrient conditions,but increased the growth of ramet pairs and decreased the growth of neighboring species under low nutrient conditions.2.In the study on the degree of physiological integration in the clonal system of V.natans under heterogeneous light conditions,increased photosynthetic capacity and decreased biomass accumulation of the mother ramet were observed when connected with shaded offspring ramets.Clonal integration increased the biomass,rhizosphere C and N availabilities,microbial biomass and extracellular enzyme activity of the first shaded ramet generation,but not the secondary and tertiary shaded ramet generation,which indicates that support from the mother ramet of V.natans may be limited to the adjacent offspring ramet in a clonal system under severe light stress,and related to ramet generation.In order to explore the effects of clonal integration on the growth and rhizosphere microbial communities of neighboring plants in heterogeneous conditions,we cultured the connected and severed ramet pairs of V.natans,conspecific or heterospecific neighbors in heterogeneous soil conditions.The results showed that clonal integration reduced the growth of the apical fragment of V.natans,but had no significant effect on the growth of clonal fragments of neighbors V.natans in heterogeneous soil environment.When the neighboring plant was Myriophyllum spicatum,clonal integration significantly increased the growth of the apical fragment of V.natans and thus decreased the growth of M.spicatum.Although neighboring plants benefited less from clonal integration,clonal integration increased extracellular enzyme activities,microbial biomass and C availability,and changed the composition of bacterial microbial community in the rhizosphere of neighboring plants V.natans.3.We constructed free-floating plant communities dominated by Salvinia natans and submerged plant communities dominated by V.natans under homogeneously different nutrient conditions to explore the effects of clonal integration on the characteristics and the relationships between functional diversity and productivity of free-floating plant communities and submerged plant communities.Clonal integration significantly reduced the growth of floating plant communities under high nutrient conditions,increased the species diversity,and changed the species composition of the community.Clonal integration and nutrient did not affect species diversity of submerged plant communities,but independently affected species composition.Under high nutrient conditions,clonal integration significantly affected three community-weighted means traits and functional evenness of floating plant communities.Three single-trait indices of functional diversity and functional evenness showed opposite correlation with productivity.The significant effect of clonal integration on functional diversity of submerged plant communities did not lead to variation in productivity,but functional evenness was negatively correlated with community productivity under low nutrient conditions.4.By studying the effects of the presence of stoloniferous clonal species on aquatic plant communities in different soil nutrient heterogeneity scales,we found that when a stoloniferous clonal plant Hydrilla verticillata was present in the community with M.spicatum,the growth advantage of H.verticillata was greater than that of M.spicatum in homogeneous patches and heterogeneous small patches,and species diversity and evenness decreased.However,the growth of M.spicatum increased in heterogeneous large patches,and species diversity and evenness increased,which supported the heterogeneity-diversity hypothesis.When two stoloniferous clonal plants H.verticillata and V.natans were present in the community with M.spicatum,the growth advantage of V.natans was greater in heterogeneous large patches,and species diversity and evenness decreased.The growth of H.verticillata and V.natans was similar in homogeneous patches and heterogeneous small patches,and species diversity and evenness increased.Therefore,the heterogeneity-diversity hypothesis is not valid when two stoloniferous clonal plants were present in the community.Four aquatic plant communities were constructed by manipulating the spatial distribution of neighboring species to explore the response of clonal population of V.natans on the spatial aggregation and heterogeneous distribution of neighboring species and the performance of plant communities.The results showed that when neighboring species were patchy-distribution,the spatial aggregation of neighboring species increased the growth of V.natans and M.spicatum,and decreased the growth of H.verticillata,but had no effect on the growth of Potamogeton malaianus;the difference in competitive ability of species increased,and the community species diversity and evenness decreased.When neighboring species were evenly distributed,spatial aggregation did not change the growth of each species in the community,and the differences in competitive ability of species,diversity,evenness and productivity of the community were not changed significantly.In conclusion,clonal integration significantly affects the growth of aquatic clonal plant population through different mechanisms in different environments,and further affects the composition and function of aquatic plant communities.This paper supplements the research content of clonal integration of aquatic plants,reveals the growth,development and adaptation mechanism of aquatic clonal plants,has an in-depth analysis on the important role of clonal integration in aquatic plant clonal population and plant community,and further enriches the content of clonal plant ecology.In addition,this paper also provides new insights for the restoration and succession of aquatic vegetation.The clonal plants,such as V.natans,with diversified habitat adaptation strategies and strong reproductive ability can be used as excellent varieties for the restoration of degraded aquatic ecosystems. |
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