| Clonal species are widely distributed in various ecosystems, as one of the unique group, it plays an important role in the vegetation restoration such as grassland, wetland and forest. During their long-term evolutionary processes, they may take the adaptive strategy-clonal integration to cope with the heterogeneous environments. Leymus chiensis (Trin.) Tzvel.(Poaceae) is a perennial rhizome clonal grass, and one of the main forage for vegetation recovery that often form monodominant stands in the L. chinensis meadow of the Songnen Plain. However, how alkalinity affects clonal integration of this species remained unknown. In this study, the clonal plant of L. chinensis was selected as our study materials, we had studied the clonal integration influences of severe rhizome and external environmental factors (soil alkalinities) and internal factors (developmental stage) on clonal plants, in the way of field investigation and simulation test, to determine the integration intensity, direction and benefits and costs under the combined effects of hetetogeneity alkalinities and plant age, to further analyze the mechanism of clonal integration on L. chinensis. Main conclusions are as follows:(1) Heterogeneity alkalinities would significantly affect the effects of clonal integtation on plants. Within the heavy heterogeneous alkalinities treatments, clonal integration had a positive effect on plant growth, reproduction and tolerance to alkalinities. Support from mother ramets in non-stressful habitats improved the biomass of daughter ramets in stressful conditions through a connecting rhizome on L. chinensis by water transportation. But it do not occur in homogeneous habitats or those with low heterogeneity. The results indicated that higher rates of clonal integration may be selected for in habitats with increased alkaline heterogeneity. Clonal integration affected the allocation pattern of below-ground organs, with the roots, rhizomes and buds of daughter ramets showing different responses to clonal integration. Under the heterogeneous high alkaline conditions in this study, the biomass allocation to buds markedly increased as did rhizome length, but these changes were not significant and had negative effects on roots. Cost-benefit analysis based on biomass measures showed that the mother ramet incurred a cost to enhance daughter ramet survival but clonal integration confers overall benefits to the entire clonal fragment. Therefore, clonal integration is an important adaptive strategy by which rhizomatous clonal plants can withstand local alkaline stress.(2) Our study has also found that the plant developmental stage is an important factor that affects the extent of clonal integration of L. chinensis, which has mother ramets that produce vegetative bulbils (clonal offspring) that pass through distinct pre-and post-rooting stages. The amount of15N translocated from mother to daughter ramets becoming increasing apparent in pre-rooting than post-rooting. In high alkaline environment, the nitrogen demands of the young ramets are supplied mainly from the mother ramets through clonal integration. The largest contribution portion of mother ramets applied was80.5%while that root of daughter ramets was19.5%.(3) The results of field test showed that cutting roots has a significant influence on community characteristics and soil nature. The total community coverage and density and biomass levels decreased firstly and increased subsequently, and the10cm cutting root depth was highest. This decline of production mainly because of clonal integration loss interconnect ramets. While the time was prolonged, the influence to weaken slowly. Cutting root significantly increased the soil bulk density and water moisture content. The number of tiller was significantly increased and had little effects on rhizome length. On the basis of comprehensive control on alkalinization L. chinensis meadow in Songnen Plain, the cutting root depth in the10-20cm more appropriate. |
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