| Climate change and anthropogenic activities have aggravated grasslands degradation,which has seriously affected the functions and services of Songnen grassland ecosystem.How to restore degraded grassland and achieve sustainable use of grassland resources is an important issue.Leymus chinensis is a dominant species in Songnen grasslands,and is important for the restoration of degraded ecosystems because of its special clonal integration properties,which can improve ecological adaptability and individual suitability in heterogeneous habitats.Previous studies found that both mowing and nitrogen addition could enhance the expansion of Leymus chinensis populations into saline patches and facilitate vegetation restoration.However,the mechanism of clonal integration on restoration of saline-alkali grasslands under the effects of mowing and nitrogen addition is still unclear.To address the above problems,this study used field combined with pot control experiments to investigate the effects of clonal integration on the spatial expansion ability,biomass distribution,root morphology and root exudate and rhizospheric microorganism of Leymus chinensis under mowing and nitrogen addition,and clarifying the restoration mechanism of clonal integration on soil physicochemical properties and nutrients content of saline patches,which has important ecological significance and scientific value for the sustainable development of grassland livestock husbandry.(1)Clonal integration significantly promoted the spatial expansion and growth of Leymus chinensis under saline stress,and the total rhizome length,number of shoots,aboveground biomass,and belowground biomass increased by 25%,32%,51%,and 69%,respectively(P <0.05).Clonal integration significantly altered the root morphology and secretions of Leymus chinensis,reducing the root length by 19%(P < 0.05)and the soluble sugar content and total organic acid content of root exudate by 42% and 51%(P < 0.05),respectively.(2)Under mowing conditions,clonal integration could promote the spatial expansion and growth of Leymus chinensis under salt-alkali stress,and the number of plant branches and aboveground biomass increased by 40% and 23%(P < 0.05).Compared with the control condition,clonal integration under mowing condition inhibited aboveground and subsurface biomass(P < 0.05),but instead elevated specific root length and total organic acid content in root exudate(P < 0.05).It is possible that removing some tissues of healthy patch Leymus chinensis reduces photosynthesis of the daughter plants,decreases their nutrient transfer to the saline patch plants,and reduces the above-and below-ground biomass of the daughter plants while promoting nutrient acquisition by their root systems.(3)Under nitrogen addition,clonal integration significantly promoted spatial expansion and growth of Leymus chinensis under salinity stress,with total rhizome length,number of shoots,aboveground biomass,and belowground biomass increased by 86%,65%,40%,and60%,respectively(P < 0.05).Meanwhile,clonal integration altered the root morphology of Leymus chinensis,with a 23% reduction in specific root length(P < 0.05).Compared with the control condition,clonal integration under nitrogen addition condition inhibited aboveground and underground biomass of Leymus chinensis in saline-alkali patch(P < 0.05),and increased total organic acid content in root exudate(P < 0.05).It is possible that excessive nitrogen addition inhibited photosynthesis in healthy patch Leymus chinensis and reduced its nutrient transfer to saline patch plants,leading to similar results to clonal integration under mowing.(4)Under mowing and nitrogen addition,clonal integration significantly promoted the spatial expansion and growth of Leymus chinensis under saline stress,and increased the total rhizome length,number of shoots,number of divisions,aboveground biomass,and belowground biomass by 61%,48%,53%,70%,and 72%,respectively(P < 0.05).Compared with the control condition,clonal integration under mowing and nitrogen addition reduced aboveground biomass of saline patches(P < 0.05)and increased the total organic acid content in their root exudate(P < 0.05)compared with under clonal integration.The interaction under mowing and nitrogen addition could not alleviate the effect from a single treatment.(5)The effect of clonal integration on soil organic carbon content of saline patch did not depend on mowing and nitrogen addition.In the field in situ experiment,clonal integration significantly enhanced the soil organic carbon content of saline patches(P < 0.05).Correlation analysis of root exudate and soil organic carbon in the pot experiment revealed a negative correlation.This may be due to the division under clonal integration did not need to resist the unfavorable environment by increasing the release of root exudate,thus reducing the turnover of soil mineral-related organic matter and increasing the soil organic carbon content.This suggests that clonal integration contributes to enhance the soil carbon sequestration.(6)The effect of clonal integration on abundance of Leymus chinensis in saline patches was not dependent on mowing and nitrogen addition.The increase of abundance of Leymus chinensis in saline patches reduced plant diversity,so clonal integration may be one of the reasons for maintaining high diversity in Leymus chinensis communities.In addition,clonal integration can reduce the electrical conductivity of saline patch soil,which is beneficial to the restoration of saline patch.In summary,mowing and nitrogen addition and their interaction on clonal integration characteristics of Leymus chinensis were complex.Clonal integration affected Leymus chinensis spatial expansion ability,biomass allocation,root morphology and root exudate and rhizospheric microorganism.Clonal integration increased nutrient content of saline patch soil by inhibiting root exudate.In addition,clonal integration may affect soil conductivity by increasing the abundaance of Leymus chinensis populations,which is beneficial to the recovery of degraded saline patchy grasslands.This experiment analyzes the regulatory mechanism of clonal integration on soil nutrients and physicochemical properties in saline alkali patches from the perspectives of root morphology,root exudates,and microorganisms,thereby enriching the research content of clonal integration;meanwhile,carrying out the influence of clonal integration on community and ecological functions is important for the research in the intersection of clonal biology and restoration ecology. |
PDF Full Text Request