Effects Of Biochar Addition On The Growth Characteristics Of Phragmites Australis And Soil Properties In Yellow River Delta

The Yellow River Delta is the youngest new-born coastal wetland ecosystem in the warm temperate zone of China.It plays an important role in biological production,biodiversity conservation and soil carbon sequestration.In recent years,continuous climate change and human activities have caused the degradation of Phragmites australis wetland in the Yellow River Delta.Scientific and effective improvements of the growth characteristics of P.australis have great significances to promoting productivity of P.australis.We conducted greenhouse and field in-situ experiments to explore the effects of different biochar addition methods(rhizosphere addition and surface addition)and biochar materials(biochar,biochar-compost and biochar-inorganic fertilizer)on the growth characteristics of P.australis and soil properties in the salty environment.It is helpful to understand the mechanism of biochar effects,and provides basic support for its practical application.The main results are as following:Biochar rhizosphere addition significantly increased total biomass of P.australis by 69.8% in 2018 and 55.8% in 2019 respectively,and biomass of fine roots increased by 122.4% and 38.9% respectively.The promotion effect was more effective in high salt level than low salt level treatment.In addition,both biochar rhizosphere addition and surface addition significantly decreased soil electrical conductivity,and the inhibition effects were more effective in medium and high salt level treatments.Biochar rhizosphere addition significantly increased height,chlorophyll content and leaf nitrogen content of P.australis;significantly increased soil carbon content;and significantly decreased inorganic nitrogen content in 2018.In generally,biochar rhizosphere addition was more beneficial to the functional traits of P.australis than surface addition,especially for the growth of fine roots.The structural equation model showed that biochar addition could directly increase the fine roots biomass of P.australis through decreasing soil electrical conductivity,and further improve total biomass of P.australis.Both biochar and biochar-compost addition significantly increased belowground biomass,root length and other root architectures of P.australis;significantly increased soil organic carbon content;decreased soil ammonia-nitrogen content and electrical conductivity.Additionally,compared to the biochar addition,biochar-compost addition increased total biomass and net photosynthesis rate of P.australis.In generally,biochar-compost addition had a more positive effect on the growth of P.australis than biochar addition alone in the saline soil.The structural equation model showed that biochar and biochar-compost addition could indirectly increase biomass of P.australis through decreasing soil electrical conductivity.The increasing belowground biomass of P.australis could enhance nitrogen uptake and decrease soil ammonia nitrogen content.Both biochar and biochar-inorganic fertilizer addition significantly increased total biomass of P.australis with the increase rate of 51.5% and 94.1%,respectively.In typhoon affected site,biocharinorganic fertilizer addition significantly increased the fine roots biomass,root surface area and other root architectures of P.australis,and biomass of fine roots increased by 156.7%,indicating that biocharinorganic fertilizer addition was helpful for the communities of P.australis to resist typhoon.In generally,biochar-inorganic fertilizer addition had a more positive effect on the growth of P.australis than biochar addition alone,especially in typhoon affected site.Biochar addition treatments had no significant effect on the alpha diversity of bacterial communities and fungial communities.The structural equation model showed that biochar and biochar-inorganic fertilizer addition could indirectly increase the biomass of P.australis through increasing the length of fine roots.Our results showed that different biochar addition methods and biochar fertilizer additions could enhance the growth of P.australis and soil physicochemical properties.It indicated that biochar,especially biochar fertilizer addition could enhance the growth of P.australis and soil physicochemical properties in the salty environment in the Yellow River Delta.These results provide the support for the productivity improvement of P.australis in the Yellow River Delta.