Differences Of Nitrogen Use Strategies Between Spartina Alterniflora And Suaeda Salsa And The Microbiological Mechanisms In The Yellow River Delta Wetlands

Invasive alien plant species pose a significant threat to global ecological security and economic development.In recent years,the invasive plant species Spartina alterniflora has experienced an exponential increase in distribution area in the northern coastal wetlands of China.Its competitive advantage for soil available nitrogen may be one of the reasons for its rapid expansion.However,previous studies have paid little attention to the interactive relationship between its nitrogen utilization strategy and rhizosphere microorganisms involved in nitrogen cycling.This study aimed to investigate the characteristics of nitrogen uptake and utilization by S.alterniflora and its native competitor Suaeda salsa for different forms of nitrogen using stable isotope tracing technology in the wetlands of the Yellow River Delta.The study also explored the differences in microbial community structure of soil bacteria,fungi,and nitrogen cycling-related functional microorganisms between the S.alterniflora and S.salsa communities using high-throughput sequencing and q PCR gene chip technology.The results will provide scientific evidence for the control of S.alterniflora and ecological restoration in the Yellow River Delta region.The main results are as follows:（1）The results of ¹⁵N stable isotope tracing showed that there was no significant preference for the absorption of two forms of nitrogen(¹⁵NO₃^-and ¹⁵NH₄⁺)between S.alterniflora and S.salsa,and there was no significant difference in the absorption rate of different forms of nitrogen.However,during the sampling period,the absorption rate of¹⁵NO₃^-(0.056±0.009μg N g^-1d.w.root h^-1)、¹⁵NH₄⁺(0.024±0.008μg N g^-1d.w.root h^-1)by S.salsa was significantly higher than that of S.alterniflora(0.011±0.001μg N g^-1d.w.root h^-1,0.013±0.002μg N g^-1d.w.root h^-1).S.alterniflora allocated more absorbed nitrogen to leaves and roots,with a lower allocation to stems;while the allocation of ¹⁵N in S.salsa was mainly concentrated in leaves and stems.（2）The invasion of S.alterniflora has changed the community structure and diversity of soil bacteria and fungi.The invasion of S.alterniflora has increased the microbial alpha diversity of soil bacterial communities,with Shannon,Ace,and Chao diversity indices being 6%,20.77%,and 21.62%higher than those of S.salsa,respectively.However,there was no significant effect on the alpha-diversity of soil fungal communities.After the invasion of S.alterniflora,the relative abundances of Bacteroidota（11.57～15.59%）,Desulfobacterota（8.13～13.62%）,and Campilobacterota（0.22～4.46%）in soil bacterial communities significantly increased,while the relative abundance of Gemmatimonadota decreased sharply from 8.82%to 2.32%.In soil fungal communities,the relative abundance of Chytridiomycota（2.95～8.47%）significantly increased,while the relative abundances of Mortierellomycota（0.35～0.06%）and Olpidiomycota（0.07～0.001%）significantly decreased.Soil salinity,conductivity and nitrogen content were the most important factors driving changes in the structure and diversity of soil bacterial and fungal communities of intercalary S.alterniflora and S.salsa ponies in the Yellow River Delta wetlands.（3）The invasion of S.alterniflora has simplified the symbiotic network relationships between soil microbial communities.The analysis of the soil microbial symbiotic network shows that the connection number,average degree,and average path length of the bacterial and fungal communities in the soil of S.alterniflora are significantly lower than those of S.salsa.This suggests that the invasion of S.alterniflora has simplified the symbiotic networks of soil microbes and weakened the interactions among them.（4）The invasion of S.alterniflora affects the functioning of soil bacterial and fungal communities.Through functional predictions,the relative abundance of bacterial functional groups related to soil nitrogen cycling,such as Aerobic chemoheterotrophy（20.67～26.86%）,Nitrate reduction（1.21～3.58%）,and Ureolysis（0.03～0.12%）,significantly increased,while the relative abundance of bacterial functional groups related to aerobic ammonia oxidation（0.20～0.01%）significantly decreased in the bacterial community.In the fungal community,the relative abundance of Saprotroph increased significantly from 12.3%to 17.53%,while the relative abundance of Pathotroph and Symbiotroph decreased significantly.However,gene chip testing results show that the invasion of S.alterniflora did not significantly alter the diversity and absolute abundance of functional genes associated with soil nitrogen cycling.The above results indicate that there are slight differences in nitrogen utilization characteristics between S.alterniflora and S.salsa.The invasion of S.alterniflora can significantly affect the structure of soil microbial communities and simplify the soil microbial symbiotic network.Future studies need to further explore the regulation of soil microbes on its nitrogen utilization characteristics under the invasion of S.alterniflora.