Effects Of Exotic Plant Invasion On Soil Nitrogen Status

Exotic plant invasion which declines biodiversity and influences structure and function of ecosystems has been a globally eco-environmental issue.More and more studies showed that influences of exotic plant invasion on soil nitrogen?N?cycles and soil N availabilities could facilitate the success and aggravation of plant invasion while there is surprisingly little integrated analyses of global data in field settings.In addition,rhizospheric soil is the main site where root exchange matter with soil and microbe.Focusing on the rhizosphere can help us assess the effects of plant invasion on soil nitrogen status more exactly.Based on the background mentioned above,we integrated soil nitrogen indexes of global invasive researches,and carried out experiments in sites invaded by Ageratina adenophora in southwest China.The main conclusions include:Based on the data analysis integrated from 107 papers,we found that contents of soil total N,ammonium-N,nitrate-N,inorganic N,microbial biomass N under invasion were significantly increased by?50±14?%,?60±24?%,?470±115?%,?69±25?%,?54±20?%relative to uninvaded areas globally.Classified comparisons of different invasive zones and plants indicated that relative variations of soil inorganic N contents under invasion were higher in temperate zones than in subtropical and tropical zones;invasion of N₂-fixing plants caused larger increments of total N and nitrate-N contents than non-N₂-fixing invasive plants;invasion of woody plants led to stronger increments of total N and nitrate-N contents than herbaceous plants.And increments of soil nitrate-N contents of different life forms increased linearly with the percentages of N₂-fixing invasive plants.Experimental results showed that Ageratina adenophora had stronger ability to absorb nitrate-N than native plants in the first area while Ageratina adenophora and Bidens pilosa L.both accelerated soil rates of nitrogen cycling in the second area.Correlative relationships between inorganic N contents and altitudes,and net nitrification rates and carbon to nitrogen ratios in non-rhizospheric soils are stronger than in rhizospheric soils,and this may attribute to stronger effects of biotic factors in the rhizosphere.Ageratina adenophora raised demand for nitrate-N with increasing time since invasion.And the phenomenon that net nitrification rate of rhizospheric soil is significantly higher than the rhizosphere's in the sites invaded by Ageratina adenophora for more than 50 years indicates that Ageratina adenophora may establish dominance by prompting soil nitrification.