Effects of water and nitrogen on growth and relative competitive ability of introduced versus native C_(4)grass species in the semi-arid Loess Plateau of China

摘要

Switchgrass is an introduced C_(4)grass in the semi-arid Loess Plateau of China,but there is a lack of information to assess its ecological invasive risk.In this study,Old World bluestems(native C_(4)grass)and switchgrass were sowed at five mixture ratios(8:0,6:2,4:4,2:6 and 0:8)under two soil water levels(80%field capacity(FC)and 40%FC)and two nitrogen(N)treatments(0 and 100 mg N/kg dry soil,termed N0-unfertilized and N1-fertilized treatments,respectively)in a pot experiment in 2012.Biomass,root morphological traits and relative competitive abilities of these two species were analyzed.Results showed that biomass of both species was significantly greater under 80%FC or N fertilization,and switchgrass had a relatively larger root:shoot ratio(RSR).Total root length(TRL)and root surface area(RSA)of switchgrass were significantly higher under 80%FC irrespective of N treatment,while those of Old World bluestems were only significantly higher under N fertilization.N had no significant effect on TRL and RSA of switchgrass,while RSA of Old World bluestems significantly increased under 80%FC and N fertilization.Under 40%FC and N0-unfertilized treatment,the aggressivity of Old World bluestems was larger than zero at 2:6 and 4:4 mixture ratios of two species,whereas it was close to zero at 6:2 mixture ratio.Root competitive ability of switchgrass significantly increased under 80%FC or N fertilization.The aggressivity of Old World bluestems was negative at 6:2 mixture ratio under 80%FC and N fertilization,while it was positive at 2:6 mixture ratio.Switchgrass may become more aggressive when N deposition or rainfall increases,while a proper mixture ratio with appropriate water and N management could help with grassland management in the semi-arid Loess Plateau.