功能性状和立地条件决定树木根系NO3--N吸收能力

[Objectives]Nutrient is an important limiting factor for tree growth in arid and barren sites,and the way trees absorb and use nutrients in arid and barren sites determines their ecological adaptation strategies.In this paper,the dynamics of root nitrogen absorption and the coupling relationship between root morphological traits were measured in situ in the field,which laid a foundation for revealing the adaptation mechanism of trees to arid and barren environments.[Methods]We taked three common ornamental tree species(Prunus davidiana,Acer truncatum and Quercus variabilis)with different growth rates in shallow mountain area of Beijing as the research object.Using modified Hogland nutrient solution with NO3--N concentration gradients of 0.0,0.2,0.4,0.6,0.8,1.0 mmol·L-1,The root uptake kinetics of trees grown in two sites of Baiwangshan Forest Park was studied by in-situ measurement,and the relationship between root nutrient uptake kinetics parameters and root morphological characteristics was studied by linear model.[Results]The difference of growth characteristics,site conditions and the interaction of the above two factors all had an significant or extremely significant on root NO3--N uptake rate and kinetic parameters,such as:Vmax,Km,Cmin,α.Three tree species all had high nitrogen affinity.The Vmax of A.truncatum was only 1/10 of P.davidiana and 1/5 of Q.variabilis.Under the site conditions of more drought and barren,fast growing tree species had compensatory absorption of NO3--N.Root functional traits and the uptake rate of NO3--N had a good coupling relationship,the result showed that RD,SRL and RTD could respectively explain 12.29%,30.38%(P<0.001)and 2.9%(P<0.05)of the variation of uptake rate.The interaction of SRA and BI,SRL and Forks,SRA and NL,RTD and NL could also significantly explain from 2.19%to 4.1%(P<0.05).When considering the linear correlation between single functional trait and NO3--N uptake rate,only RD,log10SRL,log10RTD reached a very significant level(P<0.05).[Conclusions]The NO3-uptake rate of P.davidiana and Q.variabilis with a faster growth rate decreased significantly under the extremely drought and barren site stress,while A.truncatum was the opposite.The"speed strategy"of increasing the maximum absorption rate(high Vmax)and reducing nitrogen affinity(high Km)ensured the compensatory absorption of NO3--N by the roots of fast-growing tree species.The combination of morphological traits with higher SRL,higher SRA,lower RD and lower RTD can effectively improve the uptake rate of NO3--N by roots in drought and barren sites.