Fine Root Respiration And The Influencing Factors In Woody Plants In Maoershan Mountain

Fine root respiration plays an important role in new root growth,maintance of root living,and nutrients absorption and carbon(C)cycle of forest ecosystem.However,the factors controlling the root respiration rate are still not well understood.Therefore,we measured the root respiration rate across the first five oders in 10 temperate tree species(Phellodendron amurense,Fraxinus manschurica,Padus racemosa,Albizia kalkora,Larix gmelinii,Picea koraiensis,Pinus sylvestris var.mongolica,Viburnum sargentii,Spiraea chamaedryfolia,Euonymus alatus),the root respiration rate of P.amurense and L.gmelinii at different season,and those of seven out of the 10 species at surface(0-10 cm)and subsuface(20-30 cm)soil layers,as well as the root morphology and tissue C and nitrogen contents in Maoershan mountain,Heilongjiang,China.The variaiton of the sensitivity of root respiration(Q10)to temperature among species,seasaon and soil depths within speceis were also assessed.The objectives of this study were to determine how root respiration rate varies with tree species,season and soil depth,and to elucidate the underlying mechanis for the variation.The results showed that:(1)Root respiration rates in P.amurense and L.gmelinii vary among seasons.In both species,root respiration rates of the first two orders in summer are significantly higher than those in spring and autumn,whereas roots of the third to fifth orders not.When the temperature of measurement was set at 18 ℃,root respiration rates of the first order at the surface soil in P.amurense and L.gmelinii in July were 20%and 8%higher than those in October,respectively.in top soil.The root respiration rate of the first order were correlated with total nitrogen content and root total carbon content,indicating the difference of root in metabolic activity and potential absorption function in different seasons.(2)Root respiration rate varies among tree species.Root respiration rate increased with the increasing temperature of measurement,but decreased with the ascending root order.When the temperature of measurement was set at 18 ℃,root respiration rates of the first order in L.gmelinii was the highest(26.1 nmol·g-1s-1),whereas Viburnum sargentii was the lowest(14.4 nmol.g-1·s-1).Among species,respiration rate of the first order root were correlated with root tissue density,root dry mass content and total nitrogen content.(3)Respiration rate of roots in surface soil layer was generlly higher than those in subsurface across the seven species,but the statistical significance was related to root order and the temperature of measurement.Specifically,when the temperature of measurement was set at 18 ℃,the averaged root respiration rates(26.2 nmol·g-1·s-1)of the first order across species at the surface soil lyaer was 24%higher than that(21.1 nmol-g-1·s-1)of subsurface,contrast to the value of 15%in the fifth order roots.The discrepancy of root respiration rate between soil depths can be explained by root diameter,root tissue density,total nitrogen content and total carbon content.(4)The Q10 values(the sensitivity of root respiration rate to temperature)of first order roots in surface soil layer scaled from 1.22 to 1.99 among the 10 species,but those of P.amurense and L.gmelinii showed weak differences among seasons.In comparison,the Q10 values of the seven species at surface soil layer were significantly higher than those at subsurface.In summary,root respiration rate and its sensivity to temperature varied with species,season and soil depth,which were related to root structural and functional characteristics to some degree.These findings may improve our understanding of the underlying mechanism of root repiration in temperate woody plants,and contribute to the establishment of root respiration modeling at the species level.