Rhizosphere Stimulating Effect Of Subtropical Woody Plant

Living roots of plant can regulate the carbon cycle of terrestrial ecosystems through the rhizosphere priming effect(RPE).However,the amplitude and influencing factors of RPE in subtropical mature forest species remain unknown.In this paper,the field carbon dioxide trapping system and natural 13C isotope tracer technique was employed to bury the living roots of three coniferous tree species(root δ13C,-28.79 to-27.92 ‰)and four broadleaved tree species(root δ13C,-29.98 to-28.64 ‰)in the sugarcane soil after 20-year monoculture(soil δ13C,-16.39 ‰)to study the RPE of native SOC decomposition when the roots of different tree species grew in the same soil under field conditions.The study found that the relative RPE of coniferous trees was+34.34 to+57.75%,contrarily,that in broadleaved trees was-42.63 to-21.37%.Soil mineral nitrogen(N)content in planted soil was lower than that in unplanted soil.In contrast,soil mineral N content was significantly larger for coniferous tree species than for broadleaved tree species.Microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN)in planted soil of coniferous tree species was higher than that in unplanted soil,suggesting that the increase of soil microbial activity may be the reason for the positive RPE of coniferous tree species.The MBC and MBN in planted soil of broadleaved tree species were lower than that in unplanted soil,suggesting that the competition between microorganisms and roots due to N uptake by plants may be responsible for the negative RPE of broadleaved tree species.This may be because plant photosynthesis promotes the absorption of N in soil by roots,increases the competition for N between plant roots and soil microorganisms and inhibits RPE.Overall,our results showed that to estimate the RPE of the forest soil,environmental factors that affect soil N availability must be considered.