Variations in the natural 13C and 15N abundance of plants and soils under long-term N addition and precipitation reduction:interpretation of C and N dynamics

摘要

Background:The nitrogen isotope natural abundance(δ15N)provides integrated information on ecosystem N dynamics,and carbon isotope natural abundance(δ13C)has been used to infer how water-using processes of plants change in terrestrial ecosystems.However,howδ13C andδ15N abundances in plant life and soils respond to N addition and water availability change is still unclear.Thus,δ13C andδ15N abundances in plant life and soils were used to investigate the effects of long-time(10 years)N addition(+50 kg N·ha−1·yr−1)and precipitation reduction(−30%of throughfall)in forest C and N cycling traits in a temperate forest in northern China.Results:We analyzed theδ13C andδ15N values of dominant plant foliage,litterfall,fungal sporophores,roots,and soils in the study.The results showed thatδ15N values of foliage,litterfall,and surface soil layer’s(0–10 cm)total N were significantly increased by N addition,whileδ15N values of fine roots and coarse roots were considerably decreased.Nitrogen addition also significantly increased theδ13C value of fine roots and total N concentration of the surface soil layer compared with the control.The C concentration,δ13C,andδ15N values of foliage andδ15N values of fine roots were significantly increased by precipitation reduction,while N concentration of foliage and litterfall significantly decreased.The combined effects of N addition and precipitation reduction significantly increased theδ13C andδ15N values of foliage as well as theδ15N values of fine roots andδ13C values of litterfall.Furthermore,foliarδ15N values were significantly correlated with foliageδ13C values,surface soilδ15N values,surface soil C concentration,and N concentrations.Nitrogen concentrations andδ13C values of foliage were significantly correlated withδ15N values and N concentrations of fine roots.Conclusions:This indicates that plants increasingly take up the heavier 15N under N addition and the heavier 13C and 15N under precipitation reduction,suggesting that N addition and precipitation reduction may lead to more open forest ecosystem C and N cycling and affect plant nutrient acquisition strategies.