Ecological stoichiometry focuses on the balance of chemical elements in ecological processes

in which the stoichiometric characteristics of carbon (C)

nitrogen (N) and phosphorus (P) in different components are important features of ecosystem functions and processes. At present

it is not clear how the introduction of Hippophae rhamnoides (N-fixing) affects the nutrient cycling mechanism of ecosystem in N-fixing or non-N-fixing pure plantations. Therefore

two kinds of mixed forests (H. rhamnoides + Pinus tabuliformis

HrPt; H. rhamnoides + Robinia pseudoacacia

HrRp) and the pure forests of P. tabuliformis (Pt) and R.pseudoacacia (Rp) were selected. The C

N and P contents in leaf

litter and 0—100 cm soil layer were quantified

and the effects of mixed afforestation on the synergistic variation of nutrients among different components were explored. The results indicated that:(1) Compared with Pt

the C

N

P contents (p<0.05) and the N∶P (p>0.05) increased

while C∶N and C∶P decreased (p>0.05) in the leaves of P. tabuliformis in HrPt

indicating that HrPt was helpful to relieve the restriction of N and accelerate its growth rate. Meanwhile

compared with Rp

the C

N

C∶P and N∶P decreased

while P and C∶N increased of R. pseudoacacia in HrRp (p>0.05)

suggesting that HrRp might enhance the absorption of P by R. pseudoacacia

but the sequestration of C and N would be decreased. (2) The C

N

P contents and N∶P of the litters in HrPt were significantly higher than those of Pt

and the C∶N and C∶P values were significantly lower than those of Pt

indicating that HrPt was helpful to accelerate the decomposition rate of litter and promote nutrient return. Compared with Rp

the C

N

P contents and their stoichiometric ratios of the litters in HrRp increased (p>0.05)

suggesting that HrRp did not significantly promote the decomposition of litter. (3) Compared with Pt and Rp

the soil C

N and P contents in HrPt and HrRp increased

but C∶N and C∶P decreased (p>0.05)

indicating that HrPt and HrRp were helpful to increase the utilization efficiency of N and P and improve the soil nutrient status. (4) The main stoichiometric indicators between leaf and litter had a strong synergistic effect. In addition

the correlation of N and P elements in leaf

litter and soil was more obvious than that of the C element. In summary

compared with HrRp

HrPt was more helpful to improve the supply of nutrient limiting factors and accelerate the conversion of nutrients among different components. The research results are of great significance for revealing the nutrients supply potential of the artificial mixed forest ecosystem in the Loess Plateau and formulating a reasonable forest management plan.