| Plantations,as an important component of the world’s forests,play an important role in carbon sequestration,emission reduction,and climate regulation.Litter decomposition is a key process in the carbon(C)and nutrient cycling of forest ecosystems,providing a source of nutrients for plant root absorption.The decomposition rate of litter in the soil where it originates is faster than in the soil with different plants,which is known as the home-field advantage(HFA)hypothesis.This hypothesis has been widely tested in pure forests,but it is unclear whether the HFA exists in mixed forests,especially in forests with different mixed proportions.It not only limits the understanding of nutrient mechanisms and release processes in mixed forests,but also hinders the formulation and implementation of policies to promote nutrient cycling,improve the overall level and effectiveness of forest nutrients,and improve forest productivity.Four plantation types were selected for the study: a Robinia pseudoacacia(RP)pure forest,a Hippophae rhamnoides(HR)pure forest,a mixed plantation with RP and HR at a ratio of 8:2,and a mixed plantation with RP and HR at a ratio of 5:5.Four types of woody leaf litter decomposition bags(RP,HR,mixed RP and HR at a mass ratio of 8:2,and mixed RP and HR at a mass ratio of 5:5)were designed based on the method of transplanting litter decomposition bags in the field,and the herbaceous litter was used as a control group,combining indicators such as climatic conditions,soil physicial,soil chemical properties,litter characteristics,litter mass,and element dynamics,with emphasis on studying the temporal variation process of litter decomposition and nutrient release in pure and mixed forests of RP and HR,analyzing the key regulatory factors for HFA and litter mixing effects,litter mass,and element release processes,and providing important data and insights for the material cycle mechanism in the vegetation restoration process on the Loess Plateau.The main research results are as follows:(1)After 549 days of decomposition,among the litter types,HR litter had the highest mass loss rate,while RP had the lowest mass loss rate,accounting for 53.10% and 33.08% of the initial mass,respectively.The highest release rates of C,N,and P from HR litter were59.13%,49.37%,and 60.89% of the initial storage,respectively;and the C and N release rates of the 8:2 mixed litter were the lowest,37.72% and 28.29% of the initial storage,respectively;and the P release rate of RP litter was the lowest,34.63% of the initial storage;the decomposition rate of litter in the early stage(0–105 days)was higher than that in the late stage(363–549 days);the C release patterns of different types of litter were generally consistent,showing a "release,enrich,re-release" pattern.(2)There were significant differences in the decomposition rate of litter placed in different forest types.The mass loss rate of herbaceous litter in the control group was the highest in the 5:5 mixed forest,and the lowest in the 8:2 mixed forest,which was 38.07%and 32.93% of the initial mass,respectively.The litter mass loss in the 5:5 mixed forest was the fastest,while that in the HR pure forest was the slowest.There was no significant difference in N and P release among different forest types.The mass loss of 5: 5 mixed litter generally showed additive effects in four different forest types,but 8: 2 mixed litter showed more nonadditive effects.(3)The HFA model showed that the quality index of HR litter was the highest,while that of RP litter was the lowest.Moreover,the quality index of different litter types had a consistent temporal trend.The soil in the 5:5 mixed forest had the strongest ability to decompose litter,while the ability of HR pure forest was the lowest.However,after the 363 days of litter decomposition,there was no significant difference in the decomposition ability of each stand type.In addition,there was no significant HFA effect among plantation types at each stage of decomposition.(4)The rate of litter mass loss was significantly influenced by sampling time,litter type,stand type,the interaction between sampling time and stand type,and the interaction between litter type and stand type.The difference in the composition of dominant fungal communities among the four types of plantation was greater than that of dominant bacterial communities.(5)The litter initial quality had a significant direct effect on C and N losses during the entire decomposition stage.Soil moisture and temperature could promote the C and N losses of litter,and the effects of soil moisture and temperature were mostly direct.Within each litter mass loss interval,microbial chemistry had a significant direct effect on litter C loss.The significant effect of microbial chemistry on litter N loss gradually weakened with the decomposition process,and became insignificant at the late stage of decomposition.In summary,this study verified the differences in the HFA and soil ability between mixed and pure forests with different mixing ratios,as well as the mass loss and element release differences between single litter and mixed litter with different mixing ratios,demonstrating the importance of litter quality for litter decomposition compared to soil microorganisms. |
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