Effects Of Mixing Eucalyptus And Castanopsis Hystrix On Ecological Stoichiometry Characteristics Of Plant-Soil-Microorganism

Mixing Eucalyptus and local precious tree species are considered to be an effective way to sustainable management of Eucalyptus plantation.It is of great significance to understand the influence of Eucalyptus and precious tree species on the ecological stoichiometric characteristics of plant-soil-microorganism and to further reveal the ecological stoichiometric effect of Eucalyptus and precious plant species.In this study,we researched the ecological stoichiometric characteristics of plant leaves,litter,soil nutrients,enzyme activities,and microbial biomass under three different stands,including pure Eucalyptus plantation(PE),pure Castanopsis hystrix plantation(PCH),and mixed Eucalyptus and Castanopsis hystrix plantation(MEC).The effect of mixing Castanopsis hystrix and Eucalyptus on the C,N,P content and stoichiometric ratio of plant-soil-microorganisms and their interrelation were discussed also in the Qingshan Experimental Field of Tropical Forestry Experiment Centre of Chinese Academy of Forestry,Pingxiang,Guangxi.The main results are as follows:(1)The leaf C content was PCH>MEC>PE,the leaf N content was PE>MEC>PCH,and the leaf P content was MEC>PCH>PE.The lower C/N and C/P of MEC leaves compared to the pure forest indicated that MEC had higher nutrient utilization efficiency.Leaf N/P of PE,MEC,and PCH was less than 14,indicating that all three stands were susceptible to N restriction.However,There were no significant differences in leaf C,N,and P as well as their stoichiometric ratios between different stands,the results showed that mixing Eucalyptus and Castanopsis hystrix had no significant effect on the ecological stoichiometric characteristics of leaves.(2)The litter C,P content was MEC>PCH>PE,there had a significant difference between mixed forest and pure forest.The litter N content showed MEC>PE>PCH.Compared with PE and PCH,MEC showed higher litter C/N and lower litter C/P,indicating that mixing Eucalyptus and Castanopsis hystrix affected the decomposition rate of the litter to some extent.The litter N/P appeared as MEC<PCH<PE<25,indicating that the decomposition of all three forest litters was susceptible to N restriction and reflecting that mixing Eucalyptus and Castanopsis hystrix didn’t improve the element restriction.(3)Compared with PE,MEC significantly increased the SOC content at0-100 cm soil layers.There was no significant difference in soil TP content among the three forests in each soil layer.Soil SOC,TN,and TP contents all decreased with soil depth increasing,it’s worth noting that SOC and TN at 0-10 cm soil layer were significantly higher than those in 10-20 cm soil layer.In the0-20 cm soil layer,the C/N ratio of PE,MEC,and PCH soil was lower,which was conducive to releasing the N element.Also,both soil C/P and N/P were higher,which indicated that the effectiveness of soil P element was lower in this region,and all the three forests were susceptible to P limitation.In addition,the soil C/N,C/P,and N/P showed PCH>MEC>PE,indicating that mixing Eucalyptus and Castanopsis hystrix improved the decomposition rate of soil organic matter and the availability of P element compared with PCH.(4)The contents of soil microbial biomass carbon(MBC),biomass nitrogen(MBN),and biomass phosphorus(MBP)of MEC were overall higher than those of PE and PCH at 0-20 cm soil layer,the results showed that ability of MEC soil holding C,N,P is strong.There were significant differences in soil MBN and MBP contents among different stands in the same soil layer.The contents of MBC,MBN,and MBP at 0-10 cm soil layer were significantly higher than those at 10-20 cm soil layer in the same stand.The MBC/MBP was PE>PCH>MEC on the above layers,indicating that MEC soil microorganisms had a greater potential to release P element in the process of mineralization of soil organic matter,and thus could play a supplementary role of MBP to the soil available P pool.(5)The activities of leucine aminopeptidase(LAP)were significantly increased in the mixed plantations at both 0-10 cm and 10-20 cm soil layers,the activities of β-1,4-glucosidase(BG),and acid phosphatase(ACP)were significantly reduced on the above layers,and there had non-significant effect on the activity of β-1,4-N-acetylglucosaminidase(NAG).With the increase of soil depth,the activities of these four enzymes,as well as enzymes C/P and N/P,were significantly decreased in the three stands.The soil ecoenzymatic C/N/P stoichiometry of the PE,MEC,and PCH were 1:1.08:1.37,1:1.16:1.34,and1:1.07:1.31 at 0-20 cm soil layer respectively,which were inconsistent with the1:1:1 global pattern of C/N/P stoichiometry.This result suggests that the soil microbe of the three stands were more easily restricted by P.The mean values of enzyme C/N of the three stands were lower,while C/P and N/P of the three stands enzyme were higher,which reflected the relative lack of soil N element,which means that the three stands are also vulnerable to N restriction.Additionally,the values of enzymatic C/P and N/P of the MEC were both higher than that of the PE,while its enzymatic C/N was lower than that of the PE,which indicated that the limitation of P was alleviated in MEC to some extent,but didn’t improve the limitation of N.(6)There was a weak correlation between leaf and litter,and between them and soil nutrients and microbial stoichiometric characteristics,indicating that plant stoichiometry couldn’t be used to characterize soil nutrient status and microbial activity.Soil nutrients and microbial stoichiometric characteristics showed a close relationship.Specifically,soil SOC and TN were both significantly correlated with microbial biomass C,N,P content,and enzyme activities and their stoichiometric ratios,while there was no significant correlation between soil TP and microbial stoichiometric characteristics.Therefore,it can be considered that the nutrient cycling of C,N,and P in the Eucalyptus plantation and its mixed forest ecosystems in the study area were not balanced.In conclusion,mixing Eucalyptus and Castanopsis hystrix had a non-significant effect on plant ecological stoichiometry.Compared with the pure plantation,mixed plantation improved the decomposition rate of soil organic matter and the availability of P element to some extent.It also enhanced the ability of soil microorganisms to retain nutrient elements and the potential of releasing P element,which was conducive to the improvement of P limitation but didn’t improve N limitation.Therefore,we should pay more attention to the input of N and P elements in the fertilization strategy of the Eucalyptus plantation and its mixed forest in this area in the future.