| Rubber plantation is an important economic crop and typical artificial forest ecosystem in tropic region.Rubber tree planting area rapid expansion as the natural rubber prices continued rise.Whether planting rubber tree will have negative impact.on the ecological environment caused a lot of controversy.Studies reported that the soil fertility decreased,soil erosion,and soil microbial biomass reduction after planting rubber tree.In order to properly evaluate the soil quality status of rubber plantation,and found out whether the soil quality of rubber plantations was degraded.In this paper,we investigate the soil quality from the aspects of soil physical properties(pb,porosity and water capacity),chemical properties(pH,CEC,and soil nutrition)and biological properties(Soil respiration,enzyme activity,microbial carbon biomass and microbial diversity)in a chronosequence of rubber tree plantations that were 5,10,13,18,25 and 30 years old.The soil quality of different years old rubber plantations was evaluated,and the influencing factors and reasons for the soil quality variation of rubber plantation were analyzed.At last,the corresponding regulate measures were put forward.The main findings as follows:(1)Soil physical properties variation of rubber plantationsThe soil bulk density of rubber plantations increased with increase of soil depth.Soil total porosity,capillary porosity,saturated water holding capacity and capillary water holding capacity were decreased with increase of soil depth.There was no significant difference of non capillary porosity and non capillary water holding capacity in the 0-20cm and 20-40cm soil layers.The variation of soil bulk density,porosity and water holding capacity were mainly in 0-20cm soil layer,but there was no significant difference in 20-40cm soil layer.In 0-20cm soil layer,soil bulk density was lowest in 5year-old rubber plantations,and highest in 30 year-old rubber plantations,but no significant difference in 10,13,18 and 25 year-old rubber plantations.The total soil porosity,water content and saturated water holding capacity were highest in 5 year-old rubber plantations,but no significant difference in 10,13,18,25 and 30 year-old rubber plantations.The soil capillary porosity and capillary water holding capacity were highest in 5 year-old rubber plantations,followed by 25 year-old rubber plantations,but no significant difference in other year-old of rubber plantations.There was no significant difference in non capillary porosity and non capillary water holding capacity of rubber plantations at different ages.(2)Soil chemistry properties variation of rubber plantationsThe rubber plantations had acidic soil with pH values from 4.7 to 5.2.The pH value increases with the depth of soil layer,and decreased with the increase of rubber trees age.The content of soil organic matter was moderate,and cation exchange capacity,nitrogen,phosphorus and potassium were low(especially phosphorus and potassium deficiency).The contents of soil organic matter,total phosphorus and available potassium decreased with increase of soil depth,while the contents of total nitrogenr total potassium,available nitrogen and available phosphorus were not significant difference between 0-20cm and 20-40cm soil layer.There were differences in soil nutrient content of rubber plantations at different ages.(3)Soil micro ecological characteristics variation of rubber plantationsThe soil catalase was from 0.41 mg/kg to 0.61 mg/kg,phosphatase was from 731.39ug/g to2393.05ug/g,and urease was from 271.33ug/g to 324.26ug/g.Catalase.phosphatase and urease were highest in 5 year-old rubber plantations,followed by 18,25 and 30 year-old rubber plantations,and lowest in 10 and 13 year-old rubber plantations.The soil microbial biomass carbon from 30.23 mg/kg to 85.81mg/kg,and highest in 10 and 13 year old-rubber plantations,but no significant difference in 5,18,25 and 30 year-old of rubber plantations.The soil microbial functional diversity of rubber plantations in before tapping was higher than that after tapping.The soil microbial functional diversity was difference at different year-old rubber plantations in before and after tapping.The utilization carbon capacity of soil microbial community in rubber plantation was strong for the sources of carboxylic acids.amino acids,amines and carbohydrates,but the capacity of use phenolic acids and polymers were poor.By high-throughput sequencing technology.a total of 438870 bacterial 16S rDNA gene sequences,2073 OTUs,and 563658 fungi ITS gene sequence,2521 OTUs were detected.The soil bacterial community diversity indices of Ace,Chao,Shannon-Wiener,Simpson and Coverage were from 1331 to 1695,from 1334 to 1732,from 5.46 to 6.02,from 0.007 to 0.01 8,from 0.983 to 0.987,respectively.Soil bacterial diversity of 10,13.18 and 30 year-old rubber plantations were higher than 5 and 25 year-old rubber plantations.The soil fungi community diversity indices of Ace,Chao,Shannon-Wiener,Simpson and Coverage were from 601 to 824,from 598 to 815,from 3.77 to 4.40,from 0.035 to 0.098,froln 0.991 to 0.994,respectively.There were no significant differences in Shannon and Simpson index in different rubber plantations,but there were differences in Chao,Ace and coverage index.As much as 98.99%of the bacterial sequences were found in 28 phyla,66 classes,139 orders.245 families,355 genera and 645 species,while 1.01%of bacterial sequences were unclassified.As much as 66.15%of the fungi sequences were found in 28 phyla,66 classes,139 orders,245 families,355 genera and 645 species,while 33.85%of fungi sequences were unclassified.The dominant phyla of soil bacterial communities were Acidobacleria,Proteobacteria,Chloroflexi,Actinobacteria and Verrucomicrobia.The dominant phyla of soil fungi communities were Ascomycota,Zygomycota and Basidiomycota.There were similarities and differences of soil bacteria and fungi communities in different succession stages of rubber plantations.(4)Influence factors,evaluation and regulation of soil quality in rubber plantationsSoil quality was the highest in 5 year-old rubber plantations,and lowest in 13 and 18 year-old rubber plantations,the soil quality was gradually restored in 18,25 and 30 year-old rubber plantations.Soil microbial community diversity indices of Ace and Chao,pb,SOM,TK,and soil fungal community diversity index of Shannon-Wiener were main indices to evaluate the soil quality of rubber plantations.The soil physical and chemical properties of were closely related to the productivity of rubber plantations.Soil bulk density increased with the growth of rubber tree biomass.Soil porosity and water holding capacity decreased with the increase of rubber tree biomass,and increased with the increase of vegatation biomass and plant of individual numbers.PH is closely related to rubber tree biomass,vegatation species,and plant of plant individual numbers.CEC is closely related to vegatation biomass and rubber tree biomass.Soil nutrient content is closely related to vegatation biomass,vegatation species,and plant of individua l numbers.Catalase,urease and MBC are the main factors that affect the functional diversity of soil microbial communities in rubber plantations.Rubber tree biomass,plant of individual numbers,pH and phosphatase are the major factors that affect the diversity of soil bacterial communities in rubber plantations.An,TK,AK,SOM,TN,vegatation biomass and phosphatase are the main factors that affect the diversity of soil fungal communities in rubber plantations.The main measures to regulation soil quality of rubber plantation were:take reasonable tapping system and management measures;balanced fertilization to improve soil fertility;to reduce human disturbance and build a complex ecosystem. |
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