Effects Of Seasonal Precipitation On Soil Priming Effect In Rubber Plantation With Different Planting Patterns

There is obvious seasonal change in precipitation in tropical areas with global warming.This change shows that the total precipitation remains the same,the wetter the rainy season,the drier the dry season.The seasonal precipitation change may affect soil priming effect（PE）in tropical areas.Rubber tree is one of the important economic tree species in tropical areas,and soil carbon loss is serious.Building agroforestry system is considered to be an important way to increase soil carbon.However,it is still unclear how the change of planting pattern affects the soil priming effect under the change of precipitation season.Three planting patterns were set in this study:rubber tree monoculture（CK）,rubber and Alpinia oxyphylla interplanting（AO）,and rubber and Lysimachia christinae interplanting（LC）.Three water gradient treatments:natural precipitation（NR）;dry season decreased by 30%and rainy season increased the rainfall decreased in dry season,but the annual rainfall total remained unchanged（TR）;dry season decreased by 60%and rainy season increased the rainfall decreased in dry season,but the annual rainfall total remained unchanged（SR）.Soil samples of different treatments in the dry season and rainy season were collected,and ¹³C-labeled glucose（representing active carbon）and vanillin（representing inert carbon）were added to separate ¹³C-labeled PLFA for analysis by setting up incubation experiments,and the changes of microbial groups between treatments and seasons were compared.At the same time,soil priming effect was measured to reveal the mechanism of precipitation seasonal change and vegetation composition on soil priming effect of rubber plantation.The main results are as follows:（1）In the dry season,soil carbon cumulative mineralization of single rubber plantation increased significantly with the decrease of precipitation.Under natural precipitation,the addition of glucose increased soil carbon cumulative mineralization,while the 30%and 60%reduction of precipitation decreased soil carbon cumulative mineralization.The addition of vanillin also reduced soil carbon cumulative mineralization.In the rubber and Alpinia oxyphylla interplanting model,a 30%decrease in precipitation increased soil carbon cumulative mineralization by 96%compared to natural precipitation,while a 60%decrease in precipitation increased soil carbon cumulative mineralization by 54%.Under natural precipitation conditions,the addition of glucose or vanillin increased soil carbon cumulative mineralization,but decreased soil carbon mineralization under 30%and 60%precipitation reduction.In rubber and Lysimachia christinae interplanting model,soil carbon cumulative mineralization increased by 31%with 30%less precipitation and 8%with 60%less precipitation compared with natural precipitation.The addition of glucose or vanillin increased the amount of cumulative carbon mineralization,while the addition of glucose or vanillin decreased the amount of mineralization in soil with 30%less precipitation.（2）In the rainy season,compared with the natural precipitation,increasing precipitation by 30%reduced soil carbon cumulative mineralization of single rubber plantation,and increasing precipitation by 60%increased the cumulative mineralization of soil carbon.Adding glucose or vanillin increased soil carbon cumulative mineralization in treatments of natural precipitation and increasing precipitation by 30%,while increasing precipitation by 60%reduced soil carbon cumulative mineralization.In the rubber and Alpinia oxyphylla interplanting model,compared with natural precipitation,increasing precipitation by 30%reduced the soil carbon cumulative mineralization by 74%,while increasing precipitation by 60%reduced soil carbon cumulative mineralization by 23%.In treatments of natural precipitation and increasing precipitation by 30%,the addition of glucose or vanillin increased soil carbon cumulative mineralization,while in treatments of increasing precipitation by 60%,the addition of glucose or vanillin decreased soil carbon cumulative mineralization.In rubber and Lysimachia christinae interplanting model,compared with natural precipitation,increasing precipitation by 30%decreased soil carbon cumulative mineralization,while increasing precipitation by 60%increased soil carbon cumulative mineralization.The addition of glucose and vanillin increased the cumulative mineralization of soil carbon by 3%and 94%respectively in soil treated with natural precipitation,increased the cumulative mineralization of soil carbon by 85%and 18%respectively in soil treated with increasing precipitation by 30%.Increasing precipitation by 60%,soil carbon accumulation mineralization was reduced by 51%by adding glucose and 45%by adding vanillin.（3）In single rubber plantation,although the addition of glucose under natural precipitation had a positive PE,with the decrease of precipitation in the dry season,the addition of glucose was conducive to the production of a strong negative PE.The addition of vanillin produced negative PE,but the extent of negative priming effect was lower than that of glucose.In natural precipitation,the PEs of rubber and Alpinia oxyphylla interplanting and rubber and Lysimachia christinae interplanting were positive compared with rubber tree monoculture,and the PE with glucose was the highest in rubber and Alpinia oxyphylla interplanting,while rubber and Lysimachia christinae interplanting was the lowest.In ¹³C-PLFAs,it was found that bacteria used exogenous carbons in dry season.In addition,in all precipitation treatments of rubber tree monoculture and Alpinia oxyphylla interplanting with natural precipitation,glucose and vanillin were utilized in different order.A large amount of CO₂ derived from glucose appeared obviously before the 7th day,while CO₂ derived from vanillin appeared obviously after.The decrease of precipitation improved the decomposition of exogenous carbons,but did not affect the sequence of carbon utilization.However,the difference of exogenous carbon in Lysimachia christinae interplanting could not cause the change of carbon utilization sequence.（4）In single rubber plantation during the rainy season,although the addition of exogenous carbons under natural precipitation produced positive PE,with the increase of precipitation during the rainy season,the addition of exogenous carbons produced strong negative PE.The PE produced by different planting patterns in response to exogenous carbons was different.When glucose was added,rubber and Alpinia oxyphylla interplanting was higher than single rubber plantation,but the PE extent of Lysimachia christinae interplanting was lower than single rubber plantation and was negative PE.Adding vanillin,AO and Lysimachia christinae interplanting were higher than single rubber plantation.In the rainy season,¹³C-PLFAs showed that the microorganisms using exogenous carbons and the microorganisms used were different in the soil with different precipitation and planting patterns.In single rubber plantation soil,the microorganisms using exogenous carbons were bacteria,and fungi were the main microorganisms using exogenous carbons in increasing precipitation by 60%.In natural precipitation,fungi were the main microorganisms using exogenous carbons in Lysimachia christinae interplanting soil.In Alpinia oxyphylla interplanting soil,glucose was mainly used by actinomyces,while vanillin was mainly used by fungi.In conclusion,cumulative mineralization of soil in the dry season and rainy season could be caused by changes in extreme weather,no matter decreasing precipitation in the dry season or increasing precipitation in the rainy season.When exogenous carbons entered the soil,one part was used,and another combined with POC and other substances.In general,the content of POC was low,but the mineralization was increased.Exogenous carbons leaded to PEs of different extents and even different directions,but PE was also affected by precipitation,planting patterns and other environments.Environmental changed such as precipitation and planting patterns affected the species and abundance of soil microorganisms by changing soil environmental conditions and the input of plant carbon sources,and then affected the utilization of carbons by microorganisms in soil to cause PE in different directions and extents.Under extreme drought or extreme precipitation,the planting pattern with glucose or plant compound,especially AO,produced lower mineralization than monoculture mode,which was more conducive to the rubber plantation soil adaptation to extreme weather changes.