Variation Of Soil P And Its Fractions In Larch Forests Characteristics In NE,China

Phosphorus（P）is essential for forest ecosystem functions,and different P fractions are differentially available to plants.Larch forests are typical boreal climax communities with a wide distribution in NE,China.Previous studies on soil P have mostly focused on farmland and grassland or only on total P and available P,and it is unclear that differences soil P and its fractions in concentration and stoichiometric percents in Larch and influence mechanisms.Typical larch forests were selected in our study.Based on the field sample survey,we clarified the changes of soil P and its fractions under different succession,forest types,latitude,keystone species,plant diversity and soil microbial,analyzed the causes and influencing factors of the differences.The main conclusions are as follows:1)Soil P changes in boreal Larch based on forest succession and forest type:Forest succession effects:Soil TP and nine fraction-Ps declined non-linearly under forest succession in concentration,and three organic fractions（Na HCO₃-Po,Na OH-Po,and conc.HCl-Po）showed the same trend as TP,with a similar non-linear decrease.The stoichiometric percent of Pi,conc.HCl-Pi and Na OH-Pi linearly increased（R²=0.81-0.92）,and Po,Na OH-Po,and Re-P decreased linearly（R²=0.59-0.61）.The difference of sample site distribution explained 30.8%of soil changes,so partial RDA excluding its impacts could identify the exact association between plant succession and P changes.The negative relations between biomass and organic fraction-Ps showed that P storage in tree biomass was responsible for soil P declines during plant succession,and tree diversity accelerated these P changes.The significantly higher soil P in the grass stage was due to P’s grass-upload function to surface soils.Overall,soil P was depleted,with an increasing Pi proportion during plant succession in high-latitude boreal forests.Differences in forest types:Paired-T test revealed Larch>Poplar-birch in soil TP,about 42.1%higher（p<0.05）,and it was consistent pattern in all four sites.All the eleven P concentration indicators showed Larch>Poplar-birch,about 1.2-1.7 times higher,and nine indicators were significant（p<0.05）（except HCl-Pi and Re-P）.But no significant differences were found among forest types in P stoichiometric percent with the highest medium-active Na OH-P.RDA analysis showed that Larch had higher TP and organic P fractions（Na OH-Po,conc.HCl-Po,Re-P,etc.）,while Poplar-birch was the opposite.Forest types had no effect on soil P stoichiometric percent.2)Variation of soil P among Natural Larix forests of the Greater and Lesser Khingan Mountains and Changbai Mountains in NE,China:The effects of latitude:The effect of latitude on soil P and its fractions was significant（p<0.01）except r H₂O-P.There are two main patterns:one was the highest in mid-latitude Lesser Khingan Mountains（Liangshui）.TP and five P indicators were about 1.5-4.3 times higher than other sites;Other P indicators were high P in high latitude Greater Khingan Mountains（Arctic village）,about 1.5-7.1 times higher than the other two sites.None of the effects of tree size on soil P was significant,including large tree low P type and large tree high P type.Soil P was higher（1.2-1.7 times）in high SOC areas.Variation partitioning and RDA:Soil properties had the most significant influence on soil P and its fractions,followed by geo-climates.The more SOC,carbon storage and TN,the more TP and organic P fractions.Inorganic P fractions increase（Na HCO₃-Pi,Na OH-Pi,HCl-Pi）accompanied higher longitude,lower latitude and diversity indices.3)Mechanism of action in a Larix plantation based on diversity,keystone species and microbial:Keystone species and diversity effects:Ten of the eleven P parameters in AM species were 1.4-3.3-fold higher than Ec M species（p<0.05）,much larger than diversity-related differences;Po was highest in Larch（Ec M）,while TP was lowest in Pinus-t（Ec M）.Diversity loss resulted in the decrease of Po but an increase of Pi（p<0.05）.Variation partitioning and RDA:Keystone species had the most significant influence on soil P and its fractions,followed by soil properties Keystone species mainly influenced low-active fractions,and high-and medium-active fractions were more affected by soil properties and plant diversity.Metagenomics results identified two microbial functional gene groups‘phosphatase and transporter’and‘glycerol and regulon’,related to the diversity-mycorrhizal-P-fractions regulations.Species richness indirectly increased all P fractions by enhancing P‘phosphatase and transporter’microbes,and Ec M species declined P fractions directly by species diversity-related niche-compensation.Differences in soil microbial:In species composition,Actinobacteria was significantly higher in AM species than in Ec M species,while Acidobacteria was higher in Ec M species（p<0.01）.In functional genes,gcd（quinoprotein glucose dehydrogenase）was the most abundant and higher in Ec M species,but glp K（glycerol kinase）was higher in AM species（p<0.05）.Actinobacteria,Proteobacteria,Acidobacteria and Chloroflexi played an important role in soil P cycling genes.Soil TP and nine fraction-Ps were higher in AM species than in Ec M species（p<0.05）.RDA analysis showed that:the more SOC,TN and the less organic P mineralization,inorganic P transporter and regulon genes,the more inorganic P fractions;Medium-low active fractions（Na OH-Po,conc.HCl-Po）were regulated by inorganic P solubilization functional genes.Soil carbon storage,temperature and humidity sensitivity of respiration carbon decomposition,carbohydrase enzyme and soil carbon cycling related genes significantly correlated to soil P.Soil SOC has the strongest correlation with soil P,but temperature and humidity sensitivity has little relationship with soil P.The correlation numbers of carbohydrase enzyme including AA,CE with P index were 7and 6,respectively.The genes involved in Arnon-Buchanan cycle were positively correlated with 8 P indices.To sum up,soil P and its fractions in Larch are influenced by multiple factors such as forest succession,forest type,latitude,keystone species and diversity,etc.In large scale,it was mainly influenced by soil properties,followed by geo-topography,with little plant diversity.In small scale,it was most influenced by keystone species,probably through soil microorganisms.This study provided theoretical support and data reference for Larch stand management of soil P nutrients,carbon sink function and soil microbial regulation in NE,China.