| Phosphorus(P),as one of the indispensable elements for the growth and development of trees,participates in plant photosynthesis,respiration,and nucleic acid synthesis.Phosphorus is closely related to plant growth and development and physiological metabolic reactions,and has important implications for the ecological processes and functions of subtropical forests.At present,there are many studies on phosphorus forms in forest ecosystems,most of which are concentrated in the soil,while there are few studies on plants.The application of 31P NMR technology in soil and crops is at a preliminary stage.The research on the phosphorus content of woody plants is still unclear,and the root system is a hot spot in underground ecology,and its importance cannot be ignored.This study took 18 common tree species in subtropical forests as the research object,collected root samples,divided the root system into absorbing roots,transporting roots,and supporting roots according to functions,and determined root morphological indicators(root tissue density RTD,average root diameter AD,Specific root length SRL,root specific surface area SRA),nutrient content and root phosphorus components(orthophosphate Or.P,phosphate monoesters Mo.P,phosphate diesters Di.P,pyrophosphate Py.P)content,and The diameter increase at breast height of 18 tree species in one year was measured,and the correlation between different growth rate tree species and tree species functional traits,especially phosphorus content,was analyzed.Compare the phosphorus components,root morphological indicators,nutrient content,and growth rate of the functional roots of different life-type tree species,and analyze whether there are phylogenetic signals among the functional traits of the roots.Provide theoretical basis for the transformation,release and turnover of subtropical forest phosphorus,as well as production,operation and management.The main findings are as follows:(1)The total phosphorus content of the functional roots of different life-type tree species all showed the same law.The total phosphorus content of the roots of all life-type tree species was the highest in absorption roots,followed by transport roots,and supporting roots,which were 0.73g/kg,0.52g/kg,and 0.39g/kg,respectively.The total phosphorus content of each functional root system of deciduous tree species was higher than that of coniferous tree species and evergreen broad-leaved tree species.31P NMR spectroscopy was used to detect the phosphorus components of tree roots.Four phosphorus components were detected in the extractable solution of sodium hydroxide-Ethylene Diamine Tetraacetic Acid from tree roots,namely orthophosphate,phosphate monoesters,and phosphate diesters,pyrophosphate.The roots of different life-type tree species accounted for the highest proportion of orthophosphate,followed by phosphate monoesters,phosphate diesters,and pyrophosphate,which were 54.35%,35.53%,7.95%,and 2.55%respectively.The content of phosphorus component(except phosphate monoester)and total phosphorus content of different life-type tree species in the functional root system showed the same law,which was the highest in the absorption roots and the lowest in the supporting roots.There was a significant positive correlation between the phosphorus content of tree roots and the extractable phosphorus content of sodium hydroxide-Ethylene Diamine Tetraacetic Acid.(2)The average root diameter and root tissue density of all life-type tree species are the lowest for absorption roots,followed by transport roots,and support roots are the highest,respectively 0.53mm,0.35g/cm3,1.77mm,0.43 g/cm3,4.43mm,0.47 g/cm3,and the specific root length and specific surface area of the life-type tree species are the highest for the absorption root,followed by the transport root,and the support root is the lowest,respectively 16.07 m/g,250.18 cm2/g,1.10m/g,57.65 cm2/g,0.16 m/g,20.68 cm2/g.There were significant differences in root tissue density between evergreen broad-leaved tree species and deciduous broad-leaved tree species in supporting roots.The average root diameter of each functional root system of the same life form had significant differences.The functional root systems of evergreen broad-leaved tree species and deciduous broad-leaved tree species had significant differences in the specific root length,but there was no significant difference in the specific root length of different life-type tree species.In general,the root morphology of tree species(RTD,AD,SRL,SRA)and phosphorus content basically had a significant correlation.(3)For different life-type tree species,the root nutrient content was basically SOC>TN>Ca>Al>K>Mg>Fe>TP>Mn>B.In addition to coniferous species,the root organic carbon content of evergreen broad-leaved tree species and deciduous broad-leaved tree species showed the same pattern,both of which were the lowest in absorbing roots,followed by transport roots,and the highest in supporting roots,which were 412.25g/kg and 416.73g/kg,442.53g/kg,435.25g/kg,457.64 g/kg,465.93g/kg,respectively.The total nitrogen content of the roots of different life-type tree species was the highest among the absorbing roots,followed by the transport roots,and the lowest among the supporting roots,which were 11.32g/kg,7.79g/kg,and 6.63g/kg,respectively.The root organic carbon ratio total nitrogen content and organic carbon ratio total phosphorus content of each life-type tree species showed similar results,both of which were the highest in supporting roots and the lowest in absorbing roots.The total nitrogen to total phosphorus content of roots differs among different life-type tree species.The total nitrogen to total phosphorus content of root absorption and supporting roots of deciduous broad-leaved tree species have significant differences,while the functional roots of other life-type tree species had no significant differences.The root organic carbon content of tree species had a significant negative correlation with the orthophosphate content,and the root total nitrogen content of tree species had a significant positive correlation with the orthophosphate content.(4)Among the 15 traits of 18 tree species,only the root organic carbon content showed significant phylogenetic signals(P<0.05)and strong phylogenetic signals(K=1.01),while none of the other 14 functional traits showed significant signs.Phylogenetic signals.Means other 14 functional traits(AD,RTD,SRL,SRA,TN,TP,Or.P,Mo.P,Di.P,Py.P,C/N,C/P,N/P,RGR)may be more affected by environmental factors,and the root organic carbon content in the phylogenetic position of the tree species was relatively close to that of the species,and had similar characteristics.(5)The growth rate of diameter at breast height and the relative growth rate of diameter of coniferous tree species were the highest for Cunninghamia lanceolata and the lowest for Pinus massoniana,which were 2.40mm,1.12mm,0.015cm/yr,0.0067cm/yr,respectively.The evergreen broad-leaved tree species had the highest diameter increase at breast height of Cinnamomum camphora and the lowest of Lithocarpus glaber at 7.33mm and 0.19mm,respectively.The relative growth rate of diameter was the highest for Symplocos setchuensis,and Lithocarpus glaber was the lowest at 0.046cm/yr and 0.0012cm/yr.Deciduous broad-leaved tree species have the highest increase in diameter at breast height and relative growth rate of diameter for Vernicia montana,and the lowest in Quercus fabri,7.70mm,0.32mm,0.044cm/yr,0.0024cm/yr,respectively.The increase in diameter at breast height and the relative growth rate of the diameter of tree species had a significant negative correlation with the content of phosphate diesters,but no significant correlation with the content of phosphorus components(orthophosphate,phosphate monoesters,pyrophosphate). |
