Effects Of Litter Leaf Addition Of Different Tree Species On Soil Phosphorus Components In Subtropical Region

Phosphorus（P）is an indispensable nutrient element for the growth and development of forest trees.The phosphorus required for the growth of forest trees mainly comes from soil,and the phosphorus in soil can directly determine the growth and development of plants and crop yield.However,the phosphorus in soil exists in complex forms,and the phosphorus that can be absorbed and utilized by plants accounts for a small part of the total phosphorus content.The lack of phosphorus in soil and its ability to supply directly affect the production level of forest ecosystem.Litter return is an important source of soil available P supplementation in forest ecosystem.The quality and P form of litter may have an important effect on soil available P.In this study,litters of 12 dominant tree species（divided into conifer species,deciduous broad-leaved tree species and evergreen broad-leaved tree species）in subtropical forests were collected,and 31P-NMR technology was used to analyze the phosphorus content and morphological composition of litters leaves.The litters were cultured in two layers of 0-10cm and 10-20cm soil by indoor culture method.To explore the effects of litter leaf addition of different tree species on soil phosphorus components and biological availability,analyze the improvement and contribution of litter decomposition and release of phosphorus to soil phosphorus content in subtropical areas,and provide theoretical basis for the transformation,release,turnover,absorption and utilization of phosphorus in subtropical forests.The main research results are as follows:（1）The initial C,N and P contents of litters of different tree species were significantly different（P<0.05）.The C content of Cunninghamia lanceolata was the highest(505.27g·kg^-1),while the content of Symplocos setchuensis was the lowest(378.85g·kg^-1).The highest initial N and P contents were found in Vernicia montana.The contents of orthophosphate and pyrophosphate in litters of different tree species were significantly different.Specifically,the highest content of orthophosphate(1190.03mg·kg^-1)was found in Vernicia montana,while the lowest content was found in Lithocarpus glaber(90.66mg·kg^-1).The pyrophosphate content of Choerospondias axillaris was the highest(146.66mg·kg^-1),while the content of Liriodendron chinense was the lowest(5.47mg·kg^-1).Among the functional types of different tree species,the contents of orthophosphate,phosphomonoester and pyrophosphate of deciduous broad-leaved tree species were significantly higher than those of evergreen broad-leaved tree species and conifer species,while the content of phosphodiester of conifer species was higher than that of broad-leaved tree species,indicating that the phosphorus supply potential of deciduous broad-leaved tree species was significantly higher than that of conifer species and evergreen broad-leaved tree species.（2）The experimental results of adding soil phosphorus components in litters of different tree species showed that the content of resin P decreased gradually with the passage of culture time.Compared with the litters of different tree species,the content of resin P in litters of deciduous broad-leaved tree species increased most obviously.The increase of sodium bicarbonate Pi content in litters of coniferous species was the most obvious,while the increase of sodium bicarbonate Po content in litters of evergreen broad-leaved species was the most obvious.In the two soil layers,the labile P content added by litter of deciduous broad-leaved tree species was significantly higher than that of coniferous and evergreen broad-leaved tree species.The content of sodium hydroxide P in litters of coniferous species increased significantly at the early stage of culture,and that in litters of deciduous broad-leaved tree species increased significantly at the late stage of culture.The content of moderately labile P in litters of coniferous species was higher in 0-10cm soil layer,and the content of moderately labile P in litters of deciduous broad-leaved tree species was higher in 10-20cm soil layer.The content of residual P in litters of evergreen broad-leaved trees in both soil layers was higher than that of the other two species.The content and proportion of P components in different soils were as follows:the content and proportion of residual P were the highest,followed by moderately labile P and labile P,and the content and proportion of stable P were the lowest.（3）The release of phosphorus from litters may also be affected by the decomposition rate of litters themselves.In this study,soil respiration method was used to measure soil CO₂ flux to indirectly reflect the differences in the decomposition rates of litters of different tree species.The change of soil CO₂ flux in 0-10cm soil layer was more obvious than that in 10-20cm soil layer,indicating that the decomposition of litters was better in the topsoil.The soil CO₂ flux of different tree species after litter addition was significantly higher than that of the group without litter addition,indicating that litter addition contributed to the change of soil CO₂ flux to some extent.Tree species and time showed significant correlation to the changes of soil CO₂ fluxes,and there were significant differences in the addition of litter of different tree species to soil CO₂ fluxes.Deciduous broad-leaved trees decomposed faster in the early and late stages of decomposition,and evergreen broad-leaved trees decomposed faster in the middle stages of decomposition.Soil CO₂ flux decreased with the passage of time,that is,the decomposition rate of litters of different tree species was faster in the early stage,but slowed down in the later stage.（4）The analysis of influencing factors of soil P components showed that evergreen broad-leaved tree species were larger than deciduous broad-leaved tree species and coniferous tree species in 0-10cm soil layer,and there was no significant correlation between the content of active P in litters and soil labile P at different tree species levels.In the early stage of cultivation in 10-20cm soil layer,the soil labile P content of deciduous broad-leaved tree species was higher than that of evergreen broad-leaved tree species and coniferous tree species,which was consistent with the change law of P content and components in litters.The analysis of influencing factors of soil phosphorus components showed that the initial C,N and P contents of soil were significantly correlated with sodium bicarbonate P and sodium hydroxide Pi,and were significantly correlated with resin P,indicating that soil characteristics could largely determine the availability of soil phosphorus.The-highest content of labile P in litters was that of Vernicia montana,but the highest proportion of labile P in soil was that of Cinnamomum in the indoor culture process.Therefore,there was no significant correlation between the content of labile P in litters of different tree species and the supply of soil P released by litters.The redundancy analysis showed that soil labile P was positively correlated with pyrophosphate in litters,and negatively correlated with orthophosphate and monophosphate,among which it was significantly negatively correlated with diphosphate in litters,indicating that the lower the content of diphosphate in litters,the higher the content of labile P in soil,that is,the level of diphosphate in litters is an important factor determining the content of active P in soil.In this study,the variation of soil CO₂ flux represents the difference of litter decomposition rate among different tree species.The change of litter decomposition rate has significant influence on soil sodium bicarbonate P,sodium hydroxide Pi and hydrochloric acid P,indicating that the speed of litter decomposition rate is also an important factor determining the availability of soil phosphorus.