Similarities And Differences In Root And Leaf Traits Of Pinus Massoniana And P.Elliottii And Their Responses To Mixture In Degraded Red Soil Region

Roots and leaves are the most important tree organs,and the plasticity of the root and leaf traits reflect the adaptability of trees to habitats.The selection of afforestation tree species and their mixed patterns are one of the problems that need to be solved in the vegetation restoration of the degraded red soil area in the southern China.In this study,masson pine(Pinus massoniana)pure plantation,slash pine(P.elliottii)plantation pure plantation,mixed plantation of slash pine and Schima superba established in 1991 in the typical degraded red soil region of Taihe County,Jiangxi Province,and mixed plantation formed by replanting pure masson pine plantation with S.superba and mixed plantation formed by replanting pure slash pine plantation with S.superba in 2008 were selected to studied.During the growing season(July)from 2017 to 2019,the total of 5 types of plantation stands were collected the top soil and determined the total amount and available nutrient contents;collected the roots,fresh leaves,twigs and litter leaves and twigs,estimated their biomass and determined the nutrient contents.Meanwhile,we calculated the nutrient resorption efficiency,analyzed the similarities and differences of rhizosphere soil,different functional roots biomass,nutrient content and recovery efficiency of fresh and litter twigs and leaves of different ages.Compared the response mechanisms of root and leaf traits and soil nutrients of mixed masson pine and introduced slash pine to mixed broad-leaved trees,it provides a reference for vegetation restoration in degraded red soil areas.The main results are as follows:(1)The total soil nutrients and available nutrients of masson pine and slash pine plantations were not significant(P<0.05).Mixed plantation significantly increased the total nitrogen content and the nitrogen to phosphorus ratio in the 0～10 cm layer of slash pine soil,and increased the ammonium nitrogen content in the rhizosphere soil of masson pine and non-rhizosphere soil of masson pine,but it did not significantly affect the other total and available nutrients of the two tree species.(2)The distribution of absorbed roots in the 0～10 cm soil layer of the masson pine forest was the largest,and the distribution of the transport roots in the 20～40 cm layer was the most,while the absorption roots and transport roots of the slash pine plantation were the most distributed in the 20～40 cm layer;and the distribution of soil roots in the 0～10 cm layer of masson pine replanting S.superba plantation was the most,the distribution of absorption roots was the most in the 20～40 cm layer,the distribution of absorption roots in the 0～10 cm layer of the slash pine replanting S.superba plantation was the largest,and the distribution of the transport roots in the10～20 cm layer was the most.The 0～10 cm wide soil layer of slash pine mixing with S.superba plantation had the most distribution of absorption roots,and the 20～40 cm soil layer had the most distribution of transport roots.Masson pine replanting S.superba plantation significantly reduced the absorbed root biomass of the 0～10 cm and 10～20 cm layers of masson pine soil,and significantly increased the transported root biomass of 0～10 cm;slash pine replanting S.superba plantation significantly reduced the biomass of absorbed roots in the 20～40 cm layer of slash pine soil,while slash pine mixing with S.superba plantation had no significant effect on the biomass of absorbed roots and transport roots of slash pine.In addition,the specific root length of absorption roots and transported roots of masson pine and slash pine had no sensitive to mixed responses.(3)The total nitrogen content of new and old leaves of masson pine and the total phosphorus content of old leaves were significantly higher than that of slash pine.masson pine replanting S.superba significantly increased the total phosphorus content of the old branches of masson pine,and these were not significant that the effects slash pine mixing with S.superba and slash pine replanting S.superba on the total nitrogen,total phosphorus,and nitrogen to phosphorus ratio of each organ of slash pine.(4)The amount of litter leaves of masson pine plantation was lower than that of slash pine plantation,but the mixing had no significant effect on the amount of litter leaves of masson pine and slash pine and their nitrogen and phosphorus recovery and recovery efficiency.In summary,the root and leaf properties of masson pine and slash pine have strong environmental plasticity,mainly by adjusting the spatial distribution pattern of the root system to adapt to the resource competition of mixed broad-leaved trees in the degraded red soil area.It is inferred that both tree species can be recommended as afforestation tree species for vegetation restoration in the study area,and both pure plantations can be transformed into coniferous and broad-leaved mixed plantations.