| Cunninghamia lanceolata is important afforestation tree in south China, however, high density and monoculture lead to soil fertility and forest land productivity decline.As we know, nitrogen(N) and phosphorus(P) is the limit factor of vegetation productivity. And the high iron and aluminum content in the red soil region of south China easy cause P fixed and inactivation, aggravating the P restrictions on C. lanceolata productivity in this region. Now stand structure(e.g., different densities, C. lanceolata and broad leaved forest, etc.) effect on C. lanceolata plantation soil P transformation and its organs N, P content characteristic are not clear. It seriously restricted the sustainable management of C. lanceolata plantation and its ecological function. This study sites select the similar latitude area of Fujian Sanming and Hunan Huitong. C. lanceolata grown in different densities(low, middle, high) pure forest and C. lanceolata and broad leaved forest as the research object. Collected rhizosphere and non rhizosphere soil, and then use Hedley P classification method to reveal the transformation process of C. lanceolata soil P functional components and the difference of rhizosphere affected under different forest stand structures. Using Strahler grade method classify C. lanceolata for analyzing leaves nutrient dynamic, nutrient recycling efficiency and main ecological stoichiometric ratio on different vegetative organs. All of these are for C. lanceolata forest structure optimization, and provide a scientific basis for sustainable management. Main results are as follows:(1) Stand structure significantly influence rhizosphere soil total P content of C. lanceolata, the overall trend of mixed forest and low density > medium density > high density. In addition, different stand densities significantly affect rhizosphere rapidly available P, slow available P, occluded P, which characterized by low density > density > medium density. Compared with the pure forest, mixed forest Chinese fir rhizosphere available P and occluded P increased more significantly, Fujian and Hunan province respectively high by 98% 52% and 44% 53%.(2) Chinese fir soil total P, available P, rapidly available P, slow available P in the rhizosphere effect of the pure forests and mixed forests were presented with positive effect. In the pure forest, Chinese fir soil slowly available P in the rhizosphere effect is medium density < high density. Compared with the pure forest, Chinese fir mixed forest soil rapidly available P in rhizosphere effect significantly enhancement, but the other functions of P the rhizosphere effect have no significant difference in the different forest structure.(3) In the different density of pure forest, C. lanceolata biennial branches and leaves of N and P content and N/P ratio is medium density < low density and high density. Annual branches N P content and N/P no significant difference between each density, but the mixed forest of C. lanceolata biennial branches and leaves of N P content was significantly higher than that of pure forest. in general, C. lanceolata N content in 13.72 g/kg ~ 17.91 g/kg, P content in 1.21 g/kg ~ 1.90 g/kg, N/P ratio is 7.73 ~ 11.22.(4) Different forest types have significant influence on C. lanceolata nitrogen recycling efficiency, with no significant effect on the phosphorus recycling efficiency. Low density and high density C. lanceolata with high nitrogen recycling efficiency of 51% and 52%, respectively, and the nitrogen recycling efficiency of C. lanceolata mixed 36% higher than the pure forest.To sum up, dense forest, C. lanceolata rhizosphere soil available P levels increased significantly, then the supply of soil available P can meet the demand of C. lanceolata, Where as in mixed forests, different tree species make C. lanceolata showed stronger rhizosphere effect, and improved the conversion and use of soil P. At the same time increase the branches and leaves of N nutrient recycling efficiency to promote nutrient compensation, so as to adapt to the lack of soil nutrients. |
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