| Phosphorus is one of the main nutrient elements for forest growth and net primary productivity of forest ecosystems,Due to the low availability of phosphorus in the soil,phosphorus has become a limiting factor for the growth and important ecological processes of many forest ecosystems.The importance of the phosphorus cycle in controlling the ecological processes of terrestrial ecosystems has received more attention in the past 20 years.Therefore,research on phosphorus in forest ecosystems is particularly important.In this paper,the four-year-old Eucalyptus(E.urophylla)plantation of different generations(1,2,3 and 4)in Guangxi Dongmen Forest Farm,Fusui County,By studying the phosphorus content,reserves and distribution characteristics of its ecosystem,the process of phosphorus accumulation and change during the continuous cultivation of eucalyptus was revealed,which provided a basis for the sustainable management of eucalyptus plantation.The main findings are as follows:(1)The biomass of eucalyptus plantations in the 1,2,3 and 4 generations were 98.43,88.49,83.95 and 73.48 t·hm-2,respectively,and the biomass of the arbor layer was 89.11,80.24,76.98 and 67.70 t hm-2 respectively,the biomass of understory plant layer(shrub layer and herb layer)were 4.18,3.47,2.73 and 2.19 t hm-2,respectively,and the litter layer biomass was 5.14,4.78,4.24 and 3.59 t·hm-2,respectively.The order of biomass of different organs in different planting generations eucalyptus plantations was dry material>root>branch>dry skin>leaves.(2)The net productivity of arbor layer in eucalyptus plantations of 1,2,3 and 4 generations was 22.277,20.061,19.246 and 16.925 t · hm-2· a-1,respectively,showing a decreasing trend with increasing planting generations The net productivity of different organs in different planting generations was the fastest in dry matter accumulation,which was 10.246～13.703 t · hm-2· a-1,followed by roots,branches and dry skin,respectively 2.539～3.159 t · hm-2 · a-1,1.833～2.461 t · hm-2 · a-1 and 1.517～1.956 t · hm-2 · a-1 The accumulation rate of leaves is the slowest,only 0.792～0.999 t · hm-2·a-1.(3)There are differences in phosphorus content in different structural levels of different planting generations eucalyptus plantation ecosystems.The phosphorus content of different organs in arbor is between 0.096 and 1.107 g·kg-1,among which the leaves are the highest,followed by dry skin,branches and dry materials.The content of phosphorus in soil(0～80 cm)is between 0.367 and 0.432 g·kg-1,which tends to decrease with the deepening of soil depth,and also shows an increasing trend with increasing planting generations.(4)The total phosphorus reserves of the 1,2,3 and 4 generations eucalyptus plantation ecosystems were 3827.751 3859.995,3903.692 and 3952.604 kg·hm-2,respectively,of which the arbor layers were 22.290,21.060,20.314 and 16.064 kg·hm-2,respectively.0.58%,0.55%,0.52%,and 0.41%of the reserves;the understory plant layers were 3.150,2.714,2.386,and 1.48 kg·hm-2 accounting for 0.08%,0.07%,0.06%,and 0.04%;The layers are 1.549,1.246,1.277,and 0.839 kg·hm-2,accounting for 0.04%,0.03%,0.03%,and 0.02%;the soil layers are 3800.762,3834.974,3879.764,and 3934.217 kg·hm-2,respectively,accounting for 99.30.%,99.35%,99.39%,and 99.53%.(5)The annual phosphorus accumulation in the arbor layer of the 1,2,3 and 4 generation eucalyptus plantations was 5.573,5.265,5.079 and 4.016 kg.hm-2·a-1,respectively.The net accumulation is the highest in dry materials,1.500～2.161 kg·hm-2.a-1,followed by leaves and dry skin,0.778～1.063 kg·hm-2·a-1 and 0.651～1.053 kg·hm-2·a-1;the minimum is root,which is 0.143 to 0.219 kg·hm22·a-1. |
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