| Poplar Short rotation coppice culture systems provide raw materials to production of pellet fuel and bio-alcohol fuels.Biomass harvested from ground level can produce granular fuels and biomass liquid fuels.In this paper,the effects of two kinds of poplar on the growth of biomass and fine root characteristic in three different planting densities and three different rotation periods were studied.,to explore the more suitable poplar clonal clones,planting density,rotation cycle.The main results were as followed:The vertical change rules of fine root biomass,root length density,and fine root surface area of Populus tomentosa and Europe and America were similar to those of undisturbed control stand,both of which increased with soil and showed two peaks.The first peak value of fine root biomass of all stand was in the topsoil layer of 0-20 cm,and the second peak was affected by the difference tree species,and planting density.Stumping significantly increased the surface fine roots of triploid Populus tomentosa B301 and Populus x euramericana cv.’74/76’(P<0.05).The fine root biomass of 0-20 cm layer of triploid Populus tomentosa B301 forest stand under the density of 5000 plants/hm2,10000 plants/hm2 and 20000 plants/hm2 increased by 27.2%,39%and 50%compared with CK.Stumping increased the fine root biomass of the Populus x euramericana cv.’74/76’ 0-20cm soil layers by 18.3%,28.2%,and 47.2%,respectively.The average root length density of Populus x euramericana cv.’74/76’ roots under the density of 5000 plants/hm2,10000 plants/hm2 and 20000 plants/hm2 was increased by 690%,158%,and 63%,compared with CK.Stumping increased the root length density of triploid Populus tomentosa B301 by 38.7%,42.4%and 47.2%,respectively.The results showed that the growth of the fine roots of triploid Populus tomentosa B301 was stronger than Populus x euramericana cv.’74/76’.There was a more obvious downward trend in the fine roots of deep-layer soils in the Populus x euramericana cv.’74/76’than Populus tomentosa B301.With the increase of planting density,the effect of a Stumping a on the growth of the fine roots of the surface was reduced,and the promotion effect of aa on the growth of the fine roots was improved.The ratio of bark of triploid Populus tomentosa B301 and Populus × euramericana cv.’74/76’decreases with increasing diameter,tends to be stable above 50 mm diameter,the dry weight ratio of Populus tomentosa B30 bark is stable at 15.28±1.25%,and the proportion of Populus x euramericana cv.’74/76’ bark dry weight is stable at 20.2±2.34%.The proportion of bark of bark dry weight,fresh weight,and bark of Populus × euramericana cv.’74/76’ was significantly greater than triploid Populus tomentosa B301.The density effect is obvious in Poplar Short Rotation coppice culture systems.In different rotations,the individual plant biomass decreased with the increase of planting density.However,the annual average biomass of forest stands increased significantly with the increase of planting density.Annual average biomass yields of triploid Populus tomentosa B301 and Populus x euramericana cv.’74/76’ have a maximum in the rotation period of 2 years under the density of 20000 plants/hm2.(11.32t/hm2·a and 12.47t/hm2·a)。Under the density of 20000 plants/hm2,there is no significant difference between the average annual yield and the average annual biomass yield of poplars that have grown for 3 yearsBoth triploid Populus tomentosa B301 and Populus × euramericana cv.’74/76’ had the highest biomass of the stand at the planting density of 20,000 plants/hm2 under all three rotation cycles.Planting densities of 20,000 plants/hm2 were the optimum densities for rapidly obtaining stand biomass.When the rotation period is 2 years and the planting density is 20000 plants/hm2,the annual average biomass yield of triploid Populus tomentosa B301 and Populus x euramericana cv.’74/76’ has the maximum value(11.22t/hm2·a and 12.23t/hm2·a).The biomass of the two poplar energy forests in the second flat rotation in the second year of rotation fell.The optimum planting density and rotation period of the two poplar energy forests should be planted at a density of 10,000 plants/hm2 and a rotation period of 3 years.For triploid Populus tomentosa B301 plantation was y=0.0936x2 4677,R2=0.9636,and exception found for the two years and for Populus × euramericana cv.’74/76’ was y=0.9438x2.2719,R2=0.9438.By sampling the model for testing,the model has a high degree of fit.Populus tomentosa and European and American poplar with different densities can use a general model to predict single-branch biomass and stand biomass. |
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