Mechanism Of Poplar's Productivity Increased By Mixture Of Seabuckthorn (Hippophae Rhamnoides L.) And Poplar (P.simonii Carr.)

The experiments were carried out in Ansai, shaanxi, Loess Plateau, where topography is more typical. We continuously surveyed and measured stand and habitats indexes of 26-year-old seabuchthorn ( Hippophae rhamnoides L. ) 2K poplar ( P.simonii Carr. ) mixed stand and the two pure stands. These indexes were: stand productivity, forest and aboveground biomass, stand physiological indexes, soil water conditions, soil physical characteristics, turnover of nutrients and amino acid between soil and plant, some micro-climate indexes. We expected to discover the mechanism of Poplar's productivity increased by mixture of Seabuckthorn ( Hippophae rhamnoides L.) and Poplar ( P.simonii Carr. ) .The results provided scientific basis for applicable forestation model in Loess Plateau. The main results were as follows:Forest and aboveground biomass and distribution patterns in the mixed stand were different remarkably from those in the poplar pure stand. (1) The time of the defoliation of the mixed stand was later than the pure: the time when half of the leaves were defoliated in autumn in the mixed stand was 15 days later than the poplar pure stand. (2) Mean height, diameter at breast height (DBH) and stand biomass were 44.8%, 32.7%and 139.76% higher in the mixed stand than in the poplar pure stand respectively. (3) Distribution patterns of forest biomass were, in the mixed stand: Tree layer (78.34%)>Biomass of underground (14.58%)> Shrub layer (5.7%)> Litter layer (1.36%)>Herb layer (0.02%); in the poplar pure stand: Tree layer (61.74%)>Biomass of underground (36.83%)>Litter layer (1.26%)>Herb layer (0.17%) >Shrub layer (0%). (4) Aboveground biomass of tree layer, in the mixed stand: Trunk (38.57%)>Over three year branch (30.83%)>Root stake (14.87%)>Bark (10.11%)>Dead wood (2.22%)>Leaf (2.17%)> Two year branch (0.71%) >A year branch (0.5%); in the poplar pure stand: over three year branch (35.62%)>Trunk (33.35%)>Root stake (12.81%)>Bark (7.78%)>Leaf (6.26%)>Dead wood (3.33%)> Two year branch (0.48%)>A year branch (0.36%). (5) Compared with the poplar pure stand, in the mixed stand ,poplar s root system(diameter < 10mm),which mainly served as absorbing water and nutrients, was distributed deeper and evener.2.Some physiological indexes of seabuckthorn and poplar in two pure stands and the mixed stand were different. (l)In one season, the daily course of leaf RWC, Tr and Rs in the mixed stand were different from those in the two pure stands.(2) Coefficient between Rs and RWC : the relationship of poplar in the pure stand was: Logistic Model: y=a/(l+b*exp(-cx))(r< r0.05),in the mixed stand was: Sinusoidal Fit: y=a+b*cos(cx+d) (r>r0.05); the relationship of seabuckthorn in the pure stand was: 3rd degree Polynomial Fit: y= a+bx+cx2+dx3... (r>r0.01),. in the mixed stand was: y=a+b*cos(cx+d) (r>r0.01)-(3)Coefficient between Tr and RWC: the relationship of poplar in the pure stand was: Sinusoidal Fit: y=a+b*cos(cx+d),. (r>0.01),in the mixed stand was: 3rd degree Polynomial Fit: y=a+bx+cx2 + dx3..., (r>0.01.); the relationship of seabuckthorn in the pure stand was: Quadratic Fit: y=a+bx+cx2 (r>r0.o5.),. in the mixed stand was: 3rd degree Polynomial Fit: y=a+bx+cx2+dx3... (r>o.oi);.(4) Coefficient between Tr and Rs: the relationship of poplar in the pure stand was: Rational Function: y=(a+bx)/ (1+cx+dx2)( r>r0.01) , in the mixed stand was: 3rd degree Polynomial Fit: y=a+bx+cx2+dx3.. (r>r0.01); the relationship of seabuckthorn in the pure stand was: Rational Function: y=(a+bx)/(1+cx+dx2) (r>r0.01), in the mixed stand was: 3rd degree Polynomial Fit: y=a+bx+cx2+dx3..(r>r0.01).3.Soil physical characteristics in the mixed stand were different from those in the the pure stands: in the soil depth of 0~ 40cm ,soil bulk density and porosity in the poplar pure stand was 12.02%~ 18.92% higher and 13.40%~21.78% lower than in the mixed stand respectively, in the seabuckthorn pure stand wasl.82%~ 8.62% higher and 1.51%~7.80% lower than in the mixed stand respectively. Capillary porosity, non-capillary porosity and capillary water holdi...