Growth Rhythm Of Mixed Plantation And It’s Soil Properties In The Yellow River Delta

In the Yellow River Delta, take the 1 year old, 5 years old, 13 year old, 29 years old mixed plantations of Fraxinus chinesis × Robinia pseudoacacia, 29 years old mixed plantations of Ulmus pumila×Robinia pseudoacacia and Ailanthus altissimas×Robinia pseudoacacia as research objects, take no stocked bare land and 29 years old pure forest of Robinia pseudoacacia, Fraxinus chinesis, Ulmus pumila and Ailanthus altissimas as control groups. In order to study the mixed plantation growth-development rhythm and the reciprocities between tree and soil environment, this paper researched the growth condition of forest aerial part, soil physical properties, soil nutrients condition and soil enzyme activities of different stands. This paper analyzed the mixed effects of three mixed plantations and the main limiting factors through principal component analysis. The results are as fllows:⑴In the early developing period of Fraxinus chinesis×Robinia pseudoacacia mixed plantation, diameter at breast height grow faster. In the later developing period, tree height grow faster. In the mixed plantation, Robinia pseudoacacia grow faster than Fraxinus chinesis in the early developing period; Fraxinus chinesis grow faster than Robinia pseudoacacia in the later developing period. The compound storied forest which Fraxinus chinesis with clear advantage formed at last. Robinia pseudoacacia grow condition have no obvious change in the mixed plantation, Fraxinus chinesis have intraspecific differentiations, and preserving rate show a decreasing trend.⑵As the increasing of mixed plantation age, soil physical properties improved gradually, soil bulk density get lower, soil porosity get larger, and soil secondary salinization is been inhibited obviously. In the early developing period which diameter at breast height grow faster, only 0-20 cm soil layer’ soil bulk density and soil porosity act an obvious change; In the later developing period which tree height grow faster, 20-40 cm and 40-60 cm soil physical properties get better gradually.⑶Soil enzymes activity have obvious change as the increasing of mixed plantation age. The activities of soil urease and invertase have the largest increasing rate, the activity of soil polyphenol oxidase get lower gradually. As the increasing of soil depth, the activities of different soil enzymes show increasing or reducing trend, but these change of 20-40 cm and 40-60 cm soil layer lag behind the 0-20 cm soil layer.⑷As the mixed plantation grow, the content of soil Navi and Kavi increase significantly, the content of Pavi has no obvious change, but has an increasing trend; the content of soil OM increase in the early developing period, and then decrease; except the 29 year old mixed plantation, the content of Nt and Pt have no obvious change.⑸The tree grow condition have highly significant correlation with soil porosity, soil urease and alkaline phosphatase, the content of soil nutrient changing led behind tree grow condition and soil enzyme activity. In mixed plantations of Fraxinus chinesis×Robinia pseudoacacia, soil physical properties and soil enzyme activity are the direct ones been improved. The activity of soil urease, alkaline phosphatase and the content of Pavi is the critical factor to the development of mixed plantation.⑹Robinia pseudoacacia has no obvious change in different mixed model mixed plantation, the intraspecific differentiation of Fraxinus chinesis and Ulmus pumila get lower in mixed plantation, the preserving rate is large in mixed plantation. Fraxinus chinesis×Robinia pseudoacacia mixed plantation has the biggest volume, Ulmus pumila×Robinia pseudoacacia mixed plantation has the largest increasing range.⑺Mixed plantation can improve soil physical properties in 0-20 cm and 20-40 cm soil layer significantly. Fraxinus chinesis×Robinia pseudoacacia mixed plantation is the most stabilize stand in all soil layers, and its soil physical properties are in a relatively good condition; Mixed plantation can keep a low level of soil conductivity,Fraxinus chinesis×Robinia pseudoacacia mixed plantation is better than Ulmus pumila×Robinia pseudoacacia and Ailanthus altissimas × Robinia pseudoacacia mixed plantation in reducing soil conductivity.⑻Fraxinus chinesis×Robinia pseudoacacia mixed plantation has the best nitrogen translating capacity, Ulmus pumila×Robinia pseudoacacia mixed plantation has the best phosphorus translating capacity.⑼Mixed plantations can improve soil nutrients condition obviously in 0-20 cm soil layer. Ulmus pumila×Robinia pseudoacacia mixed plantation has the biggest improvement in 0-20 cm, Fraxinus chinesis×Robinia pseudoacacia mixed plantation has the lowest content of OM in 0-20 cm soil layer, but for other soil nutritions it is the most stabilize stand in all soil layers, Ailanthus altissimas×Robinia pseudoacacia mixed plantation has the highest content of OM in 0-20 cm, for other soil nutritions the stand performs normal.⑽Score of Fraxinus chinesis×Robinia pseudoacacia mixed plantation through principal component analysis is the highest, score of Ailanthus altissimas×Robinia pseudoacacia mixed plantation is lower than pure stand. The tree growing condition, nitrogen and phosphorus translating are major factors of mixed plantation mixed effect.