Ecological Stoichiometric Characteristics Of Fraxinus Mandshurica Plantations

Taking 29 years of pure Fraxinus mandshurica plantation,Fraxinus mandshurica×Larix olgensis mixed plantation,Fraxinus mandshuricax Picea koraiensis mixed plantation and Fraxinus mandshuria×Pinus koraiensis mixed plantation which was planted on the natural forest narrow strip clear cutting land in Ashenhe-drainage basin as materials,the seasonal dynamics of leaf-litter-soil C,N and P concents and their stoichiometric ratios characteristics were studied in this paper.Results showed that:(1)During the whole growing season,the variation coefficient of C/P in leaf was the largest.Fraxinus mandshurica and Larix olgensis mixed plantation and pure Fraxinus mandshurica plantation have higher efficiency in nutrient use than the mixed plantation of Fraxinus mandshurica and Picea koraiensis or Pinus koraiensis.At early growth season,the leaves of Fraxinus mandshurica were mainly limited by N,while it turned to be restricted by both N and P when enter into the growing season.The coupling relationships among C,N,P content were significant in leaf(P<0.01).(2)The variation tendency of C,N,P and their stoichiometric characteristics of forest litters in pure Fraxinus mandshurica plantation and three mixed forest were all complicated.They showed different variability in different seasonal and also had not the same trend with leaf.The forest litter decomposition ratio of pure Frax-inus mandshurica plantation was the highest,and then followed by Fraxinus mandshurica x Larix olgensis mixed plantation,Fraxinus mandshurica x Pinus koraiensis mixed plantation,and Fraxinus mandshurica ×Picea koraiensis mixed plantation.The litter N/P in pure Fraxinus mandshurica plantation and Fraxinus mandshurica x Pinus koraiensis mixed plantation litter N/P was largely affected by P content,while it becomes to be controlled by N content in Fraxinus mandshurica × Larix olgensis and Fraxinus mandshurica × Picea koraiensis mixed plantation mostly.(3)The Fraxinus mandshurica was mixed with different coniferous trees has the function of changing soil fertility,however,the degree of fertility improvement was variable with different species.Throughout the growing season,the changing trend and differentiation of soil C,N,P content relative to different horizons were various among the pure Fraxinus mandshurica plantation and the other three mixed forests.Therefore,it cannot totally judge that the mixed plantation have a higher capacity on soil fertility promotion than pure plantation.Besides,soil C,N,P content was decreased with soil depth,and they have a significant relationship with each other based on four soils.(4)On average,the C,N content was in the order of leaf>litter>soil,leaf P content was significantly higher than litter and soil.while the C/N and C/P was in the order of litter>leaf>soil,and for N/P,it was lowest in soil,but leaf had no different than litter.In summary,considered the decomposition ratio of litters and the efficiency of nutrient use,the pure Fraxinus mandshurica plantation and Fraxinus mandshuricaxLarix olgensis mixed plantation should be a priority in study area,and then the Fraxinus mandshurica and Pinus koraiensis or Picea koraiensis mixed plantation could be also popularized.In addition,the nitrogen fertilizers should be added throughout the growing stage,and phosphate fertilizers need to be supplemented in the growing period to satisfy the requirements for forests' regular growth.