水氮耦合对轮伐末期毛白杨纸浆材生长及土壤水养特征的影响

[Objective]Water-fertilizer coupling is widely considered as one of the most effective measures to improve the productivity of forest land,but at present,most of the domestic researches are short-term water and nitrogen effect researches,and there is a lack of exploration of water and nitrogen coupling of populus tomentosa pulpwood at the end of the rotation period,and this paper aims at clarifying the optimal irrigation and fertilization strategy of populus tomentosa at the end of the rotation period.[Method]In this paper,we take the triploid populus tomentosa planted in the Northwest Shandong Plain as the research object,and adopt the drip irrigation water-nitrogen coupling test to study the spatial and temporal dynamics of leaf area index(LAI),soil volumetric water content(SVWC)of each water-nitrogen treatment in the fourth growing season(April～October)after irrigation and fertilization,as well as the growth of the trees at the end of the growing season and the nutrient pattern of the forest land,so as to determine the best fertilization strategy at the end of the rotational logging period.[Result](1)At the end of the rotation of Populus tomentosa pulpwood,the stand was fully closed,and the competition for water and nutrient resources was changed to competition for space and light resources,which resulted in no significant differences in stand growth,stand volume(V),and stand productivity(AFP)under different water and nitrogen conditions.(2)Water-nitrogen coupling could not change the trend of leaf area index(LAI)within the growing season,which showed a decreasing trend throughout the growing season,but was bimodal due to wind damage(which occurred on June 1),peaking around May 30 and July 15.(3)Irrigation,soil depth and month were the main factors affecting soil volumetric water content;in spring(May),irrigation treatments were able to increase SVWC from 0 to 200 cm soil depth,with the full irrigation level(W20)mainly increasing soil surface water in the root zone,and control(W33)and deficit irrigation(W45)mainly increasing water from 100 to 150 cm depth.In summer(July),the irrigation was able to increase SVWC from 0 to 200 cm depth,and full irrigation(W20)supplemented soil moisture better than W33 and W45 levels.After irrigation was stopped in the fall(October),deeper soil water content was higher and deep soil moisture was replenished at the W20 and W33 levels,whereas top soil became drier in the fall compared to spring and summer.(4)Soil nutrients were mainly accumulated in the shallow soil layer(0～40 cm soil layer)of the Populus tomentosa stands in each treatment,and the response of soil organic matter and total nitrogen content in the shallow soil layer to water-nitrogen coupling was weaker than that of effective phosphorus,in which the accumulation of effective phosphorus by irrigation was greater than that by fertilization.(5)Diameter at breast height(DBH)and tree height(H)of 5-year-old Populus tomentosa forests were significantly positively correlated with forest volume(V),and tree height and leaf area index were significantly negatively correlated.Soil quick-acting phosphorus(AP)content had a significant positive correlation with DBH,and nitrogen application could promote forest growth by facilitating the accumulation of soil phosphorus.Nitrogen application can promote the growth of forest trees by promoting the accumulation of soil phosphorus content.[Conclusion]Four consecutive years of water-nitrogen coupling did not significantly promote the growth of five-year old Populus tomentosa pulpwood and had limited effect on soil nutrient improvement,so it is recommended that fertilizer application should be stopped at the end of the cultivation period of Populus tomentosa pulpwood in the short-rotation logging period under similar standing conditions and adequate irrigation should be maintained(irrigation threshold of-20 kPa),so as to realize the sustainability of land strength.