| Pinus massoniana is the main afforestation tree species in southern China.In recent years,the fertility of Pinus massoniana plantation soil has been declining,which ultimately affects the productivity of Pinus massoniana plantation.In order to improve the fertility of forest land and promote the healthy management of planted forests,artificial fertilization has become an important afforestation measure.In this study,through different fertilization treatment experiments of 4-years-old and 8-years-old young Pinus massoniana plantations.At the same time,the ecological stoichiometric characteristics and nutrient cycle parameters are introduced to reveal the ecological mechanism of different fertilization schemes on plantation nutrients,which provides important scientific and practical guidance for the efficient cultivation of plantation and a reasonable fertilizer system.The main results are as follows:(1)The growth of plantation changes significantly after one year of different fertilization treatments.In the growth of 4-years-old and 8-years-old plantations,the application of nitrogen fertilizer alone did not significantly improve the control.Compared with the control tree,the height of HP increased by 0.27m and 0.35m respectively,with an increase of 39%and 41%;the trunk biomass increased by 0.47kg per tree and 4.19kg per tree,with an increase of 52%and 63%.Compared with the control,the NP treatment increased 0.27m and 0.34m in height,with an increase of 39%and 40%;the DBH increased by 0.20cm and 0.38cm,with an increase of 24%and 40%;the trunk biomass increased by 0.42kg per tree and 4.21kg per tree,An increase of 46%,62%.Compared with the control,the NPK treatment increased by 0.33m and 0.44m,with an increase of 47%and 51%;the breast diameter increased by 0.34cm and 0.43cm,with an increase of 41%and 45%;the trunk biomass increased by 0.54kg ever plant and 5.14kg ever plamt,the growth rate is 60%,75%;the total biomass growth rate is61%,76%.In the same amount of fertilization treatment for young plantations,the growth indexes of 4-year-old plantations are lower than those of 8-year-old plantations,that is,the benefits of fertilization on the growth of 8-year-old plantations are more obvious.Among them,NPK treatment(100 kg N/hm~2+50 kg P/hm~2+50kg K/hm~2)promoted the growth of plantation forest most significantly.(2)Fertilization treatment within one year of plantation soil-plant-litter nutrient measurement characteristics have different effects.In different fertilization treatments for 4-year-old and 8-year-old plantations:the effect of fertilization on soil total nitrogen is not significant.The NPK,NP,and HP treatments significantly increased the total phosphorus content of the soil,increasing by 45%and 44%,51%and 47%,60%and41%,respectively,compared to the control.In addition to the treatment with single application of phosphate fertilizer,other treatments significantly increased the total nitrogen content of needle leaves,with an increase of 40%to 78%.All fertilization treatments significantly increased the total phosphorus content of coniferous leaves,of which NPK was the most obvious,with an increase of 116%and 241%compared to the control.(3)The experiment introduces the ecological cycle coefficient of nutrients to explore the nutrient limitation of plantation and the effect mechanism of different fertilization formulas on the benefits of plantation.The results of 8-year-old fertilization showed that:NPK and NP significantly increased nitrogen retention,which increased by 31.42 kg/ha·a and 30.03kg/ha·a compared with the control,with an increase of 128%and 118%;NPK treatment significantly increased nitrogen return,Compared with the control increased by 273%.The treatment of adding high amount of phosphate fertilizer significantly increased the phosphorus retention,and the NPK and NP treatments increased the most.They increased by 3.67kg/ha·a and 2.88kg/ha·a compared with the control,with an increase of 360%and 458%.The results of 4-year-old fertilization showed that the plots added with nitrogen fertilizer significantly increased nitrogen retention,and the NP treatment was the most significant,an increase of 8.66 kg/ha·a compared with the control,an increase of 135%;while the addition of phosphate fertilizer significantly increased nitrogen return,the highest was P+treatment increased15.02 kg/ha·a compared with the control,an increase of 139%.The 8-years-old plantation nitrogen and phosphorus element cycle coefficients ranged from 0.44 to 0.56,0.50 to 0.68,and the 4-years annual change ranged from 0.62 to 0.70 and 0.38 to 0.53.There was no significant difference between different treatments.The cycle coefficient of the element decreased,that is,the vegetation layer absorbed more but returned less nutrients,thus explaining the basis for the 8-years-old plantation to require more fertilization measures than the 4-years-old plantation.Nitrogen utilization efficiency decreased by 40%to 60%after fertilization treatment,that is,the increased biomass per unit of nutrient elements decreased.The reabsorption efficiency of phosphorus increased by 15%to 40%compared with the control.At the same time,the growth of the plantation increased significantly after the addition of phosphorus fertilizer.This shows that the lack of phosphorus is the most serious among the limitations of the ground capacity of the Pinus massoniana plantation.(4)According to the results of correlation analysis,nitrogen storage was significantly positively correlated with biomass growth,the correlation coefficient reached 0.834,phosphorus absorption was significantly positively correlated with tree height,correlation coefficient reached 0.834,and phosphorus storage was significantly correlated with breast diameter and biomass The positive correlation and the correlation coefficient reached 0.806 and 0.878,which shows that there is a clear correlation between the amount of nitrogen and phosphorus and the absorption and the growth of plantation.At the same time,nitrogen retention is positively correlated with soil nitrogen and phosphorus content,with coefficients of 0.553 and 0.573,and also has a strong positive correlation with coniferous and litter nitrogen content,coefficients are0.819 and 0.839.The phosphorus content showed a strong positive correlation with a coefficient of 0.779,which also showed a strong positive correlation with the phosphorus content of needles and litter,with coefficients of 0.757 and 0.870,respectively.The nutrient stoichiometric characteristics are directly regulated by the fertilization treatment,thus establishing the correlation between growth amount-nutrient measurement characteristics-nutrient cycle.In this experiment,NPK treatment has the most obvious promotion effect on the growth of annual plantation.After fertilization treatment,the soil nitrogen and phosphorus elements increased by 25%and356%,the available nutrient elements in the soil increased,and the plant needles changed the nutrient utilization strategy,namely nitrogen,Phosphorus nutrient utilization efficiency decreased by 36%,47%,reabsorption efficiency increased by190%,503%,the content of nitrogen and phosphorus in needle leaves increased by 39%,242%compared with the control,so that the annual retention of nitrogen and phosphorus in plantation An increase of 128%,458%.The results show that the relationship between the growth of plantation growth and nutrient cycling can be applied to the cultivation of Pinus massoniana plantations in different environments.That is,by measuring the nutrient metering and cycle characteristics of the plantation,the NPK effective fertilization program was formulated more carefully to develop The economic and ecological benefits of forests play a guiding role in forest fertilization management. |
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