| Picea mongolica is a unique species in the semi-arid region of China,which plays an important role in maintaining the climate and ecological conditions in the semi-arid region.However,due to the influence of climate conditions,pests and diseases,soil nutrients and other limiting factors,the population of Picea mongolica is gradually deteriorating and even dying out.Therefore,adjusting soil nutrient content through artificial treatment is of great significance to maintain the stability of Picea mongolica population.Previous studies have found that the decomposition of forest litter can have a significant effect on soil nutrients,but there is no research on the decomposition of Picea mongolica litter and its effect on soil nutrient content,and it is not clear which forest age Picea mongolica litter decomposition has a better effect on soil nutrient content.Therefore,it is necessary to investigate the decomposition characteristics of Picea mongolica litter and its effects on soil nutrients in different stands of different ages.In this study,the effects of stand age on litter decomposition and soil nutrient composition were investigated by analyzing litter decomposition dynamics and soil nutrient changes at different depths of Picea mongolica at different stand ages.The effects of litter treatment time,stand age and soil depth on soil nutrient content,litter characteristics and environmental factors on soil nutrient content of Picea mongolica forest in different ages were studied.The main conclusions are as follows:(1)Litter treatment time,forest age of Picea mongolica,soil temperature and soil moisture had significant effects on litter decomposition.Litter decomposition rate of 30 years old and 40 years old Picea mongolica was higher than that of 5 years old Picea mongolica in different ages.The decomposition rate of litters in Picea mongolica increased with the increase of decomposition time.Soil temperature and soil moisture significantly promoted the decomposition of litter.Litterfall treatment time and the stand age of Picea mongolica had significant effects on the elemental composition of litterfall.However,soil temperature and soil moisture had no significant effect on the elemental composition of litters.with the progress of decomposition,the contents of C and K in litters of Picea mongolica of each age decreased significantly,but the contents of N increased significantly.The contents of C and K elements in litters of different forest ages were in the order of 5 years old forest>30 years old forest>40years old forest,while the contents of N element were on the contrary,indicating that the loss of N element in litters of 5 years old forest was large,while the decomposition of C and K elements was large in 40 years old forest.There was no obvious change of P with the treatment time and stand age,and the litter content of P was the highest after the decomposition treatment of 8 months in 40 years old forest.In 5 years old forests,the loss of N and P in litter was too fast,resulting in a significant increase of C/N and C/P,and a significant decrease of N/P in litter,while the opposite phenomenon occurred in 40 years old forests.Therefore,the decomposition rate of litter in 40 years old forest was significantly higher than that in young forest.(2)There were significant differences in soil nutrient contents under different litter-handling time,Picea mongolica forest age and different soil depth in different,that is,the three had significant effects on soil nutrient contents,and the specific effects were as follows:With the increase of soil depth,all soil nutrient characteristics showed a significant downward trend except Na OH-P_o,which mainly appeared in the 20-30 cm soil layer,indicating that litter treatment mainly increased soil nutrient content above 30 cm,and had little effect on the lower soil.With the progress of litter treatment,all soil nutrient contents showed a trend of increasing first and then decreasing,and their peak values mainly appeared from 6 months to 10 months after treatment.The results indicated that the amount of nutrient released from litters to soil was higher than the amount consumed and lost in soil before 10 months of litters treatment,while the amount of soil nutrient consumption was higher than the amount released by litters at the later stage of litters decomposition.After litter treatment,the nutrient content of soil in middle-age forest was usually significantly higher than that in other two forest ages.the litter processing time,Picea mongolica forest plantation age and soil depth has a significant effect on soil ecological characteristics of chemical metrology,for its specific performance,with the increase of litter processing time,soil C/N,C/P and N/P showed a trend of decline after rising first,its peak generally appear in 6～8 months,this is the same as the change trend of soil nutrient content.Soil C/N and C/P in 30 years old forest were significantly higher than that in 5years old forest,while soil N/P was significantly lower than that in 5 years old forest.With the increase of soil depth,soil C/N and C/P decreased significantly,but soil N/P did not change significantly.Higher C/N and C/P and lower N/P in 30 years old forest soil resulted in stronger nutrient retention,but at the same time,such stoichiometric characteristics resulted in decreased availability and release rate of soil nutrients.The stoichiometric characteristics of 5years old forest were opposite,so its fixation effect on soil nutrients was low and soil nutrient availability was high.In the implementation,the litter can be manually treated according to the need.(3)Soil p H,soil temperature and soil moisture all had significant effects on soil nutrient content.Specifically,soil p H was negatively correlated with soil nutrient content except inorganic phosphorus extracted from soil sodium hydroxide,that is,the highest soil p H was not conducive to the accumulation of soil nutrient content.Therefore,soil nutrient content can be interfered by artificially adjusting soil p H during production.Soil temperature and soil moisture is the important factors that affect most of the soil nutrient content,the higher the soil temperature and humidity,soil total organic carbon,total nitrogen,ammonium nitrogen,nitrate nitrogen,total phosphorus,total organic phosphorus,sodium bicarbonate,extracting organic phosphorus,sodium hydroxide extraction organic phosphorus,total phosphorus and water extraction of inorganic phosphate,sodium bicarbonate extract states inorganic phosphorus,rapidly-available potassium content is higher.The contents of C and K in litter,C/N and C/P in litter were negatively correlated with the contents of soil nutrients.The N,P and decomposition rate of litter were positively correlated with soil nutrient content.The results showed that the difference of soil nutrients in Picea mongolica at different ages was mainly due to the difference of ecological stoichiometry characteristics of litters,which resulted in the difference of nutrient release from litters to soil.(4)Phosphatase and sucrase tended to decrease with soil deepening,while phytase and urease had no significant change;The highest activity of soil phosphatase and sucrase occurred at 12 months of litter treatment in 30 years old forest,and the highest activity of soil phosphatase sucrase and urease occurred at 12 months of litter treatment in 5 years old forest,respectively The phytase activity peaked in the 5 years old and 40 years old Picea mongolica forest after litterfall treatment in 12 months,while in the 30 years old forest after litterfall treatment in 10 months.Environmental factors had different effects on the activities of the four enzymes,among which soil moisture had a significant positive correlation with soil phosphatase sucrase and phytase.Soil temperature was positively correlated with phosphatase and phytase.Soil p H was only negatively correlated with phosphatase.Except phytase,and all other soil enzymes were significantly negatively correlated with soil thickness.Among the four enzymes,only phosphatase was significantly positively correlated with litter decomposition coefficient.Phytase and urease were positively correlated with the carbon content of litter.Phytase could significantly promote the decomposition of nitrogen in litters.Phosphatase promoted the decomposition of phosphorus in litters.There was a significant positive correlation between phytase activity and potassium content in litters,indicating that phytase inhibited the decomposition of potassium in litters to a certain extent.Phosphatase removal was significantly positively correlated with the contents of C,N,K and most P components in soil.There was no correlation between sucrase activity and soil organic carbon,but a significant positive correlation between sucrase activity and soil N P and K contents.Phytase was positively correlated only with soil nitrogen and water extracted inorganic phosphorus content.Urease activity was positively correlated with soil total organic carbon and available potassiumIn conclusion,litter processing time,Picea mongolica forest age and soil conditions have significant effect on litter decomposition,litter processing time and Picea mongolica forest age of stoichiometric litter chemical composition and ecological characteristics have a significant impact,in nearly ripe forest litter for 12 months after the processing of litter decomposition rate is highest,stoichiometric characteristic is better.The two also had significant effects on soil,among which,the litter treatment of Picea mongolica in 30 years old from 8 months to 10months showed the highest soil nutrient contents except for three nitrogen components.After litterfall treatment of 6-8 months,the soil nitrogen content of each component was the highest,but the content of other nutrients was inferior to that of the previous treatment.This study systematically studied the effects of litter treatment time and Picea mongolica forest age on litter and soil,providing a theoretical basis for artificial regulation of soil nutrients in Picea mongolica forest in semi-arid sandy land. |
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