Effect Of Thinning On Soil Nitrous Oxide Fluxes In Pinus Massoniana Plantation

Based on the 29 a Pinus massoniana Plantation in the Forestry of Lishui District, Nanjing, which was thinned by different intensities?CK:0%;LIT: 25%;MIT: 45%; HIT: 65%? 9 years ago, the effects of thinning intensities on soil nitrous oxide?N2O? fluxes, denitrification enzyme activity and reactive nitrogen components were studied. The N₂O was measured by using the method of static chamber-gas chromatography, and the result showed that:?1?The soil N₂O fluxes had significant changes in different seasons. Emission peak appeared in mid-growing season?July and August?, the fluxes were 377.231 ug·m-2·h-1, In addition, the end of the growing season?September and October?> the beginning of the growing season?April, May and June?> non-growing season?November, December, January?, the average emission fluxes were 150.498 ug·m-2·h-1?51.803 ug·m-2·h-1?12.170 ug·m-2·h-1?Soil N₂O fluxes was influenced obviously by the thinning. compared to CK, the N₂O emissions of LIT and MIT were reduced by 51.49% and 40.41%, HIT increased by 1 times. The annual average fluxes was changed by: HIT?255.042 ug·m-2·h-1?> CK?124.223 ug·m-2·h-1?> MIT?74.208 ug·m-2·h-1?> LIT?60.135 ug·m-2·h-1?. Annual emissions changed by: HIT?18.878 kg·hm-2?>CK?9.351kg·hm-2?>MIT?5.572 kg·hm-2?>LIT?4.536 kg·hm-2?.?2?The active nitrogen components in soil had some seasonal variations in response to different thinning intensities. Analysed the average value whole year, the soil dissolved organic nitrogen?DON? content significantly?P<0.05? decreased in HIT, all the three thinning intensities increased the soil microbial biomass nitrogen?MBN? content significantly?P<0.05?, and MIT had the most obvious effect, was increased by more than 70%; LIT and HIT significantly?P <0.05? increased the ammonium nitrogen content of soil, ammonium nitrogen in MIT soil significantly?P<0.05? decreased; Each thinning intensity significantly?P<0.05? reduced soil nitrate nitrogen content.Soil denitrification enzyme responsing to thinning intensities varied by seasons. In spring, three thinning intensities significantly?P<0.05? reduced the Nitrate reductase?NR? and Nitrite reductase?Ni R? activity, but the Hydroxylamine reductase?Hy R? activity was significantly?P <0.05? increased. In summer and fall, thinning significantly?P<0.05? improved NR and Ni R activity,but decreased Hy R activity, the NR and Ni R activity in MIT behaved the highest activity; And in winter, the effects of thinning on denitrification enzyme had no regulations.?3?Soil N₂O fluxes significantly associated?P <0.05? with the temperature in 0-5cm soil?T5?, water content of 0-10 cm soil?Swc10? and soil available nitrogen content?NH4+-N and NO3--N?, positively correlated with T5, Swc10, NH4+-N, negative correlated with NO3--N.Denitrification enzyme had some indication in the generation of N₂O, N₂O in the middle and end of the growing season mainly generated by nitrification. HIT increased the fluxes of N₂O all of the three periods of the growing season by increasing the nitrification, LIT and MIT reduced soil N₂O fluxes in the same periods by reducing the intensity of denitrification in early growing season,and reducing nitrification in the middle and end of the growing season.In summary, as the sources of N₂O, the soil N₂O fluxes of Pinus massoniana Plantation effectively reduced in LIT and MIT. Compared to CK, the total emissions was reduced about 51% in LIT, reduced about 40% in MIT. In order to reduce N₂O emissions, 25% thinning intensity was more appropriate in the 29-year-old plantation. And it was important to implement the appropriate thinning in the future forest management.