Comparative Study On Soil Respiration Characteristics Of Pinus Tabulaeformis And Hippophae Rhamnoides Plantation And Mixed Forest In Loess Hilly Region

Soil respiration is the process of soil carbon dioxide?CO₂?released from the soil to the atmosphere,and it is the main way for the terrestrial ecosystem carbon to return to the atmosphere from CO₂ in the soil.The soil respiration?Rs?were studied base on observation of Rs,soil temperature?T?and soil water content?W?at 5 cm depth under natural group?with litterfall?and exclusive group?without litterfall?treatments in Pinus tabulaeformis and Hippophae rhamnoides plantations in the hilly Loess Plateau region.Two plots of?20 m×20 m?were established in these two plantations with 5 sampling points randomly set up in each plot.Rs,T and W were simultaneously monitored by LI-8100 soil flux system from August 2015 to July 2016 in these plots.The main conclusions are as follows:1.The dynamic characteristics of soil respiration in Pinus tabulaeformis plantation?1?The seasonal variation of Rs in the Pinus tabulaeformis plantations under natural and exclusive group had similar trend,with the highest value appeared in July,the lowest value appeared in February,and winter soil respiration accounted for 39.85% and 60.70% of the total annual respiration.?2?Contribution of litterfall respiration to soil respiration in Pinus tabulaeformis plantations was 2.81 t CO₂/?hm2·a?,the total of 10.91% in soil respiration,besides,relationship between soil respiration and litterfall accumulation is not significantly.?3?Rs under natural and exclusive groups were both exponentially correlated with Tand negative linearly correlated with W at seasonal scale in Pinus tabulaeformis plantations?p<0.05?.Soil respiration is mainly affected by interaction effect between soil temperature and moisture,and litterfall only significantly improves temperature sensitivity of Rs in the Pinus tabulaeformis plantation?p < 0.05?.2.The dynamic characteristics of soil respiration in Hippophae rhamnoides plantations?1?The seasonal variation of Rs in the Hippophae rhamnoides plantations under natural and exclusive group had similar trend,with the highest value appeared in July,the lowest value appeared in February,and winter soil respiration accounted for 29.65% and 42.91% of the total annual respiration.?2?Contribution of litterfall respiration to soil respiration in Hippophae rhamnoides plantations was 10.38 t CO₂/?hm2·a?,the total of 27.76% in soil respiration,besides,relationship between soil respiration and litterfall accumulation is not significantly.?3?Rs under natural and exclusive groups were both exponentially correlated with T and negative linearly correlated with W at seasonal scale in Hippophae rhamnoides plantations?p<0.05?.Soil respiration is mainly affected by interaction effect between soil temperature and moisture,and litterfall only significantly improves temperature sensitivity of Rs in the Hippophae rhamnoides plantation?p < 0.05?.3.The dynamic characteristics of soil respiration in the mixed forest of Pinus tabulaeformis and Hippophae rhamnoides?1?The seasonal variation of Rs in the mixed forest under natural and exclusive group had similar trend,with the highest value appeared in July,the lowest value appeared in February,and winter soil respiration accounted for 40.24% and 51.99% of the total annual respiration.?2?Contribution of litterfall respiration to soil respiration in mixed forest was 7.25 t CO₂/?hm2·a?,the total of 21.82% in soil respiration,besides,relationship between soil respiration and litterfall accumulation is not significantly.?3?Rs under natural and exclusive groups were both exponentially correlated with T and negative linearly correlated with W at seasonal scale in mixed forest?p<0.05?.Soil respiration is mainly affected by interaction effect between soil temperature andmoisture,and litterfall only significantly improves temperature sensitivity of Rs in the mixed forest?p < 0.05?.4.Litterfall significantly increased temperature sensitivity of soil respiration and soil respiration flux in Hippophae rhamnoides plantations,but only significantly improves the temperature sensitivity of soil respiration in Pinus tabulaeformis plantations and the mixed forest,annual flux did not significantly enhance.As important tree species for soil and water conservation and ecological restoration in the hilly Loess Plateau region,the P.tabulaeformis as well as the mixed forest of Pinus tabulaeformis,Hippophae rhamnoides plantations were more conducive to slow down carbon expenditure of forest land in the region.