Effects Of Litter On Soil Respiration In Two Old-growth Plantations In Pingxiang,Guangxi

Soil respiration is an important part of the global carbon cycle.It plays a pivotal role in releasing C from soil C pool to the atmosphere.Study on the temporal-spatial dynamics and effecting mechanism of soil respiration is significant to confirm the relationship between carbon sources and sinks in terrestrial ecosystems as well as the global climate change.In this paper,we conducted a DIRT(Detritus Input and Removal Treatments)experiment(Control,CK;Litter removal,LR;Litter addition,LA)in pure Pinus massoniana plantations and uneven-aged P.Massoniana × Castanopsis hystrix mixed plantations(hereinafter referred to as mixed plantations)at Pingxiang,Guangxi.From September 2017 to August 2018,the soil respiration rate main influencing factors of P.Massoniana and mixed plantations had been measured.Finally,we estimated the contribution of litter to the soil respiration.The main conclusions are as follows:(1)The monthly dynamics of litter in P.Rmassoniana plantations was similar to that in mixed plantations,showing a double peak pattern.The annual amount of litter were 6.48 ± 0.11 t.hm-2 and 8.03±0.17 t.hm-2 in P.massoniana plantations and mixed plantations,respectively.The annual litter amount of P.massoniana plantations was increased by 23.92%after it was transformed into the mixed plantations.The average annual soil temperature of P.massoniana plantations in CK,LR and LA treatments were 19,42±0.04 ?,20.30±0.03 ?and 20.05 ± 0.19 ?,respectively.And the average annual soil temperature of mixed plantations in CK,LR and LA were 20.71 ±0.04 ?,20.89±0.03 ? and 20.54 ± 0.03 ?,respectively.The average annual soil temperature of P.massoniana plantations were increased by 4.53%and 0.87%after litter removal and litter addition.And the average annual soil temperature of mixed plantations increased by 0.87%after litter removal,while decreased by 0.92%after litter addition.The average annual soil temperature of P.massoniana plantations was increased by 18.43%after it was transformed into the mixed plantations(2)The average annual soil moisture of P.massoniana plantations in CK,LR and LA treatments were 19.66 ± 0.09%,19.67 ± 0.13%and 20.41 ±0.31%,respectively.And the average annual soil moisture of mixed plantations in CK,LR and LA were 21.24±0.15%,20.44±0.14%and 22,04±0.20%,respectively.The average annual soil moisture of P.massoniana plantations were increased by 3.81%after litter addition.And the average annual soil moisture of mixed plantations decreased by 3.77%after litter removal,while decreased by 3.77%after litter addition.The average annual soil temperature of P.massoniana plantations was increased by 8.04%after it was coverted to the mixed plantations.(3)The average annual soil respiration rate of P.massoniana plantations in CK,LR and LA treatments were 2.06 ± 0.14,1.54 ±0.19 and 2.60± 0.08 ?molCO2·m-2 s-1,respectively.And the average annual soil respiration rate of mixed plantations in CK,LR and LA were 2.44 ± 0.06,1.76 ± 0.12 and 3.27 ± 0.29 ?molC02·m-2s-1,respectively.The average annual soil respiration rate of P.massoniana plantations and mixed plantations were decreased by 25.24%and 27.87%,respectively,after litter removal.And the average annual soil respiration rate of mixed plantations increased by 26.21%and 34.02%after litter addition.(4)The annual cumulative emissions of soil respiration in P.massoniana plantations in CK,LR and LA treatments were 8.03±0.23 t·C·hm-2,6.00±0.33 t·C·hm-2 and 10.01±0.14 t· C·hm-2,respectively.And the cumulative annual emissions of soil respiration in mixed plantations in CK,LR and LA were 9.51±0.12 t· C ·hm-2,6.88±0.21 t·C·hm-2 and 12.70±0.53 t ·C ·hm-2,respectively.The annual cumulative emissions of soil respiration in P.massoniana plantations and mixed plantations were reduced by 25.28%and 27.66%after litter removal,while increased by 24.66%and 33.54%after litter addition.(5)There was a significant exponential correlation between soil respiration rate and soil temperature under both P.massoniana plantations and mixed plantations(p<0.05).The soil temperature could describe 83.87%?88.46%and 74.26%?94.28%of monthly variation in soil respiration in P.Massoniana plantations and mixed plantations,respectively.In the P.massoniana plantations,soil respiration rate was found significantly and positively related to soil moisture in the litter addition treatment of the mixed plantations.(6)The temperature sensitivity coefficient of soil respiration Q10 of CK,LR and LA were 1.83,2.09 and 1.92 in P.massoniana plantations,respectively,and they presented the order of CK>LR>LA,which in the mixed plantations,they presented the order of LR(2.13)>CK(2.01)>LA(1.94).