| As a main feature of global climate change,precipitation regime change has huge impact on terrestrial ecosystem C sequestration in continental and subcontinental scale.Soil,the largest C stock in terrestrial ecosystem,plays an important role in global C cycle,its responses to climate change contribute to the uncertainty of terrestrial ecosystem feedback.Under future climate change,most subtropical and middle latitude regions in China were expected to suffer more intensive and frequent drought risk.Quercus forests represent the largest vegetation C stock,which accounts for ~ 18% of all forest vegetation C in China.It yet remains unclear how these important forest ecosystems are affected by decreasing precipitation.A throughfall reduction(TFR)experiment was conducted in a warm-temperate oak forest in central China,rain-out shelters excluded ~ 50% of the growing-season to examine effects of reduced summer precipitation on soil carbon dynamics.1)? 50% throughfall reduction(TFR)during growing seasons,deceased 31.5%,25.6% and 27.5% of annual rainfall in 2014,2015 and 2016,respectively.TFR significantly decreased soil moisture of un-trenched subplots by 5.7 vol%,6.1 vol%,3.9 vol% and 8.5 vol% in 2013,2014,2015 and 2016,respectively;and decreased soil moisture of trenched subplots by 4.5 vol%,6.4 vol%,7.1 vol% and 8.3 vol%,respectively2)Trench method was employed to partition heterotrophic soil respiration(HR)and autotrophic soil respiration(AR)from total soil respiration(SR),and 38 months continuous measurements was conducted in a warm-temperate oak forest in central China to examine effects of reduced summer precipitation on SR,HR,AR,soil microbial biomass,and fine root biomass from 2013 to 2016.Although soil moisture was significantly reduced during TFR(May – Sept),microbial biomass and HR remained unaffected.SR,AR,as well as fine root biomass increased during TFR in a comparable dry year,but remained unaffected during all other years.Annual rates of SR(TFR: 5.7-5.8 ton ha-1 y-1;control: 5.0-6.0 ton ha-1 y-1),HR(TFR: 4.2-4.9 ton ha-1 y-1;control: 3.9-5.0 ton ha-1 y-1),and AR(TFR: 0.9 – 1.5 ton ha-1 y-1;control: 1.0-1.1 ton ha-1 y-1)were all unaffected by TFR.Our results indicate that a mild,steady,reduction in summer precipitation does not affect soil organic matter decomposition in the oak forest ecosystem studied.Low SR rates during a natural dry-spell indicate that SR can be significantly decreased under more severe drought than imposed by the TFR treatment.Our data suggest a comparable low soil moisture threshold of ~ 10 vol% for SR in the studied soil.3)Method of root exudates collection in situ was employed to examine the effects of throughfall reduction on root exudation and root morphology.The results showed throughfall reduction profoundly decreased root exudation rates 1(specific root biomass),root exudation rates 2(specific root length),root exudation rates 3(specific root area)and root exudation rates 4(specific root volume)by 8.5%,15.8%,22.1% and 25.6%,respectively.TFR significantly decreased coarse/fine root ratio while significantly increased FRV by 34.1% and mycorrhiza infection by 14.8%.4)Decomposition mesh bags were applied to examine the throughfall reduction effects on decomposition rate of litters and fine roots.The results showed throughfall reduction significantly increased the decomposition of litter but retarded the decay of fine roots.5)To examine the effects of reduced precipitation on soil methane uptake,soil CH4 and N2 O flux was measured for a whole year using static chambers.The results showed throughfall reduction significantly decreased soil moisture by 5.6 vol%,and profoundly increased soil CH4 uptake by 4.8 times and annual cumulative flux by 6.39 kg CH4 ha-1,while markedly decreased soil N2 O emission by 44.1% and annual cumulative flux by 0.27 kg N2 O ha-1.Our results indicated that the negative feedback for regional climate induced by CH4 uptake increase and N2 O emission decrease resulting from future drought should not be ignored. |
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