Effects Of Litter Caused By Ice Storm Input On Soil Carbon, Nitrogen And Greenhouse Gases Flux In Subtropical Forests Of China

An greatest extreme ice-snow disaster swept across the most areas of southern China inearly2008. The snow, ice and sleet caused severe forest losses and destroyed1.98×107ha offorests, or nearly13%of the China's forests, in19provinces of China. There were more50%of woody stands suffered from top breakage, stem bending, trunk breakage, uprooting andlodging, in which stem bending was the most common damage. The damaged area was full ofbroken branches, tree trunks and leaves. Preliminary estimated: the abnormal litter wasequivalent to the sum of several years normal litter sum. Priming effects (PEs) are strong andgenerally short-term changes in turnover of SOC, soil carbon stock and nitrogen induced byorganic substrates added to the soil. The most of PEs researches were controlled or simulatedin lab. However, information on PEs influence by huge natural disasters, especially byice-storm, is relatively limited. There are very few studies of soil carbon, nitrogen andgreenhouse gas (GHG) flux influence responses to abnormal litter in subtropical forests, and toour knowledge there is no such information from China.Abnormal litter ab experiment has been established in an evergreen and deciduousbroadleaved mixed forest with three forest community types selected along different elevation,in Yangdongshan Shierdushui Natural Reserve, Guangdong province. The concentration of soilorganic carbon and carbon stock, soil available nitrogen and nitrogen in situ minimization weremeasured every quarter, and the greenhouse gas fluxes from forest soils were monthlymeasured using static chamber-gas chromatograph technique. Several key findings were givenas follows:1.The soil organic carbon concentration and soil carbon stock in different depths werecontinued to increase in destroyed forest communities until abnormal litter completivedecomposition was completed in2011, at soil depth of10⁵0cm soil organic carbon concentration has a decline trend. Compared with the control plots,soil organic carbon contentdecreased significantly in abnormal litter removed plots, with a decline range from12.14%to55.34%. The soil organic carbon concentration at depth0³0cm declined more than at depth30⁵0cm. Soil organic carbon concentration has a significant linear correlation with littercarbon mass loss, soil C and N ratio and soil temperature. Abnormal litter significantlyaffected water stable aggregates distribution (<2mm), the content of macro aggregates(>0.25mm) and micro aggregates(<0.25mm) after ice-storm disaster. The abnormal litterremoved significantly affected organic carbon of four size water stable aggregates'distributioncompared to the control, especially the large aggregates of2.0-1.0mm and1.0-0.5mm grainsize were lower than30.4%and36.7%, respectively. But there were no obvious differencescontrast to post-disaster.2. The concentration of soil available nitrogen was continued to significantly increase indestroyed forest communities,but soil available nitrogen concentration at the soil depth10⁵0cm of start to decline beganing2010. The abnormal litter removed significantly affectedsoil available nitrogen, rate of net ammonification, net nitrification and mineralization. The soilnitrogen mineralization rate has a significant positive correlation with soil temperature, littercarbon mass loss, soil C/N and N/P. The net nitrification rate of Catanopsis eyrei andC.cargesii communities have significant relationship with soil moisture, but not for C．fordiicommunity. The rate of net mineralization and nitrification has no significant correlation withlitter C/N, but it is significantly related to soil C/N and N/P.3. The annually mean fluxes of both ground CO₂and N₂O significantly decreased byremoving the abnormal litter at the forest sites compared to controlled sites. The plots with'abnormal litter' removing increased, in particular during the growth seasons, the absorption ofCH₄, e.g. with11.1%,10.51%,12.56%in Catanopsis eyrei,C.cargesii communities andC．fordii communities,respectively. The results indicated that the3forests could absorb CH₄.4. The effect of environmental factors on the fluxes of GHG differed from each otheramong the3forests. Both the litter organic carbon mass loss and soil temperature werepositively correlated to fluxes. The CO₂flux was found positively and negatively correlated with soil NO₃^-N, soil NH4-N and C/N, respectively. On the contrary, the flux of N₂O wasrevealed a significant-positive correlation with soil NO₃^-N and NH4-N, while asignificant-negative related to one with the ratio of C/N. For the flux of CH₄, the statisticallypositive relationships with soil NO₃^-N was only found in Catanopsis eyrei community, andwith soil ratio of C/N, were found in t C．fordii community locating at high altitude. The flux ofN₂O was found positively correlated with soil N/P.Our results suggest that the response of soil carbon,soil nitrogen and soil GHG fluxes toabnormal litter after ice-storm disaster vary depending on the status of litter decomposing inputsubstrates, forest type, the soil temperature, soil moisture and soil C/N.