Effects Of Multiple Environmental Variables On Greenhouse Gas Fluxes From Antarctic Tundra

Antarctic tundra ecosystems would be the most vulnerable to climate change in the world,and warming climate might cause several consequences in the tundra ecosystem,especially in the source and sink of greenhouse gases and global carbon and nitrogen cycles.During the 15th Antarctic expedition for Chinese scientists,scholars from Institute of Polar Environment,University of Science and Technology of China,for the first time observed greenhouse gases?mainly of N₂O and CH₄?fluxes on Fildes Peninsula in maritime Antarctic tundra.And then after the first,scholars from the USA,Brazil,Canada and Italy also observed greenhouse gas fluxes in Polar regions.However,these previous studies mainly focused on the macro-observation of greenhouse gases fluxes,studies on the underlying production mechanisms are scare.Especially the effects of solar ultraviolet radiation,sunlight and microtopography on greenhouse gases fluxes have received little attention in the Antarctic tundra.Therefore,we observed greenhouse gas fluxes from the maritime Antarctic tundra.Based on the years of field experiments?the static chamber technique and the CO₂ flux system?LI-8100??,and combined with simulation experiments in laboratories,the processes of greenhouse gas production and emission and effects of multiple environmental factors?solar ultraviolet radiation,sunlight,microtopography,soil temperature,soil moisture,vegetation types,snow coverage and animal activity?on greenhouse gases fluxes were studied.In addition,as the supplement and extension of the study,spatial variability in greenhouse gas fluxes from Shengjin Lake Marsh in China was also studied,to explore effects of soil moisture,animal colonization,and land use on wetland GHG fluxes.Main contents are as follows:?1?Potential effects of ultraviolet radiation reduction on tundra greenhouse gases fluxes in maritime AntarcticaStratospheric ozone has begun to recover in Antarctica since the implementation of the Montreal Protocol.However,the effects of ultraviolet?UV?radiation on tundra greenhouse gas fluxes are rarely reported for Polar Regions.In the present study,tundra N₂O,CH₄ and CO₂ exchanges were measured under the simulated reduction of UV radiation in maritime Antarctica over the last three-year summers.Significantly enhanced N₂O,CH₄ and CO₂ emissions occurred at tundra sites under the simulated reduction of UV radiation.Compared with the ambient normal UV level,a 20%reduction in UV radiation increased tundra emissions by an average of 8 ?g N₂O m^-2 h^-1,93?g CH₄ m^-2 h^-1 and 76 mg CO₂ m^-2 h^-1,whereas a 50%reduction in UV radiation increased their emissions by an average of 17 ?g N₂O m^-2 h^-1,128 ?g CH₄ m^-2 h^-1 and 118 mg CO₂ m^-2 h^-1.No statistically significant correlation?P>0.05?was found between GHG fluxes and soil temperature,soil moisture,total carbon,total nitrogen,NO₃^--N and NH₄⁺-N contents.Our results confirmed that UV radiation intensity is an important factor affecting tundra GHG fluxes in maritime Antarctica.Exclusion of the effects of reduced UV radiation might underestimate their budgets in Polar Regions with the recovery of stratospheric ozone.?2?Effects of sunlight presence on tundra nitrous oxide and methane fluxes in maritime AntarcticaThe relationships of N₂O and CH₄ emissions to environmental parameters have been investigated in Antarctic terrestrial ecosystems.However,effects of sunlight on tundra N₂O and CH₄ fluxes are highly neglected in Antarctica.Here,N₂O and CH₄ fluxes from maritime Antarctic tundra were measured in the presence and total absence of sunlight over the three-year summers.The N₂O and CH₄ fluxes averaged-4.6±1.2?g N₂O m^-2 h^-1 and 119.8±24.5?9 CH₄ m^-2 h^-1 in the absence of sunlight,respectively,whereas enhanced N₂O emission and CH₄ uptake occurred at all the tundra sites in the presence of sunlight.No statistically significant correlation?P>0.05?was found between N₂O,CH₄ fluxes and soil temperatures,soil moisture,total organic carbon,total nitrogen,NO₃^--N and NH₄⁺-N contents.Sunlight increased tundra N₂O emissions by mean 10.3 ?g N₂O m^-2 h^-1 and increased CH₄ uptake by mean 160.3 ?g CH₄ m^-2 h^-1,compared with the absence of sunlight.Therefore sunlight was an important factor affecting tundra N₂O and CH₄ fluxes in maritime Antarctica.Sunlight might have an important effect on tundra N₂O and CH₄ budgets,and the exclusion of effects of sunlight might underestimate tundra N₂O budget,but overestimate CH₄ budget in maritime Antarctica,these results were comparable to those from the High Arctic tundra.?3?Summertime ecosystem respiration in an upland tundra of maritime AntarcticaSummertime ecosystem respiration?ER?rates through seven sites were measured at the tundra on Fildes Peninsula in maritime Antarctica to investigate effects of topographic gradient,vegetation types,climatic factors and animal activity on tundra ER rates.Overall the highest ER rates occurred at the tundra top(mean 91.2±10.6 mg CO₂ m^-2 h^-1),followed at the middle slope(mean 76.9±11.4 mg CO₂ m^-2 h^-1),and the lowest rates at the lower slope(mean 67.3±9,5 mg CO₂ m^-2 h^-1).The daily highest ER rates occurred at noon whereas the lowest at 6 am.There was a significant positive correlation?P<0.05?between tundra ER and 0-10 cm soil temperature,but a significant negative correlation?P<0.01?between ER and soil moisture.A high Q10 value of 2.69 was obtained when all the data were combined,indicating soil temperature sensitivity of tundra ER.The mean ER at the tundra sites with moss coverage(72.2±4.4 mg CO₂ m^-2 h^-1)was significantly higher?P<0.01?than that at the sites with lichen coverage(46.8±8.7 mg CO₂ m^-2 h^-1).The tundra sites without snow coverage experienced significant CO₂ release(mean 67.2±11.1 mg CO₂ m^-2 h^-1),whereas the emission through ER was very low at the tundra sites with snow coverage(mean 5.7±1.3 mg CO₂ m^-2 h^-1).In addition,ER rates at penguin colony tundra sites(mean 201.3±31.4 mg CO₂ m^-2 h^-1)were significantly higher?P<0.01?than those at penguin-lacking tundra sites(64.0-87.1 mg CO₂ m^-2 h^-1).Our results indicated that topographic gradient,soil temperature,soil moisture,vegetation types,snow coverage and animal activity might affect tundra ER in maritime Antarctica.?4?Potential methane production rates and its carbon isotopic composition from ornithogenic tundra soils in coastal AntarcticaMethane?CH₄?is one of important greenhouse gases with chemical activity.The determination of isotopic compositions for CH₄ emitted from the soils helps us to understand its production mechanisms.CH₄ isotope measurements have been conducted for different types of global terrestrial ecosystems.However,no isotopic data of CH₄ have been reported from Antarctic tundra soils.In this paper,the ornithogenic soil profiles were collected from four penguin colonies,and potential CH₄ production rates and its ?¹³C were investigated based upon laboratory incubation experiments.The mean CH₄ production rates are highly variable in these soil profiles,ranging from 0.7 to 20.3 ?g CH₄-C kg^-1 h^-1.These ornithogenic soils had high potential production rates of CH₄ under ambient air incubation or under N₂ incubation,indicating the importance of potential CH₄ emissions from penguin colonies.Most of soil samples had higher ?¹³C-CH₄ under N₂ incubation?-39.28%?-43.53%?than under the ambient air incubation?-42.81%?57.19%?.Highly anaerobic conditions were conductive to the production of CH₄ enriched in ¹³C,and acetic acid reduction under N₂ incubation might be predominant source for soil CH₄ production.Overall the 8¹³C-CH₄ showed a significant negative correlation with CH₄ production rates in ornithogenic tundra soils under N₂ incubation?R2=0.41,p<0.01?or under the ambient air incubation?R2=0.50,p<0.01?.Potential CH₄ production from ornithogenic soils showed a significant positive correlation with total phosphorus?TP?and NH₄⁺-N contents,pH and soil moisture?Mc?,but the?¹³C-CH₄ showed a significant negative correlation with TP and NH₄⁺-N contents,pH and Mc,indicating that the deposition amount of penguin guano increased potential CH₄ production rates from tundra soils,but decreased the 8¹³C-CH₄.The CH₄ emissions from the ornithogenic soils affect carbon isotopic compositions of atmospheric CH₄ in coastal Antarctica.?5?Spatial variability in greenhouse gas fluxes from a temperate freshwater marsh in China:effects of soil moisture,animal activities and land useThe Middle-Lower Yangtze Floodplain?MLYP?wetlands in China have been experiencing anthropogenic and natural disturbances,which might lead to spatial variability in wetland greenhouse gas?GHG?emissions.Nevertheless,the data about GHG fluxes and their affecting factors are still lacking in the MLYP wetlands.Here,the greenhouse gas?CH₄,N₂O and CO₂?fluxes from Shengjin Lake Marsh?SLM?,as a typical temperate freshwater wetland in the MLYP,were in situ investigated at the undisturbed and disturbed sites,to explore effects of soil moisture,animal colonization,and land use on wetland GHG fluxes.Overall the CH₄ emissions from the wet sites were one order of magnitude higher than those from the mesic or dry sites,whereas higher N₂O emissions and net CO₂ uptake occurred at dry sites than at mesic and wet sites.Soil moisture was the predominant factor controlling the spatial variability in marsh CH₄ and N₂O fluxes and NEE at undisturbed sites.The multivariate analyses revealed that GHG fluxes from the disturbed marsh sites were involved in more complicated factors than from undisturbed sites.Mean CH₄ fluxes from migrating water bird and poultry active areas showed no statistical significant differences from the undisturbed sites,but their activities significantly increased N₂O emissions and decreased marsh CO₂ sink,with the highest N₂O fluxes(mean 49.5±11.9 ?g N₂O m^-2 h^-1)in poultry active areas.Animal activities and animal-derived NO₃^--N input significantly enhanced N₂O emissions?R=0.75,P<0.001?in the SLM.The conversion of the marsh into agricultural field and landfill did not significantly change CH₄ and N₂O fluxes,but significantly decrease CO₂ sink.Our results revealed that the accurate evaluation of GHG budget for the SLM and other similar temperate wetlands should be involved in soil water regimes,water bird colonization and human-induced influences.