Methane and nitrous oxide fluxes across an elevation gradient in the tropical Peruvian Andes
Methane and nitrous oxide fluxes across an elevation gradient in the tropical Peruvian Andes
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DOI：
10.5194/bg-11-2325-2014
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发表时间：
2014-04
期刊：
影响因子：
4.9
通讯作者：
Y. Teh;T. Diem;S. Jones;L. P. H. Quispe;E. Baggs;N. Morley;M. Richards;Pete Smith;P. Meir
中科院分区：
文献类型：
--
作者：
Y. Teh;T. Diem;S. Jones;L. P. H. Quispe;E. Baggs;N. Morley;M. Richards;Pete Smith;P. Meir
遥感和反模拟研究表明，热带地区排放的CH4和N2O比自下而上的排放清单预测的要多，这表明陆地源比先前认为的更强或更多。热带高地是CH4和N2O的一个潜在的巨大而重要的来源，但过去的经验和模拟研究往往忽视了这一点。为了解决这一认识差距，我们调查了土壤CH4和N2O通量在长海拔梯度(600-3700ma.s.l)上的空间、时间和环境趋势。在秘鲁安第斯山脉南部的科斯尼-帕塔山谷，这经历了降雨量的季节性波动。这项工作的目的是对该区域内典型生境的土壤CH4和N2O通量进行初步估计，并确定对土壤CH4和N2O动态的最近控制。面积加权通量计算表明，该海拔梯度上的生态系统在每年的基础上既是大气中的甲烷源，也是甲烷的汇。山地草原(3200-3700ma.s.l)均为强大气源，1年排放CH4-C 56.94±7.81 kg。上山地森林(2200-3200 m a.s.l)和较低的山地森林(1200-2200 m a.s.l)净大气汇(分别为2.99±0.29和2.34±0.29 kg CH4-C ha，1年)，前山森林(600-1200 m a.s.l)根据季节在源或汇之间波动(雨季：1.86±1.50公斤CH4-C公顷1年；旱季：1.17±0.40公斤CH4-C公顷1年)。对研究区土壤CH4通量的空间、时间和环境趋势分析表明，土壤氧化还原作用是土壤CH4净通量的主要控制因素。土壤CH4排放量在生境、地貌和土壤亚缺氧时期最大，土壤CH4排放与土壤O2浓度呈负相关(Spearman‘s=0.45，P<；0.0001)，与充水孔隙呈正相关(Spear-man’s=0.63，P<；0.0001)。整个区域的生态系统是大气N2O的净来源。土壤N2O通量随海拔升高呈下降趋势，按面积加权通量计算表明，山地前、山地下部、山地上部和山地草原的N2O排放量分别为2.23±1.31、1.68±0.44、0.44±0.47和0.15±1.10 kg/hm2·a-1。来自前山地和低山地森林的土壤N2O通量超过了该地区先前的模型预测。对野外和室内资料的综合研究表明，该地区土壤N2O通量主要受反硝化作用的驱动，硝酸盐(NO3)有效性是土壤N2O通量的主要制约因素，土壤水分和充水孔隙度在调节N2O排放中起次要作用。当前和未来在N管理或人为N沉积方面的任何变化都可能导致这些热带山地生态系统的土壤N2O净通量发生变化，从而进一步加强这一排放源。
Remote sensing and inverse modelling studies in- dicate that the tropics emit more CH4 and N2O than pre- dicted by bottom-up emissions inventories, suggesting that terrestrial sources are stronger or more numerous than pre- viously thought. Tropical uplands are a potentially large and important source of CH4 and N2O often overlooked by past empirical and modelling studies. To address this knowledge gap, we investigated spatial, temporal and en- vironmental trends in soil CH4 and N2O fluxes across a long elevation gradient (600-3700 m a.s.l.) in the Kosni- pata Valley, in the southern Peruvian Andes, that experi- ences seasonal fluctuations in rainfall. The aim of this work was to produce preliminary estimates of soil CH4 and N2O fluxes from representative habitats within this region, and to identify the proximate controls on soil CH4 and N2O dynamics. Area-weighted flux calculations indicated that ecosystems across this altitudinal gradient were both at- mospheric sources and sinks of CH4 on an annual basis. Montane grasslands (3200-3700 m a.s.l.) were strong atmo- spheric sources, emitting 56.94 ± 7.81 kg CH4-C ha 1 yr 1 . Upper montane forest (2200-3200 m a.s.l.) and lower mon- tane forest (1200-2200 m a.s.l.) were net atmospheric sinks ( 2.99± 0.29 and 2.34± 0.29 kg CH4-C ha 1 yr 1 , re- spectively); while premontane forests (600-1200 m a.s.l.) fluctuated between source or sink depending on the season (wet season: 1.86± 1.50 kg CH4-C ha 1 yr 1 ; dry season: 1.17± 0.40 kg CH4-C ha 1 yr 1 ). Analysis of spatial, tem- poral and environmental trends in soil CH4 flux across the study site suggest that soil redox was a dominant control on net soil CH4 flux. Soil CH 4 emissions were greatest from habitats, landforms and during times of year when soils were suboxic, and soil CH4 efflux was inversely correlated with soil O2 concentration (Spearman's = 0.45, P < 0.0001) and positively correlated with water-filled pore space (Spear- man's = 0.63, P < 0.0001). Ecosystems across the region were net atmospheric N2O sources. Soil N2O fluxes de- clined with increasing elevation; area-weighted flux calcu- lations indicated that N2O emissions from premontane for- est, lower montane forest, upper montane forest and montane grasslands averaged 2.23± 1.31, 1.68± 0.44, 0.44± 0.47 and 0.15± 1.10 kg N2O-N ha 1 yr 1 , respectively. Soil N2O fluxes from premontane and lower montane forests exceeded prior model predictions for the region. Comprehensive in- vestigation of field and laboratory data collected in this study suggest that soil N2O fluxes from this region were primar- ily driven by denitrification; that nitrate (NO 3 ) availability was the principal constraint on soil N2O fluxes; and that soil moisture and water-filled porosity played a secondary role in modulating N2O emissions. Any current and future changes in N management or anthropogenic N deposition may cause shifts in net soil N2O fluxes from these tropical montane ecosystems, further enhancing this emission source.