Ago Expedit Evariste, Serça Dominique, Agbossou Euloge Kossi, Galle Sylvie, Aubinet Marc
Axe Exchange Ecosystems-Atmosphere, Department of Biosystem Engineering (BIOSE), University of Liege, Gembloux Agro Bio Tech, 8, Avenue de la Faculté, 5030 Gembloux, Belgium ; Laboratoire d'Hydraulique et de Maîtrise de l'Eau, Faculté des Sciences Agronomiques (FSA), Université d'Abomey-Calavi (UAC), BP 2819, Cotonou, Benin.
Laboratoire d'Aérologie, UMR CNRS 5560, Université Paul Sabatier, Toulouse, France.
Carbon Balance Manag. 2015 Sep 17;10:22. doi: 10.1186/s13021-015-0033-6. eCollection 2015 Dec.
In West Africa, natural ecosystems such as woodlands are the main source for energy, building poles and livestock fodder. They probably behave like net carbon sinks, but there are only few studies focusing on their carbon exchange with the atmosphere. Here, we have analyzed CO fluxes measured for 17 months by an eddy-covariance system over a degraded woodland in northern Benin. Specially, temporal evolution of the fluxes and their relationships with the main environmental factors were investigated between the seasons.
This study shows a clear response of CO absorption to photosynthetic photon flux density (Q), but it varies according to the seasons. After a significant and long dry period, the ecosystem respiration (R) has increased immediately to the first significant rains. No clear dependency of ecosystem respiration on temperature has been observed. The degraded woodlands are probably the "carbon neutral" at the annual scale. The net ecosystem exchange (NEE) was negative during wet season and positive during dry season, and its annual accumulation was equal to +29 ± 16 g C m. The ecosystem appears to be more efficient in the morning and during the wet season than in the afternoon and during the dry season.
This study shows diurnal and seasonal contrasted variations in the CO fluxes in relation to the alternation between dry and wet seasons. The Nangatchori site is close to the equilibrium state according to its carbon exchanges with the atmosphere. The length of the observation period was too short to justify the hypothesis about the "carbon neutrality" of the degraded woodlands at the annual scale in West Africa. Besides, the annual net ecosystem exchange depends on the intensity of disturbances due to the site management system. Further research works are needed to define a woodland management policy that might keep these ecosystems as carbon sinks.
在西非，林地等自然生态系统是能源、建筑用木材和牲畜饲料的主要来源。它们可能表现为净碳汇，但仅有少数研究关注其与大气的碳交换。在此，我们分析了贝宁北部一片退化林地的涡度协方差系统在17个月内测量的二氧化碳通量。特别地，研究了不同季节通量的时间演变及其与主要环境因素的关系。
本研究表明二氧化碳吸收对光合有效辐射（Q）有明显响应，但随季节变化。在经历显著且漫长的干旱期后，生态系统呼吸（R）在首次显著降雨后立即增加。未观察到生态系统呼吸对温度有明显依赖性。退化林地在年尺度上可能是“碳中性”的。净生态系统交换（NEE）在雨季为负，旱季为正，其年累积量等于+29±16克碳/平方米。生态系统在早晨和雨季似乎比下午和旱季更高效。
本研究表明，与干湿季交替相关，二氧化碳通量存在昼夜和季节的对比变化。根据与大气的碳交换，南加乔里站点接近平衡状态。观测期长度过短，无法证明关于西非退化林地年尺度“碳中性”假设的合理性。此外，年净生态系统交换取决于场地管理系统造成的干扰强度。需要进一步开展研究工作，以制定可能使这些生态系统保持为碳汇的林地管理政策。
