黄河口潮间盐沼湿地生长季净生态系统CO_2交换特征及其影响因素

Net ecosystem CO_2 exchange and its controlling factors during the growing season in an inter-tidal salt marsh in the Yellow River Estuary,China

潮间盐沼湿地生物地球化学过程独特,生态系统CO2交换存在着极大的复杂性和不确定性。利用2012年黄河口潮间盐沼湿地生态系统生长季(4—10月)连续的涡度相关观测数据,分析了潮间盐沼湿地的净生态系统CO2交换(NEE)、总初级生产力(GPP)和生态系统呼吸(Reco)的变化特征及其影响因素。结果表明:生长季,生态系统NEE具有明显的日变化和季节变化。日尺度上,表现为白天CO2净吸收,夜间CO2净释放,NEE日平均值为-0.38 g CO2m-2d-1;月尺度上,平均气温最高的7月生态系统释放CO2最多(15.16 g C/m2),6月生态系统吸收CO2最多(25.07 g C/m2)。潮间盐沼湿地生态系统的CO2交换受到光合有效辐射(PAR)、土壤温度(Ts)、土壤含水量(SWC)和潮汐淹水的共同影响。白天NEE主要受控于PAR,且生态系统表观初始光能利用率(α)和最大光合速率(NEEsat)分别在6月和5月达到最大值,分别为(0.0086±0.0019)μmol CO2μmol-1光子和(4.79±1.52)μmol CO2m-2s-1。夜间NEE随Ts呈指数增加趋势,生态系统呼吸的温度敏感性(Q10)为1.33,且SWC越高,Q10值越大。研究典型晴天(6月19日—6月25日)表明,潮汐淹水增强了生态系统白天对CO2的吸收,同时也增强了夜间CO2释放,研究时段内,潮汐淹水使生态系统净CO2吸收增加了0.76 g CO2m-2d-1。整个生长季,黄河口潮间盐沼湿地生态系统表现为CO2的汇,NEE为-22.28 g C/m2(其中,吸收118.34 g C/m2,释放96.28 g C/m2)。研究结果利于对潮间盐沼湿地源汇功能和影响机制的进一步认识与研究。

Inter-tidal salt marsh plays a great important role in the global carbon cycle as a considerable potential capacity of the carbon sink. Compared to other types of wetlands, the inter-tidal salt marsh has a unique biogeochemical process under the combined action between freshwater and seawater. Therefore, there is considerable variability and uncertainty in its net ecosystem CO2 exchange （NEE）. However, few studies provide insights regarding the variability of NEE and its controlling factors in an inter-tidal salt marsh. Using the Eddy Covariance （EC） technique, we analyzed temporal variation in NEE and determined its control mechanisms coupled with meteorological and tidal inundation variables during the growing season （from April to October） of 2012 in an inter-tidal salt marsh in the Yellow River Estuary. The results showed that it was net COs absorption in the daytime and net COs release in the nighttime on a diurnal scale. The daily average NEE during the growing season was -0.38 g CO2 m-2 d-1, with a maximum daily CO2 uptake rate of -3.13 g COsm-s d-1（ June 27） and a maximum release rate of 1.47 g CO2 m-2 d-l（ August 12）. The monthly average NEE increased rapidly from May, and peaked in June, then decreasing gradually from July. The maximum monthly ecosystem respiration （Reco ） was 15.16 g C/mE in June when the hightest soil temperature was 27.5 ℃. The monthly gross primary productivity （GPP） reached its peaking value （25.07 g C/ms） in July. During the growing season, NEE was mainly dominated by photosynthetic active radiation （PAR）, soil temperature （Ts ）, soil water content （SWC） and tidal inundation. There was a rectangular hyperbolic relationship between the daytime net ecosystem COs exchange （NEEdaytime ） and PAR. The maximum ecosystem apparent quantum yield （a） and maximum photosynthesis rate （NEEsat） appeared in June （（0.0086＋0.0019） mol COs mol-1 photons） and in May （（4.79＋ 1.52） μmol COs m-2 s-1）, respectively. In addition, NEEday,ime also was positively correlated with T, and SWC. During the growing season, NEEaytlme had an exponential relationship with Ts The mean value of Q10 was 1.33, and it was positively related to SWC. During the typical sunny day of June 19 to June 25, tidal inundation enhanced daytime net absorption of CO2 and nighttime CO2 release. As a result, tidal inundation increased the net ecosystem CO2 absorption by an average of 0.76 g CO2 m-2 d-1. During the growing season, the inter-tidal salt marsh was an obvious C02sink （22.28 g C/m2） , with a cumulative emission of 96.28 g C/m2 and a cumulative aborption of 118.34 g C/ms.