Environmental Controls on Net Ecosystem CO2 Exchange Over a Reed (Phragmites australis) Wetland in the Yellow River Delta, China

Abstract

Using the Eddy Covariance (EC) technique, we analyzed temporal variation in net ecosystem CO 2 exchange (NEE) and determined the effects of environmental factors on the balance between ecosystem photosynthesis and respiration in a reed (Phragmites australis) wetland in the Yellow River Delta, China. Our results indicated that diurnal and seasonal patterns of NEE and its components (ecosystem respiration (R eco ), gross primary production (GPP)) varied markedly among months for the growing season (May to October). The cumulative CO 2 emission was 1,657 g CO 2 m . The ratio of R eco to GPP in reed wetland was 0.68, which was close to other temperate wetlands. Soil temperature and soil moisture exerted the primary controls on R eco during the growing season. Daytime NEE values during the growing season were strongly correlated with photosynthetically active radiation. Aboveground biomass showed significant linear relationships with 24-h average NEE, daytime GPP, and R eco , respectively. Thus, we conclude that the coastal wetland acted as a carbon sink during the growing season despite the variations in environmental conditions, and long-term flux measurements over these ecosystems are undoubtedly necessary.

Ecosystem photosynthesis regulates soil respiration on a diurnal scale with a short-term time lag in a coastal wetland

“…The original vegetation of coastal wetlands in the Yellow River Delta is composed of halophytic plant communities predominated by herb and shrub species, such as Phragmites australis, Suaeda salsa, and Imperata cylindrical (Han et al, 2013). The terrain of the station is quite flat, with relatively homogeneous vegetation dominated by reed (Phragmites australis), which usually bud during the end of March and the first 10 days of April, and head in the middle 10 days of October (Xie et al, 2011;Han et al, 2013). The climate in the Yellow River Delta is a warm-temperate and continental monsoon climate with distinctive seasons.…”

“…Large gaps (more than 2 h) were filled based on empirical models separately for daytime and nighttime data. More details about flux data processing, quality control and gap filling presented elsewhere (Han et al, 2013).…”

“…Based on the assumption that daytime ecosystem respiration (R eco, day ) follows the same temperature response, R eco, day was determined using the exponential relationships developed for nighttime periods (Han et al, 2013). Using the values of R eco, day , GPP was calculated as the balance between R eco, day and daytime NEE: GPP ¼ R eco, day e NEE.…”

Influences of anthropogenic cultivation on C, N and P stoichiometry of reed-dominated coastal wetlands in the Yellow River Delta

“…It has been estimated that~1300 ha territory land is formed here annually. As a newly formed estuarine delta, it has been naturally characterized by extensive coverage of primary salinization, which was mainly due to the presence of a shallow, saline water table and marine sediments (Han et al, 2012;Zhang et al, 2011). The region, which is rainy from June to August, is submitted to warm temperate continental monsoon climate.…”

Allocation of photosynthestically-fixed carbon in plant and soil during growth of reed (Phragmites australis) in two saline soils

“…The region is characterized by a temperate, semi-humid continental monsoon climate with an average annual rainfall of 600 mm, evaporation of 2000 mm, and an annual average temperature of 12.5°C. Extensive primary salinization is a natural characteristic of this region and is derived from the shallow, saline water table and marine sediments (Wang et al 2010;Han et al 2013). The typical soil type is Salic Fluvisol (FAO 2002).…”