Temporal and spatial variations in the stable carbon isotope composition and carbon and nitrogen contents in current-season twigs of Tamarix chinensis Lour. and their relationships to environmental factors in the Laizhou Bay wetland in China

• Responses of the halophyte Tamarix chinensis to temporal-spatial variability with environmental factors are focused.
• Variations in the season, sunlight, soil salinity, air temperature and relative humidity control the changes in δ13C.
• C content varies with seasonal variations in the air temperature, precipitation and relative humidity.
• Differences in the N content can be explained by differences in the quantity of sunlight received.
• The C:N ratio is mainly affected by sunlight received and significantly correlated with the N content while weakly correlated with the C content.

Coastal wetlands are highly vulnerable ecosystems exposed to tidal and storm events and soil alkalinization. Tamarix chinensis, highly adapted to flooded and salty conditions, is an important pioneer foundation species of salty riparian habitats, ensuring the ecological stability of wetlands. To better understand the physiological responses to environmental conditions across the T. chinensis community in the Laizhou Bay wetland in China, we analysed δ13C, C and N in 108 samples of current-season twigs at three different density levels (dense, sparse and fringe) and at three different light intensities (shade, sun and top) from September 2011 to August 2012. The results showed that the δ13C and C changed with seasonal variations and the δ13C, N and the C:N ratio were mainly affected by sunlight. Whereas, density levels did not affect any of the δ13C, C, N and the C:N ratio by GLM (generalized linear model) analysis. Then the C:N ratio was correlated with C and N and no relationships existed in the δ13C, C and N. In addition, the δ13C, C and N contents were influenced by variations of environmental factors. δ13C was primarily correlated with soil salinity, air temperature and relative humidity. Air temperature, precipitation and relative humidity were the key contributors to the C content. The C:N ratio were weakly influenced by wind speed. Above all, our results provide valuable information on the eco-physiological responses of the T. chinensis community under environmental stress in wetlands.