Search

Variations of plant C: N: P stoichiometry could be affected by both some environmental fluctuations and plant physiological processes. However, the trade-off mechanism between them and their influencial factors were not understood completely. In this study, C, N, P contents and their stoichiometry of S. salsa’s plant organs (leaves, stems, and roots), together with their environmental factors including salinity, pH, soil N and soil P, were examined in the intertidal and supratidal habitats of coastal wetlands during the different sampling times (May, July, September, November). The results showed that both plant organ and sampling times affected C, N, and P and stoichiometry of S. salsa in the intertidal and supratidal habitats, however, their influencial conditions and mechanisms were different. In the intertidal habitat, the different slopes of C-P and N-P within interspecific organs suggested that plant P, C:P and N:P of S. salsa were modulated by P concentrations that allocated in the specific organs. However, the slopes of C-N were found to be not significant within interspecific organs, but during the sampling times. These differences of plant N and C:N were related with the physiological demand for N in the specific life history stage. In the supratidal habitat, no significant differences were found in the slopes of C-N, C-P, and N-P within interspecific organs. However, different slopes of C-N among the sampling times also indicated a self-regulation strategy for plant N and C:N of S. salsa in different ontogenetic stages. In contrast to the intertidal habitat, seasonal variations of P, C:P and N:P ratios within interspecific organs reflected the soil P characteristics in the supratidal habitat. Our results showed that the stoichiometric constraint strategy of plant S. salsa in this region was strongly correlated with the local soil nutrient conditions. [ABSTRACT FROM AUTHOR]

Background: The tidal flat is one of the important components of coastal wetland systems in the Yellow River Delta (YRD). It can stabilize shorelines and protect coastal biodiversity. The erosion risk in tidal flats in coastal wetlands was seldom been studied. Characterizing changes of soil particle size distribution (PSD) is an important way to quantity soil erosion in tidal flats. Method/Principal findings: Based on the fractal scale theory and network analysis, we determined the fractal characterizations (singular fractal dimension and multifractal dimension) soil PSD in a successional series of tidal flats in a coastal wetland in the YRD in eastern China. The results showed that the major soil texture was from silt loam to sandy loam. The values of fractal dimensions, ranging from 2.35 to 2.55, decreased from the low tidal flat to the high tidal flat. We also found that the percent of particles with size ranging between 0.4 and 126 μm was related with fractal dimensions. Tide played a great effort on soil PSD than vegetation by increasing soil organic matter (SOM) content and salinity in the coastal wetland in the YRD. Conclusions/Significance: Tidal flats in coastal wetlands in the YRD, especially low tidal flats, are facing the risk of soil erosion. This study will be essential to provide a firm basis for the coast erosion control and assessment, as well as wetland ecosystem restoration. [ABSTRACT FROM AUTHOR]

Little is known about the impacts of agricultural exploitation of coastal wetlands on ecosystem CO 2 exchange, although coastal wetlands have been widely reclaimed for agricultural use across the world. We measured net ecosystem CO 2 exchange (NEE) and its major components, gross primary production (GPP) and ecosystem respiration ( R eco ) using an eddy covariance flux technique in a natural coastal wetland (reed) and an adjacent, newly reclaimed farmland (cotton) in the Yellow River Delta, China. The results showed that agricultural reclamation changed the ecosystem CO 2 exchange of the coastal wetland at three distinct levels. Initially, the conversion from the wetland to farmland changed the light response parameters ( α , A max , and R eco, day ) of NEE and temperature sensitivity ( Q 10 ) of R eco mainly by changing the dominant vegetation type. Over the growing season, NEE, R eco and GPP were significantly correlated with LAI at both sites and aboveground biomass at the farmland site. Next, the reclamation of wetland modified the diurnal and seasonal dynamics of ecosystem CO 2 exchange. Significant differences in diurnal variations of NEE between the wetland and farmland sites were found during the growing season (with the exception of June and July). Seasonal means of daily GPP and R eco values at the wetland site were higher than those at the farmland. Ultimately, the agricultural reclamation altered the CO 2 sequestration capacity of the coastal wetland. The cumulative NEE in the wetland (−237.4 g C m −2 ) was higher than that in the farmland (−202.0 g C m −2 ). When biomass removal was taken into account, the farmland was a strong source for CO 2 of around 131.9 g C m −2 during the growing season. Overall, land use changes by reclamation altered ecosystem CO 2 exchange at several ecological scales by changing the dominant vegetation type and altering the ecosystem's natural development. [ABSTRACT FROM AUTHOR]