C,N And P Stoichiometry Of Suaeda Salsa In Coastal Wetlands, China

Coastal wetlands in the paralic zone affected by the ocean and land are vulnerable ecologically sensitive regions. Suaeda salsa is one of the typical populations in coastal wetlands which play an important regulatory role in moving, transferring and assimilating coastal nutrient substance and supplys critical habitat for some birds and macroinvertebrates. In addition, Suaeda salsa can significantly reduce the salt content of soil, increase soil organic matter content and improve soil microbial flora. Therefore, studying the change of stoichiometric characteristics contribute to understanding the health status of Suaeda salsa and supply-demand relationship between environment nutrient and plants, which is of great importance for recovering, reconstructing and protecting coastal wetland.We collected S. salsa’s leaves in different growth phases and soil samples in different layers from June to November,2010, in Yancheng coastal wetlands, Jiangsu Province. The C, N and P contents of the leaves and soil were measured. Different researches were made by statistic test and correlation analysis from different aspects: stoichiometry differences between the different organs, stoichiometry in leaf of Suaeda salsa in different growth phases, stoichiometry of the soil nutrient element contents and the correlativity between soil and plant, so as to reveal stoichiometry of Suaeda salsa integrally and make judgments on nutrition limiting factors in the Suaeda salsa’s growth preliminarily. The results showed that:(1) There were significantly different among the different organs of C, N, P nutrient element content of the coastal Suaeda salsa (p<0.05). The high-low order of C content was stem>root>flower>leaf, the order of N content was flower>leaf>root>stem, and the order of P content was flower>leaf>root>stem. Obviously, N and P content between the different organs had the same performance. The different organs had different structures as a result of functional differentiation, finally resulting in the differences of the chemical nutrient element contents.(2) Correlation analysis found that there were significant positive correlation between the stems (p<0.05), leaves and flowers C content, significant negative correlation between the root and leaf, stem and leaf N content, widespread positive correlation between the P content of the four organs. A positive correlation showed there was a synergistic effect in the process of assimilating C, P elements of different organs. Similarly, a negative correlation indicated a competition in the distribution of N among the different organs and also showed the N elements was lacking.(3) We found N:P ratios of four different organs, root, stem, leaf and flower were far less than10by analysing stoichiometric ratios. In contrast to the existing research conclusion, the result showed that the growth of coastal S. salsa was limited by N content in a large extent. As a result, increasing N fertilizer will lead to effective improvement of population productivity.(4) The leaf C content of S. salsa had significant differences among three different phases with the lowest in growth phase and the highest in decline phase (p<0.05); the leaf N content in decline phase is significantly lower than in mature and growth phases; the leaf P content was quite stable in different phases, among which no significant difference was found. C:N and C:P in the stage of plant growth and development was gradually increasing while N:P showed a gradually decreasing trend. The correlation analysis indicated that C:N and C:P were negatively correlated with corresponding N, P content in three different phases; N content was positive linear correlation with P content, indicating consistent demand of N and P for S. salsa.(5) C, N, P content and corresponding stoichiometric ratios of soil in vertical section presented some variation. C content of the topsoil was higher enrichment and was inverted pyramid-like distribution from top to bottom; N content presented first increased and then decreased from the0-10cm,10-20cm to20-30cm, which looked like a shuttle; there were no significant difference on P content in three soil layers, so it liked a cylinder.(6) By studying the stoichiometric correlations between soil and plant, we found soil C, N content and plant C, N content had a certain degree of dynamic changes similarity but non-significant (p>0.05). The result showed the absorption process to C, N of plant was relatively independent. Consistency btween soil P and plant P was in good condition. Soil P content effectively increased the P content of the plants confirmed by significant positive correlation btween them. C:P ratio of plant was positively related to soil C and soil N, but was negative correlation with soil P. There was a positive relationship between C:P ratio of pant and soil. The nutrient input and output of ecosystem has a consistent proportion indicating that the system has good stability.