Seasonal variations in C, N and P stoichiometry of Bidens alba under two invasive degrees

To explore the carbon, nitrogen and phosphorus stoichiometry and resource allocation in different organs of Bidens alba in different invasion degrees and seasons; the contents of organic C, total N and total P in different organs (roots, stem and leaves) of B. alba and soil in dry and wet seasons were determined under two invasion degrees (mild invasion “coverage < 30%” and severe invasion “coverage > 60%” ) in the abandoned farmlands of Puer City suburb. The results showed that: 1) the contents of soil organic carbon, total nitrogen and total phosphorus in the dry season were higher than those in the wet season, with the results of the two invasion degrees being consistent. Soil organic C and total N content was higher in the heavily invaded soil than in the lightly invaded soil, which was obvious in the wet season but not in the dry season. 2) Different seasons showed significant effects on the content of C in roots, stem and leaves, P in roots and stem, and N in leaves. In both dry and wet seasons, more N was allocated to the leaves. In the wet season, more P is distributed to the leaves, while in the dry season, it is distributed to both stem and leaves. The total N content in the stem of the severely invaded plants was significantly higher in the dry season than in wet season. The degree of invasion significantly affected the total P content in leaves and total N content in the stem of B. alba during the wet season. 3) There were significant differences in N ꞉ P values among different organs (leaves > roots > stem), and there were no significant differences between season and degree of invasion. In the wet season, there were significant differences in C ꞉ N value (stem > roots > leaves) and C ꞉ P value (roots > stem > leaves ) in different organs, but these differences became insignificant in the dry season. In the wet season, the C ꞉ N value of the stem was significantly higher than that of light invasion, and the C ꞉ P value and N ꞉ P value of leaves were significantly higher than that of light invasion. 4) The correlation between nutrient elements of the plant and the soil was affected due to seasons. In the wet season, leaf organic C content, stem total N content and soil total N content showed a significant negative correlation. The total C content and total N content in the stem were negatively correlated with the total C content in soil. There was a significant positive correlation between total P content in stem and soil, and between total P content in leaf and total N content in soil. In conclusion, C, N, P contents, C ꞉ N values, N ꞉ P values in B. alba were affected due to different seasons and different degrees of invasion due to different strategies of nutrient allocation, and these strategies ensured that B. alba could be benefited from competition and survival.