Eco-stoichiometric characteristics of carbon, nitrogen and phosphorus in Alternanthera philoxeroides-A. sessilis and their responses to heterogeneous environments

Objective  To explore the difference of stoichiometric ratios between the invasive plant Alternanthera philoxeroides and the native congeneric species A. sessilis as well as the environmental driving forces, and clarify their resource allocation pattern and nutrition strategy.

Method  We totally set up six A.sessilis-A. philoxeroides coexistent plots and seven A. sessilis single plots in the wild habitats of Guangxi, Guangdong, Jiangxi and Henan Provinces. We measured w(C), w(N), w(P) and C∶N, C∶P, N∶P of these two species, and recorded the environmental indicators in each plot. We then used regression analysis and canonical correspondence analysis (CCA) to examine the difference of nutrition strategies between A. sessilis and A. philoxeroides and their responses to the heterogeneous habitats.

Result  In the coexistent communities, there was no significant difference of w(C), w(N), w(P) and their stoichiometric ratios between these two plant species. The w(C) all showed the ‘first rising and then decreasing’ trend with the increase of temperature. The w(N) of A. philoxeroides decreased with the increased precipitation, while the w(N) of A. sessilis showed the ‘first decreasing and then rising’ trend with the increase of precipitation. The w(P) of A. sessilis increased with the increase of elevation. C∶N of these two plant species all showed the trend of ‘first descending and then rising’ with the elevation rising. C∶P of A. sessilis decreased with the increase of elevation, and N∶P decreased with the increase of soil w(N). The C∶P and N∶P of A. philoxeroides had no significant relationship with the environmental factors. In the A. sessilis single communities, the w(C) of A. sessilis decreased with the increase of soil w(NH₄⁺-N), and increased with the increased precipitation; w(P) decreased with the increase of elevation and soil w(N); C∶N decreased with the increase of soil w(NH₄⁺-N) and w(NO₃⁻-N), and C∶P increased with the increase of soil w(N).

Conclusion  The eco-stoichiometric characteristics of C, N, P in A. sessilis are more responsive to the heterogeneous environments than those of A. philoxeroides. A. sessilis chooses the ‘growth competition strategy’ for resisting A. philoxeroides invasion in higher elevation regions. The finding provides a theoretical basis for predicting the invasiveness of alien species and understanding the species coexistence mechanism in depth.