In soil, CaCO 3 can reduce the availability of phosphorus in arid and semi-arid regions, thereby influencing plant growth. However, the effects of soil stoichiometry of the CaCO 3 /available phosphorus ratio (CaCO 3 /AP ratio) on plant density are unknown. In this study, we examined 4 Artemisia ordosica communities located in arid and semi-arid regions, and performed a pot experiment with an orthogonal design to examine the relationships between the soil CaCO 3 /AP ratio and plant density. The results showed that the soil stoichiometry of the CaCO 3 /AP ratio had a greater effect on growth of A. ordosica than either CaCO 3 or AP as single factor. The influence of the soil CaCO 3 /AP ratio on density of A. ordosica was related to the climatic zone and the types and/or amplitudes of increases in the soil CaCO 3 /AP ratio. When the soil CaCO 3 /AP ratio was within the same amplitude and was less than 2.5, the A. ordosica density increased in the semi-arid region, whereas the density decreased with increasing soil CaCO 3 /AP ratios in the arid region. In the semi-arid region, when the soil CaCO 3 /AP ratio was within the same amplitude and the increase in the soil CaCO 3 content was greater than the increase in soil AP, the A. ordosica density increased with increasing soil CaCO 3 /AP ratios. This means that the relationship between the soil CaCO 3 /AP ratio and the A. ordosica density remained the same. In the arid region, an increase in the soil CaCO 3 /AP ratio as a result of increased soil CaCO 3 content and decreased soil AP resulted in increased density of A. ordosica. Therefore, the relationship between soil CaCO 3 /AP ratios and density of A. ordosica was altered by these changes in soil chemistry. Thus, the soil stoichiometry of the CaCO 3 /AP ratio is an important factor affecting the density of A. ordosica in arid and semi-arid regions.Artemisia ordosica, soil CaCO 3 , soil available phosphorus, soil CaCO 3 /available phosphorus ratio (soil CaCO 3 /AP ratio), stoichiometry, plant density Citation:Zhao X L, He X D, Xue P P, et al. Effects of soil stoichiometry of the CaCO 3 /available phosphorus ratio on plant density in Artemisia ordosica communities.

Plant phenotypic plasticity is a common feature that is crucial for explaining interspecific competition, dynamics and biological evolution of plant communities. In this study, we tested the effects of soil CaCO 3 (calcium carbonate) on the phenotypic plasticity of a psammophyte, Artemisia ordosica, an important plant species on sandy lands in arid and semi-arid areas of China, by performing pot experiments under different CaCO 3 contents with a two-factor randomized block design and two orthogonal designs. We analyzed the growth responses (including plant height, root length, shoot-leaf biomass and root biomass) of A. ordosica seedlings to different soil CaCO 3 contents. The results revealed that, with a greater soil CaCO 3 content, A. ordosica seedlings gradually grew more slowly, with their relative growth rates of plant height, root length, shoot-leaf biomass and root biomass all decreasing significantly. Root N/P ratios showed significant negative correlations with the relative growth rates of plant height, shoot-leaf biomass and root length of A. ordosica seedlings; however, the relative growth rate of root length increased significantly with the root P concentration increased, showing a positive correlation. These results demonstrate that soil CaCO 3 reduces the local P availability in soil, which produces a non-adaptive phenotypic plasticity to A. ordosica seedlings. This study should prove useful for planning and promoting the restoration of damaged/degraded vegetation in arid and semi-arid areas of China.