*Article* **Arbuscular Mycorrhizal Fungi Alter Plant and Soil C:N:P Stoichiometries Under Warming and Nitrogen Input in a Semiarid Meadow of China**

### **Linlin Mei, Xue Yang, Hongbing Cao, Tao Zhang \* and Jixun Guo \***

Institute of Grassland Science, Northeast Normal University, Key Laboratory of Vegetation Ecology, Ministry of Education, Changchun 130024, China; meill641@nenu.edu.cn (L.M.); yangx014@nenu.edu.cn (X.Y.); meilinlinmll@126.com (H.C.)

**\*** Correspondence: zhangt946@nenu.edu.cn (T.Z.); gjixun@nenu.edu.cn (J.G.)

Received: 28 December 2018; Accepted: 29 January 2019; Published: 31 January 2019

**Abstract:** Ecological stoichiometry has been widely used to determine how plant-soil systems respond to global change and to reveal which factors limit plant growth. Arbuscular mycorrhizal fungi (AMF) can increase plants' uptake of nutrients such as nitrogen (N) and phosphorus (P), thereby altering plant and soil stoichiometries. To understand the regulatory effect of AMF feedback on plants and soil stoichiometry under global change, a microcosm experiment was conducted with warming and N input. The C4 grass *Setaria viridis*, C3 grass *Leymus chinensis*, and Chenopodiaceae species *Suaeda corniculata* were studied. The results showed that the mycorrhizal benefits for the C4 grass *S. viridis* were greater than those for the C3 grass *L. chinensis*, whereas for the Chenopodiaceae species *S. corniculata*, AMF symbiosis was antagonistic. Under N input and a combination of warming and N input, AMF significantly decreased the N:P ratios of all three species. Under N input, the soil N content and the N:P ratio were decreased significantly in the presence of AMF, whereas the soil C:N ratio was increased. These results showed that AMF can reduce the P limitation caused by N input and improve the efficiency of nutrient utilization, slow the negative influence of global change on plant growth, and promote grassland sustainability.

**Keywords:** arbuscular mycorrhizal fungi; global change; grassland ecosystem; stoichiometry; phosphorus limitation
