**Understory Plant Functional Types Alter Stoichiometry Correlations between Litter and Soil in Chinese Fir Plantations with N and P Addition**

### **Junyi Xie, Haifu Fang, Qiang Zhang, Mengyun Chen, Xintong Xu, Jun Pan, Yu Gao, Xiangmin Fang, Xiaomin Guo and Ling Zhang \***

Jiangxi Provincial Key Laboratory of Silviculture, Jiangxi Agricultural University, Nanchang 330045, China **\*** Correspondence: lingzhang@jxau.edu.cn or lingzhang09@126.com; Tel.: +86-79183813243

Received: 25 July 2019; Accepted: 23 August 2019; Published: 28 August 2019

**Abstract:** Research Highlights: This study identifies the e ffect of nitrogen (N) and phosphorus (P) addition on stoichiometry correlations between understory plants and soil in subtropical Chinese fir plantations. Background and Objectives: Nitrogen and P are two nutrients limiting forest ecosystem production. To obtain more wood production, N and P are usually applied in plantation management. Changes in soil N and P will generally alter the stoichiometric characteristics of understory plants, which control carbon (C) and nutrient cycles between plants and soil. However, di fferent correlations between plant and soil stoichiometry among functional groups of understory plants have not been investigated, which also impacted element cycling between plants and soil. Materials and Methods: Subtropical Chinese fir plantations were selected for N (100 kg ha−<sup>1</sup> year<sup>−</sup>1) and P (50 kg ha−<sup>1</sup> year<sup>−</sup>1) addition study. We collected fresh litter and the corresponding soil of four understory plants (*Lophatherum gracile* Brongn., *Woodwardia japonica* (L.f.) Sm., *Dryopteris atrata* (Kunze) Ching and *Dicranopteris dichotoma* (Thunb.) Berhn.) for study of C, N, and P stoichiometric ratios. Results: Nitrogen and P addition a ffected C, N, and P concentrations and stoichiometric ratios in litter and soil as well as correlations between litter and soil stoichiometric ratios. Understory plant species with di fferent functional types impacted the correlations between plants and soil in C, N, and P stoichiometric ratios, especially correlations between litter C and soil C and N. Conclusions: Changes in soil N and P a ffect the stoichiometric ratios of understory plants. Functional groups impacted the correlation in C, N, and P stoichiometric ratios between plants and soil, indicating functional groups varied in their impacts on element cycling between plants and soil in plantations with exogenous nutrient addition, which should be considered in future managemen<sup>t</sup> of plantations with intensive fertilization practice.

**Keywords:** nitrogen and phosphorus addition; understory plants; stoichiometric ratio; litter decomposition
