Effects of Water-Fertilizer Coupling on Growth Characteristics and Water Use Efficiency of Camellia petelotii Seedlings

Camellia petelotii (Merr.) Sealy is an endangered Chinese native species that originates from Guangxi Zhuang Autonomous Region, China. Previous research demonstrated that proper water and fertilizer treatments could improve the growth and quality of Camellia species. This study uses a three-factor, fi ve-level quadratic rotational combination experimental design to investigate the impact of water-fertilizer coupling on plant growth characteristics and the most suitable treatment for 24-month-old grafted C. petelotii seedlings. The experimental design includes irrigation levels [30%, 40%, 55%, 70%, 80% of fi eld capacity (FC)], nitrogen application (0, 2.17, 5.43, 8.70, 10.87 g<middle dot>plant-1), and phosphorus application (0, 0.96, 2.40, 3.85, 4.81 g<middle dot>plant-1). The results indicated that: (1) Water-nitrogen and water-phosphorus interactions significantly affected ground diameter, chlorophyll content and specific leaf weight (SLW), while water-nitrogen interactions significantly affected plant height and photosynthesis; (2) Application of nitrogen (8.70 g<middle dot>plant-1) and phosphorus (3.85 g<middle dot>plant-1) fertilizers under appropriate irrigation conditions (40% FC and 70% FC) improved growth. Applying fertilizers containing either nitrogen (10.87 g<middle dot>plant-1) or phosphorus (4.81 g<middle dot>plant-1) under adequate irrigation (55% FC) increased the Chl content. However, high nitrogen levels (10.87 g<middle dot>plant-1) reduced photosynthesis. Conversely, it was enhanced under appropriate phosphorus (4.81 g<middle dot>plant-1) when the irrigation level was 55% FC, indicating the sensitivity of C. petelotii seedlings to nitrogen fertilizer. (3) Under specific conditions of 40% FC or 70% FC irrigation and 8.70 g<middle dot>plant-1 or 2.17 g<middle dot>plant-1 nitrogen fertilizer application, 3.85 g<middle dot>plant-1 phosphorus addition boosted the SLW whereas, 0.96 g<middle dot>plant-1 phosphorus addition inhibited it. Under W = 55% FC, deficiencies in either nitrogen (N = 0 g<middle dot>plant-1) or phosphorus (P = 0 g<middle dot>plant-1) significantly decreased leaf growth, affecting SLW. In summary, C. petelotii was more sensitive to nitrogen fertilizer at W = 55% FC, and nitrogen deficiency inhibited C. petelotii growth in terms of ground diameter more than phosphorus deficiency. The C. petelotii seedlings performed best when treated with 55% FC, 5.43 g<middle dot>plant-1 nitrogen, 2.40 g<middle dot>plant-1 phosphorus per plant. These parameter estimates could optimize water and fertilizer application for C. petelotii seedlings.