# The Effects of Fertilization on the Growth and Physiological Characteristics of _Ginkgo biloba_ L.
## 4 Discussion  
Nutrient deficiency is generally considered the major factor limiting growth, and fertilization is the main way to supplement the lack of nutrition. The fertilization effects have shown different results under different quantities of fertilizer, the number of years since fertilization treatment, and the nutrition status of the forest site [31]. Our study was carried out in 2014 and 2015. The single factor experiments suggested that DBH, H, NSL, and V showed significant differences between the different levels of single N or P fertilizer application. The orthogonal test results showed that the nine treatments all promoted the growth of _Ginkgo_, and Treatment 7 (N: 400 g-tree\({}^{-1}\), P: 200 g-tree\({}^{-1}\), K: 90 g-tree\({}^{-1}\)) was the most effective one. The response to fertilization in _Ginkgo_ plantations depended on the degree of mismatch between nutrient supply from the soil and the plant nutrient demand [32]. With an increment in the N fertilizer, there was also an increment in the growth, foliar nutrient status, and photosynthesis rate of the _Ginkgo_ plantation. Phosphorus supply affected photosynthesis, leaf metabolites, and allocation to roots versus leaves and growth. In our study, the growth indicators improved with the P fertilizer dosage. However, excess P supply in the soil is a major environmental concern. The accumulation of P in the soil from applications of chemical fertilizer exceed the requirement of plant and can increase the risk of P movement to surface and groundwater [33]. Thus, we should be very circumspect in the application of P fertilizer. Many investigations have shown that improved N and P nutrition increased growth and yield in many tree species [34]. N and P deficiency cause negative effects on plants [35; 36]. However, [PERSON] et al. (2014) proposed that single N application had negative effects on tree growth, while single P had positive effects on _Pinus patula_ growth at Charter Forests. This may be because N is not a limiting factor to tree growth in the first few years after planting and may be readily available in the soil [19]. Additionally, [PERSON] et al. Figure 4: Effects of combined N, P, and K fertilizer application on _G. biloba_ leaf N, P, and K contents in EXP2. Figure 3: Effects of single K fertilizer application on _G. biloba_ leaf N, P, and K contents in EXP1. (2004) reported clearly that N fertilization is unnecessary on the nitrogen-rich sites, and additional N increased growth only at the most barren sites [37]. In our study, the promotion effect of a single K fertilizer on _Ginkgo_ growth indicators was not significant, though it was better than the unfertilized plots. A previous study showed that fertilization with K was causing a decreased allocation to roots, which enables increased growth in height and leaf number [38]. Moreover, the viewpoint that an optimal potassium nutrition status can reduce the effects of abiotic stresses, such as drought, heat, high light intensity, or salinity has been well established [14; 39; 40]. The characteristic of our study site is coastal sandy saline-alkali soil; thus, K fertilizer is essential in Yellow Sea Forest Park. In general, N played a key role in the growth of _Ginkgo_, and P and K were important nutrient elements playing a major role in _Ginkgo_ growth and development. According to the classification standard of soil nutrients in China, the analysis of soil elements in our experimental plots reveals that contents of N, P, and K are basically at low levels. Therefore, supplementary fertilization may be required on the experimental plots, particularly as the soil nutrient availability cannot meet the demand of the trees. Photosynthesis is the basis of growth and yield formation, and the effects of nutrition on growth may be driven primarily by photosynthesis [41]. Fertilization can increase the photosynthetic efficiency, prolong the duration of photosynthesis, and enlarge the leaf area index (LAI).