# The Effects of Fertilization on the Growth and Physiological Characteristics of _Ginkgo biloba_ L.
## 4 Discussion
In the present study, \(\mathrm{G_{s}}\) and \(\mathrm{P_{n}}\) showed significant differences between the different levels of single N or P fertilizer applications, while single K fertilizer only affected \(\mathrm{P_{n}}\). Combined N, P, and K fertilizers had significant promoting effects on \(\mathrm{C_{i}}\), \(\mathrm{G_{s}}\), and \(\mathrm{P_{n}}\). N played a vital role in the enzymatic activities of photosynthetic processes, and N addition improved the _Ginkgo_ photosynthesis rate and growth response. Among species there is often a strong positive correlation between maximum rates of photosynthesis and N [42]. Greater application of N fertilizer and greater allocation of N to metabolically active tissues, such as leaves and new stems, in the previous study promoted \(\mathrm{P_{n}}\) by increasing LAI and chlorophyll concentration of leaves, which, in turn, supported better plant growth [43]. There was also a strong connection between P and the maximum rate of photosynthesis [44]; a partial explanation may lie in a positive relationship between the concentration of P and the amount of Rubisco. Inorganic phosphate (Pi) is a prerequisite for RuBP and also a competitive inhibitor of RUBP [45; 46]. Additionally, there was a strong correlation between K concentrations and Rubisco [21]. [PERSON] et al. (2014) also reported that rates of photosynthesis were positively correlated with application rates of K [47]. K deficiency reduces photosynthesis by decreasing stomatal conductance [48]. However, the differences of stomatal conductance were not significant between different amounts of K fertilizer in our research. Possibly owing to the high mobility of K in both soils and plants, growth is expected to improve in response to added K, as shown in sandy soils [49]. Under this circumstance, deficiency of K may be so severe that fertilization is necessary to sustain tree growth until the end of rotation [50; 51]. Transpiration and leaf water status are coordinated to minimize plant water loss and avoid hydraulic failure [52]. \(\mathrm{T_{r}}\) of different levels of fertilization had no significant difference in our study. Probably because the climate characteristic of the site belongs to seasonal pluvial heat and significant monsoon, the rainfalls mainly occur in summer. Many studies have shown that growth of _Populus_ was related to increasing water availability and fertilization on nutrient-limited soils [53; 54]. Thus, sufficient rainfall and appropriate fertilization contributed to better growth in _Ginkgo_ plantations in Yellow Sea Forest Park. Nutrient concentrations of foliage have been accepted as adequate indicators of growth and soil fertility in forest stands [55; 56]. Maintaining near-optimal foliar nutrient status of trees is especially critical to the maintenance of growth, the establishment of cold tolerance, and the evaluation of soil fertility at sites [56; 57]. Our results suggested that N and P contents showed a significant influence of single N fertilizer application. Single P fertilizer only improved foliar P content, and high P fertilizer dosage had an inhibiting effect on K content. Single K fertilizer application improved N and K content in _Ginkgo_ leaves. Effects of different combined N, P, and K fertilizer treatments on the nutrient content of _Ginkgo_ leaves were different. In this study, we found that foliar N concentration was significantly correlated with N fertilizer application, which might result primarily from the supply status of soil nutrient elements. Moreover, foliar N concentration was significantly correlated with K fertilizer application, which might result from K-increased N use efficiency [58]. A previous study has showed that the maximum photosynthetic carbon assimilation rate positively correlated with foliar N concentrations [59]. A greater allocation of N to metabolically-active tissues, such as leaves and new stems in the fertilization treatment, increases the LAI and chlorophyll concentration of leaves, further supporting a better growth of _Ginkgo_ plantations.