Responses of Planting Modes to Photosynthetic Characteristics and Fluorescence Parameters of Fokienia hodginsii Seedlings in a Heterogeneous Nutrient Environment

Fokienia hodginsii seedlings tend to vary significantly in response to differences in the surrounding environment, especially when the nutrient environment is heterogeneous and neighboring plants are in competition. Plant physiological differences occur not only in the root system, but also in the photosynthetic characteristics and fluorescence parameters of the leaves. Therefore, in this experiment, three planting modes (single planting, pure planting of F. hodginsii and mixed planting of F. hodginsii and Cunninghamia lanceolata) were set up to simulate different competition patterns. Three heterogeneous nutrient environments (N, P, K heterogeneous nutrient environment) were planted in this experiment, and the homogeneous environments were used as controls to determine the differences in photosynthetic characteristics, fluorescence parameters and the interaction of different environmental factors on each index in different heterogeneous nutrient and planting environments. The interactions of different environmental factors with various indicators were measured. In addition, all treatment combinations were evaluated and ranked by principal components analysis. The results showed that the net photosynthetic rate (P-n) was on average 28.8% and 22.3% higher under monoculture treatment compared to pure and mixed planting in each nutrient environment. Transpiration rate (T-r) and stomatal conductance (G(s)) were the lowest under pure planting mode, and the overall mean of Tr was 27.2% and 5.5% lower than monoculture and mixed planting, respectively, and the overall mean of Gs was 36.5% and 14.7% lower, respectively. Intercellular CO2 concentration (C-i) was higher under mixed and pure planting mode than monoculture, but their overall increments were not significant. P-n, T-r and G(s) values of F. hodginsii in the N and P patches were significantly higher than those in the homogeneous patches, whereas the average values of P-n, T-r and G(s) in the K patches were slightly higher than those in the homogeneous patches. The average values of leaf F-o, F-v/F-m and qP in each nutrient patch under single planting were higher than those under pure and mixed planting, but most of the differences were not significant. The actual photochemical efficiency (yield), photosynthetic electron transfer rate (ETR) and F-v/F-m in N and P patches were significantly higher than those in the homogeneous patches, whereas qP and NPQ in N and P patches differed due to different planting patterns. Most fluorescence parameters in the K patches were lower than those in the homogeneous patches. Planting patterns and nutrient heterogeneity showed significant interaction effects on P-n, G(s), Yield, ETR, F-v/F-m and NPQ. The highest scores for photosynthetic characteristics and fluorescence parameters of F. hodginsii single planting were in N and P nutrient patches.