Dynamic Effects of Forest Window Size on the Growth and Photosynthetic Characteristics of Schima superba Seedlings in the Understory of Pinus massoniana

In order to analyze the response mechanism of forest window size on the growth and photosynthetic physiology of Schima superba planted in the understory of Pinus massoniana, the following experimental materials were used. We took 2-year-old S. superba seedlings as experimental materials, set up different forest window treatments without opening forest windows(CK) and with forest window areas of 50 m²(T₁), 100 m²(T₂), 200 m²(T₃), and 400 m²(T₄), and analyzed the effects of different forest window areas on growth and photosynthetic indexes of S. superba. The results showed that the increase of forest window area increased the relative air temperature and decreased the relative humidity inside the forest window; the different area of forest window in different seasons had a significant effect on the height, diameter and biomass of S. superba seedlings, which showed winter<autumn<summer in seasons, and the highest value of the growth in summer(July) was in the T₄ treatment (47.42 cm), and the lowest value was in the CK treatment(16.52 cm), and the highest value was in the CK treatment (16.52 cm), and the lowest value was in the CK treatment(16.52 cm). Different forest window treatments were CK<T₁<T₂<T₃<T₄, and T₄ was significantly different from T₁ and CK; the net photosynthetic rate(P_n) and stomatal conductance (G_s) of S. superba leaves reached the highest value at T₄ treatment in summer, which were 9.95 μmol/(m²·s) and 0.09 μmol/(m²·s), and carbon dioxide CO₂(C_i) and transpiration rate (T_r) varied in a V-shape with the increase of the forest window area; whereas, all the treatments of forest window size did not have significant effects on the maximal fluorescence efficiency of the PSII reaction centers (F_v/F_m) and the potential fluorescence activity(F_v/F₀); there exist correlations among the forest microenvironment, photosynthetic traits, and growth indicators of S. superba. Temperature and humidity display a noteworthy negative correlation. Tree height, ground diameter, and P_n demonstrate a significant positive correlation. Ground diameter exhibits a significant positive correlation with T_r and G_s. P_n and G_s, T_r and tree height, as well as tree height and ground diameter, all exhibit an extremely significant positive correlation. From the perspective of growth and photosynthesis, the forest window area of 400 square meters was more conducive to the growth of S. superba and met the growth conditions of S. superba with strong light-loving growth.