Effects of simulated expansion of Phyllostachys edulis on growth and photosynthetic physiological characteristics of endangered plant Sinomanglietia glauca

<bold>Objective</bold> By simulating key environmental changes，specifically understory shading and soil nutrient alterations，that occur during the expansion of moso bamboo，this study aims to clarify the mechanisms by which these changes affect morphological growth，nutrient absorption，and photosynthetic physiological characteristics in seedlings of the endangered plant species <italic>Sinomanglietia glauca</italic>. <bold>Method</bold> Based on the ecological process wherein the expansion of moso bamboo leads to the formation of a highly closed canopy and altered soil nutrient conditions，this study employed an experimental simulation using different shading and fertilization treatments.A total of seven treatment combinations were established：full light without fertilization（L0N0）was used to simulate the original environment prior to bamboo expansion，serving as the baseline control；full light with fertilization（L0N1），50% shading with fertilization（L1N1），50% shading without fertilization（L1N0），75% shading with fertilization（L2N1），and 75% shading without fertilization（L2N0）were implemented to simulate varying light and soil nutrient conditions under different degrees of bamboo expansion.At the same time，bamboo forest habitat was used as a realistic control，reflecting the actual environmental conditions after expansion.The differences in growth，photosynthetic physiology，and nutrient absorption of <italic>Sinomanglietia glauca</italic> seedlings under various treatments were compared and analyzed. <bold>Result</bold> （1）Shading significantly inhibited the growth of plant height and ground diameter（<italic>P</italic>&lt;0.001），but the effect of fertilization was not significant（<italic>P</italic>&gt;0.05），and there was no interaction between them.The inhibition effect of bamboo forest group on growth was similar to that of 75% shading group.（2）The net photosynthetic rate of <italic>Sinomanglietia glauca</italic> decreased with the increase of shading.Shading significantly reduced the maximum photosynthetic rate（<italic>P</italic>_max），dark respiration rate（<italic>R</italic>_d），light saturation point（LSP）and light compensation point（LCP），while fertilization only increased the maximum photosynthetic rate（<italic>P</italic>_max），and there was a significant interaction between the two on <italic>R</italic>_d and LCP.（3）Sufficient light was beneficial to improve stomatal conductance，transpiration rate and water use efficiency，reduce intercellular CO₂ concentration，and thus enhance photosynthesis，while shading significantly inhibited these light response parameters，leading to the decline of photosynthesis and water use efficiency.（4）There was no significant difference in N content between the bamboo forest group and the full sunlight non fertilization group，but it was significantly lower than other treatments（<italic>P</italic>&lt;0.05）.At the same time，the N∶P ratio of the bamboo forest group was the lowest（11.67）and significantly lower than other treatment groups（<italic>P</italic>&lt;0.05），which showed that nitrogen was the key factor limiting the regeneration of <italic>Sinomanglietia glauca</italic> seedlings in the bamboo forest habitat. <bold>Conclusion</bold> The inhibition of photosynthesis and growth of <italic>Sinomanglietia glauca</italic> seedlings by light limitation and nitrogen competition during the expansion of <italic>Phyllostachys edulis</italic> is the key factor to aggravate its endangerment.To mitigate these effects，it is recommended to implement forest management interventions such as selective thinning of bamboo stands to improve light penetration through the creation of canopy gaps.Concurrently，targeted fertilization strategies，particularly nitrogen supplementation，should be applied to alleviate nutrient competition and support the natural regeneration process of <italic>Sinomanglietia glauca</italic> populations.