Abstract: To explore the adaptation strategies of Amorphophallus xiei to light intensity changes, we analyzed the photosynthetic characteristics, photosynthetic induction characteristics, fluorescence characteristics, and energy allocation of A. xiei under relay intercropping conditions in rubber plantations of different ages (3-year-old, with understory light transmittance of 65%-75%, high light; 5-year-old, with understory light transmittance of 30%-45%, medium light; 8-year-old, with understory light transmittance of 10%-15%, low light). The results showed that under the 8-year-old rubber plantation, A. xiei was characterized by lower light saturation point (LSP) and light compensation point (LCP), but higher apparent quantum yield (AQY) and maximum carboxylation rate (V_cmax). The time required to reach 50% and 90% of the maximum net photosynthetic rate after dark-adapted light induction (t_50%A, t_90%A) was relatively short, and the percentages to maximum net photosynthetic rate at 1, 5, and 10 minutes of induction (IS_{1 min}, IS_{5 min}, IS_{10 min}) were relatively high. In addition, a higher initial stomatal conductance (G_s-initial) was observed in A. xiei under the 8-year-old plantation, with G_s-initial being negatively correlated with the time required to reach 30% of the maximum net photosynthetic rate after dark-adapted light induction (t_30%A), t_50%A and t_90%A. The maximum net photosynthetic rate (A_max) under the 5-year-old plantation was higher than that under the other two aged plantations, along with a higher CO₂ compensation point (Γ^*) and maximum electron transfer rate (J_max). Meanwhile, the non-photochemical quenching (NPQ) and apparent electron transfer rate (ETR) of chlorophyll fluorescence were higher. t_30%A was relatively short under the 3-year-old plantation, while t_50%A and t_90%A were relatively shorter under both 5- and 8-year-old plantations. A larger proportion of light energy was allocated to non-photochemical quenching (Ф_NPQ) under 5- and 8-year-old plantations. When exposed to an instantaneous high light intensity of 1500 μmol·m^-2·s^-1, the proportion of light energy allocated to fluorescence dissipation (Ф_f,D) increased rapidly but slightly, then decreased and gradually stabilized. The highest Ф_f,D value was recorded under the 3-year-old plantation. It was demonstrated that the light adaptation strategies of A. xiei under the rubber plantation varied with light intensity. Under low light (transmittance 10%-15%) and medium light (transmittance 30%-45%) conditions, photosynthesis was stronger, the photosynthetic induction rate was faster, and A. xiei maintained a relatively high carboxylation capacity to utilize light energy. Meanwhile, a stronger thermal dissipation capacity of A. xiei protected itself from photoinhibition. In contrast, photoinhibition was identified as the main reason why A. xiei could not grow normally under high light stress (transmittance 65%-75%).

Key words: understory intercropping, photosynthetic performance, energy partitioning, Amorphophallus xiei, rubber plantation