为揭示同域入侵植物意大利苍耳与刺苍耳通过光合-水分策略分化实现共存的生态机制,以内蒙古海流水库为研究区,利用Li-6800光合仪测定叶片光合日动态参数(净光合速率P_n、蒸腾速率T_r、气孔导度G_s),结合土壤含水量空间自相关分析,拟合物种分布-水分响应曲线。结果表明:1)意大利苍耳光合曲线呈“双峰型”,午间光抑制程度低,最大净光合速率为47.91 μmol/(m²·s),比刺苍耳的最大净光合速率[17.2 μmol/(m²·s)]提高178.5%;刺苍耳则以晨间高光响应速率抢占碳同化先机。2)意大利苍耳主导高水分生境,土壤含水量大于20.4%,刺苍耳适应干旱区,土壤含水量小于12.7%,二者共存的阈值区间为14.8%~18.3%。3)意大利苍耳的水分利用效率随土壤含水量增加而增加(R²=0.83),符合水分集约利用策略;刺苍耳在土壤含水量为16.5%时水分利用效率峰值偏移,通过气孔振荡适应水分波动。二者通过“高光效-高蒸腾”策略组合实现光能-水分资源分割,其“光合-水分生态位互补”机制为入侵种协同扩散提供了生理生态学基础。

To elucidate the ecological mechanisms underlying the coexistence of two sympatric invasive species,Xanthium strumanum subsp.italicum and X.spinosum,through differentiation in photosynthetic-water utilization strategies,this study was conducted at Hailiu Reservoir in Inner Mongolia.The experimental design included establishing equidistant sampling plots from nearshore to offshore,encompassing monospecific stands(single-species dominant communities)and mixed communities.Leaf photosynthetic diurnal dynamics(net photosynthetic rate P_n,transpiration rate T_r,and stomatal conductance G_s)were measured using a Li-6800 photosynthesis system,and spatial autocorrelation analysis of soil water content was used to construct species distribution and water response curves.Key findings showed that:1)X. strumarium subsp. italicum exhibited a "bimodal" photosynthetic curve,with a maximum P_n of 47.91 μmol/(m²·s).This rate is 178.5% higher compared to that of X.spinosum[17.2 μmol/(m²·s)]and was associated with lower midday photoinhibition.In contrast,X.spinosum achieved a higher photosynthetic rate during morning hours,enabling it to seize an advantage in carbon assimilation early in the day.2)X.strumarium subsp. italicum dominated high-moisture habitats(>20.4%),while X.spinosum prevailed in arid zones(<12.7%),with coexistence occurring within a threshold interval of 14.8%-18.3%.3)X. strumarium subsp. italicum showed linearly increasing WUE with moisture(R²=0.83),indicative of water-conservative strategies,whereas X.spinosum displayed a WUE peak shift at a moisture level of 16.5%,regulated by stomatal oscillation.These results demonstrate that the two invaders achieve niche complementarity through "high photosynthetic efficiency/high transpiration" resource partitioning strategies,with their "photosynthetic-hydrological niche complementarity" mechanism providing a physiological basis for synergistic invasion.The findings offer critical insights for precision management of invasive plants in arid reservoir ecosystems.