Fig.3 Mixing Model_RPM

<br><b>• Background and Aims </b>Freshwater nitrogen inputs are increasing globally, altering the structure and function of wetland ecosystems adapted to low nutrient conditions. Carnivorous wetland plants of the genus <i>Utricularia </i>are hypothesized to reduce their reliance on carnivory and increase their assimilation of environmental nutrients when the supply of ambient nutrients increases. Despite success in using stable isotope approaches to quantify carnivory of terrestrial carnivorous plants, quantifying carnivory of aquatic <i>Utricularia </i>requires improvement.<b>• Methods </b>We developed stable isotope mixing models to quantify aquatic plant carnivory and used these models to measure dietary changes of three <i>Utricularia </i>species, <i>Utricularia australis</i>, <i>U. gibba </i>and <i>U. uliginosa</i>, in 11 wetlands across a 794-km gradient in eastern Australia. Diet was assessed using multiple models that compared variations in the natural-abundance nitrogen isotope composition (δ15N) of <i>Utricularia </i>spp. with that of non-carnivorous plants, and environmental and carnivorous nitrogen sources.<b>• Key Results </b>Carnivory supplied 40–100 % of plant nitrogen. The lowest carnivory rates coincided with the highest availability of ammonium and dissolved organic carbon.<b>• Conclusions </b>Our findings suggest that <i>Utricularia </i>populations may adapt to high nutrient environments by shifting away from energetically costly carnivory. This has implications for species conservation as anthropogenic impacts continue to affect global wetland ecosystems.

• 研究背景与目的 全球范围内淡水生态系统的氮输入量持续攀升，改变了适应低营养条件的湿地生态系统的结构与功能。学界假设，狸藻属（Utricularia）食肉湿地植物在环境营养供给增加时，会降低对食肉习性的依赖，提升对环境营养的吸收效率。尽管利用稳定同位素技术量化陆生食肉植物食肉性的方法已取得一定进展，但水生狸藻属植物食肉性的量化方法仍有待完善。
• 研究方法 本研究构建了稳定同位素混合模型（stable isotope mixing models）以量化水生植物的食肉性，并依托该模型测量了澳大利亚东部794公里梯度范围内11处湿地中3种狸藻属植物：Utricularia australis、U. gibba与U. uliginosa的食性变化。本研究通过多种模型开展食性评估，将狸藻属植物的自然丰度氮同位素组成（δ¹⁵N）与非食肉植物、环境氮源及食肉来源氮的同位素变化进行对比分析。
• 主要研究结果 食肉习性可为植物提供40%~100%的氮源。最低食肉率与铵态氮和溶解性有机碳的最高可用性相吻合。
• 研究结论 本研究结果表明，狸藻属（Utricularia）种群可通过摒弃能量成本高昂的食肉习性，以适应高营养环境。随着人类活动持续影响全球湿地生态系统，该发现对物种保护工作具有重要参考价值。