Increasing evidence indicates that plant productivity is constrained by water and nutrient availability under natural conditions of the stimulatory effects of elevated CO2 concentration (eCO2). However, it remains unclear how plant traits related to water and nitrogen acquisition and utilization acclimate to the soil water and nitrogen limitations on productivity. To address this, we investigated isotopic and functional traits and net primary productivity (NPP) of three dominant species of Pinus elliottii, Cunninghamia lanceolata, and Pinus massoniana in a subtropical coniferous plantation from 2011 to 2022 along with environmental parameters. Faced with increasing soil water and nitrogen stress, stomatal conductance (gs, 1/leaf δ18O enrichment) decreased with eCO2 in all species. Stomatal closure enhanced intrinsic water use efficiency (iWUE, derived from leaf δ13C using photosynthetic discrimination model) in P. elliottii and P. massoniana but not in C. lanceolata. Although eCO2 compensate for productivity losses resulting from drought-induced decreases in gs, increased NPP was observed only in P. elliottii, reflecting differences in the species' abilities to acclimate and overcome resource limitations. All species showed increased mycorrhizal dependency (the difference in δ15N between leaves and soil, |△15N|), high leaf nitrogen content, but reduced nitrogen use efficiency, leaf water content and specific leaf area. This suggested that plants increased nitrogen investment through biological adaption to mitigate productivity limitations caused by water and nutrient stress. The increased NPP in P. elliottii was due to high nitrogen uptake and low leaf nitrogen demand, compensating for water limitations. Conversely, reductions in NPP in C. lanceolata and P. massoniana were attributed to the relatively low nitrogen uptake and high leaf nitrogen demand, which failed to offset water limitations. This implies that the magnitude and direction of vegetation productivity responses to eCO2 are determined by species-specific differences in plant adaptations to water and nutrient limitations.

中文翻译：

---

年代际同位素和功能性状证据表明水和氮对三种亚热带针叶树的生产力有限制


越来越多的证据表明，植物生产力受到自然条件下水和养分可用性的限制，以及 CO2 浓度升高 （eCO2） 的刺激作用。然而，目前尚不清楚与水和氮获取和利用相关的植物性状如何适应土壤水和氮对生产力的限制。为了解决这个问题，我们研究了 2011 年至 2022 年亚热带针叶林中 Pinus elliottii、Cunninghamia lanceolata 和 Pinus massoniana 三个优势物种的同位素和功能性状以及净初级生产力 （NPP） 以及环境参数。面对土壤水分和氮胁迫的增加，所有物种的气孔导度 （gs， 1/leaf δ18O 富集） 均随 eCO2 的添加而降低。气孔关闭提高了 P. elliottii 和 P. massoniana 的内在水分利用效率 （iWUE，使用光合鉴别模型从叶片 δ13C 得出），但在 C. lanceolata 中没有。尽管 eCO2 补偿了因干旱引起的 gs 减少而导致的生产力损失，但仅在 P. elliottii 中观察到 NPP 增加，这反映了该物种适应和克服资源限制的能力存在差异。所有物种均表现出菌根依赖性增加（叶片和土壤之间 δ15N 的差异，|△15N|），叶片氮含量高，但氮利用效率、叶片含水量和比叶面积降低。这表明植物通过生物适应来增加氮投资，以减轻水和养分胁迫造成的生产力限制。P. elliottii NPP 的增加是由于高氮吸收和低叶片氮需求，补偿了水分的限制。相反，C. lanceolata 和 P 中 NPP 的降低。 Massoniana 归因于相对较低的氮吸收和高叶片氮需求，这未能抵消水分限制。这意味着植被生产力对 eCO2 的反应的大小和方向是由植物对水和养分限制的适应的物种特异性差异决定的。