Investigating the combined effects of elevated CO₂ concentration and water-deficit on weed plants is crucial to gaining a thorough understanding of plant performance and modifying agricultural processes under changing climate conditions. This study examined the effect of elevated CO₂ concentration and water-deficit conditions on leaf gas exchange, water use efficiency, carboxylation efficiency and the photosystem II (PSII) activity of two Salvia verbenaca L., varieties. These varieties were grown under two CO₂ concentrations (ambient conditions of 400 ppm and elevated conditions of 700 ppm) and two water regimes (well-watered [100% field capacity] and water-deficit conditions [60% field capacity]) in laboratory growth chambers. For 12 days, at 2-day intervals, (i) leaf gas exchange parameters (photosynthesis rate, stomatal conductance, transpiration rate (E) and intercellular CO₂ concentration (Ci)), (ii) water use efficiency (WUE), (iii) intrinsic water use efficiency (IWUE), (iv) instantaneous carboxylation efficiency and (v) PSII activity (fluorescence, quantum yield of PSII, photochemical efficiency of PSII, photochemical quenching and photosynthetic electron transport) were measured. Water-deficit conditions had negative effects on studied parameters of both varieties, whereas elevated CO₂ concentration had positive effects on the gas exchange, water use efficiency and PSII activity of both. Salvia verbenaca varieties grown under water-deficit conditions from Day 0 to Day 5 showed a partial recovery in most of the parameters when the resumption of the well-watered regime was reinstituted on Day 6. Salvia verbenaca varieties grown under water-deficit conditions were re-watered on day 6 and indicated a partial recovery in all the parameters. A comparison of the two varieties showed that var. vernalis recorded higher values of gas exchange, quantum yield of PSII and photochemical efficiency of PSII than var. verbenaca, but the water use efficiency of var. verbenaca was higher than that of var. vernalis. These differences serve to illustrate the complexity of such studies and suggest that a detailed understanding of the nature of weed infestations is essential if optimum management control is to be practiced. Elevated CO2 concentration mitigated the adverse effects of water-deficit conditions and thereby enhanced the adaptive mechanism of this weed by improving its water use efficiency. It is thus likely that S. verbenaca has the potential to take advantage of climate change by increasing its relative competitiveness with other plants in drought-prone areas, suggesting that it could significantly expand its invasive range under such conditions.

中文翻译：

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高二氧化碳和缺水条件下鼠尾草的光合活性和水分利用效率

研究 CO ₂浓度升高和缺水对杂草植物的综合影响对于深入了解植物性能和在不断变化的气候条件下改变农业过程至关重要。本研究考察了升高的 CO ₂浓度和缺水条件对两种鼠尾草品种叶片气体交换、水分利用效率、羧化效率和光系统 II (PSII) 活性的影响。这些品种在两种 CO _2下生长浓度（400 ppm 的环境条件和 700 ppm 的升高条件）和两种水分状况（充分浇水 [100% 田间容量] 和缺水条件 [60% 田间容量]）。12 天，每隔 2 天，(i) 叶片气体交换参数（光合作用速率、气孔导度、蒸腾速率 (E) 和细胞间 CO ₂浓度 (Ci)），(ii) 水分利用效率 (WUE)，( iii) 测量了内在水分利用效率 (IWUE)、(iv) 瞬时羧化效率和 (v) PSII 活性（荧光、PSII 的量子产率、PSII 的光化学效率、光化学猝灭和光合电子传输）。缺水条件对两个品种的研究参数都有负面影响，而 CO _2升高浓度对两者的气体交换、水分利用效率和PSII活性都有积极影响。在第 0 天到第 5 天在缺水条件下种植的丹参马鞭草品种在第 6 天恢复充分浇水后，在大多数参数中显示出部分恢复。丹参马鞭草在缺水条件下种植的品种在第 6 天重新浇水，所有参数均显示部分恢复。两个品种的比较表明，变种。vernalis 记录的气体交换值、PSII 的量子产率和 PSII 的光化学效率高于 var。马鞭草，但var的水分利用效率。马鞭草高于var。春日。这些差异说明了此类研究的复杂性，并表明如果要实施最佳管理控制，必须详细了解杂草侵扰的性质。升高的二氧化碳浓度减轻了缺水条件的不利影响，从而通过提高其水分利用效率来增强这种杂草的适应机制。因此，马鞭草很可能具有利用气候变化的潜力，通过提高其与干旱多发地区其他植物的相对竞争力，这表明它可以在这种条件下显着扩大其入侵范围。