Photosynthetic activity and water use efficiency of Salvia verbenaca L. under elevated CO2 and water-deficit conditions

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.

Automated summary

This study investigates the combined effects of elevated CO2 concentration and water-deficit on two varieties of Salvia verbenaca plants. It found that elevated CO2 concentration had positive effects on gas exchange, water use efficiency, and photosystem II activity, while water-deficit conditions had negative effects. When water supply was resumed, the parameters of the plants partially recovered. Additionally, one variety showed higher values in gas exchange and photosystem II activity, while the other variety had higher water use efficiency. These findings suggest that Salvia verbenaca has the potential to expand its invasive range in drought-prone areas.