Seasonal ecophysiological variations of Echinocactus platyacanthus, a specially protected cactus species: Effect of induced climate warming

Cactus species are key components in American deserts and have a high socioeconomic value. Climate change exerts a threat to biodiversity, structure and functioning within deserts and many cactus species are predicted to face extinction because of climate change. Defining which plant species could tolerate climate change effects in desert ecosystems acquires crucial importance to promote conservation of these species. Echinocactus platyacanthus is a specially protected cactus species, widely distributed in desert areas of Mexico; however, long-term implications of climate change on survival and physiological responses of this species are still unclear. We assessed the effect of induced warming in the photosynthetic performance and survival on five-years old individuals of Echinocactus platyacanthus for a year. Open-top chambers (OTCs) were used to simulate the effect of global warming (a drive of climate change), while controls were exposed to the current climatic conditions. A generalized canonical correlation analysis was used to measure the intensity of the relationship among environmental variables (mean air temperature, evapotranspiration, global photon flux density, and rainfall), micro-environmental (mean temperature, mean relative humidity and photosynthetic photon flux density) and ecophysiological variables [effective quantum yield of photosystem II (ΦPSII) and electron transport rate (ETR), both within and outside of OTCs]. OTCs had higher temperature than control plots through the seasons. Echinocactus platyacanthus showed higher seasonal variations in photosynthetic performance under warming than in current temperature; nevertheless, 100% survival in both treatments were found. The ΦPSII and ETR values were lower in summer inside OTCs but increased in autumn and winter. We found a strongest correlation between environmental and micro-environmental variables, as well as between micro-environmental and ecophysiological ones, which support the premise that the young individuals of E. platyacanthus depends on the microenvironment to survive. Although after a continuous year under induced warming, individuals of E. platyacanthus showed a decrease in the ΦPSII values during summer and spring and an increase in autumn and winter, survival was not affected. These results reflect the high tolerance in early developmental phases of E. platyacanthus, an adequate functioning of the photosynthetic apparatus of this species could be an efficient physiologic