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We assessed inter-seasonal dynamics of seed banks, dormancy and seed germination in three endemic Chihuahuan Desert succulent species, under simulated soil warming conditions. Hexagonal open top-chambers (OTCs) were used to increase soil temperature. Seeds of Echinocactus platyacanthus (Cactaceae), Yucca filifera and Agave striata (Asparagaceae) were collected and buried within and outside OTCs. During the course of one year, at the end of each season, seed batches were exhumed to test viability and germination. Soil temperature in OTCs was higher than in control plots. Yucca filifera seeds always had high germination independently of warming treatment and season. Agave striata seeds from OTCs had higher germination than those from control plots. Agave striata exhibited low germination in fresh seeds, but high germination in spring. Seeds from this species lost viability throughout the experimental timeframe, and had no viable seeds remaining in the soil. Echinocactus platyacanthus showed high germination in fresh seeds and displayed dormancy cycling, leading to high germination in spring, low germination in summer and autumn, and high germination in winter. Germination of this species was also higher in seeds from OTCs than those from control plots. Echinocactus platyacanthus formed soil seed banks and its cycle of inter-seasonal dormancy/germination could be an efficient physiological mechanism in a climate change scenario. Under global warming projections, our results suggest that future temperatures may still fall within the three studied species' thermal germination range. However, higher germination for A. striata and E. platyacanthus at warmer temperatures may reduce the number of seeds retained in the seed bank, and this could be interpreted as limiting their ability to spread risk over time. This is the first experimental study projecting an increase in soil temperature to assess population traits of succulent plants under a climate change scenario for American deserts. [ABSTRACT FROM AUTHOR]

Human-induced warming may increase the risk of local extinction for plant species with low tolerance of elevated temperatures. The Chihuahuan desert harbors the highest diversity of globose cacti in the world and most of them are at risk of extinction. Predictive models of climate change indicate an increase in summer temperature of 1-2°C by 2030 for this desert. Nevertheless, studies on the vulnerability of cacti species in early development phases to future climate change are scarce. We assessed the survival of three threatened cacti species from the Chihuahuan desert under induced warming. Open-top chambers ( OTCs) were used to simulate the effect of global warming on 2-year seedlings of E chinocactus platyacanthus f. visnaga, F erocactus histrix and S tenocactus coptonogonus. OTCs had higher temperature and lower humidity than control plots, and these elevated temperatures reduced seedling survival. Within the OTCs, no living individuals of any species were found after 105 days. Conversely, in the control plots, the three cacti species showed variable numbers of survivors after this period. Therefore the predicted global warming scenarios will greatly limit plant recruitment and the long-term persistence of natural populations of Mexican endemic cacti species. [ABSTRACT FROM AUTHOR]

The responses of desert plants to climate warming have been poorly assessed, perhaps due to the overall expectation that desert vegetation will expand as a consequence of this component of climate change. However, determining what plant species will tolerate the expected increase in temperature is a question that remains unanswered. The Chihuahuan Desert is the largest warm desert of North America, and predictive models of climate change indicate that summer temperatures in this desert will increase by 1–2 °C in the next decade. This study experimentally assessed the performance of an endangered cacti species from the Chihuahuan Desert under simulated warming conditions. Hexagonal open top-chambers (OTCs) were used to simulate the effects of global warming on five-years-old individuals of the specially protected species Echinocactus platyacanthus . Temperature was 1.9 °C higher in open top-chambers than in control plots. In contrast, relative humidity was 3.1% higher in control plots than in open top-chambers. E. platyacanthus showed 100% survival for 14 weeks in both OTC and control plots. However, induced warming negatively affected the photosynthetic performance of this species. Cacti located within OTCs displayed lower maximum quantum efficiency of photosystem II ( F v / F m ), effective quantum yield of photosystem II (Φ PSII ), and electron transport rate (ETR) values, but higher non-photochemical quenching (NPQ) values, than cacti from control plots. This is the first study focused on the potential impact of climate warming on survival and photosynthetic performance of young individuals of a succulent species from American deserts. Induced warming negatively affected the photosynthetic performance of young E. platyacanthus , but it also increased non-photochemical quenching, a mechanism for avoiding photoinhibition. [ABSTRACT FROM AUTHOR]

• We assessed the effect of induced warming on an economically important Agave species. • Both developmental phases showed high tolerance under induced global warming. • The younger plants had higher chlorophyll and carotenoid content than older plants. • Our target species displayed higher photochemical activity than other succulents. Agave species are a key component of the structure vegetation in the American drylands and have various anthropogenic uses. Agave angustifolia subsp. tequilana is an economically and culturally important Mexican species. Negative impacts on biodiversity are expected as a consequence of global warming; however, it has been documented that some Agave species are not affected by projected warming. Previous studies on some succulent species under induced global warming have shown a certain level of tolerance to temperature stress. We evaluated the potential temperature stress tolerance of two early developmental phases of A. angustifolia subsp. tequilana , by means of the following photochemical parameters: maximum quantum efficiency of photosystem II (F v /F m); effective quantum yield of PSII (Φ PSII); electron transport rate (ETR); non-photochemical quenching (NPQ); and pigment content (total chlorophyll, carotenoids and anthocyanins) in two-year-old plants and five-year-old plants under induced warming. Temperature and vapor pressure deficit (VPD) were higher in open-top chamber (OTCs) induced warming treatment than control plots, reproducing current climatic conditions. Both developmental phases showed high F v /F m values in both OTCs and control plots. Two-year-old plants displayed higher NPQ values than five-year-old plants under warming. The Φ PSII and ETR values were low in both warming treatments and developmental phases. Low anthocyanin content was found in both treatments and developmental phases. Independently of warming, the two-year-old plants showed higher total chlorophyll and carotenoid content values than the five-year-old plants. Despite that induced warming affected the photochemical activity of A. angustifolia subsp. tequilana , the high NPQ and pigment values indicate that this species has a high tolerance to future global warming. Our results provide novel evidence of the high physiological tolerance that could act in the early developmental phases of a key Agave species to cope the effects of global warming. [ABSTRACT FROM AUTHOR]