Dew Can Prolong Photosynthesis and Water Status During Drought in Some Epiphytic Bromeliads From a Seasonally Dry Tropical Forest

Abstract

Dew can represent an alternate water source in epiphytic bromeliads. However, the physiological relevance of dew to withstand the dry season, within seasonal forests, is not fully understood. To study the effect of dew deposition in the physiological response of four Tillandsia species with contrasting morphologies, we performed an experiment in the tropical dry deciduous forest of Dzibilchalt un, Mexico, during the transition from the wet to the dry season. Half of the individuals were covered every night with a plastic tarp to prevent dew deposition. Environmental variables were monitored, and physiological variables (relative water content, leaf succulence, nocturnal tissue acidification and electron transport rate) were measured at the beginning and end of the experiment. We found that throughout the drought, there was consistent nighttime dew formation for >4 h. Both the time the leaves spent at a temperature below dew point of the air and the effect on water and carbon metabolism was species-specific, as evidenced by the comparison among the exposed and covered (dew-deprived) plants. Tillandsia elongata and Tillandsia brachycaulos had longer times of dew formation and showed higher water content at the end of the experiment when exposed to dew, the latter species also had a significant effect of dew on nocturnal acidity. In contrast, neither Tillandsia yucatana nor Tillandsia fasciculata seemed to be using dew as a relevant source of water during the dry period. We discuss the species' morphoanatomical traits that may be related to the differences in dew formation and use.

Physiological ecology of Mexican CAM plants: history, progress, and opportunities

“…However, the epiphytic orchids E. nematocaulon, C. ascendens and Lophiaris oerstedii show slight variation in foliar acidity and relative water content in the three seasons in a semi-deciduous tropical forest also located in Yucatán, but with a two-fold mean annual rainfall that of the tropical dry deciduous forest (de la Rosa-Manzano et al 2014). The lower nocturnal temperature in the early dry season, as well as the low vapor pressure deficit, which increases the probability of dew deposition, can favor CAM in these tropical forests (Andrade 2003, de la Rosa-Manzano et al 2014, Chávez-Sahagún et al 2019.…”

“…Epiphytic orchids accomplish the same thing through the velamen, a tissue consisting of a spongy epidermis with multiple layers at the roots (Goh & Kluge 1989). In Bromeliaceae, leaf morphology in some tank species allow a decrease in leaf temperature, which is usually below air temperature in the early morning, promoting dew condensation, contributing to maintain a high-water balance (Andrade 2003, Reyes-García et al 2012, Chávez-Sahagún et al 2019. Also, nebulophyte morphology, characterized by long and thin leaves with a small boundary layer, allow for the small fog droplets to be intercepted (Martorell & Ezcurra 2002, Reyes-García et al 2012.…”

Studies of plant hydraulics and water relations in Mexican environments: adaptation, physiology, and applications

“…In a similar adaptation to cacti, epiphytic members of Bromeliaceae have evolved leaves that cool radiatively during the night and condense dew (Chávez-Sahagún et al 2019) or that have small boundary layers that enable the interception of the small water droplets present in fog (termed nebulophytes; Martorell & Ezcurra 2007, Reyes-García et al 2012). These bromeliads have lost most root absorptive capacity (Benzing 2000, Leroy et al 2019) and rely on complex trichomes for water absorption directly into the leaf (Benzing 1976, Pierce et al 2001, Ohrui et al 2007.…”

Seasonal changes in photosynthesis for the epiphytic bromeliad Tillandsia brachycaulos in a tropical dry deciduous forest

“…Epiphytes have been postulated as species particularly vulnerable to prolonged droughts, given their strong coupling to the frequency of rain events, and their lack of access to water stored in the ground (Benzing 1998, de la Rosa-Manzano et al 2014, Reyes-García & Griffiths 2009, Reyes-García et al 2012, Zotz & Bader 2009. Moreover, epiphytic bromeliads show a low root to shoot ratio and the absorption of water and nutrients is primarily made by foliar trichomes (Benzing 2000, Zotz 2016); and, occasionally, they may rely on alternative sources of water other than rain, such as fog and dew, especially during part of the dry season (Andrade 2003, Guevara-Escobar et al 2011, Reyes-García et al 2012, Chávez-Sahagún et al 2019. The aim of this study was to investigate the capacity for photosynthetic acclimation, under seasonal light micro-environment, for the CAM epiphytic bromeliad Tillandsia brachycaulos Schltdl., by measuring seasonal changes in chlorophyll fluorescence, nocturnal accumulation of tissue acidity, and water potentials, to characterize its responses to high light in the field.…”