Do photosynthetic metabolism and habitat influence foliar water uptake in orchids?

Abstract

Epiphytic and rupicolous plants inhabit environments with limited water resources.Such plants commonly use Crassulacean Acid Metabolism (CAM), a photosynthetic pathway that accumulates organic acids in cell vacuoles at night, so reducing their leaf water potential and favouring water absorption. Foliar water uptake (FWU) aids plant survival during drought events in environments with high water deficits. We hypothesized that FWU represents a strategy employed by epiphytic and rupicolous orchids for water acquisition and that CAM will favour increased water absorption.• We examined 6 epiphyte, 4 terrestrial and 6 rupicolous orchids that use C3 (n = 9) or CAM (n = 7) pathways. Five individuals per species were used to evaluate FWU, structural characteristics and leaf water balance.• Rupicolous species with C3 metabolism had higher FWU than other species. FWU (C max and k) could be related to succulence, SLM and leaf RWC. The results indicated that high orchid leaf densities favoured FWU, as area available for water storage increases with leaf density. Structural characteristics linked to water storage (e.g. high RWC, succulence), on the other hand, could limit leaf water absorption by favouring high internal leaf water potentials.• Epiphytic, rupicolous and terrestrial orchids showed FWU. Rupicolous species had high levels of FWU, probably through absorption from mist. However, succulence in plants with CAM appears to mitigate FWU.

Foliar Water Uptake and Its Relationship with Photosynthetic Capacity and Anatomical Structure between Female and Male Populus euphratica at Different Growth Stages

“…During the whole growth period, the response of the leaf structure and physiology of male and female P. euphratica to humidification exhibited both similarities and differences. In addition to WUE, there was a positive correlation between predawn water potential and photosynthetic capacity in male and female P. euphratica, indicating that an improvement in leaf water status due to humidification was beneficial to the process of carbon assimilation [59]. After comparing the fluorescence parameters, we found that qP and ETR were negatively correlated with the leaf predawn water potential.…”

Revisiting an ecophysiological oddity: Hydathode‐mediated foliar water uptake in Crassula species from southern Africa

“…As hypothesised by Berry et al (2019), differences in C should influence FWU, with high values of C resulting in relatively constant FWU rates that can be sustained for longer. In fact, a trade‐off between C and FWU has been suggested, whereby species with high C usually exhibit lower FWU capacities and/or rates (Gotsch et al, 2015; Lima et al, 2023). However, under drought conditions and declining leaf Ψ, a higher C implies that succulents capable of FWU such as Crassula will be able to absorb greater amounts of atmospheric water to buffer Ψ.…”

“…and Sedum, have only marginal hydathodes or a single (sub)apical one (Caballero & Jiménez, 1977;'t Hart & Bleij, 2003;Moreira et al, 2012;Thiede & Eggli, 2007), and even though there are reports of laminar hydathodes in some Cotyledon species (Weingart, 1935) constant FWU rates that can be sustained for longer. In fact, a tradeoff between C and FWU has been suggested, whereby species with high C usually exhibit lower FWU capacities and/or rates (Gotsch et al, 2015;Lima et al, 2023). However, under drought conditions and declining leaf Ψ, a higher C implies that succulents capable of FWU such as Crassula will be able to absorb greater amounts of atmospheric water to buffer Ψ.…”

“…Several morpho-anatomical and biochemical traits can influence FWU capacity (i.e., how much water can be absorbed) and rate (i.e., how fast water is absorbed) (Boanares et al, 2018a(Boanares et al, , 2018bEller et al, 2016;Lima et al, 2023;Limm et al, 2009;dos Santos Garcia et al, 2022). Deposition of liquid water on leaf surfaces is governed by their wettability, which in turn is determined by features such as trichomes, hygroscopic salts and epicuticular waxes (Barthlott et al, 2017;Konrad et al, 2015), and water entering the leaves through FWU must overcome a series of hydraulic resistances until it reaches the cells or the vasculature (Boanares et al, 2020;Buckley, 2015).…”