A field portable method for the semi‐quantitative estimation of dehydration tolerance of photosynthetic tissues across distantly related land plants

Abstract

Desiccation tolerant (DT) plants withstand complete cellular dehydration, reaching relative water contents (RWC) below 30% in their photosynthetic tissues. Desiccation sensitive (DS) plants exhibit different degrees of dehydration tolerance (DHT), never surviving water loss >70%. To date, no procedure for the quantitative evaluation of DHT extent exists that is able to discriminate DS species with differing degrees of DHT from truly DT plants. We developed a simple, feasible and portable protocol to differentiate between DT and different degrees of DHT in the photosynthetic tissues of seed plants and between fast desiccation (< 24 h) tolerant (FDT) and sensitive (FDS) bryophytes. The protocol is based on (1) controlled desiccation inside Falcon tubes equilibrated at three different relative humidities that, consequently, induce three different speeds and extents of dehydration and (2) an evaluation of the average percentage of maximal photochemical efficiency of PSII (F v /fm) recovery after rehydration. Applying the method to 10 bryophytes and 28 tracheophytes from various locations, we found that (1) imbibition of absorbent material with concentrated salt-solutions inside the tubes provides stable relative humidity and avoids direct contact with samples; (2) for 50 ml capacity tubes, the optimal plant amount is 50-200 mg fresh weight; (3) the method is useful in remote locations due to minimal instrumental requirements; and (4) a threshold of 30% recovery of the initial F v /fm upon reaching RWC ≤ 30% correctly categorises DT species, with three exceptions: two poikilochlorophyllous species and one gymnosperm. The protocol provides a semi-quantitative expression of DHT that facilitates comparisons of species with different morpho-physiological traits and/or ecological attributes.

Desiccation tolerance in bryophytes relates to elasticity but is independent of cell wall thickness and photosynthesis

“…In order to test the desiccation tolerance of the studied species, the “Falcon Test” method was modified after López‐Pozo, Flexas, et al (2019) as described in Perera‐Castro et al (2021) for bryophytes. Briefly, it is based on the capacity of the specimens to recover maximum quantum yield of PSII ( F v / F m ) when rehydrated after short/long storage in dried conditions (relative water content at equilibrium <1%–5%) inside 50 ml Falcon tubes with 12 g of silica gel with a relative humidity lower than 10% in equilibrium, which corresponds to a water potential of −310 MPa (Gaff & Oliver, 2013).…”

“…This index was developed by using the strongest desiccant tested by López‐Pozo, Flexas, et al (2019), the silica gel, varying the length of dry state seeing the high percentage of bryophytes that fully recover F v / F m after 24 h of fast desiccation and rehydration. Thus, only species with values of DTI equal to 0 were considered fast desiccation sensitive (DS), while species with DTI > 0 were attributed qualitatively to fast desiccation tolerant species (DT).…”

“…The excess of interstitial water was removed from the full hydrated specimen by gently pressing them against a dry tissue. Hundred milligrams of fresh weight per sample and tube were used, resulting in a rate of drying of 62 mg g −1 dry weight per hour (López‐Pozo, Flexas, et al, 2019). A thin net avoided direct contact of plant material with the silica gel.…”

Is zeaxanthin needed for desiccation tolerance? Sustained forms of thermal dissipation in tolerant versus sensitive bryophytes

“…Initial desiccation experiments were conducted to determine the relative DT of each species using the Falcon tube method described by López‐Pozo et al, 2018. This involved initial dark acclimation in fully hydrating conditions for 24 h to determine initial hydrated values for F v / F m .…”

Coexistent Heteroblastic Needles of Adult Pinus canariensis C.Sm. ex DC. in Buch Trees Differ Structurally and Physiologically

“…Two desiccation experiments were performed. In a first experiment, a modification of the "Falcon method", described in López-Pozo et al (2019) [45], was used to compare the tolerance to severe dehydration in both needle types [45]. Briefly, approximately 120 mg of needle pieces were desiccated at ca.…”