Desiccation tolerance of Sphagnum revisited: a puzzle resolved

Abstract

As ecosystem engineers, Sphagnum mosses control their surroundings through water retention, acidification and peat accumulation. Because water retention avoids desiccation, sphagna are generally intolerant to drought; however, the literature on Sphagnum desiccation tolerance (DT) provides puzzling results, indicating the inducible nature of their DT. To test this, various Sphagnum species and other mesic bryophytes were hardened to drought by (i) slow drying; (ii) ABA application and (iii) chilling or frost. DT tolerance was assessed as recovery of chlorophyll fluorescence parameters after severe desiccation. We monitored the seasonal course of DT in bog bryophytes. Under laboratory conditions, following initial de-hardening, untreated Sphagnum shoots lacked DT; however, DT was induced by all hardening treatments except chilling, notably by slow drying, and in Sphagnum species of the section Cuspidata. In the field, sphagna in hollows and lawns developed DT several times during the growing season, responding to reduced precipitation and a lowered water table. Hummock and aquatic species developed DT only in late autumn, probably as a response to frost. Sphagnum protonemata failed to develop DT; hence, desiccation may limit Sphagnum establishment in drier habitats with suitable substrate chemistry. Desiccation avoiders among sphagna form compact hummocks or live submerged; thus, they do not develop DT in the field, lacking the initial desiccation experience, which is frequent in hollow and lawn habitats. We confirmed the morpho-physiological trade-off: in contrast to typical hollow sphagna, hummock species invest more resources in water retention (desiccation avoidance), while they have a lower ability to develop physiological DT.

Biochemical determinants of litter quality in 15 species of Sphagnum

“…Although the metabolites that increase decay resistance determine the trade-off between growth and decay and thereby represent a cost, they also have positive effects on growth, mostly by alleviating the abiotic stress in hummock environments: (1) The large water retention capacity provide the hummock sphagna with a desiccation avoidance strategy that allows them to maintain photosynthetic C assimilation and growth during drought, while hollow sphagna or other bryophytes have to rely on their ability to tolerate desiccation (Hájek and Vicherová 2013). The desiccation avoidance strategy is possible only when the cell walls are strong enough to prevent collapse of the large capillary spaces as discussed above.…”

Effects of climate warming on Sphagnum photosynthesis in peatlands depend on peat moisture and species‐specific anatomical traits

“…S. fallax ) have been shown to survive slow rates of desiccation (Wagner & Titus, ) because they harden in the early stages of dehydration by forming a cellular protection. Hardening avoids cell damages, such as degradation of chlorophyll and rupture of cell membranes, and allows Sphagnum to tolerate and recover from drought (Hájek & Vicherová, ). While S. medium can be sensitive to repeated extreme desiccations (Schipperges & Rydin, ), our results show that S. fallax photosynthesis, and most likely growth, promptly recover following rain drops, suggesting that this species could acclimate to frequent drought events.…”

The Impact of Moss Species and Biomass on the Growth of Pinus sylvestris Tree Seedlings at Different Precipitation Frequencies

“…Moss species that are adapted to shady conditions with low evaporation rates generally have large shoots, which could potentially allow these species to be more effective light competitors, while also making these species more sensitive to desiccation [21]. In addition, moss species vary substantially in their water retention capacity [21,22], which can determine their desiccation rate and their recovery following drought [23,24]. Differences in water retention capacity among species may determine how severely the moss layer is impacted by drought, and this could, in turn, have consequences for seedling performance [25,26].…”