Photosynthetic Light Responses May Explain Vertical Distribution of Hymenophyllaceae Species in a Temperate Rainforest of Southern Chile

Abstract

Some epiphytic Hymenophyllaceae are restricted to lower parts of the host (<60 cm; 10–100 μmol photons m-2 s-1) in a secondary forest of Southern Chile; other species occupy the whole host height (≥10 m; max PPFD >1000 μmol photons m-2 s-1). Our aim was to study the photosynthetic light responses of two Hymenophyllaceae species in relation to their contrasting distribution. We determined light tolerance of Hymenoglossum cruentum and Hymenophyllum dentatum by measuring gas exchange, PSI and PSII light energy partitioning, NPQ components, and pigment contents. H. dentatum showed lower maximum photosynthesis rates (Amax) than H. cruentum, but the former species kept its net rates (An) near Amax across a wide light range. In contrast, in the latter one, An declined at PPFDs >60 μmol photons m-2 s-1. H. cruentum, the shadiest plant, showed higher chlorophyll contents than H. dentatum. Differences in energy partitioning at PSI and PSII were consistent with gas exchange results. H. dentatum exhibited a higher light compensation point of the partitioning of absorbed energy between photochemical Y(PSII) and non-photochemical Y(NPQ) processes. Hence, both species allocated energy mainly toward photochemistry instead of heat dissipation at their light saturation points. Above saturation, H. cruentum had higher heat dissipation than H. dentatum. PSI yield (YPSI) remained higher in H. dentatum than H. cruentum in a wider light range. In both species, the main cause of heat dissipation at PSI was a donor side limitation. An early dynamic photo-inhibition of PSII may have caused an over reduction of the Qa+ pool decreasing the efficiency of electron donation to PSI. In H. dentatum, a slight increase in heat dissipation due to acceptor side limitation of PSI was observed above 300 μmol photons m-2s-1. Differences in photosynthetic responses to light suggest that light tolerance and species plasticity could explain their contrasting vertical distribution.

Changes in photosynthetic rate and stress volatile emissions through desiccation‐rehydration cycles in desiccation‐tolerant epiphytic filmy ferns (Hymenophyllaceae)

“…Filmy ferns have only one cell layer, and thus, their photosynthetic capacity is generally low, between ca. 1–4 μmol m −2 s −1 (Parra et al, ; Parra et al, ) as was also observed in the current study in fully hydrated samples (Table , Figure ). Due to lack of stomata and water‐permeable cuticular layer, the RWC of filmy ferns rapidly decreases in dry atmospheres, resulting in concomitant reductions in foliage photosynthetic characteristics (Flores‐Bavestrello et al, ; Proctor, ; Saldaña et al, ) as observed in our study (Figure , Table ).…”

“…We suggest that the LOX emissions during the desiccation primarily reflect the oxidative burst generated upon transfer of ferns from lower light/high humidity atmosphere to higher light/lower humidity atmosphere and associated generation of oxidative stress due to a certain overexcitation of photosynthetic machinery. In fact, low light/high humidity to high light/low humidity transitions are common during high intensity lighflecks and result in a large share of excess quantum flux density that can lead to photoinhibition of filmy ferns (Parra et al, ). Rapid responses to altered light and humidity conditions are consistent with previous observations of induction of LOX emission responses by higher light level (Loreto, Barta, Brilli, & Nogues, ).…”

“…The studied species differ in their vertical distribution in the stem of the host trees in Chilean temperate rainforest canopy. H. cruentum and H. caudiculatum colonize more humid and deeper shade habitats with their cover on tree stems extending from tree base to up to 3 m in the canopy, H. dentatum colonizes habitats with lower humidity and greater light intensity on tree stems between 1 and 9 m, and H. plicatum is a generalist with dispersal between 0 and 9 m (Flores‐Bavestrello et al, ; Parra et al, ; Saldaña et al, ). We hypothesized that desiccation stress results in enhancement of stress volatile emissions and that these emissions are particularly enhanced upon rewatering.…”

Reversible in vivo cellular changes occur during desiccation and recovery: Desiccation tolerance of the resurrection filmy fern Hymenophyllum dentatum Cav.

“…Although previous studies with Hymenophyllaceae species have shown valuable empirical evidence of an evolutionary shift of adaptive strategy from typical vascular plant adaptation to the poikilohydry most typical of bryophytes (Proctor et al 2012, Parra et al 2015, we are far from understanding the family or its diversity and Chile is one of the best places in the world to begin (Michael Proctor pers. comm.).…”

Photosynthesis and photosynthetic efficiencies along the terrestrial plant’s phylogeny: lessons for improving crop photosynthesis

“…Additionally, mosses of the genus Polytrichum , which have at least partially functional hydroids (i.e. a ‘pseudovascular’ system) present the largest A area and g m determined among bryophytes (Carriquí et al ., ) while, by contrast, ferns of the Hymenophyllaceae family, which have through evolution lost stomata and functionality of the vascular system, present moss‐like low photosynthesis rates (Parra et al ., ). In this sense, the already mentioned source/sink balance should also be considered as improving the source capacity (photosynthesis) may require larger sinks.…”