Ecophysiological consequences of contrasting microenvironments on the desiccation tolerant moss Tortula ruralis

Abstract

Tortula ruralis is a homoiochlorophyllous-desiccation-tolerant (HDT) moss that retains all pigments when dehydrated and rapidly recovers physiological function upon rehydration. This moss forms extensive cover in exposed and shaded areas in the sandy semi-arid grasslands of Central Europe. We hypothesized that contrasting drying regimes between these microhabitats would affect plant N status, constraints to gas exchange and growth, as well as result in altered pigment concentrations and ratios, and photochemical light-response dynamics. Furthermore, we believed T. ruralis's HDT habit would limit its ability to acclimate to altered light environment. We found that sun plant T. ruralis had lower plant mass, as well as lower tissue N, C, total photosynthetic pigment concentrations and carbon isotope discrimination (Δ) values compared to shade plant counterparts. Carotenoid/chlorophyll ratios in sun plants were typical of high light-adapted tissue, but chlorophyll a/chlorophyll b ratios were lower, more characteristic of low light-adapted tissue. This unique combination of pigment responses was accompanied by sustained lower levels of optimal quantum efficiency of PSII (F /F) in sun plant T. ruralis, even during favorable diurnal conditions, and reduced engagement of energy-dependent thermal dissipation (NPQ). Reciprocal transplants of sun and shade plants showed that T. ruralis is capable of short-term adjustment to altered light level, as evidenced by increases in F /F, NPQ, and light-adapted PSII yield (φ) in transplanted sun plants, and concurrent decreases in sun-transplanted shade plants. However, the performance of transplanted sun plants remained consistently below that of undisturbed shade plants. These findings show that microenvironmental variation results in different patterns of resource acquisition in this HDT moss, and that growth in the open imparts greater desiccation tolerance, and the development of a greater standing engagement of slowly reversing photoprotective mechanisms. In contrast, prolonged activity and greater resource acquisition in shaded populations may allow T. ruralis to rapidly adjust to changes following disturbance to the plant canopy, fostering the persistence of T. ruralis in these semi-arid grasslands.

Bromus tectorum litter alters photosynthetic characteristics of biological soil crusts from a semiarid shrubland

“…In general, plants growing under high light intensity have higher rates of NPQ than those growing at low light intensity (Demmig-Adams, 1998;Marschall and Proctor, 2004). However, exceptions to this pattern have been reported for Syntrichia ruralis and B. argenteum growing in central Europe and Antarctica, respectively (Hamerlynck et al, 2002;Schroeter et al, 2012). In both of these studies, mosses exposed to full sunlight had lower NPQ values than those growing at lower light intensities, which is similar to the results observed in the present study.…”

“…Low light intensities due to topography, seasonal changes, or shade by adjacent vegetation tend to increase F v /F m values (Hamerlynck et al, 2002;Backor et al, 2006;Vráblíková et al, 2006). In B. argenteum and D. muscorum, litter cover had a similar effect, but only for the samples collected in December.…”

“…In both of these studies, mosses exposed to full sunlight had lower NPQ values than those growing at lower light intensities, which is similar to the results observed in the present study. The advantage for the mosses to maintain high NPQ under shaded conditions is not clear, but one possibility would be to protect them from photodamage if light conditions change (Hamerlynck et al, 2002). Such changes could occur, for example, due to litter movement by wind or animals.…”

Physiological consequences of desiccation in the aquatic bryophyte Fontinalis antipyretica

“…We also observed that in slow-dried samples the storage time at low RWC influences F v /F m recovery, perhaps reflecting damage to the D1 protein of PSII (Smirnoff 1993). Alternatively, there may be down-regulation of PSII itself (Deltoro et al 1998;Hamerlynck et al 2002) in order to protect the complex while the cell maintains energy levels sufficient to counteract ROS formation during recovery. This would explain why in field-desiccated bryophytes (drying time and rate unknown) low F v /F m values persisted after a few days of recovery.…”

Desiccation tolerance in red and green gametophytes of Jamesoniella colorata in relation to photoprotection

“…7). Enhanced NPQ capacities during dehydration can provide photoprotection for the photosynthetic apparatus by means of increased thermal dissipation of excess excitation energy (Deltoro et al 1998a, b;Csintalan et al 1999;Hamerlynck et al 2002). NPQ processes, however, are unlikely to explain the difference in tolerance between the two colour morphs of J. colorata since both phenotypes showed a similar dissipation activity under drying conditions (Fig.…”