Ana Pintado

Ecophysiology of Desiccation/Rehydration Cycles in Mosses and Lichens

Although both lichens and bryophytes are all poikilohydric the groups seem to behave very differently. Bryophytes also show a clear preference for wetter areas and this seems to be a result of the different structures of the organisms. A lichen is algae (or cyanobacteria) suspended in a mycobiont with excess water often having a negative effect on photosynthesis. Bryophytes, in contrast, are true multicellular plants and can construct photosynthetic tissues that can effectively separate their photosynthetic and water storage functions. Under dry atmospheric conditions lichens and bryophytes will desiccate to low water contents and they become dormant. Ability to tolerate desiccation varies considerably both between and within the groups. Somewhat surprisingly, lichens appear to show less ability to tolerate long periods of desiccation than bryophytes, and even some vascular plants. Actual mechanisms of desiccation have been best studied in bryophytes and appear to be constitutive, no protein synthesis is required on rehydration to enable the commencement of metabolism and the necessary protection appears to be always present. Consistently high sucrose levels, for instance are reported from bryophytes. Cellular structure is often maintained when desiccated. Recovery from dryness also differs between the groups with bryophytes generally hydrating more slowly but there are large species differences. In general, rate of recovery may be related to the length of the hydrated activity period, species that hydrate and then dry rapidly, as on rock surfaces, recover rapidly. Species in habitats that remain wet for long periods once hydrated appear to recover more slowly from dryness. In addition to a photosynthetic response to light and temperature, the poikilohydric lichens and bryophytes also have a photosynthetic response to thallus water content. Starting with a dry thallus, addition of water will both increase the thallus water content and also allow photosynthesis and respiration to commence. Both processes increase almost linearly with further hydration at low water contents. Photosynthesis reaches a maximum at an optimal thallus water content (WCopt) that is strongly species dependant. In both groups this photosynthetic optimum represents full cellular turgor. At water contents above this optimum surface or external water can interfere with carbon dioxide uptake and can severely limit photosynthetic rates, especially in lichens. When thallus water contents are normalised to WCopt = 1, then the net photosynthesis (NP) response curves at water contents below WCopt are very similar for liverworts, mosses and higher plants, suggesting a common mechanism in controlling NP. It is suggested that this might be an inhibitor acting on Rubisco activity. In contrast to vascular plants both groups can carry out photosynthesis at lower, suboptimal thallus water contents and very low water potentials but the contribution that this makes to total carbon budget appears to be a major difference between the groups. Bryophytes seem to pass rapidly through this water content range when both drying and hydrating for tens of minutes are often enough. In contrast, it is now apparent that lichens are often active at low thallus water contents. They can not only hydrate from humid air alone, or from dew and fog, but can use these water sources very effectively, often achieving a major part of their annual carbon gain. Information on when the lichens and bryophytes are actually active is only recently starting to appear but, again, the groups seem to differ. Bryophytes strongly prefer wetter habitats and can be active and fully hydrated for long periods and seem to have excellent capacity to tolerate high light and UV radiation when wet. In contrast many lichens, in particular those with green algal symbionts, rarely seem to be hydrated for long periods, especially in high light conditions, and rapidly dry out. Lichens seem to be active mainly under suboptimal conditions one of which is suboptimal water content.

Functional and spatial pressures on terrestrial vegetation in Antarctica forced by global warming

There is growing interest in what controls the present distribution of terrestrial vegetation in Antarctica because of the potential use of biodiversity as an indicator or predictor of the effects of climate change. Recent advances in knowledge of distribution and ecophysiological performance of terrestrial vegetation means that an initial analysis of the potential influence of temperature is now possible. Regressions of species numbers of lichens, mosses and hepatics on latitude and mean annual temperature (standard macroclimatic data) were carried out, and the terrestrial vegetation in Antarctica could be divided into two zones. The microenvironmental zone lies south of around 72°S, and biodiversity (richness and location) is uncoupled from the macroenvironment and is, instead, determined by the occasional coincidences of warmth, water, light and shelter. The macroenvironmental zone lies north of about 72°S, and biodiversity (richness, cover and growth) is strongly positively linked to mean annual temperature; species numbers increase at about 9–10% per K (24.0, 9.3 and 1.8 species for lichens, mosses and hepatics, respectively) probably due to improved water availability through increased precipitation and longer active period (monthly degree-days also reach zero at about 72°S) allowing greater productivity, completion of metabolic processes and a switch from survival to growth strategies. Cyanobacterial lichens appear to be a special case and may be expanding after being forced into northerly refugia. Warming will cause a southward movement of the boundary between the two zones but distribution in the microenvironmental zone will remain determined by local coincidences of environment and resources.

Functional ecology of the biological soil crust in semiarid SE Spain: sun and shade populations of Diploschistes diacapsis (Ach.) Lumbsch.

The Tabernas badlands in semiarid south-east Spain is one of the driest regions in Europe with a mean annual precipitation of c. 240 mm. The landscape is deeply dissected, with canyons, ramblas and sparsely vegetated eroded badland slopes. The vegetation is predominantly a biological soil crust consisting of different types of lichen-rich communities, one of the more conspicuous being dominated by Diploschistes diacapsis (Ach.) Lumbsch. This lichen is mainly restricted to the north- facing slopes, where it forms extensive whitish carpets and probably plays an important role in preventing erosion of the slopes and allowing plant colonization. South-facing slopes are much more eroded and generally lack vegetation. The photosynthetic performance of north (shade) and south-facing (sun) populations of D. diacapsis was studied to determine if these different populations showed any adaptations to the microclimatic conditions of their individual habitats. The response of CO2 exchange to light intensity, temperature and water content was measured under controlled conditions in the laboratory. Dry weight-based net photosynthetic rates were higher in the southern-exposed population but quantum efficiency, and light compensation points were similar. Thallus weight per unit area (LMA) was considerably higher for shade specimens but maximum water content and optimal water content were very similar and chlorophyll content on a dry weight basis was also similar. Chlorophyll content on an area basis was higher in the northern-exposed population and always much larger than those reported in other studies on the same species (up to 8 times larger) with the result that NP values on a chlorophyll basis were relatively low. The larger LMA meant that shade thalli stored more water per unit area which should ensure longer active periods than sun thalli. The results support a strategy pair of high NP and short active time versus low NP and long active time, both having been reported for other soil crust species. However, the visibly larger biomass of the shade D. diacapsis suggests that the lichen is at the limit of its adaptability in these habitats.

Bryophyte-Cyanobacteria Associations during Primary Succession in Recently Deglaciated Areas of Tierra del Fuego (Chile)

Bryophyte establishment represents a positive feedback process that enhances soil development in newly exposed terrain. Further, biological nitrogen (N) fixation by cyanobacteria in association with mosses can be an important supply of N to terrestrial ecosystems, however the role of these associations during post-glacial primary succession is not yet fully understood. Here, we analyzed chronosequences in front of two receding glaciers with contrasting climatic conditions (wetter vs drier) at Cordillera Darwin (Tierra del Fuego) and found that most mosses had the capacity to support an epiphytic flora of cyanobacteria and exhibited high rates of N2 fixation. Pioneer moss-cyanobacteria associations showed the highest N2 fixation rates (4.60 and 4.96 µg N g−1 bryo. d−1) very early after glacier retreat (4 and 7 years) which may help accelerate soil development under wetter conditions. In drier climate, N2 fixation on bryophyte-cyanobacteria associations was also high (0.94 and 1.42 µg N g−1 bryo. d−1) but peaked at intermediate-aged sites (26 and 66 years). N2 fixation capacity on bryophytes was primarily driven by epiphytic cyanobacteria abundance rather than community composition. Most liverworts showed low colonization and N2 fixation rates, and mosses did not exhibit consistent differences across life forms and habitat (saxicolous vs terricolous). We also found a clear relationship between cyanobacteria genera and the stages of ecological succession, but no relationship was found with host species identity. Glacier forelands in Tierra del Fuego show fast rates of soil transformation which imply large quantities of N inputs. Our results highlight the potential contribution of bryophyte-cyanobacteria associations to N accumulation during post-glacial primary succession and further describe the factors that drive N2-fixation rates in post-glacial areas with very low N deposition.

Comparative ecophysiology of three Placopsis species, pioneer lichens in recently exposed Chilean glacial forelands

Lichen species belonging to the genus Placopsis are early colonisers on snow free moraines of exposed land surfaces in the subantarctic region of Tierra de Fuego, South Chile. The physiological performance of three co-occurring species, P. pycnotheca, (terricolous), and P. perrugosa, and P. stenophylla (both saxicolous) was studied. All, possess green algal photobionts but have cyanobacteria in cephalodia. It was found that there was (i) a strong positive correlation between the acetylene reduction rate (AR) and the maximum photosynthetic rate (Amax), between the N content and the AR rate, and between the N and P contents, and (ii) the relationship between the CO2-exchange rates and the responses obtained in the laboratory reflected the ecology of these three lichens in the field. The results provide new information about the dynamics of some of the fastest growing crustose lichens. We hypothesize that the performance of these three species may have developed as a response to growing in an unstable environment that resulted from frequent glacial fluctuations.

Recent Warming and Cooling in the Antarctic Peninsula Region has Rapid and Large Effects on Lichen Vegetation

The Antarctic Peninsula has had a globally large increase in mean annual temperature from the 1951 to 1998 followed by a decline that still continues. The challenge is now to unveil whether these recent, complex and somewhat unexpected climatic changes are biologically relevant. We were able to do this by determining the growth of six lichen species on recently deglaciated surfaces over the last 24 years. Between 1991 and 2002, when mean summer temperature (MST) rose by 0.42 °C, five of the six species responded with increased growth. MST declined by 0.58 °C between 2002 and 2015 with most species showing a fall in growth rate and two of which showed a collapse with the loss of large individuals due to a combination of increased snow fall and longer snow cover duration. Increased precipitation can, counter-intuitively, have major negative effects when it falls as snow at cooler temperatures. The recent Antarctic cooling is having easily detectable and deleterious impacts on slow growing and highly stress-tolerant crustose lichens, which are comparable in extent and dynamics, and reverses the gains observed over the previous decades of exceptional warming.

Microbial succession dynamics along glacier forefield chronosequences in Tierra del Fuego (Chile)

Following the retreat of a glacier, microbial colonization paves the way for future plant successions as nutrients are gradually introduced into the ecosystem. Characterizing the dynamics of this initial microbial colonization process is a key to understanding how these rapidly receding glacier areas are colonized. This study examines primary successions of bacteria, fungi and algae in two glacier forefields chronosequences on opposite slopes of Cordillera Darwin (Tierra del Fuego, Chile). Both slopes (southern and northern) show contrasting climate factors along with rapid rates of plant succession. Through a high-throughput sequencing approach, we identified Cyanobacteria as the dominant bacteria in younger soils close to the glacier terminus, whereas abundances of Alphaproteobacteria and Acidobacteria increased with soil surface age. Lichen-forming fungi and parasitic fungi were the most abundant fungal groups in younger succession stages, while saprophytic and mycorrhizal orders dominated later stages. The order Prasiolales predominated algal communities close to the glacier terminus, while Microthamniales and Chlamydomonadales orders dominated subsequent succession stages. Our observations reflect a changing community structure over time of the three microbial groups examined, and the replacement of taxa during the succession. Changes in composition are especially marked between the youngest succession states and subsequent ones in both forefields. Simultaneous analysis of bacterial, fungal and algal communities revealed the different trajectories of the three groups, with bacterial and fungal communities showing more marked succession patterns. Our results point to more relevant roles for bacteria at the initial stages of succession, while fungi could play a dominant role over bacteria as succession progresses. The ubiquity of algal taxa along the chronosequences was also observed. The two glacier forefields showed different microbial temporal dynamics, indicating that local factors affect the rate of microbial community assembly and, consequently, drive the primary succession process.

Four lichen species new to Spain

Four species of Lichens are reported as new to Spain, namely Aspicilia moenium, Lecanora stenotropa, Vezdaea leprosa and Xanthoparmelia plitii . The species are probably not rare, but overlooked, since they are either inconspicuous or morphologically similar to other species.

Sodium chloride accumulation in glycophyte plants with cyanobacterial symbionts.

We have found a novel group of plants that appear to obligately accumulate salt (sodium chloride) although the level in their environment is low. The group is taxonomically diverse including angiosperms (Gunnera spp.), gymnosperms (Cycas) and a fern (Azolla species) but all of them form a symbiosis with a cyanobacterium (blue-green alga) that carries out nitrogen fixation, a rare occurrence in plants. The functional basis for the high salt contents is not clear and, despite the high internal salt levels, the plants are unable to grow in high salt environments.