Introduction

The vegetation of the continental Antarctica (that main body of the continent excluding the Antarctic Peninsula) is dominated by lichens and mosses (Green et al. 2007). Lichens and mosses are poikilohydric, their water content tends to equilibrium with the air so that when the environment is dry they are dormant, and when it is wet they are active. All species are obviously able to withstand desiccation. Recovery after rewetting can be very rapid, under 2 h to attain maximal gross photosynthesis for the lichen Umbilicaria aprina after about 9 months desiccation through the Antarctic winter (Schlensog et al. 2004a). Dormancy through poikilohydry also acts as a mechanism to avoid or tolerate stresses like cold temperatures (Kappen and Valladares 2007). However, poikilohydry also limits potential carbon gain to those periods when sufficient water is available to activate the lichens and mosses. The distribution of the vegetation is limited to sites where there is a regular and consistent availability of water (Kennedy 1993; Kappen and Schroeter 2002). The erratic nature of the water supply means that photosynthetic activity can vary markedly from season to season. Pannewitz et al. (2005) showed very clearly that, for three moss species at two locations separated by five degrees latitude (Granite Harbour 77°S, and Cape Hallett, 72°S), differences in the photosynthetic performance between two seasons could exceed those between the two sites. A reliable estimate of annual or seasonal carbon gain is only possible if long-term measurements of activity are made (Schroeter et al. 1995), but most research in this extreme environment is brief and spans only a part of a complete summer season (Kappen and Redon 1987; Schroeter et al. 1992; Hovenden et al. 1994; Sancho et al. 1997; Kappen 1993, 2000; Pannewitz et al. 2006). There have also been substantial methodological limitations, equipment has been relatively bulky and field camps need to be well equipped in order to carry out field measurements of CO2 exchange over long periods. The introduction of the highly portable PAM chlorophyll fluorometers vastly improved the situation and allowed extensive non-contact measurements of chlorophyll a fluorescence to be made in the field (Schroeter et al. 1991, 1992; Schroeter 1994; Schreiber et al. 1994; Schlensog and Schroeter 2001; Green et al. 2002). Modified versions of these fluorometers allow continuous measurements to be made at selected time intervals over long periods, and thus open up the possibility to track lichen or bryophyte activity. This technique has been applied successfully in the Antarctic Peninsula (Schroeter et al. 1991, 2000; Schlensog and Schroeter 2000, 2001) and elsewhere under temperate conditions (Leisner et al. 1997; Pintado et al. 2010). In continental Antarctica, the more extreme conditions and the scale of the logistics has meant that there is only relatively brief and discontinuous data for the photosynthetic activity of continental Antarctic cryptogams (Schroeter et al. 1997).

It is known that the growth rates of Buellia spp., crustose lichens, can differ by nearly 100-fold along a latitudinal gradient from Livingston Island in the maritime Antarctic (62°S) to the Dry Valleys in the Ross Sea region (77°S) (Sancho et al. 2007). However, we are, at the moment, not certain what environmental or organism factors actually drive this large difference in growth, the most likely possibilities are temperature and water availability. The growing interest in the effects of global climate change means that we need to know what factors control photosynthesis in lichens so that the information can be used in modelling and forecasting the effects of any changes. Long-term monitoring of activity using chlorophyll a fluorescence coupled with microclimate information offer an excellent opportunity to determine vegetation active periods and to determine the main controlling factors. In this paper, we present the results of three years of activity and microclimate recordings on the lichen Umbilicaria aprina at Botany Bay, Ross Sea region, continental Antarctica.

Materials and methods

Site description and plant material

Site: Botany Bay is situated in the south-western corner of Granite Harbour, southern Victoria Land, at 162°32′52″E, 77°00′14″S, approximately 100 km north-west of Ross Island (Fig. 1). The area consists of raised boulder beach terraces, weathered rocky steppes and irregular rock platforms around Cape Geology, rising rapidly to the south to include a well-defined elevated cirque containing a small ice field. The bedrock geology at Cape Geology has been described as a porphyritic grey biotite–granite, with phenocrysts of orthoclase of reddish colour, casting the weathered rock with a reddish tinge. The area faces north and is well protected from strong winds. The impact of the sun is also magnified by the ice sheet. Botany Bay, in particular, is much warmer than expected, and air temperatures can reach almost 10°C. Botany Bay is ASPA 154 (Antarctic Specially Protected Area No 154) and is a restricted zone within the Dry Valleys ASPA (Antarctic Specially Managed Area) (Antarctic Treaty Secretariat: http://www.ats.aq/e/ep_protected.htm).

Fig. 1
figure 1

Location map for Botany Bay. Botany Bay lies within Granite Harbour on the south side and facing almost directly north. The sea within the sector of Granite Harbour in front of Botany Bay normally remains ice covered until late January, and some years does not break out at all. ANTO 10 AWS (Automatic Weather Station) is on the beach just to the west of Cape Geology. Botany Bay is just south of 77°S latitude

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The area is extremely rich botanically for such a high-latitude location––it is also one of the richest sites in the whole of continental Antarctica. There is a high diversity and abundance of lichens (more than 30 species) and mosses (nine species), and the structure and development of these communities are similar to those found 10° of latitude further north. The boulder beach has rich populations of both epilithic and endolithic lichens. The area is the type locality for the lichens Buellia frigida (Darbishire 1910) and Caloplaca coeruleofrigida Søchting and Seppelt (2003). The area contains the by far most southerly record of a hepatic (Cephaloziella varians (Gottsche) Steph.) and the mosses Bryoerythrophyllum recurvirostrum (Hedw.) Chen and possibly Ceratodon purpureus (Hedw.) Brid. (Seppelt and Green 1998).

Plant material: the chlorophyll a fluorescence measurements were made on the lichen Umbilicaria aprina Nyl., a widespread, locally abundant, species in Ross Sea region. Specimens of this species are particularly large in Botany Bay and can reach 15 cm diameter in sheltered spots (Schroeter et al. 1994; Seppelt et al. 1995; Sancho et al. 2003). The particular specimen monitored in this investigation grew on a sloping granite boulder at the back of the bay and was surrounded by many other large thalli. Prior observations indicated that this represented a typical habitat for the species and that rehydration was from melt water sourced from the ice cap in the corrie behind and above Botany Bay.

Sampling, entry into protected areas and equipment deployment were approved by the New Zealand authorities; the monitoring equipment has since been removed.

Chlorophyll fluorescence measurements

A pulse amplitude fluorometer (BBE-Moldaenke, Germany; for further detail see Schroeter et al. 1991) especially designed for cold conditions was used with the capacity to store data for several years measurements. The machine has a fibre optic that delivers the modulated measuring light and saturating pulse to the lichen and receives the induced fluorescence from the photosystem II reaction centres of the chloroplasts. The free end of the fibre optic was adjusted so that it was close to the upper surface of the lichen thallus and held in place using a holding device secured to the rock. The close proximity of the fibre optic end to the lichen helped prevent the entry of snow crystals between the thallus and the fibre optic that would have prevented optimal measurements of chlorophyll a fluorescence. A measurement was made every 2 or 3 h, an interval chosen to provide sufficient pulses to establish daily patterns of activity but also large enough to save on battery power, especially at low temperatures as the system had to work unattended for a period of 8–9 months. In addition, the fluorescence system was programmed to go dormant at temperatures below −20°C to prevent electronic damage due to very low temperatures and again to save battery power. Also, field and laboratory measurements in Umbilicaria aprina showed that photosynthetic activity ceased at temperatures below −17°C, and LTSEM revealed that thallus hydration was too low for metabolic activity at these low temperatures (Schroeter et al. 1994; Schroeter and Scheidegger 1995). At each measurement, a low intensity modulated light was first applied and minimal fluorescence in the light measured (F). A saturating light pulse followed, and the maximal fluorescence with all reaction centres closed obtained (F m′). Normally, the apparent quantum use efficiency of PSII {ΔF/F m′ = (F m′ − F)/Fm′)} of the photobionts can be calculated. However, the delivery of power from the batteries was decreased at very low temperatures, and it was impossible to be certain that a full strength saturation pulse had been achieved. For this reason, the recorded fluorescence data are interpreted solely as the lichen being active or inactive. Chlorophyll a fluorescence of F < 14 relative units with no difference between F and Fm′ was considered as an indication of inactivity (Schroeter et al. 1991; Schroeter et al. 1992; Schroeter 1994; Pannewitz et al. 2003). Permanent power was supplied by a north-facing solar panel (BP 240F; BP Solar, New Zealand) and stored using 75-Ah gel cell batteries.

Measurements were made continuously for about three years from January 2001 to January 2004.

Microclimatic data

Climatic data were recorded every hour using CR10X data logger specified to −50°C (Campbell, UK) for the same time period as the chlorophyll fluorescence. A PPFD sensor (photosynthetic photon flux density in the 400–700 nm waveband, μmol photon m−2 s−1, Skye SKP 215, Skye Instruments, UK) was installed in the direct vicinity of the thallus. These sensors are not especially screened against back-scatter (see Körner 1999), so PPFD might be enhanced under snow. Thallus temperature (TT) measurements were made using a microthermistor (Campbell) placed in contact with the lower side of the thallus. Air temperature (T air, Campbell) and relative air humidity (rH, capacity probe, Vaisalla, SF) were recorded in a ventilated screen at 1 m above the ground. Relative humidity was not measured in the direct vicinity of the thallus because of technical restrictions. Although not programmed to turn off at very low temperatures, the datalogger stopped recording during some of the months without sunshine due to low battery voltage.

Results

Climatic conditions at lichen recording site

Microclimatic recordings were successfully made from January 2001 to January 2004 with the exception in all three winters of the period between approximately mid-May to the end of August. It appears that this gap is due to the battery voltage being too low over that time and the return to active recording occurs soon after the sun reappeared at the middle of August. Botany Bay, at 77°S, lies well within the Antarctic Circle, and there is no sun between 28th April and 16th August, and potentially continuous sunlight between 26th October and 17th February (Fig. 2). The large change in sun radiation is the main driver of the local climate. The microclimate data are summarised in Tables 1, 2 and 3 for the 8 months each year when recordings were successful (September to April) and in Fig. 2. Instantaneous incident PPFD (photosynthetic photon flux density, μmol photon m−2 s−1) reached very high maxima, in excess of 2,000 μmol photon m−2 s−1, in every month when the sun shone and often showed very large diel cycles. The high PPFD values were due to a combination of exceptionally clear air, low cloud cover and a probable contribution from reflection from the sea ice that lies to the north of Botany Bay for most of the summer. From October to January, minimal PPFD was never zero and could be as high as 70 μmol photon m−2 s−1 (Figs. 2, 3; Table 1). The strongly skewed form of the PPFD during 2001/2002 summer (Fig. 2) in Botany Bay was almost certainly due to a snow fall in winter which remained until early November (see later section, the effect of snow). Once the snow had melted, there was a rapid increase to near maximal values of PPFD.

Fig. 2
figure 2

Air temperature (upper panel, °C), thallus temperature (centre panel, °C) and incident light (lower panel, PPFD, μmol m−2 s−1) from 1st February 2001 to 31st December 2003, the entire period monitored. The gaps are times when recording was stopped by low battery voltage. The skewed nature of the PPFD curves is due to the presence of early season snow covering the light sensor and lichen. The approximate times of complete snow melt when the sensor is uncovered are marked by the black arrows and are 23rd October 2001, 2nd November 2002 and 4th December 2003

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Table 1 Monthly mean PPFD (μmol m−2 s−1) incident on Umbilicaria aprina (Nyl.) in Granite Harbour, continental Antarctica, during the months with activity from January 2001 to December 2003
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Table 2 Monthly maximal (T max), minimal (T min) and mean (Ø) air temperature (T air °C) conditions of Umbilicaria aprina during the months with activity from January 2001 to December 2003
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Table 3 Monthly maximal (T max), minimal (T min) and mean (Ø) thallus temperatures (TT) of Umbilicaria aprina during the months with activity from January 2001 to December 2003
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Fig. 3
figure 3

Temperatures and light during a snow melt period at Botany Bay from 1st November 2003 (decimal 3.84) to 19th December 2003 (decimal 3.97). Upper panel is thallus temperature (°C); centre panel is air temperature (°C); lower panel is incident PPFD in μmol m−2 s−1 with the sensor placed by the lichen thallus; the arrow marks the 1st December 2003. Final snow melt occurs on 5th December with a dramatic increase in PPFD; at the same time, the thallus temperature shifts from being lower than ambient air due to snow insulation to above ambient air due to thallus heating

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Solar radiation strongly determined the seasonal and daily changes in air temperature (T air) with instantaneous values that ranged from −35°C to +9.6°C (Fig. 2, Table 2). Mean T air had a summer maximum in December (2001, 0.1°C) or January (2002/2003, −0.6 and −0.5°C). The warmest days were in late December and early January when T air was above freezing point for some days (Fig. 2). Annual mean temperatures and absolute minima cannot be determined from our data set owing to the period in mid-winter with no recordings. An automatic weather station (AWS) is now operating on the beach about 600 m from Botany Bay. Information from this machine is available on the United States Department of Agriculture web pages and has the identification ANTO 10 AWS (USDA ID: K123_1999_2008_NZ_1). It forms part of the Circumpolar Active Layer Monitoring Program (CALM). It recorded, in 2004 to 2008, annual means from −15 to −19°C, absolute maxima of 2°C and deepest minimum of −40°C. The protected location of Botany Bay almost certainly explains its very warm climate for the latitude. Wind speeds at the more exposed ANTO 10 AWS were below 3.0 m s−1 most of the time with stronger winds only reaching 7 m s−1 from a direction of 240°. Relative humidity at ANTO 10 over the years 2004 to 2008 ranged from 32 to 94% with an annual mean of 63%. At the lichen site in Botany Bay, the monthly mean relative air humidity was between 46 and 71%. Highest values were measured between December and January and lowest (20% rh) in October. Only about 3% of all data measured during 2001–2003 were >90% rh (at Ø T air = −2.7°C).

The effect of snow

The lack of high PPFD levels in the early season appeared to be linked to snow fall (Fig. 2). The effect of a substantial snow fall was to bury the lichen thallus, the PPFD sensor and the temperature sensors attached to the thallus. The most obvious effect was to keep PPFD low until the snow melted after which PPFD rose rapidly; this point is marked by black arrows in Fig. 2 and occurred on 23rd October in 2001, 2nd November in 2002 and a very late 4th December in 2003. The 2003 event is shown in more detail in Fig. 3, and the depression in thallus temperature that occurred until just before the snow disappears is clear. This phenomenon by which the snow blanket retains the cold winter temperatures and, in combination with low PPFD, effectively depresses lichen activity has previously been demonstrated by Pannewitz et al. (2003).

Chlorophyll a fluorescence measurements

A monthly summary of the complete monitored period from February 2001 to December 2003 is given in Fig. 4. Only the months September to April were recorded as the instrumentation shut down because of cold temperatures (<20°C) in the remaining months. In total, results are presented from 23 months out of 34 possible; the lichen would have been inactive the remaining months due to low temperature and darkness (see Schroeter et al. 1994; Schroeter and Scheidegger 1995). The lichen was active for a total of 1,726 h, or 7%, of the whole measurement period. Whereas PPFD, thallus temperature and air temperature all show a bell-shaped pattern through the summer with maxima in December or January, the lichen activity was very irregular. Activity as % possible hours was 28.7, 0.0 and 0.89% in February 2001, 2002 and 2003, respectively. Activities for December 2001, 2002 and 2003 were 34.95, 6.85 and 80.24%, respectively. A part of the complete record, for December 2001, is given in Fig. 5 when there was activity for a total of 200 h (about 24% of the month) in three main periods (Fig. 5). The first, for 4 days from 5th to 8th as continuous and must represent a period of high melt and continuous water flow. During this period of continuous activity in early December, the active lichens were exposed to the highest PPFD during the middle of the day, reaching 2,743 μmol photon m−2 s−1 and even overnight incident PPFD could still be around 110 μmol photon m−2 s−1. Mean PPFD when the lichen was active was a very high 880 μmol photon m−2 s−1. The second and third periods occurred between the 18th to 21st and 27th to 31st; however, the activity was not continuous, but there were active periods of 14 to 18 h each day separated by a dormant period. On these days, activity started in the evening at about 2000 with the arrival of melt water and ended at around 1030 next day with a peak during the night at 0330. Botany Bay is in shadow overnight, so the active periods were in the time of lower PPFD. Even so, the lowest PPFD were 95 to 110 μmol photon m−2 s−1 and the highest from 204 to 2,079 μmol photon m−2 s−1 with means from 154 to 456 μmol photon m−2 s−1 (Table 4).

Fig. 4
figure 4

Monthly mean incident PPFD (triangle, left hand axis), thallus temperature (TT, O, inner right hand axis), ambient temperature (T air open square, inner right hand axis) and percentage of potential monthly PSII activity (bars, outer right hand axis) of Umbilicaria aprina at Botany Bay from February 2001 to December 2003. Note: months with no activity have been omitted (May to October, inclusive, each year)

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Fig. 5
figure 5

Fluorescence signal (relative units), incident PPFD (μmol m−2 s−1) and thallus temperature (°C) for the lichen Umbilicaria aprina in Botany Bay for December 2001. PPFD and thallus temperature were recorded hourly, and chlorophyll a fluorescence every 2 h

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Table 4 Summary of hours active and PPFD for three periods of activity in December 2001. In period 1, the lichen was continuously active for almost four days (76 h); in periods 2 and 3, activity also occurred on 4 days, but the lichen desiccated and became inactive each day; total active time for the 4 days was 64 h and 48 h in periods 2 and 3, respectively
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Lichen microclimate and activity

Thallus temperatures (Fig. 4) tracked insolation, and the highest measured TT, between 28 and 29.8°C, were recorded in December and January (Table 2). At the other extreme, −34.8°C was measured in September 2003. Thallus and air temperatures were allocated to one degree classes from −35 to +35°C and represented as a proportion of the total number of records (Fig. 6). Thallus temperatures were underrepresented in relation to air temperatures in the −15 to +10°C classes, and no air temperatures were recorded above about +11°C although thallus temperature was often above this value reaching nearly 30°C (Fig. 6). Such high values are not uncommon for dry Antarctic lichens (Kappen 1993). Thallus temperatures were also overrepresented in the range −25 to −15°C, and this represents periods in early spring when the lichens were buried under snow, the insulation properties of which prevented them from warming (Pannewitz et al. 2003). If we consider only the thallus temperatures when the lichen was active (Fig. 7), then these were predominantly above −10°C with a peak at around 0 to 1°C. This differs markedly from the mean temperature of about −19°C for the air. The lichen was most active at PPFD between 100 and 150 μmol photon m−2 s−1, levels that occur during the night (Fig. 8). However, activity occurred across the entire presented PPFD range from 0 to >2,500 μmol photon m−2 s−1. There is a marked difference between inactive (25% relative activity) and active (<0.5% relative activity) at zero light (inset Fig. 8). Because of the 24-h diurnal period at Botany Bay in the summer, the lichen is continuously photosynthetically active and has no period with only dark respiration.

Fig. 6
figure 6

Relative frequency (%) of temperature classes between −35 and +35°C for ambient air temperature (dashed black line) and thallus temperature (solid black line) of Umbilicaria aprina (Nyl.) recorded during the total research period between 2001 and 2003

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Fig. 7
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Relative frequency as a % of total occasions for thallus temperature of Umbilicaria aprina for all measurements (black line with grey fill) and when the lichen was active and showed a positive fluorescence signal (black line alone)

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Fig. 8
figure 8

Relative frequency (%) of PPFD classes between 0 and 2,500 μmol m−2 s−1 for incident PPFD on Umbilicaria aprina in Botany Bay during the total research period 2001–2003 (solid black line with grey infill) and whilst the thallus showed potential PSII activity defined as F m > 14 r.u. (relative units) (solid black line without infill). The inset is for PPFD between 0 and 200 μmol m−2 s−1

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Discussion

The studied thallus of Umbilicaria aprina in Botany Bay was active for 1,726 h out of the 35 months monitored, or about 7% of the time. Despite an annual mean air temperature of −15 to −19°C and a highest monthly mean air temperature of 1.3°C, activity was recorded at some time in every month in which the sun shone, from September to April. Mean monthly air temperatures were as low as −21°C for April and September 2002, months with activity, and mean thallus temperatures were similarly low. Although temperature followed a regular annual pattern, lichen activity did not, and there was large variability through the active season and between the same months in different years. In 2002, activity ranged from 35.0% of available time in December to no activity at all in February. However, the latter month had 28.7% activity in 2001. The absolute highest activity for any month was December 2003, with a very high 80.24%, and it must be remembered that this is always in the light and photosynthetic as there is potentially 24-h sunshine. If, for each summer season, we remove the values for the month with the highest activity, then mean activity falls to <3%.

Three factors appear to particularly contribute to this variability, early season snow cover, warm or cold periods, and resource utilisation, with all of them influencing water availability.

Snow cover has its greatest impact at the start of the summer season. In all three years, there appeared to be some snow cover at the start of the season. This can be detected as dramatically reduced PPFD which slowly start to recover and then rapidly reach maximal values over a period of one or two days as the snow disappeared (Fig. 2). In some seasons, the snow is so thick that it remains present into December (2003, Fig. 3), whilst in others it disappeared much earlier in October (2001). The snow cover not only depressed the PPFD that reach the lichen but also acts as an insulation layer so that the lichen is not warmed by the air. This effect has been shown by Pannewitz et al. (2003) and contrasts completely with the alpine situation where the snow maintains warm ground temperatures (Körner 2003). It has been shown in laboratory experiments that lichens in Antarctica are able to rehydrate from snow at subzero temperature and, on occasions in the field, lichens become rehydrated and perform photosynthetic activity under snow as long as the temperatures are at or only slightly below zero and as long as the snow cover allows PPFD to pass through (Schroeter et al. 1994; Schroeter and Scheidegger 1995; Kappen and Schroeter 1997; Pannewitz et al. 2003). The combination of the very low temperatures and low PPFD meant that reduced, to no, lichen activity occurred when snow was present, and significant activity could be delayed for months. However, the month following the snow can then have very high activity, in part because of the melting of the snow elsewhere above Botany Bay, and thus providing an enhanced water flow.

Warm/cold periods are important as they influence the amount of melt at any particular time. A good example was December 2002 when some periods gave sufficient water to keep the lichen active continuously for several days, whilst, at other times, the lichen was only active for part of the day and dried out before rewetting again the next day.

Resource use: once melted, snow cannot be reused, so once the snow cover in Botany Bay itself, in the rocky higher areas above the Bay and on the icefields even higher above had melted, then later melt events will be much lower. There is a general appearance in the activity patterns of lower absolute activities after mid-summer, and this probably indicated melting of any available snow earlier in the season. It must be remembered that even an unusually heavy snow fall will give a coverage depth of no more than about 20 cm and that precipitation is very low in this area.

All three above-mentioned factors combine to make it difficult or impossible to predict the activity of this lichen from normal meteorological measurements. Climate changes affecting temperature are not likely to have much influence, but changes in snow fall will have major consequences. Later in the summer, such a fall would increase activity considerably, but early in the season it would prolong coverage, decrease activity and even lead to lichen death. At present, we have few ideas about the possible changes in snow fall.

The mean activity of about 7% seems low, but it must be remembered that the lichen is continuously in the light at this time, so photosynthesis would be possible at some level every time it is hydrated and active (Schroeter et al. 1994; Schroeter and Scheidegger 1995). In the maritime Antarctic, the long-term studies on Usnea aurantiaco-atra give a mean annual activity from 46 to 55% with 14–16% of the total time being photosynthesis, a much longer period of activity (Schroeter 1997; Schroeter et al. 2000).

This can be compared to the studies on the temperate lichen Lecanora muralis in Germany (Lange 2003a, b) which had an annual activity of 35.6% but with only 16.7% being photosynthesis, about double that of U. aprina in Botany Bay but in the same range as Usnea aurantiaco-atra in Livingston Island. Once hydrated, Umbilicaria aprina can be exposed to some extreme conditions, especially of light. Many other studies of activity in lichens have shown that, in general, lichens avoid high light, usually by desiccation and operate mainly in suboptimal light conditions (Lange 2003a; Green 2009). This is certainly not the case for U. aprina. When wet continuously for several days, it faced PPFD that exceeded 2,700 μmol m−2 s−1 (full sunlight is rated at 2,000 μmol m−2 s−1) and, even when it was active overnight and desiccated in the morning, it received up to 2,000 μmol m−2 s−1 and a mean PPFD of up to 400 μmol m−2 s−1. It has been previously shown that this species can tolerate full sunlight immediately after rewetting from winter dormancy under snow (Kappen et al. 1998). Subzero temperatures when active, which must be common with mean temperature of about 0°C, appear to cause few problems.

Botany Bay has an unusually warm microclimate for such a southern location, and this certainly is the explanation for the excellent lichen and bryophyte growth found there. However, the species of lichen growing there, as well as the bryophytes, must withstand some conditions that are extreme in comparison with temperature areas. Perhaps surprisingly, the main stress is probably light as U. aprina is unusual for a lichen in carrying out photosynthesis under full sunlight or higher. There is little doubt that this species and many others in the area achieve this by having excellent light filters that exclude most of the light (cortex absorption/reflection through dead air-filled fungal cells (see Gauslaa and Solhaug 2001). The bryophytes, which typically live in areas of flowing water, are also heavily pigmented and can build light protection rapidly (Lud et al. 2003; Schlensog et al. 2004b; Green et al. 2005; Clarke and Robinson 2008). The high variability found in maximum net photosynthesis within a population of U. aprina in Botany Bay (Sancho et al. 2003) might reflect a different individual adaptation to high irradiance events. Pannewitz et al. (2005) in the only available multi-year comparison showed high variability between both sites and years for the moss species studied. It is likely that such variation also occurs for U. aprina and combined with the obvious limitation that only one sample was studied mean that care is needed in extrapolating from the results presented. However, apart from these limitations in the 3-year dataset on microclimatic conditions and metabolic activity in Umbilicaria aprina presented here, the data give a first insight into environmental limitations on photosynthetic activity in Antarctic lichens over several years in one of the most extreme environments. The data clearly emphasize the need for long-term measurements of microclimate and metabolic activity of lichens if the effect of global climate change in the terrestrial environments in Antarctica is to be predicted.