Received Date: August 16, 2016; Accepted Date: October 5, 2016; Published Date: October 12, 2016
Citation: Wieners M, Reinhard A, Förschler M, Scholler M (2016) The Rare Polypore Antrodiella citrinella and Its Special Phenology in the Black Forest National Park (Germany). J Biodivers Endanger Species 4:168. doi: 10.4172/2332-2543.1000168
Copyright: © 2016 Wieners M, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.
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In the old growth spruce-fir forest “Wilder See”, a long-term protected zone of the Black Forest National Park (Baden-Wuerttemberg, Germany), the phenology of two associated polypore fungus species on Picea abies logs, Fomitopsis pinicola and the rare red-data list species Antrodiella citrinella were investigated. We combined detailed field studies and temperature-related in-vitro growth studies. Whereas perennial fruitbodies of F. pinicola developed from late spring to autumn, the annual A. citrinella fruitbodies were formed mainly in late autumn (October, November) and again in spring (April and May). Growth studies on agar media confirm that A. citrinella grows faster at lower temperatures (5-10 °C), whereas F. pinicola is clearly superior in growth rate between 15 °C and 25 °C. This indicates that A. citrinella is a generally rare, but locally common species that may have been overlooked because of its special phenology in colder periods. The “Wilder See” area in the National Park seems to be an important refuge for the species. Its existence seems to depend on high humidity, high amount of woody debris (P. abies) and the occurrence of F. pinicola. In the presence of living A. citrinella fruitbodies, fruitbodies of F. pinicola were found to be always dead. This supports earlier speculations that the relation may be parasitic.
Fungi; Picea abies ; Fomitopsis pinicola ; Mycoparasitism; Temperature preferences; Old growth forest; Dead wood density; Indicator species
Antrodiella citrinella Niemelä & Ryvarden (Flaviporus citrinellus (Niemela & Ryvarden) Ginns; Lemon-colored Antrodiella) is a rare wood-inhabiting annual polypore causing white rot mainly on Picea abies preferring wet swampy localities . Fruitbodies have a pale to bright citrine yellow pore surface forming small spores and develop resupinate to very narrowly reflex on wood. Its distribution in Europe follows that of a very common perennial polypore, Fomitopsis pinicola (Sw.) P. Karst. (Red-Belt Conk), causing brown rot on a wide range of trees, preferably on conifers but also on deciduous tree species. Known localities of A. citrinella are from natural spruce forests in Scandinavia and mountains of central Europe, France, Poland and the Czech Republic [1-4]. In Germany, the species is only known from oldgrowth forests in Bavaria and listed as “extremely rare” (category R) in the red-data list of macrofungi in Germany . A. citrinella usually grows on old P. abies logs on or close to the basidiocarps of F. pinicola.
The former Bannwald (closed protected forest) “Wilder See” in the Black Forest National Park  measuring 150 ha is an old growth European spruce (P. abies) and Silver fir (A. alba ) forest with P. abies as dominant species (Figure 1). Within the framework of a (still ongoing) mycological inventory of the Wilder See area  we specifically looked for A. citrinella and finally found it for the first time on 29 September 2014 and again in November in the same year. It was not found (no fruitbodies were formed) in the warmer months. In contrast, growing and sporulating perennial fruitbodies of F. pinicola were found throughout the snow-free periods of the year.
The objective of this study is to find out whether Antrodiella citrinella’s phenology of fruitbody formation is different from the one of the associated F. pinicola and whether this corresponds with temperature preferences.
The study area is the western part (Figure 2) of the nature reserve „Wilder See - Hornisgrinde“, a core zone of the Black Forest National Park (Baden-Wuerttemberg, Germany), with a size of 98 ha. Logging in the study area was banned for more than 100 years. The eastern part was not studied because it is hardly accessible. The altitude of the study area is 840-1.050 m. Roughly the area consists of a more or less even southwestern belt above 1020 m and a cirque below 1.020 m. The plateau is dry and open with P. abies , A. alba and P. mugo as dominant tree species (Figure 3). Below 1020 m is the cirque with a glacial lake at 910 m altitude. The headwall of the cirque is steep in the south and west and flatter in the north. The form of abrasion is in the east. The cirque vegetation is characterized by P. abies as dominant tree species, by high humidity and by dense woody debris (decaying logs) of P. abies (Figure 4). The high density of P. abies logs is a consequence of bark beetle (Ips typographicus ) infestation. 60 % of the attacked trees were killed within two decades after 1991 .
The climate is humid-montane and (humid) high-montane . The temperature is 5-6 °C on annual average, the annual precipitation is 2.000-2.200 mm . The average monthly temperatures shown in Figure 5 where obtained from DWD Climate Data Center (CDC) (station-ID: 1468; 797 mNN; ftp://ftp-cdc.dwd.de/pub/CDC/observations_germany/climate/daily/kl/recent/) and hight-adjusted (0, 65 °C per 100 m).
Field studies: distribution and phenology
In a pre-study at below 0 °C January 18, 2015 we looked for both fungus species and only found the perennial fruitbodies of F. pinicola . Therefore, a survey on phenology and distribution of A. citrinella was performed in the mainly frost-free periods from September 2015 to August 2016, once or twice a month for one day.
On each day different areas including geographical parts, the higher elevation plateau area and the cirque area below 1020 m was searched for A. citrinella on woody debris. Fruitbodies of A. citrinella on one piece of wood or fungal fruitbody were treated as one record . In addition, the co-existence of F. pinicola was recorded by measuring the distance to A. citrinella . Also, it was recorded whether fruitbodies were living or dead.
In-vitro growth and temperature
Pure cultures of A. citrinella and F. pinicola were obtained from fresh fruitbody trama collected in the study area. Mycelium was grown on 8.5 cm malt agar plates (25 g malt extract (powder), 20g Agar and 1.000 mL aqua dest.) at 18 °C. From these preliminary cultures circular 1 cm pieces where cut off and placed in the middle of 8.5 cm malt agar plates. Cultures were incubated at 5, 10, 15 and 25 °C at 62 ± 5 % relative humidity. Three (and at 10 °C four) replicates per species/ temperature were used. The colony diameter was measured after 7 (in the 10 °C replicates after 6, 8), 14 and after 21 days (if possible). The growth rate was defined as mean radial increment at two sides divided by the number of days at the last possible measurement.
Voucher specimens and cultures
Dried specimens of some records of A. citrinella and F. pinicola were placed in the fungus collections of the Natural History Museum Karlsruhe (Karlsruhe, Germany). (KR; see http://www.smnk.de/ sammlungen/botanik/pilze/digitaler-katalog/). Living cultures were deposited in the fungus collections of the Department of Bacterial Physiology SBUG, University of Greifswald (Greifswald, Germany). Accession numbers: A. citrinella SBUG-M 1723 (this culture corresponds with herbarium specimen KR-M-0037905), F. pinicola SBUG-M 1724.
Living fruitbodies of Antrodiella citrinella were found 18 times and always in association with dead fruitbodies of F. pinicola . They were either found in close neighborhood of F. pinicola (Figure 7) or on fruitbodies of F. pinicola directly (Figure 6). Whilst the closest fruitbodies (up to 30 cm distant) were always dead, fruitbodies further away on the same log were often alive.
A. citrinella was found scattered throughout the cirque area up to 1010 m altitude. It was not recorded on the plateau above 1.020 m altitude (Figure 2). In contrast, F. pinicola was found all over the study area including the plateau (Figure 3).
Antrodiella citrinella was found eighteen times in five months, namely in late autumn 2015 (October, November), in spring 2016 (April, May) and in summer 2016 (July; Figure 5). The number of records (days per month) are listed in Table 1. Perennial living and growing fruitbodies of F. pinicola were observed all over the snow-free periods.
|Number of records of Antrodiella citrinella|
|No. of Investigation days||2||2||2||1||2||1||2||1|
|No. of records of A. citrinella||0||4||7||5||1||0||1||0|
Table 1: Number of investigation days and number of Antrodiella citrinella records observed in the snow-free months in the Wilder See study area.
Growth rate in pure culture
The growth rates are shown in Figure 8. Both species grew most slowly at 5 °C and fastest at 25 °C. A. citrinella grew significantly faster than F. pinicola at 5 °C and at 10 °C, whereas F. pinicola grew slightly faster at 15 °C and much (two times) faster at 25 °C (p <0,001). The growth rate of A. citrinella clearly increases from 5 to 15 °C but at 25 °C it is hardly higher than at 15 °C. In contrast, the growth rate of F. pinicola continuously increases from 10 to 25 °C.
Antrodiella citrinella is a rare species in Germany and records in the Black Forest National Park were the first for the federal state of Baden- Wuerttemberg. We could show that the species is fairly common in moist and near-natural stands of European spruce within the cirque of the “Wilder See” (steep slopes between 930 and 1020 m altitude) but was not observed in the more open and dryer regions in the western and southwestern plateau zone, between 1020 and 1050 m altitude (Figure 4). For sure, the major fructification periods of A. citrinella in the study area will be the snow-free late autumn and spring periods. But we do not exclude that the species may also grow and form fruitbodies in mild winter weeks.
Numerous (17) A. citrinella fruitbodies were found in late autumn from October to November and again in spring from April to May. One record was obtained in summer (20 July 2016; Table 1); it was a very small and poorly developed single fruitbody found on a wet log. Fruiting may then have been supported by an intense rain on 13 July which caused a cold snap from 19.4 °C to 9.2 °C within 3 days.
Mycologists usually do not explore macrofungi at higher elevations in the cold months from October to May. Therefore, the generally rare species may easily have been overlooked. In addition, it seems to be limited to forests with considerable and dense dead P. abies wood (as already indicated by Ryvarden & Gilbertson)  and continuous high air humidity. Concluding from the overall conditions in the study area, there should be more suitable habitats in the Black Forest. A. citrinella was common in the study area in April 2016 with 5 recorded stands.
We looked for it and F. pinicola in the same month in other similar stands with woody P. abies debris, but more open and drier climatic conditions within the Black Forest National Park (“Huzenbacher See” area, “Lotharpfad” and “Pommertswald”). We found living F. pinicola fruitbodies in high quantity but A. citrinella only once at “Lotharpfad”, a windthrow area with even higher dead wood density than in the “Wilder See” area. This indicates that the “Wilder See” protected area with its moist habitats, wet climate and high proportion of dead wood within the cirque is an important retreat area for A. citrinella. The species is an indicator species for montane old-growth forests like this. In the future, when authorities and conservationists discuss and have to decide whether areas like this should be protected or not, we suggest considering the Lemon-colored Antrodiella in late autumn as a major indicator.
With our In-vitro study results we confirm an observation in Scandinavia that A. citrinella replaces F. pinicola . This replacement obviously takes place at low temperatures in late autumn and spring when average temperatures are around 10 °C or below. This corresponds well with our In-vitro growth observations that show A. citrinella growing faster than F. pinicola between 5 and 10 °C. Our results support that A. citrinella replaces F. pinicola . Rayner and Boddy emphasized in 1988  that replacement may not only take place by decayers but also by parasites of the pioneer species. Holmer et al. 1997  concluded from In-vitro studies that A. citrinella is a secondary wood decayer. But their studies were carried out at room temperature, which is substantially too warm to simulate the situation in nature. We rather think that the association is parasitic based on the following observations: First, we found that A. citrinella is always associated specifically with F. pinicola - but not vice versa. Furthermore, A. citrinella fruitbodies are never associated with living but always with dead F. pinicola fruitbodies. These perennial fruitbodies - in contrast to A. citrinella - were often found small and young. Also, we could not confirm fresh and living F. pinicola in 2016 at sites where we had found A. citrinella in 2015 but not in 2016. This may also be a consequence of mycoparasitism. Although these fruitbodies are often overgrown with A. citrinella, it need not necessarily be fruitbody colonization but mycelial parasitism in the substrate as we know it from e.g. many Tremellales . Mycelial parasitism may explain why fruitbodies of A. citrinella can be formed at distances of up to 30 cm from its putative host.
Vampola already assumed in 1991 that there are mycoparasitic relations between A. parasitica Vampola and A. semisupina (Berk. & M.A. Curtis) Ryvarden and their associated polypores . This is also supported by a recent phylogenetic study showing that all fungicolous and possibly mycoparasitic species of Antrodiella , including A. citrinella and A. parasitica , are closely related . To provide final evidence for a parasitic mode of interaction, however, more growth and micromorphological studies are required.
This study is supported by the Black Forest National Park and a travel grant for M. W. from Studienstiftung Mykologische Systematik und Ökologie (München). We thank Claus Bässler, Walter Gams, Martin Schnittler and Christian Wieners for reading the manuscript and giving advice. Harald Kellner confirmed identification of the A. citrinella culture using ITS sequence data. Josef Christan found A. citrinella for the first time in the Black Forest in 2014 and kindly provided record data and specimens.