Influence of substrate features on distribution of polypores (Fungi: Basidiomycota) in central part of Peechi Vazhani Wildlife Sanctuary, Kerala, India

Article

INTRODUCTION

Polypores are Basidiomycetes bearing club-shaped basidia typically on the inside of the hymenium lining pores or cavities of tubes formed on the under surface of the fruiting body. Based on the nature of rot formation, the wood decaying fungi (polypores) are classified into ‘white rot’ fungi that decompose all components of the wood including lignin and ‘brown rot’ fungi that decompose the cellulose and its associated pentoses, leaving the lignin more or less unaffected (Leelavathy & Ganesh 2000). They are distinguished by their macroscopic basidiocarps with pores. They decompose coarse woody debris like fallen trunks, branches, twigs and stumps and play a pioneer role in ecosystem functioning such as nutrient cycling and transport (Peace 1962). Thus, the ecological role of polypores as decomposers and their dependency on wood for existence have made them to be regarded as good indicators of conservation value (Niemela 2005). Each woody substrate constitutes a dynamic habitat that the fungi can only utilize for a limited time of microclimatic optima or stage of decomposition. Different types of woody substrates like dead standing trees, fallen trunks, roots, branches and twigs constitute discrete patches, where both species richness and composition change substantially over time due to deterministic succession of species accompanying the wood decomposition (Norden et al. 2004). Moreover, some polypores normally inhabit only living trees and as when the tree dies, they are replaced by fungi which are better adapted to saprophytic nutrition (Kuffer et al. 2008). Substrate size is an important factor that determines the occurrence of wood-inhabiting fungi on trees. Studies have shown that these fungi have different preferences for substrate diameter. Bader et al. (1995) suggested that log size significantly influenced total species number, number of threatened species, number of species per log, as well as the hymenial surface area per log. Besides the size of the log, stage of decomposition is also an important determinant for polypores species composition. Renvall (1995) noted the stage of decomposition, that many threatened polypores have distinct preferences for large logs in intermediate stages of decay. Thus, species richness and abundance of polypores depend on the qualities and quantities of the dead wood. The substrate utilization by polypores has been shown to be critical for the species assemblage in the temperate forests (Norden et al. 2004; Juutilainen et al. 2011). The same has shown that species vary in their preferences regarding the features of substrate they colonize in nature. Similar studies undertaken in tropical forests reveal that substrate features are determinant in the occurrence and preference of polypores (Hattori & Lee 2003; Yamashita et al. 2009). Decay class/decay stage is considered as an important measurement when compared to the diameter of the woody substrate. In decay class, a hump-shaped curve has been observed with more species at the intermediate decay stage with that of the early or final stages (Junninen et al. 2007; Jonsson et al. 2008). The proportion of studies in tropical forests dealing with ecology of fungi is seldom reported (Lonsdale et al. 2008). With the available data on the taxonomic studies (Manimohan & Leelavathy 1995; Leelavathy & Ganesh 2000; Manimohan et al. 2004; Kumar & Manimohan 2005; Mohanan 2011) undertaken on polypore diversity in the natural stands of Kerala, it is difficult to conclude the effect of deadwood, decay-class and climatic influence on diversity and abundance. Earlier studies on polypores in the natural stands of Kerala were mainly focused on morphology (Iqbal et al. 2016a,b); no comprehensive studies on the ecology of polypore fungi in Kerala have been undertaken. A detailed analysis of the polypore fungi and the substrate features will give a better picture of the distribution pattern of these fungi. With this background, the present study has been conducted in the moist deciduous forests of Peechi-Vazhani Wildlife Sanctuary to analyse the importance of substrate features in the diversity and distribution of polypores.

MATERIALS AND METHODS

Study Area

Peechi-Vazhani Wildlife Sanctuary (PVWS) lies within the geographical extremes of 10026’–10040’N & 76015–76028’E, covering an area of 125km2 in Thrissur District, Kerala State (Fig. 1). Annual average precipitation in the sanctuary is 3,000mm and it is situated at an altitude of 45–900 m. As per Champion & Seth (1986), the forest type of PVWS consists of nearly 80% moist deciduous forest, 15% evergreen and semi-evergreen and the remaining five per cent is under teak and soft wood plantations.

Survey, Collection and Identification of fungi

The survey was conducted during January 2012 to October 2014 in PVWS, Kerala for the collection of polypores. Three permanent fixed size sample plots of 100x100 m were established in three different locations, viz., Vellani, Mannamangalam and Olakkara sections of the sanctuary as per the methods of earlier fungal studies (Yamashita et al. 2010; Mohanan 2011). Also subplots of 10x10 m were fixed in each permanent plot for detailed analysis. The sample plots were visited during pre-monsoon (January–May), monsoon (June–September) and post monsoon (October–December) periods for the documentation of polypores. A total area of 30,000 m2 was surveyed during each climatic seasons. Additional collection of polypores was also made along the transect other than the permanent plots (“off plots”) in the study area. The polypore specimens collected from the study area were kept in paper bags and brought to the lab. The specimens were properly air dried or oven dried and stored in polythene zip-cover under less humid conditions. The identification key provided by Bakshi (1971) and Leelavathy & Ganesh (2000) were used for the confirmation of polypores. The micro-morphological characteristics of the polypores were drawn with the help of camera lucida. Some of the specimens were compared with those in the Herbaria at the Kerala Forest Research Institute, Peechi. All the specimens collected during the study period were catalogued and kept under less humid conditions in the refrigerator in the Department of Forest Management and Utilization, College of Forestry at Kerala Agricultural University (Appendix 1). After proper nomenclature and identification, the current names of the identified polypores were accessed from the website: www.mycobank.org (accessed on 15 January 2015). All fruiting bodies of the same species on a substrate were counted as single occurrence, independent of the number of fruiting bodies. Also if there were several clusters, they were treated as single occurrence. Attempts were made to calculate the number of individuals on all the substrates. To understand the diameter class preference, polypores with more than 10 total occurrences on different diameter classes only were considered. Out of this, more than 50% occurrence on a particular diameter class was selected as preference for diameter class. The distribution of polypores on different substrate type was studied by dividing the substrates into four types, viz., snag (dead standing tree), log, branch/twig and living tree. The decay stage of the substrate was determined according to a 5-grade scale based on decay classification system of Pyle & Brown (1998). A correspondence analysis has been done in version 16.6.04 of XLSTAT 2014 to understand the succession pattern of polypores and decomposition stages of wood during different seasons in moist deciduous forests.

RESULTS AND DISCUSSION

Substrate diameter

Of total individuals, 2861 (56%) occurred on substrates in the two smallest diameter classes (11-<20 cm and 21-<30 cm) and 305 (6%) individuals occurred on substrates in the largest diameter class (51-<60 cm and 61cm and above) (Table 1). Three polypore species (Daedalea flavida Lev., Fomitopsis feei (Fr.) Kreisel and Microporellus obovatus (Jungh.) Ryvarden) constitute two-third of individuals on substrates in the small diameter class. The reason could be the large diameter substrates decay at a slower rate and persist for longer as well. They have been shown to serve as an important refuge for fungal species that require woody debris in advanced decay (Heilmann-Clausen & Christensen 2004). It is noteworthy that in the hardwood zone of North America Brazee et al. (2014) found a similar pattern of diversity for polypores in different diameter classes. Moreover small diameter substrates have a higher surface to volume ratio for colonization (Norden et al. 2004), hence results of the present study highlights that the small diameter class substrates are also important in maintaining species richness of the polypore fungal community.

On average, a more competition free substrate, could favour the establishment of the common pioneer species (Berglund et al. 2011). Therefore, the diameter class range and preference of polypores have been recorded based on the number of occurrences. The occurrence of polypores showed an interesting pattern of distribution. Species like Daedalea flavida, Fomitopsis feei and Earliella scabrosa (Pers.) Gilb. & Ryvarden have a wide range of diameter class, while species like Hexagonia tenuis (Hook.) Fr. and Microporus xanthopus (Fr.) Kuntze have only a very narrow range of diameter class (Table 2). Similarly, the wide range diameter class and preference for a particular diameter class was observed for wood-inhabiting Aphyllophorales in a cool temperate area of Japan (Yamashita et al. 2010).

A total of seven polypores species showed a possible preference for a diameter class as defined by having more than 50% of their occurrence on a single diameter class (Table 2). Hexagonia tenuis, Microporus xanthopus and Microporus affinis (Blume & T.Nees) Kuntze. showed preference for very small diameter class (0-<10 cm). Notably in lowland rainforests in Malaysia, Microporus xanthopus are mostly restricted to <10 cm diameter class, whereas perennials like Erythromyces crocicreas (Berk. & Br.) Hjorts. & Ryv., Ganoderma australe (Fr.) Pat., and Phellinus lamaensis (Murr.) Heim. occur mostly on larger substrates (Hattori & Lee 2003; Yamashita et al. 2009) and these species are considered important decomposers of coarse woody debris in that forest type.

 

 

Substrate type

A box plot analysis was also done for the association of polypores with substrate types (Fig 2). In case of snag, the polypore density varied with a minimum of 13 individuals to a maximum of 543 individuals while in the case of living trees, the density varied with a minimum of 32 individuals to a maximum of 81 individuals. In the case of logs, the density of polypores varied by eight to 565 individuals and in the case of branch/twig, the density ranged from a minimum of six to a maximum of 276 individuals. Among the substrate types, the maximum number of individuals was observed in logs (2,480), followed by branch/twig (1,469) and snag (1,012). The living trees supported very few polypores individuals (113). The living trees supported only 2% of the total (113 individuals) (Table 3). F. feei, D. flavida and T. cotonea made up more than half of their total individuals in trunk and M. affinis, M. xanthopus, P. grammocephalus and H. tenuis made up more than half of the their total individuals in branch/ twig. Higher richness of fungal species was found in the branches and logs in the hardwood zone of North America (Brazee et al. 2014). F. feei, a brown rot fungus showed a high preference for snag (dead standing trees) and Hymenochaetaceae members like P. dependens and F. nilgheriensis were observed on living trees; no other species were observed on living trees during the entire study period. These living trees belonged to Xylia xylocarpa. D. flavida, T.cotonea, M. affinis, M. xanthopus, P. grammocephalus and H. tenuis have wide spread occurrence in trunk (fallen log) and branch/twig. Mohanan (1994) reported that M. affinis and M. xanthopus were common in the forest stands of Kerala, which caused mainly white-rot of branches and twigs, and brown fungi including Fomitopsis spp. have wide spread occurrence. It was also discussed that despite the diversity of the microbes associated with heart rot of living trees, the degradation of the cell wall components is still ascribable to hymenomycetes.

Substrate decay class

The correspondence analysis for the pre-monsoon season indicated that during this season the species distribution was related with the decay class 1, 2 and 3 while in monsoon and post monsoon seasons, decay class 4 plays a significant role in the distribution of polypores (Figs. 3, 4 & 5). The values for various parameters in the test of association reveals the significance of the correspondence test (Table 4). In all three seasons the chi-square observed value is greater than the critical value and the p-value is below the chosen level alpha; hence it is concluded that the rows (polypore fungi) and the columns (decay class) are significantly associated.

During the pre-monsoon season, species like M. affinis, M. xanthopus and M.nigra have a strong affinity towards decay class 3 and Phellinus spp. and Trametes spp. showed affinity for decay 1 and 2 respectively. Also species like Nigroporus vinosus was found in late decay stages (decay class 3). In this study, P. dependens, F. nilgheriensis, Fuscoporia spp. and Trametes spp. were the dominant species, comprising more than 70% of the fruit bodies encountered and decay classes 1 and 2 are the advanced decay class. It was widely accepted that dominant species, and in particular their functional traits, are most important in determining current magnitude, rate and direction of ecosystem processes, whereas subordinate and rare species play a minor role in present ecosystem dynamics (Walker et al. 1999; Díaz & Cabido 2001). Yamashitha et al. (2010), however, revealed that in the cool temperate regions of Japan some polypores species occur mainly in the early decay stages of decomposition whereas others form fruiting bodies in later stages of decomposition.

The decomposition of wood materials on the forest floor proceeds through sequential colonization by fungal species with different decay types and their interspecific interactions, which leads to a fungal succession during decomposition (Rayner & Boddy 1988). Apart from the pre monsoon season, during the monsoon season and post monsoon, the newly germinated white rot species like E. scabrosa, T. cingulata, G. lucidum, M. obovatus, C. telfarii and C. sanguinaria showed a high association with decay class 2. Fukasawa et al. (2009) suggested that white-rot basidiomycetes, play a central role in the simultaneous decomposition of acid-unhydrolyzable residue (AUR) and holocellulose in the first phase of decomposition. In the early stages of decay (decay class 2), F. feei, M. obovatus and T. hirsuta have high similarity between each other. Among these species F. feei showed high abundance in the monsoon and post monsoon seasons. The reason could be that inter-specific mycelial interactions among brown rot fungi and white rot fungi resulted in either deadlock or replacement of one fungus by the other and some brown rot fungi are capable of invading and occupying domains within white rot fungal communities in decaying wood (Owens et al. 1994).

Species with annual, small sized fruit bodies like M. affinis, M. xanthopus, P. grammocephalus, H. tenuis and P. arcularius are highly associated with decay class 3, where there is less energy available. It was also observed that during all seasons, species belonging to genera such as, Phellinus, Fulvifomes, Fomitopsis, Ganoderma and Fuscoporia with long lived fruit bodies are more abundant in decay class 1 and decay class 2 (i.e., less decayed wood samples), which would typically hold more available energy. These results support the idea of an energy driven control of fruit body production for some species (Schmit 2005). Although, sporophore production, particularly regarding species with short lived sporophores, may also be triggered by other factors, such as shifts in temperature and humidity as well as interspecific interactions (Moore et al. 2008).

M. xanthopus has shown a sign of decay class shift; during the pre- monsoon season it is associated with decay class 3 and during the monsoon and post monsoon seasons, it showed a shift towards decay class 2 and was equally distributed in decay class 2 and 3. This reflects a species turnover towards a community that depends upon a pre-modified wood environment as well as the presence of senescing mycelia (Kubartova et al. 2012). Other polypores species D. flavida found in decay class 1 to decay class 4 supports the view that once a primary species is established in a fallen trunk, it may persist in the community for a long time (Vetrovsky et al. 2011). Thus, they can be considered as stress-selected species that move towards competitive-selected life histories as the substrate proceeds to higher decay classes.

CONCLUSION

The findings of the study made clear that the substrate utilization by polypores is critical for the species assemblage in the moist deciduous forests. It can be concluded that compared to the diameter of woody substrate, the decay class is a more subjective measure to study the polypore establishment. Finally this might be the first study in Kerala which explains the relationship with substrate features and polypore assemblage in detail.

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