Fungal communities and fire associated to pinus pinaster in a mediterranean region

Resumen

The aim of this investigation was to study how fungal communities in Mediterranean forests dominated by maritime pine (Pinus pinaster Ait.) are influenced by fire and different edaphoclimatic conditions specifically in areas where degraded and poor soils are predominant. Sporocarps were collected and identified from 100 m2 transects during the autumn seasons of 2003-2006 period in a post-fire scenario and another from 2006 to 2012 in an undisturbed situation. The data collected that were used to assess fungal richness, production and diversity, were grouped into categories (saprotrophic/mycorrhizal; edible/inedible) for statistical analysis and modeling procedures. On the other hand a greenhouse experiment was carried out during 2008 until 2009 where the fire severity on the ectomycorrhizal seedling colonization along its influence on plant development was also assessed. Firstly, the results showed remarkably high fungal production and richness when associated with P. pinaster in extreme but undisturbed Mediterranean conditions composed by natural forests in calcareous and sandy soils and from reforestations in siliceous soils. The same trend was observed in forests associated to the effects of wildfire, an essential factor in the dynamics of Mediterranean forests. In the undisturbed situation, total fungal production and richness were much higher in the siliceous and calcareous forests than in the inner sandy dune site. The results showed a similar trend when the production of mycorrhizal taxa and diversity index for saprotrophic fungi were also analyzed. On the other hand, the fungal community was mainly correlated with climatic variables, such as precipitation and temperature. Additionally, nitrogen and potassium soil contents significantly affected the distribution of species for both saprophytic and mycorrhizal functional groups. Some of the collected taxa were adapted to a broad range of ecological conditions such as Lycoperdon perlatum, Russula torulosa, and species within genus Galerina and Mycena. However, other recorded fungi were only found in very specific environmental conditions. Within this group, all the species included within Macrolepiota genera were collected in the calcareous soils, whereas Laccaria laccata and L. bicolor were exclusively associated with higher amounts precipitation and nitrogen in the siliceous plots. Secondly, to assess the effect of fire we examined the succession of fungal communities following fire in a Mediterranean ecosystem in Northwest Spain, dominated by Pinus pinaster Ait. A large wildfire occurred on August 2002. During the autumns 2003 until 2006, fruiting bodies were collected and identified, production in both burned (early stage) and unburned (late stage) areas were measured. Data were grouped into categories (saprotrophic/mycorrhizal; edible/inedible) for statistical analysis. 115 fungal taxa were collected during the four year sampling (85 in the late stage and 60 in the early one). Mycorrhizal population not only increased the number of species from early to late stage but also shifted in composition across the chronosequence. Fire strongly affected the production of fungal species. Thus, yields in the early stage treatment were significantly lower than those observed in the late one. Total fungal fresh weight decreased from 209.95 kg fw ha-1 in late stage to 162.45 kg fw ha-1 in the early where richness and production of mycorrhizal species and production of edible fungi were significantly lower. Fresh weight for saprotrophic and inedible species was higher than for mycorrhizal fungi in the early stage treatment. Thirdly, from the data from burned and non burned areas from the period 2003-2006, our results provide the first classificatory simple model for fungal production in P. pinaster forests. Climate variables related with the sporocarp production were included in the modelling procedure (discriminant functions) to classify the productions into four yield categories. Nine discriminant classificatory models were studied to determine these four yield categories within each dependent variable according to edibility and functional group. Models for edible and edible-mycorrhizal were fitted to allow an estimate of the production class (R2 =0.92 and 0.85 respectively). Finally, mycorrhizal fungi in the soil play a key role in the processes of evolution of Mediterranean forests after wildfire. However, the impact of fire on these fungal communities is poorly understood. Therefore a broader understanding of an important typical pyrophitic species as P. pinaster and its fungal symbionts is necessary for forest restoration. We analyzed the effect of a wildfire in Central Spain that took place in 2008 comparing the ectomycorrhizal community checked in P. pinaster root apexes from 3 different burned severities sites. The work was conducted in a greenhouse, where P. pinaster seedlings were used as bioassay to examine the influence of fire severity on soil characteristics, root ectomycorrhization at two horizon depths and plant development. The ectomycorrhizal degree was higher in the unburned bioassays than in those that have been affected by the fire, for both depth layers. While that plant parameters increased their values according fire severity. This study suggests that fire affects soil properties, mycorrhizal inoculum and plant development after a year. These findings could represent ecological and economical implications that may be important for managers to consider when seeking new options in order to optimize the management and harvesting of these more and more appreciated non wood resource, therefore adding value to these Mediterranean forests, especially into fire-impacted areas, in which ectomycorrhizal fungi play a role as a biological tool in restoring disturbed forest ecosystems. Therefore, having a positive impact on rural communities that depend on forest resources, edible mushroom production can provide supplementary economical incomes for population as complement to those obtained from wood resources in forestry areas.