Fruiting in the Natural Environment

It is well known that the majority of Basidiomycota fruit in autumn, following mycelial growth and decomposer activity in spring and summer. Temperature and rainfall are considered to be the two main factors affecting productivity (Salerni et al., 2002). In a 21-year fruit body survey of a forest plot in Switzerland, there was considerable variation between years in species richness and productivity, only litter decomposing saprotrophs, Collybia butyracea var. asema and C. dryophila, appearing in all years (Straatsma et al., 2001). Appearance of fruit bodies was correlated with July and August temperatures, an increase of 1°C resulting in a delay of fruiting by saprotrophs of ^7 days. In contrast, fruit body productivity was correlated with precipitation from June to October (Straatsma et al., 2001), and similar relationships have also been found in Britain and Sweden (Wilkins and Harris, 1946; Wasterlund and Ingelog, 1981).

In a 3-year study of Mediterranean oak forests, there was no evidence for influence of temperature on fruit body species diversity or productivity by most saprotrophs, though there was strong positive correlation between species diversity of wood decay fungi and maximum temperature, and with spring and summer rainfall (Salerni et al., 2002). Temperature and rainfall in the 5 days prior to surveying seemed to have little effect on fruiting, but did so between 10 and 30 days prior to survey.

Climate change has resulted in phenological changes in plants, insects and birds (Parmesan and Yohe, 2003), and this has recently been shown to be the case for fungi (Gange et al., 2007). Analysis of a data set of fruiting records of 200 species of decomposer Basidiomycota in Wiltshire, UK, each of which had been recorded over more than 20 years during 1950-2005, revealed that mean first fruiting date averaged across all species is now significantly earlier, while mean last fruiting date is now significantly later (Figure 3; A.C. Gange, E.G. Gange, T.H. Sparks and L. Boddy, unpublished data). Thus, the fruiting season has been extended since the 1970s. Not all species fruit earlier (47% show an advancement), or produce fruit bodies later into the year (55% continue fruiting later) but of those saprotrophic Basidiomycota that showed significantly earlier fruiting dates (n = 94), the average advancement was 7.9 days per decade, while for those with significantly later last fruiting dates (n = 110) the delay was 7.2 days per decade. The response differs depending on habitat type: 13% of grassland species fruiting earlier, 48% having later last fruiting; 53% of wood decay fungi fruited earlier, with 20% having later last fruiting. There was a significant relationship between mean fruiting date of those species that normally fruit early in the season (September) and late summer temperature and rainfall (Figure 4). Local July and August mean temperatures have significantly increased (July, P < 0.05; August, P < 0.01), while rainfall has decreased, though less markedly, over the 56 years of the survey.

1945 1955 1965 1975 1985 1995 2005 Year

Figure 3 Mean first fruiting date (lower line) and mean last fruiting date (upper line) for 200 saprotrophic basidiomycota over 56 years. Splitting the data into two equal (28 Year) periods reveals no trend in the first half (P = 0.97) but a highly significant trend (P<0.001) in the second half (A.C. Gange, E.G. Gange, T.H. Sparks and L. Boddy, unpublished data).

12 13 14 15 16 17 18 19 20 Mean August temperature, °C

0 20 40 60 80 100 120 140 160 Mean total August rainfall, mm

Figure 4 Relationship between mean fruiting date of saprotrophic basidiomycota species that normally fruit early in the season (September) and (a) August temperature (R2 = 0.299, F154 = 23.056, P = 0.007) and (b) August rainfall (R2 = 0.126, F154 = 7.790, P = 0.000) (A.C. Gange, E.G. Gange, T.H. Sparks and L. Boddy, unpublished data).

Grassland Deciduous saprotrophs Litter saprotrophs

Coniferous Wood litter decayers saprotrophs

Figure 5 The proportion of saprotrophic basidiomycota in different habitat groups that, before 1975, were not recorded as fruiting in spring, but after this time did so in at least 1 year (A.C. Gange, E.G. Gange, T.H. Sparks and L. Boddy, unpublished data).

As well as changes to autumn fruiting patterns, significant numbers of species that previously only fruited in autumn now also fruit in spring (Figure 5). Since mycelia must be active in uptake of water, nutrients and energy sources before fruit bodies can be produced this suggests that these fungi may now be more active in winter and spring than they were in the past.

Other aspects of the environment can also influence fruiting by affecting microclimate (e.g. ground vegetation and logging waste), providing additional resources or inhibitory compounds. For example, in managed forests: there was lower fruit body biomass where Pteridium aquilinum was abundant; in dry years Mycena species were more abundant in areas with logging waste, but in wet years they were equally or more abundant in areas without logging waste; fruit body biomass was negatively correlated with grass cover in dry autumns, but positively correlated in wet autumns (Wasterlund and Ingelog, 1981).

As well as the physical size of a fruit body, a significant feature in the ecology of the organism is the length of time that the fruit body remains sufficiently intact to distribute spores. This varies from a few days or weeks for fleshy fungi to several years for perennial brackets, longevity of the latter being associated with structural physical characteristics and production of chemicals that inhibit invertebrate feeding or are toxic to them (Kahlos et al., 1994; Stadler and Sterner, 1998). There appears only to be one detailed study of the lifespan of an agaric, an analysis of the fruit bodies of A. bisporus grown in an experimental mushroom farm over 36 days (Umar and Van Griensven, 1997). The fruit bodies remained healthy for 18 days before localised cytological indications of senescence became evident (nuclear and cytoplasmic lysis, permeable cytoplasmic membranes and structural changes to the cell wall). Cells of the fruit body collapsed irregularly

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