Climate Change and Fungal Community | Term Paper | Geography

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Climate Change and Fungal Community

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Term Paper Contents:

1. Term Paper on the Introduction to Climate Change
2. Term Paper on Fungal Fruiting in Response to Precipitation and Temperature Change
3. Term Paper on Elevated CO₂ and Ectomycorrhizal Fungi (ECM)
4. Term Paper on Climate Change and Distribution of Macro-Fungi
5. Term Paper on the Remarks on Climate Change and Fungal Community

Term Paper # 1. Introduction to Climate Change:

Climate may be thought of as a description of the regularities and extremes in weather for a particular location, which is governed naturally by a set of known variables mainly related to changes in ocean currents or sea-surface temperatures, volcanic eruptions, alterations in the sun’s output of energy and many more complex phenomenon. However, the industrial revolution and subsequent anthropogenic burden of greenhouse gases has played key role in driving the earth’s climate change.

Global warming is the most substantial manifestation of climate change, which can be attributed to increased temperature and elevated CO₂. There has been 0.3°C to 0.6°C rise in global mean temperature since the late 19^th century and global sea levels have also risen between 10 and 25 cm. The Intergovernmental Panel on Climate Change (IPCC) in 2001 has estimated that the globally averaged surface temperature will increase by between 1.4 and 5.8°C over the period 1990 to 2100.

Recent climate change has resulted in changes in the timing of phenological events in many organisms, global meta-analysis involving 1700 species have documented significant range shifts averaging 6.1 km per decade towards poles and significant mean advancement of spring events by 2.3 days per decade. Although, fungi are among the most diverse, important and omnipresent groups of organisms on earth, relatively little attention has been paid to how fungi and other micro-organisms respond to climate change, therefore related studies are mostly inadequate worldwide.

Along with other microorganisms, fungi not only make conditions suitable for the evolution and existence of macroscopic life forms, but also continue to drive many of the ecological processes like bioremediation, biogeochemical cycle, nutrient recycling, litter decomposition, soil formation, indicating perturbation within the environment and ecosystem maintenance related to anthropogenic activities.

Mycorrhizal fungi are the key functional components of a forest ecosystem where they form symbiotic associations with the roots of 75-80 per cent of vascular plants, enabling plants towards better nutrient uptake, which is especially crucial under adverse edaphic conditions. Furthermore, fungi (in particular the mushroom-forming species) serve as valuable food sources for numerous invertebrate and vertebrate forest inhabitants. Besides that, fungi find utilization in industry, agriculture, medicine, food and textile industries.

Climate is a complex and crucial factor in fungal growth, fruiting and distribution. Seasonal and spatial distribution of macro-fungi, the number of sporocarps and fungal pathogenesis are influenced by the temperature and moisture, where high levels of precipitation resulting in high humidity and soil moisture, along with warm temperatures, favour both fungal productivity as well as disease incidents from pathogenic species.

The major concern arising from the climate change issue is the impact it may have on fungi and its reciprocal interactions with the environment, which ultimately would pose the questions on the planet’s ecosystem and human sustainability.

Term Paper # 2. Fungal Fruiting in Response to Precipitation and Temperature Change:

The influences of precipitation and temperature on fungal fruiting have been studied by authors in different parts of the world. Due to difficulties in collecting phenological data pertaining to the ephemeral nature of fungal fructification, most of the studies regarding the effect of climate change on fungi are based on either herbarium data or climate change simulations. Herbarium data gives potential phenological information about the fungi, whereas it also enables us to understand and predict climate-induced ecological changes in the future.

One of the important effects of climate change on fungi is the change in phenology. Some studies from Norway and the UK have reported shifts in the phenology of fungal fruiting over the last 50 years, as depicted in Figure 8.1. In UK, an extension of autumnal fruiting season in both directions has been observed (i.e., earlier onset and later finish) both for mycorrhizal and saprotrophic species.

The extended activity of fungi to winter and spring is viewed by Moore et al. (2008) as a result of gain of more thermal energy before fruiting which would help in more rapid nutrient acquisition and therefore helping fungi to fruit earlier in the year. However, Kauserud et al. (2009) argue that a warm October maybe unfavorable for mycelial growth, leading to a delay in resource acquisition and fruiting.

The time and resources required for mycelial growth and subsequent fruit body production are unknown for the vast majority of fungal species. In particular, the July temperature and precipitation during August is found to promote an earlier average fruiting.

Studying the effects of climatic predictors on the fruiting time during the study period 1960-2007, Kauserud et al (2009) suggested that the higher July and winter temperature were responsible for driving earlier spring fruiting both in Norway and UK. 1°C increase in July temperature caused nearly three days earlier fruiting and the annual linear trend was estimated to be 20.37 ± 0.07, suggesting on average 18 days earlier fruiting over the entire study period and 3.8 days per decade.

In Norway, 1°C warming of January climate has been linked to approximately one-day earlier fruiting (average fruiting time normalized on species and geography) whereas in UK the warming of January and February by 1°C amount to approximately three days earlier fruiting. Many species of fleshy fungi that were formerly reported to fruit only in autumn are currently producing sporocarps in spring.

This indicates that the state of below- ground mycelia of fungi (including the fruiting potential) is determined by climatic conditions over more than a single year. A delayed effect of August precipitation the year before was also found, indicating that a wet summer is associated with earlier fruiting the next season. Thus, in general, the results suggest that a warm and wet summer produce earlier fruiting next year, and in combination with a cooler autumn but warm winter will give early average fruiting dates.

Temperature is found to play an important role in influencing evapo-transpiration (ETP) processes, with rise in temperatures causing higher ETP rates. De Aragon et al (2007), argue that it is the difference between rainfall and ETP which gives better estimation of the water available to plant and fungi than the rain gauge reading.

ETP rates higher than the rainfall may pose threat of physiological drought to plant and fungal communities. Temperature hot only has direct effects on microbial activity, but eventually it can also affect the temperature dependency of the community. This would result in communities performing better over time in response to increased temperatures.

Barcenas-Moreno et al (2009) have shown that for soil fungi growing in maritime climate with mean soil temperature of 10°C showed optimal growth rates around 30°C, which decreased rapidly with increasing temperature, with no significant fungal growth at 45°C and above, concluding that the environmental temperatures above optimum have greatest effect on temperature response.

The studies of individual climate variables have shown a clear relationship with mushroom production and rainfall. De Aragon et al (2007) through their five year inventory (1997-2001) in the forests of pre-Pyrenees mountains, Spain, have shown that there is positive correlation between total sporocarp production and mean annual rainfall (R² = 0.27; P < 0.001) and the best climate equation (R²= 0.66; P < 0.001) for annual sporocarp estimation was based on the difference between monthly mean precipitation and accumulated monthly mean evapo-transpiration for the months of September and October and the monthly mean minimum soil temperature in August.

They also observed that timing of rainfall, soil water availability and temperatures in the month of August were influencing overall sporocarp production in Spanish set of conditions. Species richness, like total production is influenced by climate and forest stand characteristics. O’Dell et al (1999) observed that with an increase in mean annual precipitation there was an increase in number of species.

Keizer and Arnolds (1994) observed an increase in fungal diversity with an increase in forest stand age. In many mushrooms, fruiting can be induced experimentally after vegetative growth by reducing the temperature by at least 5°C and this might be an important environmental cue that has been delayed because of global warming.

Term Paper # 3. Elevated CO₂ and Ectomycorrhizal Fungi (ECM):

Anthropogenic global carbon dioxide (CO₂) emissions have been accelerating, with their growth rate increasing from 1.1 per cent per year between 1990 and 1999, to more than 3 per cent per year between 2000 and 2004. Increased levels of CO₂ in the atmosphere are known to affect both host plants and mycorrhizal fungi. Increased production of mycelium due to elevated CO₂ has been reported for several ECM species as well as for aibuscular mycorrhizal (AM) fungi. The increase in fungal biomass is sustained by the extra carbon fixed by and supplied from the host plant under enriched CO₂ regimes.

In a study, the changes in the ectomycorrhizal fungal community structure in a 37 year old Norway spruce forest in Sweden after factorial combinations of elevated CO₂ (700 ppm) and balanced nutrient addition during 1998-2000, Fransson et al (2001) noted that there was an increase in the mean value of morphotypes per tree, from 6.4 ± 0.8 in 1997 to 7.1 ± 0.3 in 2000.

The level of colonization was also found to increase in 2000 when the mean colonization level was 97.9 per cent ± 1.1 compared to 85.2 per cent ± 4.3 in 1997. Significantly more unidentified ECM morphotypes were found on the elevated CO₂ trees than control, thus increasing the ECM fungal diversity. The shift in community structure was also linked to the change in abundance of a few common morphotypes.

Rey and Jarvis (1997) indicated the shift in mycorrhizal species composition in birch towards later successional stages after CO₂ treatment. It was interpreted as an acceleration of tree ontogeny leading to the trees supporting ECM fungal species with a higher carbon demand, which was in accordance with the conclusions of Godbold et al. (1997).

Under elevated CO₂, trees were found to invest more carbon into fine roots and there was increased production of mycelia contributing to more efficient nutrient acquisition by plants. About three times as much carbon is stored in terrestrial vegetation and soil than is stored in the atmosphere. Fungal mycelia network, alive or dead, may account for a very large proportion of the soil microbial biomass.

There are several ways in which mycorrhizal carbon may enter the soil:

(a) Hyphal turnover;

(b) Grazing of the extra-radical hyphae by soil fauna (and subsequent defecation); and

(c) Passive carbon losses from the mycelial network (similar to leaching and exudations from roots) as suggested by Olsson et al. (1999).

However, the turnover of mycelium is likely to be faster compared to roots and an increase in the amount of mycelium could lead to a faster turnover of carbon within the plant-fungus system.

Term Paper # 4. Climate Change and Distribution of Macro-Fungi:

Kauserud et al (2008) showed that geographic location was an important factor determining the fungal fruiting time. They found that appearance of fruit bodies was considerably earlier (in the range of 10-20 days) in northern, continental and alpine regions of Norway compared with more southern and oceanic regions. This latitudinal pattern correlates well with the general trends known from plant phenology. In Canadian context, Taylor and Taylor (1997) suggested that global warming could set southern fungal species north bound.

The retreating glaciers would create new habitats for some alpine species although some may lose habitat at lower elevations from encroaching tree lines. However, loss of species from pioneering communities is predicted if the glaciers melt completely. In forests, where tree and shrub species are affected (such as by replacement of climax forests with young forests through short rotation timber harvest), their associated mycological communities might well also be affected.

Term Paper # 5. Remarks on Climate Change and Fungal Community:

Our knowledge of fungi and their requirements is so limited that it is very difficult to say which, if any, would be negatively affected by climate change. Major oscillations in climates will certainly increase the likelihood of community disruption for species that can only be found under particular climatic conditions, whereas, rise in global temperature would cause the replacement of cold-adapted species by warm-adapted species.

Increased climatic stress will also increase the susceptibility of trees to facultative or ‘opportunist’ pathogens like Armillaria gallica, which appear to be almost entirely dependent on host stress to impair host resistance before they can infect. High summer temperatures (the preceding year) and winter temperatures were associated with early fruiting in countries like Norway and in the UK, which point towards global warming as an underlying cause for the observed displacements in fruiting time.

The magnitude of the response amounts to nearly 1-3 day shift towards earlier fruiting in response to an increase of 1°C during the winter/spring period. Alleviated CO₂ would promote mycelial ramifications in soil and their subsequent carbon sequestration activity would have negative feedback effect on the rising atmospheric CO₂ level.

Most of the disturbances in fungal population and diversity are the result of problems deep-rooted in the fabric of modern society. We now are aware that the lack of stakeholder’s attention, simple fragmentation, as well as outright destruction of our natural areas is leading to an ever increasing decline in fungal diversity worldwide. Since range shift is an international issue, trans-boundary multinational management system is required to be set up which will require new administrative structures, new political agreements, jointly implemented research agendas, technology transfer and training.

However, the recent exclusion of fungi as a priority for conservation in New Zealand and Australia, despite their importance to biodiversity, ecosystem functioning and humanity, is a serious blow to global fungal conservation initiatives. So, there is a need to amend the approach of policy makers about fungi. Loss of biodiversity is a silent crisis, therefore, urgent issues like inventorisation of risk areas and studies related to synergy of changing climate and other factors upon mycological realm needs to be conducted for arriving at a definite conclusion.