Effect of Global Warming on the Aymbi-otic Relationship between Fungi and Plants

The ecosystems of mycorrhizal fungi take place below ground in symbiosis with plants. These ecosystems are not well researched despite their significant contribution to their surroundings. The fungi under study are ericoid mycorrhizal (ErM) fungi, fine endophytic (FE) fungi, and dark septate endophytic (DSE) fungi. ErM fungi can decompose a broad range of organic compounds such as protein, chitin, cellulose<!–[if supportFields]> XE “cellulose” <![endif]–><!–[if supportFields]><![endif]–>, hemicellulose, and starch. This decomposition<!–[if supportFields]> XE “decomposition” <![endif]–><!–[if supportFields]><![endif]–> releases amino acids<!–[if supportFields]> XE “amino acids” <![endif]–><!–[if supportFields]><![endif]–> and amino sugars which are then received by the symbiotic plant. FE fungi can improve host nutrient uptake. DSE fungi are ascomycetous but perform as mycorrhizal fungi in harsh environments. Plants in symbiosis with DSE fungi can resist droughts and infections better. In return, fungal symbionts receive approximately 20% of their plants’ net primary production<!–[if supportFields]> XE “net primary production (NPP)” <![endif]–><!–[if supportFields]><![endif]–>. Olsrud et al. (2010) present research of the effect on these symbiotic relationships due to global warming factors, elevated atmospheric CO2, and temperature. The area under study is a subarctic birch forest<!–[if supportFields]> XE “forest” <![endif]–><!–[if supportFields]><![endif]–> understory in Sweden<!–[if supportFields]> XE “Sweden” <![endif]–><!–[if supportFields]><![endif]–> at latitude 68°21’N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>. Compared to regions of low latitude, global warming will have an appreciable effect on regions of high latitude. —Daniella Barraza
Olsrud, M., Carlsson, B., Svensson, B., Michelsen, A., Melillo, J., 2010. Responses of fungal root colonization, plant cover and leaf nutrients to long-term exposure to elevated atmospheric CO2 and warming in a subartic birch forest<!–[if supportFields]> XE “forest” <![endif]–><!–[if supportFields]><![endif]–> understory. Global Change Biology 16, 1820–1829.

Olsrud et al. conducted a six-year long study (2000–2006) on the responses of the three fungi to global warming. How plant cover and C, N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>, and P concentrations in leaves responded to global warming was also examined. Six 0.45 m by 0.75 m experimental plots were established and surrounded by an open-top chamber (OTC). Each plot was divided into fifteen 0.15 by 0.15 m subplots. Four out of the six chambers were randomly selected for treatment. One of the chambers was heated so that soil and air temperatures were 5 °C above ambient temperatures. Another chamber was CO2enriched to double the ambient concentrations. The third chamber was both heated and CO2 enriched. Finally, the last chamber was a control so there was no change in CO2 or temperature from the ambient. For the heated chambers, resistance cables were run through the upper layer of the soil to warm the soil. These were controlled by a data logger which was programmed to switch on and off every two minutes to maintain the temperature difference. To heat the air, infrared lamps were suspended above the soil surface. For the CO2 enriched chambers, CO2 concentration was increased to 730 ± 25 ppm. Two tanks were placed on opposite sides of the chamber to blow CO2enriched air into the chamber. Their position was to maintain an even concentration of CO2, to maintain an even blowing effect, and to reduce convective heating.
In each of the four experimental plots, one subplot was randomly chosen for analysis. The presence of symbiotic plants was recorded using point-frequency analysis. This involved recorded the species present at 5 cm intervals using a sheet of Plexiglass with 97 holes of 5 mm diameters. The plant cover, roots and leaves, was then harvested to calculate for biomass. Plant cover and biomass increased throughout the study. The three dominant plants found were Vaccinium myrtillus<!–[if supportFields]> XE “Vaccinium myrtillus” <![endif]–><!–[if supportFields]><![endif]–>, Vaccinium vitis-idaea<!–[if supportFields]>XE “Vaccinium vitis-idaea” <![endif]–><!–[if supportFields]><![endif]–>, and Deschampisa flexuosa<!–[if supportFields]> XE “Deschampisa flexuosa” <![endif]–><!–[if supportFields]><![endif]–>. The leaves and roots of these plants were then analyzed for C, N<!–[if supportFields]>XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–>, and P concentrations.
To examine the fungi, soil samples were taken. Three soil samples of 2.1 cm in diameter and 7 cm in depth were obtained from the center of each of the randomly selected subplots. The soil samples were placed on ice and transported to a cooling room at 2 °C in the laboratory. There, the soil samples were sorted for hair roots and grass roots. Hair roots belong to V. myrtillus and V. vitis-idaea whose symbiotic fungi is ErM. Further analysis of ErM Fungi involved a staining method and a visual examination. Grass roots belong to D. flexuosa whose main symbiotic fungi are FE and DSE fungi. Colonization of these fungi also involved visual examination. Visual examination refers to the process where 81 cm roots are examined under X400 magnification and 0.5 cm intervals.
Warming, CO2, and fungi root colonization were analyzed using two-way ANOVA<!–[if supportFields]> XE “ANOVA” <![endif]–><!–[if supportFields]><![endif]–>. There was a significant increase in plant cover under elevated temperatures, but not under elevated CO2. Under elevated CO2, V. myrtillus and V. vitis-idaea had a lower N<!–[if supportFields]> XE “nitrogen, N” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–> concentration in leaves, and the C to N ratio was higher. Nitrogen deficiency prevents plants from growing, but not root density. ErM colonization in these plants increased under elevated CO2 since plants will transfer more carbon to the fungi to obtain more N. Future global warming will allow ErM fungi to dominate the ecosystem. In D. flexuosa, FE fungi colonization was lower in CO2 treated and in higher temperature plots. DSE fungi colonization increased in warmer temperature plots, but there was no significant change in CO2 enriched plots. A reason FE fungi are affected by temperature is because they are not adapted to dry conditions. Higher temperatures can lead to dryer conditions. The response of FE fungi to CO2 can be explained by their slow growth compared to the fast growth of the roots. For DSE fungi, the main explanation for their response is competition with FE fungi. Under lower FE fungi density, they were able to flourish. However, further investigation needs to be done on their functional capabilities. There were no significant changes in P concentration for none of the plants.

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