Effect of Environmental Factors on the Diversity of Ecto-Mycorrhizal Association in the Family Fagaceae in Eastern Himalayas

Patra, Rounak (2018) Effect of Environmental Factors on the Diversity of Ecto-Mycorrhizal Association in the Family Fagaceae in Eastern Himalayas. Masters thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

Mycorrhizae are fungal species that form mutualistic, non-pathogenic associations with roots of higher plants. They are known to have a significant influence on the host plant’s ability to acquire nutrients and withstand pathogens, and thereby influence plant growth and survival. The nature of mycorrhizal associations varies with plant host species and habitat, but the diversity of fungal associations as a function of environmental factors is not well known. With emerging climate change and other environmental changes, mycorrhizal associations may be disrupted, altering plant species distributions and major ecosystem function. One of these mycorrhizal interactions is ectomycorrhizae, which are known to occur naturally in woody plants in many plant families and genera, including the Birches (family: Betulaceae), Eucalypts (Family: Myrtaceae), Oaks (Family: Fagaceae), Pines (Family: Pinaceae), and Dipterocarps (Family: Dipterocarpaceae). These ectomycorrhizal interactions are relatively well studied for temperate ecosystems, but may well be critically important for the structure and function of tropical forest ecosystems. Here we study the diversity of fungal species in mycorrhizal associations with 10 species of trees in the order Fagales that occur in the Sikkim Himalaya. We chose these species as the Fagales are known to have ectomycorrhizal relationships and these species are important components of forests in the region. These tree species had varied altitudinal ranges and we studied them across their altitudinal range to understand the diversity of mycorrhizal fungi within and among species as a function of elevation. We document diversity using DNA sequence variation in fungal samples obtained from the roots of the trees species and relate changes in diversity with associated environmental change with elevation. We collected the root samples for all 10 species from Khangchendzonga Biosphere Reserve in four adjacent altitudinal bands for a full range of 1200m to 2800 m above mean sea level. Using molecular methods, we confirmed the presence of mycorrhizal fungi in 41 of the 51 root samples we collected. We are investigating further refinements in sampling and isolation of fungi to improve detection of ectomycorrhizal species associated with the roots. We also sampled soils to study nutrient variation with elevation and obtained climatic parameters from global datasets. We developed a protocol for extraction of ectomycorrhizal DNA from root tips and subsequent amplification using fungal-specific ITS primers. Sequencing and identification of EM species using high-throughput methods should provide comprehensive coverage of the diversity of ectomycorrhizal taxa associated with different plant taxa. This work is currently in the sequencing stage and results are awaited. We tried and abandoned more targeted clone library approaches for documenting diversity as they proved to be difficult with these samples obtained from forest ecosystems, in addition to the effort involved in documenting largely unknown diversity. Soil analyses showed that soil pH decreased with elevation, while total organic carbon increased and plant available nitrogen decreased. Lower temperatures are known to decrease enzymatic activity at higher elevations, slowing decomposition of organic matter and reducing nitrogen availability. Elevation can act as a proxy to study the potential impact of climate changes on biotic interactions, so our study may shed light on the potential climate change impacts. Increasing temperature and irregular rainfall patterns due to climate change may alter soil nutrient cycling and availability, and thus change the nature of mycorrhizal associations that are selected in a given environment. This, in turn, will drive changes in tree species distributions and abundance with consequences for broader ecosystem properties.

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