Improving drought resistance in lodgepole pine in the face of climate change

About this project

This "class project" has been designed as a part of an assignment for the course RENR 580 (Applied statistics for the environmental sciences), instructed by Dr. Andreas. The concept behind this study has been taken from my PhD research proposal. However, the results represented in this study, and their interpretation is based on our expectations as the data used in this study is not real, and generated and/or simulated using "data simulation" tools. Therefore, the results and forthcoming outcomes of this project should not be considered legit. That being said, sharing and distribution of the results is not advised!

Study Background

Rapidly changing environment has caused sudden changes in weather regimes, which has led to problems like high temperatures, droughts and salinization (Pereira, 2016; Onyekachi et al., 2019; Weigandt et al., 2022). Among many important plant stressors, heat and drought are considered to be the most threatening environmental limitations for plant growth and survival. However, plants are equipped with biosynthetic machinery strategically operating to supply thousands of biocompounds required to perform vital physiological processes including those related to unfavorable growth conditions (Takahashi et al., 2018; Zandalinas et al., 2018; Shah and Smith, 2020).

Studies have been conducted to understand metabolic pathways and/or physiological processes as plant resistance against drought stress, for instance, intra-plant hormonal signaling (Zhu, 2002; Qi et al., 2018; Chen et al., 2021), tissue-specific responses (Okamoto et al., 2013; Martignago et al., 2020), specific gene expression (Ramanjulu and Bartels, 2002; Shinozaki et al., 2003), and morphological adaptations (Brunner et al., 2015). However, plants inbuilt defense strategies are not always strong enough to eliminate or at least reduce the effects of extreme environmental stresses to levels that could guarantee plant recovery and survival. Interestingly, external factors; with the potential of regulating plant resistance and metabolism, have been found reasonably helpful against an array of abiotic stresses, including drought stress. One of the most effective, and certainly the most sustainable factor is soil-dwelling beneficial microbes, which have played a crucial role in plant evolution and survival. Plants modify themselves by making morphological and biochemical changes, and very often “cry for help” from plant-helpers, for instance, beneficial microbes. Similarly, soil-dwelling microbes co-evolved with associated plants in the changing environment, and possibly these changes, not all however, may induced by the host plant.

This proposed study, therefore, revolves around the concept that plant-associated microbes evolve with changing environmental conditions, and to that, may develop stress-resistant traits which to some extent may help the plants to withstand that particular stress or possibly others!

Research problem and study gap

A little is known about plant-associated symbionts yet, however, knowledge in this area is rapidly increasing as recent studies continue to unveil the ecological niche of these entities. The most extensively studied plant-microbe relationship is the mutualistic associations that plants establish with beneficial microbes within their immediate environment (rhizosphere). Of these, the most abundant, perhaps one of the oldest and beneficial relationship established by plants is mycorrhizae; a mutualistic relationship between plants and fungal species of Glomeromycota, Basidiomycota and Ascomycota. Mycorrhizal fungi benefit plants in many ways, however, the most prominent and well-known is to provide plants access to mineral nutrients and water in the soil through extended extrametrical mycelium which are otherwise not accessible by plants themselves. In return, mycorrhizal fungi receive carbon-rich organics for their growth and survival (Fig 1).

Fig 1: Pre-association cross-talks between host tree and ECM fungi

Mycorrhizal associations happen to occur between plants and members of fungi into two prominent classes: endomycorrhizae, and ectomycorrhizae (ECM). However, ECM associations tend to form symbiotic relationships with only 5-10% of terrestrial plant species: mostly woody plants including pines (Pinus), spruce (Picea), oak (Quercus) and fir (Abies) unlike endomycorrhizal fungi which assumingly being less host-specific make symbiotic associations with 70 - 80% of plant species with the distinction of making specialized structures in host roots referred as arbuscules (van der Heijden et al., 2015). ECM fungi, however, produce specialized mycelial structures that could be categorized into three elementary organs : (1) ectomycorrhizas where both fungi and host plant exchange resources; (2) sporocarps that are dominant fruiting and reproductive structures carrying fungal spores; (3) extrametrical mycelium; the hyphal network, originates from host roots and extend to surrounding soil foraging for resources (Fernandez, 2021). The role of ECM fungi has highly been appreciated in a way that they assess plants to rehabilitate from what has caused by water scarcity by providing more access to bulk soil water and mineral nutrients. For instance, ECM fungi increased drought resistance in seedlings through enhanced enzymatic activity, and increased antioxidation via higher peroxidase activity and proline content together with higher water use efficiency thereby significantly enhancing seedling growth and resistance (Li et al., 2021).

Frequent occurrence of environmental limitations may influence the capacity of mycorrhizal fungi in stress remediation in a way they adapt to the very stressful environment as a behavioral change and exhibit resistant traits than those that are not adapted to that environment. For instance, in similar observations, it was suggested that host plants established mycorrhizas with drought-adapted mycorrhizal fungi conferring drought tolerance may exhibit enhanced growth and survival than those associated with non-adapted mycorrhizal fungi (Mudge et al., 1987). Although, there are potential studies available for ECM fungi being “plant-helpers” in many ways, however, their ecological niche has rarely been considered as a stimulatory factor of fungal behavior, changes in behavior, and their subsequent effects on plant growth and resistance. However, the phenomenon underlying these mechanisms by which mycorrhizal fungi undergo “environmentally induced” modifications, and subsequently, their effects on host water relations, are yet to be known.

Therefore, in this proposed research; by considering the ecological niche of ECM fungi and its subsequent effects on fungal behavior, ECM fungal communities have been isolated from drought and non-drought regions, which have been studied for their plant growth-promoting effects on lodgepole pine seedlings, and resistance against drought stress.

Research Hypothesis and objectives

The main hypothesis of this intended study is that “Ectomycorrhizal (ECM) fungal communities from drought lodgepole pine stands can better improve drought tolerance in lodgepole pine seedlings while being equally effective under optimal growth conditions as compared to ECM fungal communities from non-drought stands”.

Objectives

To study the ECM fungal diversity as affected by changing soil parameters in distinct ecological regions
To study the plant growth responses towards ECM fungal inoculation under drought stress and optimal growth condition.

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