Question

Which plant seeds cannot be germinated and established without the presence of mycorrhizae? (a) Mango (b) Pulses (c) Pinus (d) Selaginella

Short answer

The plant seeds of Pinus cannot be germinated and established effectively without the presence of mycorrhizae.

Step-by-step solution

Understanding mycorrhizae

Mycorrhizae are symbiotic relationships that form between fungi and plants. The fungi colonize the root system of a host plant, providing increased water and nutrient absorption capabilities while the plant provides the fungus with carbohydrates formed from photosynthesis.

Review the plants

Now, let's review the relationship of each plant with mycorrhizae: (a) Mango: Mango trees have endomycorrhizae, which can assist the plant, but are not strictly essential for germination. (b) Pulses: Pulses also have mutualism with mycorrhizae, but they can germinate and grow without them. (c) Pinus: Pinus, or pine trees, generally rely on ectomycorrhizae (a type of mycorrhizae) for their growth, especially in nutrient-deficient soils. They require mycorrhizae for effective establishment and growth. (d) Selaginella: Selaginella, as a type of fern, does not require mycorrhizae for germination or growth.

Conclusion

Based on the information explained above, Pinus (c) is the plant seed that cannot be germinated and established effectively without the presence of mycorrhizae.

Key concepts

Symbiotic Relationships in Plants

In the realm of plant biology, symbiotic relationships are pivotal for the survival and prosperity of many plant species. One of the most remarkable examples is the association between plants and mycorrhizal fungi, wherein each party provides something essential to the other. Fungi that form mycorrhizae anchor themselves to plant roots and extend their mycelium into the surrounding soil. This mutually beneficial partnership enables plants to absorb nutrients and water more effectively than they would on their own. In exchange, the fungi receive vital carbohydrates produced by the plants through photosynthesis.

The symbiosis can vary in its necessity for different plants. While some, like many hardwood tree species, form associations that benefit growth but are not critical for survival, others, such as Pinus (Pine trees), rely heavily on their fungal partners, particularly in nutrient-poor environments. It is important to note that not all plant species require mycorrhizae to thrive, as seen with Selaginella. Understanding these symbiotic relationships allows us to appreciate the complexities of plant ecosystems and their dependencies.

Plant Physiology

Delving into plant physiology, we explore the intricate functions within plants that enable life, growth, and reproduction. Mycorrhizae play a vital role in plant physiology by affecting various physiological processes. They enhance water uptake, improve nutrient assimilation – especially of phosphorus and nitrogen – and can help in stabilizing the soil structure, which benefits root growth. These functions are central to plant health and directly impact a plant's ability to conduct photosynthesis, grow, flower, and produce seeds.

In the context of mycorrhizae, it's fascinating to see how the fungi penetrate the root cells to create a network. This network, known as the arbuscular mycorrhizal network in the case of many agricultural crops, acts like an extended root system, reaching areas of the soil that roots alone cannot. This symbiotic relationship alters the physiological makeup of the plant, making it more resilient to environmental stresses such as drought or pathogen attacks. The efficiency of this partnership is such that certain plants have evolved to be almost entirely dependent on it for their nutrient intake.

Seed Germination

When we focus on seed germination, the process by which a plant emerges from a seed and begins its growth cycle, we must acknowledge the role of environmental factors, water, oxygen, and in some cases, the presence of mycorrhizae. Germination commences when a seed absorbs water, swells, and bursts its outer coat. The embryonic plant inside then starts to grow, fueled by nutrients stored in the seed.

For some plants, such as Pinus species, the presence of mycorrhizae is a significant factor in the success of seed germination and seedling establishment. This is due to the mycorrhizae's ability to provide essential nutrients that are scarce in the soil, allowing the seedlings to overcome the initial nutrient limitation.

Importance of Mycorrhizae in Seedling Growth

In the critical stages following germination, mycorrhizae become especially important, as they significantly enhance the young plant's capacity for nutrient and water uptake during this vulnerable phase of establishment. Consequently, seedlings without this symbiotic support may exhibit stunted growth or higher mortality rates. Hence, understanding the role of mycorrhizae during seed germination and seedling development is vital for conservation efforts, forestry management, and agriculture.