Botany TCD: From Organisms to Ecosystems

Key Concepts Overview

  • Terrestrial Ecosystems: Focus on deserts, tundra, and peatlands, which are essential for understanding biodiversity, climate interactions, and ecological importance on Earth. Each ecosystem supports unique flora and fauna adapted to their environments.

  • Climograph: Represents the relationship between climate and biomes, illustrating mean annual temperature and precipitation, crucial for predicting vegetation distribution and recognizing climate change effects.

  • Global Distribution of Biomes: Includes tropical forests, savannas, deserts, grasslands, tundra, and others; each biome is characterized by distinct climatic conditions, biodiversity, and ecosystem services, influencing global carbon cycles.

  • Air Mass Movement:

    • Hadley Cells: Air circulation patterns influence climate and desert formation by driving moist air towards the equator and pushing dry air towards the subtropics.

    • Descending Dry Air: This mechanism leads to arid conditions by absorbing moisture, resulting in deserts formed in the rain shadow areas of mountains.

Deserts
Characteristics of Deserts

  • Rainfall: - Low and unpredictable (< 250 mm/year), making water a scarce resource.

    • High evaporation rates significantly contribute to quick water loss, with potential for extreme drought conditions affecting flora and fauna.

  • Temperature: - Can be categorized into hot (e.g., Sahara) and cold deserts (e.g., Antarctic desert). Despite overall low temperatures, deserts can experience large diurnal temperature variations (day-night temperature differences), presenting challenges for adaptive strategies in species.

Location

  • Determined by:

    • Global atmospheric circulation that shapes regional precipitation patterns.

    • Rain shadows (e.g., Atacama Desert), where moisture-laden winds lose precipitation on windward slopes.

    • Continental interiors (e.g., Gobi Desert), where distance from moisture sources limits available rainfall.

Plant Adaptations to Desert Conditions

  1. Avoiding Drought:

    • Timed life cycles (e.g., annuals - therophytes) that allow species to germinate, reproduce, and die within a short period, typically after rare rainfall events.

  2. Tolerating Drought:

    • Water Absorption Mechanisms:

      • Shallow spreading roots capturing surface moisture, and deep taproots (up to 15 m) accessing groundwater.

      • Some species utilize dew or fog as additional moisture sources, maximizing survival in arid environments.

    • Reduced Transpiration:

      • Adaptations such as sunken stomata to minimize water loss, rolling leaves to reduce surface area exposed to sunlight, hairy/scaly leaves to reduce direct evaporation, and retention of leaves during dry seasons to conserve energy.

  3. CAM Photosynthesis:

    • Stomata are closed during the day to minimize water loss; CO2 is stored as organic acids at night and released during the day for photosynthesis, enhancing efficiency in water use.

Raunkiaer Plant Life Forms in Deserts

  • Emphasis on the prevalence of therophytes (annuals), which represent a significant portion of desert vegetation due to their unique adaptation strategies that favor survival during extreme dryness.

Tundra
Physical Characteristics

  • Cold Climate:

    • Low precipitation, predominantly as snow, with conditions preventing extensive vegetation growth.

    • Presence of permafrost, a permanently frozen layer beneath the surface, which restricts root growth and contributes to distinct soil profiles.

    • Short growing seasons, typically 6-10 weeks, limiting the period for plant growth and reproduction.

  • Botanical Diversity:

    • Low diversity, dominated by perennials with low stature (e.g., mosses, lichens, and small shrubs), which have adapted to harsh climatic conditions.

Nutrient Cycling in Tundras

  • Low Nutrient Availability:

    • Due to low temperatures, limited precipitation, and permafrost, biological activity is drastically reduced, leading to slow nutrient cycling rates. This condition results in nutrient-poor soils and limits the growth potential of flora.

Peatlands
Definition

  • Peat: Partially decayed organic matter that accumulates in wet, anaerobic conditions, with a production rate greater than decomposition, creating unique ecosystems.

Formation of Peatlands

  • Develop through hydrosere succession: lakes transitioning to swamps, and ultimately peat bogs due to sediment accumulation and plant growth, followed by waterlogging.

  • Characteristics of ombrotrophic bogs:

    • Very low nutrient levels, waterlogged conditions resulting in anaerobic decomposition, and acidic pH levels that inhibit decomposer activity.

Ecological Importance of Peatlands

  • Act as major carbon sinks, storing more carbon than tropical rainforests and playing a crucial role in global carbon cycles.

  • Critical for maintaining local biodiversity, resilience of ecosystems, and water quality, providing important habitats for various species.

Peatland Conservation vs. Exploitation

  • Balancing act between utilizing peat for fuel, horticulture, and maintaining its ecological functions, such as carbon storage and habitat provision, highlighting the need for sustainable management practices.

Irish Peatland Carbon Storage

  • Accounting for over 1.1 billion tons of carbon, which contributes significantly to global carbon levels; its conservation is vital in combating climate change.

References

  • Beckle, S.-W. (2002). Walter's Vegetation of the Earth.

  • Charman et al. (2013). Climate-related changes in peatland carbon accumulation during the last millennium. Biogeosciences 10, 929-944.

  • Notes compiled in Markdown format, organized for clarity.

  • Key concepts emphasized for exam preparation, focusing on ecosystems, adaptations, and environmental significance.