Heat Stress on Tropical Plants in Western Ghats

Recent studies reveal alarming impacts of rising temperatures on tropical forest and agroforestry species in the Western Ghats. Researchers monitored leaf temperatures of various species in Karnataka. They found that many plants are nearing critical heat thresholds. This research raises concerns about the future of these species as global temperatures continue to rise.

About Leaf Temperature Thresholds

Leaves are crucial for photosynthesis and transpiration. The T₅₀ parameter indicates the temperature at which a leaf’s photosynthetic efficiency declines by half. Exceeding this threshold can lead to irreversible damage. Many tropical species are already experiencing temperatures that approach or exceed these critical limits.

Study Overview

The study examined 13 agroforestry species and four native forest species over a 4.5-month period. The research site was Hosagadde village, an area with frequent high temperatures, sometimes exceeding 40 degrees Celsius. The findings show that leaf temperatures can exceed surrounding air temperatures by 10 to 12 degrees Celsius during peak sun exposure.

Species Under Investigation

Commercially valuable agroforestry species studied include cardamom, cashew, cocoa, and vanilla. Some of these species, like cocoa and coffee, showed leaf temperatures that could potentially cause damage. However, the duration of exposure was often brief, suggesting that immediate irreversible damage is unlikely.

Physiological Responses to Heat

Leaves play a vital role in regulating temperature through water loss. They sense environmental factors such as temperature and light. The study brought into light that leaf thermal responses are crucial for understanding how plants cope with heat stress. Some plants exhibited visible damage, such as blackened leaf areas, which may indicate thermal injury.

Factors Influencing Heat Stress

While heat is factor, other stressors like pathogens and water deficits may also contribute to visible leaf damage. The research team cautioned against attributing symptoms solely to heat. A comprehensive understanding of all stressors is necessary to assess plant health accurately.

Importance of Thermal Safety Margins

Thermal safety margins represent the difference between a leaf’s temperature and its T₅₀ threshold. Smaller margins indicate greater vulnerability to heat stress. The study found that many tropical species are experiencing increasingly narrow thermal buffers, raising concerns about their future resilience.

Implications for Agroforestry Economies

About the thermal limits of leaves is essential for economically important species in agroforestry. The findings highlight the need for further research on how frequently plants exceed these thermal thresholds in real-world conditions. This knowledge is vital for the sustainability of agroforestry systems in the Western Ghats.

Questions for UPSC:

1. Critically analyse the role of leaf temperature in the photosynthesis process of plants.
2. Estimate the impact of global warming on agroforestry species in tropical regions.
3. Point out the various factors that contribute to heat stress in tropical plants.
4. What are thermal safety margins? How do they relate to plant resilience against climate change?

Answer Hints:

1. Critically analyse the role of leaf temperature in the photosynthesis process of plants.

1. Leaf temperature affects photosynthetic efficiency; higher temperatures can lead to reduced photosynthesis.
2. The T₅₀ threshold indicates the critical temperature where photosynthesis declines by half.
3. Leaves regulate temperature through transpiration, cooling themselves and maintaining photosynthesis.
4. Extreme leaf temperatures can cause irreversible cellular damage and plant death.
5. About leaf temperature dynamics is crucial for assessing plant health and productivity.

2. Estimate the impact of global warming on agroforestry species in tropical regions.

1. Global warming is projected to raise temperatures by up to 2°C or more, affecting tropical species.
2. Many agroforestry species are already near their thermal tolerance limits, increasing vulnerability.
3. Increased mean temperatures and extreme heat events can lead to reduced crop yields and quality.
4. Short exposure durations to high temperatures may still cause stress and damage.
5. Future climate scenarios indicate narrowing thermal safety margins for many species, threatening agroforestry economies.

3. Point out the various factors that contribute to heat stress in tropical plants.

1. High ambient temperatures, often exceeding 40°C, directly contribute to heat stress.
2. Leaf temperatures can exceed air temperatures by 10-12°C during peak sunlight, exacerbating stress.
3. Water deficits and drought conditions can intensify the effects of heat stress on plants.
4. Pathogens and pests can further weaken plants, making them more susceptible to heat damage.
5. Soil conditions and nutrient availability also influence a plant’s ability to cope with heat stress.

4. What are thermal safety margins? How do they relate to plant resilience against climate change?

1. Thermal safety margins are the difference between a leaf’s temperature and its T₅₀ threshold.
2. Smaller margins indicate higher vulnerability to heat stress and potential damage.
3. About these margins helps assess the resilience of species to climate change impacts.
4. As global temperatures rise, many species are experiencing narrower thermal buffers.
5. Maintaining wider thermal safety margins is crucial for the sustainability of agroforestry systems.