Understanding Environmental Changes Under a Tree at Night

The question asks about the environmental change that leads to the advice against sleeping under a tree at night. This advice is commonly given and is related to the natural processes that plants undergo.

Photosynthesis and Respiration in Plants

• During the daytime, plants perform photosynthesis using sunlight. In this process, they take in carbon dioxide ($\text{CO}_2$) from the air and release oxygen ($\text{O}_2$). This makes the air around plants rich in oxygen during the day.
• However, at night, when there is no sunlight, photosynthesis stops. Plants continue to respire, just like humans and animals.
• During respiration, plants take in oxygen ($\text{O}_2$) and release carbon dioxide ($\text{CO}_2$).

Why Sleeping Under a Tree at Night is Advised Against

When a person sleeps very close to a tree, especially under its canopy, they are in the immediate environment where the tree is respiring. At night, the tree is consuming oxygen and releasing carbon dioxide. While the overall effect in open air is usually not drastic, being in a concentrated area near the plant at night means:

• The quantity of oxygen in the air immediately around the tree might decrease slightly.
• The quantity of carbon dioxide in the air immediately around the tree might increase slightly.

A slight deficiency in oxygen can feel uncomfortable or lead to a feeling of suffocation, especially in confined spaces or if multiple people are present. The increase in carbon dioxide also contributes to poorer air quality in the immediate vicinity. Therefore, the advice not to sleep under a tree at night is linked to these changes in the air composition due to plant respiration.

Analyzing the Options

Let's look at the given options in light of this understanding:

1. Deficiency of carbondioxide gas: At night, trees release $\text{CO}_2$, so there would be an increase, not a deficiency. This option is incorrect.
2. Increase of carbondioxide gas: This is true; $\text{CO}_2$ increases at night due to respiration. However, the core concern is often related to oxygen.
3. Deficiency in quantity of oxygen: This is also true; oxygen is consumed by the tree during respiration at night, leading to a slight deficiency in the immediate area. This directly affects the air a person breathes.
4. Increase in quantity of oxygen: Oxygen decreases at night due to respiration. This option is incorrect.

Between an increase in carbon dioxide and a deficiency in oxygen, the deficiency in oxygen is typically considered the more direct reason for the advice, as it impacts the essential gas needed for breathing.

Based on the process of plant respiration at night, the environmental change that is the reason behind the advice is the decrease in the quantity of oxygen in the air around the tree.