Why don’t trees suffocate during autumn for they carry out respiration through leaves?

Carbon dioxide is required by vegetation not for respiration but for manufacturing nutrients. Leaves manufacture food substance through chemical process of photosynthesis using carbon dioxide together with sunlight and water. All the water is not used up in photosynthesis. Some stock of water escapes in the air through evaporation. For example, a birch tree having about 2,00,000 leaves evaporates about 400 liters water daily in the air during summer. It has to replace this loss of water by the fresh supply from the ground.

In autumn when adequate supply of water is not available manufacturing of nutrients goes into low gear. A tree starts absorbing nutrients from its leaves into the branches and sheds dry, nutrientionless leaves. Till the new leaves sprout after the end of the autumn the tree curtails its need for carbon dioxide.

More reading:
Autumn (Wikipedia)
Photosynthesis (Wikipedia)
Respiratory system (Wikipedia)

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