VPD（饱和水汽压差）是空气中实际水汽含量与该温度下空气所能容纳的最大水汽量之间的差值。在受控种植环境中，VPD决定了植物蒸腾速率，影响养分吸收、气孔行为和整体生长速率。
关键事实
- Measured in kilopascals (kPa); optimal range for most crops is 0.8–1.2 kPa
- Low VPD (high humidity): stomata close, transpiration slows, nutrient uptake drops
- High VPD (low humidity): excessive transpiration, wilting, tip burn risk
- VPD is determined by both temperature and relative humidity together
- Seedlings and clones prefer low VPD (0.4–0.8 kPa); mature plants prefer 1.0–1.5 kPa
- Controlling VPD requires coordinating temperature, humidity, and airflow together