Hi Adam! Thank you for your question! The effect of air pressure on plant growth definitely differs based on the plant species. Some plants are adapted to grow under relatively high atmospheric pressure (near sea level), and others under lower atmospheric pressure (like on mountain tops).

The main reason why pressure changes can affect plant growth is because it will alter the rate of gas exchange between this plant and the air. It's actually pretty similar to the reason we feel shortness of breath at high altitudes. Plants need to be able to take in CO₂ to photosynthesize and grow. So, being at high altitude (low atmospheric pressure) can prevent plants from growing as fast because they are not able to take in as much CO₂ as they could at sea level."

Accelerating Seed Germination and Plant Growth through Manipulation of Atmospheric Pressure. This abstract says that "research conducted a few years ago indicated that subjecting seeds and plants to frequent changes in atmospheric pressure may shorten germination time, improve the rate of growth of young plants, and cause more massive and rapid root growth."

This link presents "results on young tomato plants grown hydroponically, which had been treated with various combinations of air pressure (400-700-1000 hPa), CO₂ concentration and wind intensity for seven days. At the lowest pressure transpiration was enhanced considerably, and the plants became sturdier. On the other hand growth was retarded to a certain extent, attributable to secondary air pressure effects. Therefore, even greater limitations of plant productivity are expected after more extended periods of low pressure treatment."

The aim of this study "is to investigate the effects of an artificially controlled pressure, on net photosynthesis and respiration during plant growth. In this study, the effects of elevated total pressure on the rates of net photosynthesis and respiration of a model plant, Arabidopsis thaliana, were investigated in a chamber that newly developed in this study to control the total pressure. The results clearly showed that the rate of respiration decreased linearly with increasing total pressure at a high humidity".

Good question.

Pressure correlates with temperature, and temperature affects plants in a number of ways.

The best way to test this would be to ask how people grow house plants on top of mountains versus in low lands. Because they are house plants, they will be grown at room temperature and given adequate water, but the high-altitude houses will have lower pressure.

Having grown house plants at different altitudes myself, I have not seen a perceptible difference. However, that may be simply because I have not measured closely enough.