In the morning, transpiration increases. At that time, the roots cannot supply enough water and the plant uses its internal water reserves from the stem to meet the transpirational demand. As a result, the stem diameter shrinks.
At the end of the day, transpiration decreases, and the plant is able to refill its internal reserves. This causes the stem diameter to increases again.
During the night, a positive pressure in the stem cells allows the plant to grow.
Long term diameter variations show a rapid growth at the start of the growing season, followed by a more modest growth near the end of the growing season.
Greenhouse climate and crop load contribute to growth slow downs and increases.
Long term daily sap flow follows the seasonal radiation pattern.
During the night, the plants are not irrigated and they gradually dry out as they use their internally stored water reserves to supplement the night-time transpiration (stem diameter decrease).
In the morning, the plants are irrigated 3 times (indicated by lines and arrows). At these times, sap flow increases due to the water uptake. Stem diameter also increases as the plants refills their internal reserves in the stem.
Two identical (potted) plants are grown in the same conditions. At a certain point in time, irrigation is stopped for one of the plants.
After already 5 days, the drought stress can be detected using diameter variation measurements. Daily growth stops and the diameter even shrinks. The diameter variations during the day also increase.
Only after 10 days, the drought stress becomes visually noticeable (wilting of the leaves). At this point, irrigation is resumed and the plant recovers (but not entirely).
Whiteflies damage plants by tapping into the phloem at the underside of the leaves. The plant loses turgor pressure and reacts to the toxic saliva of the whiteflies. Whiteflies also secrete honeydew which can cause additional mould growth.
During a severe whitefly infection, daily growth of the stem stops and even shrinkage can be observed. Stem diameter variations during the day also increase significantly.
After treatment, the plant slowly recovers. Daily growth of the stem diameter is restored and daily fluctuations become smaller again.
Diameter variation measurements can be used to distinguish between generative (investment in fruits) and vegetative (investment in leaves) plant growth.
Due to a too high fruit load, stem diameter growth decreases and becomes zero. After harvesting a part of the fruits, the plant growth resumes.
Tube heating in the greenhouse is increased at 4am. This causes VPD to rise suddenly and plant transpiration to increase.
Due to this increase in transpiration, the plant is no longer able to refill its internal water reserves. This causes the stem diameter to stop growing and to start shrinking prematurely.