Final answer:
The student's question is about photoperiodism, specifically in short-day plants like goldenrod and poinsettia, which flower when the night is longer than a certain critical value. The study focuses on how these plants use day length to regulate flowering time.
Step-by-step explanation:
The plant physiologist is studying photoperiodism, a biological response to the timing and duration of day and night that controls flowering in plants, among other things. Short-day plants, like goldenrod and poinsettia, require longer periods of darkness each day (a short day) to initiate flowering. This response is influenced by the phytochrome system, which allows plants to sense seasonal changes and regulate their floral development accordingly.
While temperature and light intensity can impact plant growth, they are not as reliable for indicating seasons as day length is. This is because day length changes predictably throughout the year, thereby providing plants with a consistent environmental cue to trigger important physiological changes such as flowering.