Temperature is a fundamental environmental factor that profoundly influences the physiological processes of sweet pea (Lathyrus odoratus) plants, from the initial breaking of seed dormancy to the establishment of robust vegetative growth. Its effect is not singular but varies in intensity and mechanism across different developmental stages.
For a sweet pea seed, germination begins with the imbibition of water, a process whose rate is initially governed by water potential but soon becomes highly temperature-dependent. Enzymatic activity within the seed endosperm, crucial for converting stored starches into soluble sugars to fuel the emerging radicle, is regulated by temperature. Each enzyme has an optimal temperature range. Within a moderate range (approximately 55-65°F or 13-18°C), enzymatic reactions proceed efficiently, leading to a high and uniform germination percentage. Temperatures below this range drastically slow these metabolic processes, resulting in delayed, uneven, or failed germination. Conversely, excessively high temperatures can denature these critical proteins, permanently halting the germination process before it even begins.
Once the seedling emerges, temperature continues to dictate the pace of its metabolism. In optimal thermal conditions, respiration and photosynthesis operate at peak efficiency. The plant can effectively produce carbohydrates (photosynthate) and then utilize this energy (through respiration) for cell division and expansion. This efficient energy budget allows for the rapid development of true leaves and a strong root system. Cool temperatures suppress overall metabolic activity, causing sluggish growth as energy production and consumption slow down. Excessively warm temperatures, however, can increase the respiratory rate disproportionately. This means the plant may burn through its energy reserves faster than it can create them through photosynthesis, leading to spindly, weak growth as energy is diverted from structural development to basic metabolic maintenance.
The growth and function of the root system, vital for water and mineral nutrient acquisition, are exceptionally sensitive to soil temperature. Cool soil conditions hinder root cell division and elongation, resulting in a shallower, less developed root system. This physically limits the plant's ability to explore the soil for resources, potentially leading to nutrient deficiencies even in rich soil. Furthermore, the active transport mechanisms responsible for moving ions from the soil into root cells are temperature-sensitive biological processes. In cold soils, this uptake is inefficient, starving the plant of essential elements like nitrogen and phosphorus needed for building proteins and nucleic acids, thereby stunting overall growth.
Temperature directly influences plant morphology through its effect on plant hormones and developmental genes. In consistently cool environments, sweet pea plants often exhibit shorter internodes (the stem segments between leaves), resulting in a more compact, bushy habit. Warmer temperatures typically promote longer internodes, which can lead to taller but potentially weaker and more leggy plants as they stretch towards the light. This thermomorphogenic response is mediated by complex hormonal signaling networks, including auxins and gibberellins, which regulate cell elongation. Temperature fluctuations can therefore directly sculpt the physical architecture of the sweet pea plant.
