Environmental Factors (External) That Influence Plant Growth 1. Nutrition The nutrients that plants need are not only CO2 and H2 O but also other elements. Table: Mineral elements needed by higher plants and his role 2. 3. Water The functions of water include: a. For photosynthesis. b. Activates enzyme reactions. c. Helps the process of seed germination. d. Maintain (retain moisture). e. For transpiration. f. Increases turgor pressure thereby stimulating cell division. g. Eliminates abscission acid. Light Every plant needs light for growth, because light plays a very important role in photosynthesis and photomorphogenesis. Plant seeds that germinate and grow in a dark place/no light apparently grow abnormally, characterized by very fast growth, the plant looks tall and slender, the stems are weak and the stems are not green but pale. 4. 5. 6. This symptom is called etiolation.The length of exposure has a specific influence on growth and developmentplant. The length of the daily light period is called photoperiod, while the reaction of plants to photoperiods of different lengths is called photoperiodism.Based on day length requirements for flowering, in partLarge plants are divided into three main groups, namely: a. Short day plants (short day plants) Flowers if the day length is less than a certain critical period, for example poinsettia (Euphorbia pulcherima), sweet potato (Ipomoea batatas), pineapple (Ananas commosus), and rice (Oryza sativa). Day length must be less than 11 to 15 hours for flowering to occur. b. Long day plants (long day plants) Flowers if the day length is longer than a certain critical period, for example castor oil plants (Rhicinus communis) and potatoes (Solanum tuberosum).Daylength must be more than 12 to 14 hours for flowering to occur. c. Day-neutral plants. Flowering does not depend on day length, it can produce flowers at any time of the year, for example maize (Zea mays). Temperature The optimum temperature (15°C to 30°C) is the best temperature for growth. The minimum temperature (± 10°C) is the lowest temperature at which plants can still grow. The maximum temperature (30°C to 38°C) is the highest temperature at which plants can still grow. Humidity Humidity is related to the rate of transpiration through the leaves because transpiration is related to the rate of transport of water and dissolved nutrients. If moist conditions can be maintained, more water will be absorbed by plants and less will be evaporated. This condition supports cell elongation activity so that cells reach their maximum size more quickly and grow larger. Oxygen For the breakdown of large molecular compounds (during respiration) to produce the energy needed for the growth and development process.