FACTORS AFFECTING PLANT GROWTH MEASURING GROWTH Increase in

FACTORS AFFECTING PLANT GROWTH

MEASURING GROWTH • • • Increase in fresh weight Increase in dry weight Volume Length Height Surface area

HOW PLANTS GROW • Meristems – Dicots • Apical meristems – vegetative buds – shoot tips – axils of leaves • Cells divide/redivide by mitosis/cytokinesis • Cell division/elongation causes shoot growth • Similar meristematic cells at root tips

HOW PLANTS GROW • Meristems (cont) • Secondary growth in woody perennials – Increase in diameter » due to meristematic regions – vascular cambium » xylem to inside, phloem to outside – cork cambium » external to vascular cambium » produces cork in the bark layer

Plant Growth and Development • Photosynthesis • Respiration • Transpiration • The above 3 items drive plant growth

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH • Light • Temperature • Water • Humidity • Gases • Nutrition

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH • Light – Sun’s radiation • not all reaches earth; atmosphere absorbs much • visible (and some invisible) rays pass, warming surface • reradiation warms atmosphere – Intensity • • high in deserts; no clouds, dry air low in cloudy, humid regions earth tilted on axis; rays strike more directly in summer day length varies during year due to tilt

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH PAR (Photosynthetically Active Radiation) • Plants absorb blue and red light. Blue light is mainly responsible for vegetative growth. • Red light when combined with blue light encourages flowering.

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH • Light (cont) – Photoperiodism – response to varying length of light and dark • It was first believed that day length was the main factor affecting plant flowering. However, it was later found out that it was the length of darkness.

Plants are classified into 3 day length categories: • Short day length plants flower when they are exposed to less than 12 hr. sunlight (mums, Xmas cactus, poinsettias) • Long day plants flower when the day length exceeds 12 hours. This includes most summer flowering plants and vegetables. • Day neutral plants flower regardless of day length such as tomatoes, corn, cucumber, and strawberry.

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH • Temperature – high light intensity creates heat; sunburned – low temp injury associated with frosts • Low temperatures reduce energy use and increase sugar storage. Citrus is sweeter after cold weather. • Adverse temp. may cause stunted growth and poor quality. High temperatures cause bitter lettuce.

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH • Water – most growing plants contain about 90% water – amount needed for growth varies with plant and light intensity – transpiration drives water uptake from soil • water pulled through xylem • exits via stomates – evapotranspiration - total loss of water from soil • loss from soil evaporation and plant transpiration

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH • Gases – Nitrogen is most abundant – Oxygen and carbon dioxide are most important plants use CO 2 for photosynthesis; give off O 2 plants use O 2 for respiration; give off CO 2 stomatal opening and closing related to CO 2 levels oxygen for respiration limited in waterlogged soils increased CO 2 levels in atmosphere associated with global warming • additional pollutants harm plants • • •