VII.TEMPERATURE IMPORTANCE A. Greenhouse Crops affects plant growth rate important for crop timing involved in flower bud initiation controls crop quality a significant operating cost

Temperature increase Carbohydrate produced Photosynthesis Light intensity & Carbon dioxide significantly above optimum & constant Temperature increase Carbohydrate metabolized Respiration Photosynthesis Light intensity increase Carbohydrate produced Temp 70 & 85; CO2 340 ppm Temp 70; CO ppm Temp 85; CO ppm Optimizing light, temperature and CO 2

Optimum Linear range

1. Photosynthesis and respiration - temperature a. Compensation point –Carbohydrate produced = carbohydrate metabolized for whole plant (1 or several days) Apparent carbohydrate produced –(Respiration Rate = Photosynthesis Rate for whole plant Apparent photosynthesis) b. Types of compensation points –Instantaneous –Daily –Young vs. old leaf –Temp. comp. pt. at increasing light intensity

Factors affecting compensation pt light intensity Leaf location CO 2 Temperature increase Carbohydrate metabolized or produced Photosynthesis Respiration Compensation point Apparent photosynthesis

B.Plant g rowth 1. Optimum Day temperature depends on light intensity CO 2 Species Stage of growth Quality needed

2. Night temperature depends on Day conditions (carbohydrate end of day) Quality needed Type of growth –Rooting Propagation Warm roots, cool shoot –Breaks Cool temperatures promote breaks Energy costs

3. Optimum temperature –Quality vs quantity a. young plant –Higher temperatures Most leaves exposed to light Photo. area = Resp. area higher temp initially, gradually lowered b. old plant –Lower temperatures Top leaves; high rate photo Lower leaves; low rate photo intensifies color improves keeping quality

4. Grower objectives –Best possible quality –Greatest quantity –Shortest time –Greatest profit

5. Practical control 1) Thermostats (cooler months) Night (adjusted for day environment) Cloudy day +0-5° Sunny day 10-15° 2) Thermostats (warmer months) lose control: low as possible Day: Ambient outside Night: Ambient outside 3) Computers

C. Flowering Bud initiation –Phytochrome temp range Bud development D. Transpiration Lower - reduces stress

E. DIF height control 1.Night/Day relationship DIF = Day temperature - Night temperature Ex. DNAve.DIF Temp* – – – –*assumes day length = night length

2.DIF - Management a. –Change in +DIF towards -DIF – Either decrease day temp. or Increase night temp. –Effects internode length –Benefits less growth regulators less cost for regulators less labor

DNAve.DIF – – – Disadvantage –Energy cost? –Management skills b. Flowering time Same if average daily temp. same

Height control of greenhouse crop with DIF

c. Additional information –Species dependent –Flowering may be inhibited Ex. Poinsettia above 73° –Chlorosis at greater -DIF –Downward curling of leaves at greater- dif –Alternatives Lower temp. 2 hr after sunrise

E. Storage Cuttings, seedlings, flowers Reduce respiration; conserve carbohydrates Temp: 35° - 40°; as low as 31-33°