Run for Cover! What’s Covering Your Greenhouse and How is it Affecting Seedling Growth? Jeremy Pinto Botanist Trainee/Tribal Nursery Coordinator USDA Forest Service, Southern Research Station Kas Dumroese National Nursery Specialist USDA Forest Service, Southern Research Station

OutlineIntroduction Background Background Problem ProblemObjectivesMethods Analysis Analysis Results / Discussion Conclusion

Greenhouse Coverings Ideal Properties: Capture sunlight Capture sunlight Maintain temperature, humidity, and CO 2 for a specified species Maintain temperature, humidity, and CO 2 for a specified species

Greenhouse Cover Types MaterialOperational considerationsLight (%PAR)Thermal Conductance Lifespan (yrs) AdvantageDisadvantage FiberglassLow cost, strong, light- weight Surface degrades easily, highly flammable 90 single layer 70 double layer 1.2 < PolyethyleneLow cost, light- weight, easy to install Short life, high thermal conductance 85 single layer 76 double layer PolycarbonateHigh impact resistance, low flammability High cost, high expansion and contraction 94 single layer 83 double layer >

Important Greenhouse Cover Considerations Cost Cost Life Span Life Span Strength Strength Weight Weight Light Transmittance Light Transmittance Thermal Conductance Thermal Conductance

Problem Greenhouse Cover Life Span Fiberglass covers decrease light transmittance significantly over time Fiberglass covers decrease light transmittance significantly over time How is it affecting seedling growth? How is it affecting seedling growth?

Atmospheric factors affecting tree seedling growth

The Nature of Light

Light influences two factors in plant growth Photosynthesis Photosynthesis Photomorphogenesis Photomorphogenesis

The Nature of Light The Visible Spectrum provides the light needed for photosynthesis nm Most active wavelengths for photosynthesis peak at 430 and 680 nm Associated with photosynthetically active radiation (PAR) Captured by carotene and chlorophyll pigments Produces chemical energy for plant growth and metabolism

The Nature of Light The Visible Spectrum and Near Infrared light influence photomorphogenesis and nm Phytochrome system controls seed germination and budset ( nm) Morphological development: branching, shoot elongation, and shoot sturdiness ( nm)

Temperature Temperature response for photosynthesis and respiration

Temperature Temperature effects on germination and establishment

Objectives Examine the effects of an old fiberglass greenhouse cover and a new polycarbonate cover on seedling growth Measure morphological characteristics of: height, root collar diameter (RCD), seedling dry weight, shoot-to-root ratio, and sturdiness coefficient Measure percentage germination and germination rates

Methods Ponderosa pine seedlings were sown in 2 x 3 factorial design with three replicates per treatment Treatments consisted of two cover types (old fiberglass and new polycarbonate) and three fertilizer rates (20, 40, and 60 mg N applied seedling -1 )

Methods Seedlings were grown in 6 growing structures made of the treatment cover type – 3 replicates per cover

Methods Three fertilizer treatment replicates per growing structure

Methods All seedlings were exponentially fertilized at their respective treatment rates (Ingestad and Lund 1986, Timmer and Aidelbaum 1996) Fertilizer application and irrigation rates were gravimetrically determined

Methods cont’d Morphological Characteristic Sampling Height, Root collar diameter (RCD), and biomass Shoot-to-root ratio = Shoot biomass/Root biomass Sturdiness coefficient = Height/RCD

Analysis

Analysis General linear model in SAS Analysis of variance (α = 0.05) Multiple comparisons, with Tukey-Kramer inequality adjustments (α = 0.05)

Results/Discussion Morphological Variables Cover x fertilizer interactions were present in root dry weights and shoot-to-root ratios (p<0.0001) Fertilizer effects were observed for all morphological measurements (p>0.04) No cover effects were observed for RCD, shoot dry weight, and total seedling dry weight (p>0.05)

Seedling Height (cm) Seedling growth curve from June to November

Seedling Height (cm) * *Bars with the same letter are not significantly different

Root Collar Diameter (RCD) Seedling root collar diameter curve from June to November

Root Collar Diameter (RCD)

Shoot Dry Weight (g)

Root Dry Weight (g)

Total Seedling Dry Weight (g)

Shoot-to-Root Ratio

Sturdiness Coefficient

Germination Data Significant differences (p<0.05) between greenhouse cover types in: Cumulative germination percent (GC) Peak value germination (PV) Germination value (GV) Germination value prime (GV’) No significant difference (p=0.11) in germination rate prime 50% (GR’ 50 )

Germination Data GC (%)PVGVGV’GR’ 50 New Polycarbonate Old Fiberglass standard error p-value

Light Data New polycarbonate showed a 40% reduction in PAR light New polycarbonate showed a 40% reduction in PAR light Old fiberglass showed a 57% reduction in PAR light Old fiberglass showed a 57% reduction in PAR light

Discussion Trends for increasing height, RCD, seedling biomass in response to fertilizer treatments were expected and observed Trends for increasing height, RCD, seedling biomass in response to fertilizer treatments were expected and observed Lack of significant differences between cover types was not expected Lack of significant differences between cover types was not expected Unexpected germination data suggests that other variables could be involved such as heat Unexpected germination data suggests that other variables could be involved such as heat

Conclusion “Stats are like a bikini. What they reveal is suggestive, but what they conceal is vital.” Aaron Levenstein

Conclusions TREES GROW THE TALLEST

Conclusions Greenhouse cover type did have an effect on seedling height, and sturdiness coefficient across all fertilizer treatments Greenhouse cover type did have an effect on seedling height, and sturdiness coefficient across all fertilizer treatments Increasing fertilizer rates increased seedling height, RCD, and biomass under the old fiberglass cover type Increasing fertilizer rates increased seedling height, RCD, and biomass under the old fiberglass cover type No differences were observed between the two highest fertilizer treatments of the new polycarbonate cover type No differences were observed between the two highest fertilizer treatments of the new polycarbonate cover type Germination percentage and values were better under the old fiberglass but lack of temperature data makes conclusions difficult Germination percentage and values were better under the old fiberglass but lack of temperature data makes conclusions difficult

Conclusions Although differences between cover types were few in this study, results illustrate the importance of monitoring and adjusting cultural treatments when there are changes in any one of the factors that affect seedling growth Although differences between cover types were few in this study, results illustrate the importance of monitoring and adjusting cultural treatments when there are changes in any one of the factors that affect seedling growth

Acknowledgements Dr. John D. Marshall, UI plant physiology Dr. John D. Marshall, UI plant physiology Jennifer Nader, nursery culture and data collection Jennifer Nader, nursery culture and data collection University of Idaho Center for Forest Nursery and Seedling Research University of Idaho Center for Forest Nursery and Seedling Research Statistical Help: Stephanie Kane (UI – SCC) Statistical Help: Stephanie Kane (UI – SCC)