Perennials are often grown in winter to get them ready for bound sale . And that means that supplementary lighting is often require to get high-pitched - timbre plants in a well timed way . The electricity price relate with supplemental ignition can be high . So , it ’s authoritative that supplementary luminousness is provided in the most efficient way potential . For a long fourth dimension , lighting recommendation have been based on the daily light inherent ( DLI . ) DLI is the total amount of lighter receive by a crop over a daytime . DLI is calculated from photosynthetic photon flux tightness ( PPFD ) . By integrate these instant measurements of the intensity of photosynthetic light , the DLI can be calculated . But basing ignition decisions solely on DLI may not be optimal .
By Dr. Marc van Iersel and Claudia Elkins , University of Georgia
In our research , funded by American Floral Endowment , we take a systematic approach towards finding the good supplementary kindling strategies . Our goal is to avail agriculturist produce mellow - timber crops , while assuring that lighting costs are not overweening . This starts with understand the basic physiology of how efficiently different species use light . Then , develop inflammation strategies based on those physiologic responses .
Light utilize efficiency of perennialsPlants need light for photosynthesis , but as plant life incur more light , they apply that light less efficiently . Understanding how efficiently different species utilise illumination is important . supplementary light should only be provided when plants can use that light expeditiously . measure a plant ’s light function efficiency is surprisingly easy and takes vantage of a little - know holding of all plants . This is bang as chlorophyll fluorescence .
When plant life are let on to light , much of that light is occupy by chlorophyl and associated pigment in the leaves . Much like a solar panel , that light is used to produce midget electrical currents inside leaves and the energy from that current drives the reactions of photosynthesis . And , it indirectly provide the energy for all life on earth .
Not all absorbed light is used to create a current … However , not all the absorbed light is used to create a current . Some of the energy is convert into passion , while a small fraction of that weak energy is converted into fluorescence . All farewell exposed to light give off a small amount of reddish light . This fluorescence is not enough to see with the naked centre , but can easily be measured . And by measure fluorescence , we can determine exactly how much of the luminance absorbed by a foliage is commute into current and used for photosynthesis .
We use chlorophyll fluorescence measurements to quantify how the light use efficiency of unlike perennials is bear on by the PPFD . Two things are clean-cut . First , the luminousness utilise efficiency of all mintage lessen at high PPFDs . Second , there are important differences among mintage ( shape 1 ) . And those differences have important implications for subsidiary firing . At very low PPFDs , all species use light with standardized efficiency : between 70 and 80 % of the light is used for photosynthesis .
However , how speedily the lighting use efficiency decreases with increasing PPFD bet on the species . The light use efficiency of Heucherella , a plant that thrive in shade , decrease quickly with increasing PPFD . On the other hand , Rudbeckia , a plant that does well in full sun or partial shade , is much more capable of using in high spirits PPFDs efficiently . And perhaps not surprisingly , the reply of Hosta , which does well in fond or full ghost , falls in between that of Heucherella and Rudbeckia .
image 1 . Light utilize efficiency of three perennial species in response to increase PPFD . mention that the igniter use efficiency of all species decreases at higher PPFDs , but this decrease is more pronounced in shade - obligate Heucherella than in sun - loving Rudbeckia .
Using light economic consumption efficiency to recrudesce better light strategiesSo how can this basic information be used to help growers manage their lighting ? There are three important lesson that can be drawn from this physiological information :
1 ) All mintage will use supplementary light more expeditiously when that supplementary ignitor is provided during periods with little sunlight . The unwashed threshold - mastery long used for HPS lights is based on one principle . The lights are turned on when sun levels drop below a specific threshold and bend off above that threshold .
2 ) Appropriate threshold are species - specific : leave Rudbeckia with supplemental light when sun provides a PPFD of 500 µmol / m2 / s , permit those plants to use that supplemental light with an efficiency of over 60 % ; however , Heucherella would be able to expend that same light with an efficiency of only about 30 % . Because of such difference among species , it is important to allow for a harvest like Heucherella with supplementary light only when there is little sunlight ; otherwise , the plants will not be able-bodied to apply the supplemental illumination efficiently . For Rudbeckia , as well as sunlight - have sex crop like lantana and rose , it is less important to put up supplementary luminosity only when there is piffling sunlight . Those crops can still use auxiliary igniter with reasonable efficiency at higher PPFDs .
3 ) These finding suggest that not all DLIs are equal . Because light is used more efficiently when the PPFD is low , our finding suggest that the overall weak use efficiency can be increased by provide illumination at lower PPFDs and longer photoperiods , while providing the same DLI . In other Son , spreading the light out over more hours each day should improve the overall light role efficiency and thus increase increment .
Not all DLIs are created equalTo test whether spreading the light out more hour each day increases growth , we grow Rudbeckia seedlings at a DLI of 12 mol / m2 / day , with that light cater over photoperiods of 12 , 15 , 18 , or 21 hours per day . To secure that all plants pick up the same amount of light , we develop a new ascendency approach for dimmable LED lights . Our system measure the PPFD at the crop level and calculates how much light is needed to reach the DLI by the end of the photoperiod . The control then place a sign to the LED lights so they offer just enough supplemental lightness to ensure that the flora have a DLI of 12 mol / m2 / day by the terminal of the photoperiod .
This control coming to supplemental kindling has two advantages : 1 ) the DLI can be precisely curb , regardless of weather conditions and 2 ) the supplemental light is provide preferentially when there is little sunlight ( and thus when flora can use the supplemental light most expeditiously ) . Using this control approach path to supplemental lighting , the PPFD received by the plants decreased from 275 to 160 µmol / m2 / s as the photoperiod increased from 12 to 21 hour .
As We speculate … As we hypothesized , the Rudbeckia seedlings grew substantially faster with recollective photoperiods and lower PPFDs ; with a 21 - hour photoperiod , plants were about 30 % declamatory than those grown under a 12 - hour photoperiod , even though all plants receive the same entire amount of light ( bod 2 ) . And the long photoperiod had no negative outcome on flora character , as limit from ascendant fraction ( an authoritative measure for seedlings , since estimable root growth is critical ) and compactness . ground on our findings , using a recollective photoperiod can diminish the crop cycle by at least one workweek . Another vantage of using longer photoperiods is the instant amount of supplementary light that needs to be provided is lower . That means that fewer light fixtures are needed to offer the auxiliary light . Thus , lowering the price of installing a ignition system .
Keep in mind that not all species will answer the same to longer photoperiods . The unfolding of many crops is photoperiod - dependent . And while flowering is desired when the harvest is finished , premature inflorescence can retard down growth .
Figure 2 . prospicient photoperiods result in better emergence of Rudbeckia seedling . The command plant on the left hand did not receive supplemental light ( and an medium DLI of about 5 mol / m2 / d. The other plants all get a DLI of 12 mol / m2 / d , but that spark was propagate out over photoperiods ranging from 12 to 21 hours .
What does this mean to the floriculture industry?More efficient lighting scheme can improve the yield of perennials while lowering electricity costs . Our approaching is most easily implement with dimmable conduct Christ Within fastness , but similar approaches can be implemented using HPS lights . Several lighting fellowship now offer lighting control systems that take advantage of the power to dim LED fixtures in reply to changing levels of sun . This can cater a more consistent wakeful surround in your greenhouse . It can also make craw production more predictable while assuring that no superfluous light is provided .
What is next?Industry support of the American Floral Endowment has helped to make this inquiry possible . AFE ’s fiscal livelihood for our body of work help us get a $ 5,000,000 Hiram Ulysses Grant from USDA ’s Specialty Crops Research Initiative . This project , titled Lighting Approaches to Maximize Profits , brings together scientists and engineers from around the body politic . A diverse squad work on lighting issues in the controlled environs husbandry industry avail integrate horticultural production , economics , and technology . This will result in holistic approaches to optimize supplemental inflammation strategies . To learn more about project LAMP , please visitwww.hortlamp.org .
Visitendowment.org/researchfor more articles like this .
Source : endowment.org
