Effect of UV-A light on photosynthesis of lettuce (Lactuca sativa L.)

V magistrski nalogi smo preučevali vpliv UV-A na fotosintezno aktivnost zelenolistne in rdečelistne solate (Lactuca sativa L.). V eksperimentalnem delu, opravljenem v rastlinjaku, v obdobju od aprila do junija 2019, smo uporabili dve sorti zelenolistne solate, \u27Kyrio\u27 in \u27Hawking\u27, ter rdečelistno sorto \u27Oakly\u27. V dveh samostojnih poskusih smo rastline izpostavili trem svetlobnim režimom: kontrolna skupina je bila s fotoperiodo 12 ur osvetljevana le z osnovno osvetlitvijo iz modre in rdeče svetlobe s PPFD 400 μmol m-2 s-1obravnavanji UV1 in UV2 pa poleg tega še z UV-A svetlobo s PFD 1,6 μmol m-2 s-1 (vrh pri 399 nm), za obdobje 4 oziroma 8 ur dnevno. Učinek UV-A na rast solate smo zaznali le pri sorti \u27Hawking\u27, kjer se je pri 8-urni dnevni izpostavitvi sveža masa zmanjšala za 17, 3 %, medtem ko je bil učinek pri rdečelistni sorti \u27Oakly\u27 značilen, a velikostno nepomemben, zanemarljiv, sorta \u27Kyrio\u27 pa se ni odzvala. Vpliv dosvetljevanja z UV-A na vsebnost klorofila smo zaznali le v enem od dveh poskusov (zamanjšanje) in bi ga bilo potrebno preveriti z natančnejšimi kemičnimi analizami. Obsevane rastline niso odražale radiacijskega stresa, so pa imele rastline vseh treh obravnavanj znižano fotokemično učinkovitost, kar smo pripisali temperaturnemu stresu v segretem rastlinjaku ter možnim nihanjem v vsebnosti vode pri namakanju. Neto fotosinteza je bila v 1. poskusu pri rastlinah, obsevanih z UV-A 8 ur dnevno, značilno višja od kontrole. Ker se podoben trend nakazuje tudi pri dejanski fotokemični učinkovitosti, predvidevamo, da gre povečanje na račun vzpodbuditve varovalnih mehanizmov fotosinteznega aparata, manj verjetneje pa je rezultat dodatne energije modre svetlobe prisotne v uporabljenih UV-A diodah, saj so rastline prejemale dovolj velik osnovni PPFD.In the Master’s thesis, we studied the influence of UV-A on photosynthetic activities of the green and red lettuce (Lactuca sativa L.). In the experimental part, performed in a greenhouse, in the period from April to June 2019, we used two varieties of the green lettuce, \u27Kyrio\u27 and \u27Hawking\u27, and the red variety \u27Oakly\u27. In two separate experiments we exposed the plants to the following light regimes: the control group was under 12 h photoperiod illuminated only with the basal lighting of blue and red light with PPFD 400 μmol m-2 s-1while the UV1 and UV2 treatments received additional UV-A light with PFD 1,6 μmol m-2 s-1 (λmax = 399 nm), for a period of 4 or 8 hours daily, respectively. The effect of UV-A on the lettuce growth was observed only for the \u27Hawking\u27, where the fresh mass decreased by 17,3 % under 8 hours of daily exposure. On the other hand, the effect in the case of the red lettuce \u27Oakly\u27 was significant but small - with negligible ecological relevance and in the case of the \u27Kyrio\u27 there was no response. The influence of additional lighting with UV-A on the chlorophyll was observed only in one of two experiments (reduction) and would have to be checked with more accurate chemical analyses. The irradiated plants did not show signs of radiation stress, but plants of all treatments had reduced photochemical efficiency, which we attributed to temperature stress in the heated greenhouse and possible fluctuations in the amount of water for irrigation. The net photosynthesis of UV2 plants was higher than in controls. Since the same trend is indicated for photochemical efficiency, it is to presume that this increase is due to the enhancement of protection mechanisms in the photosynthetic apparatus. It is less likely that photosynthetic rate is increased due to the additional energy of blue light, present in the spectrum, radiating by the UV-A diodes since plants received sufficient PPFD