## 4 Discussion
However, several papers (including the present study) have clearly demonstrated that the application of photoconversion films increases crop yields [30; 31; 32; 51; 52; 53; 55; 56; 57; 58; 59; 60; 61; 69; 70; 71; 72; 73; 74; 75; 76]. There are several possible reasons for the activation of plant development under films. Firstly, the functioning of phytochromes, which are very sensitive to the change in the proportion of far-red light: the phytochrome system can regulate plant growth and increase resistance to adverse environmental conditions [55; 77; 78]. Moreover, a decrease in far-red availability may induce a reduction in chlorophyll content [79] that correlates well with our data (Table 1). Secondly, the positive effects of photoluminescence particles as protectants against UV: UVA radiation can damage the photosynthetic apparatus due to destruction of the pigments and pigment-protein complexes [80; 81]. Previously, it was shown that, under insufficient illumination, photoconversion coatings change the content of phytochromones and thus affect plant growth [82]. Importantly, the described coatings luminesced in the red region. Furthermore, photoconversion films can affect soil microflora as well as plants. It was shown that PCF-induced changes in light spectrum stimulated reproduction of native soil microflora, which enhances the effect of transformed light on plant growth [61; 83]. Changes in the partitioning of absorbed light energy and the inhibition of plant grow (Figure 3) are most likely induced by the appearance of UVA; although, the addition of UVA can play a positive role in plant development [81]. Later, plants acclimatize to the action of a stress factor, which is reflected in the restoration of the activity of the photosynthetic apparatus. Photoconversion films speed up this process, making it easier for the plant to withstand stress. The different rates of the restoration of the initial activity of the photosynthetic apparatus may be due to the slow establishment of a balance between electron transport and NADPH in control plants, as well as different degrees of damage to the water-oxidizing complex of photosystem II in control and experimental plants [84]. It is not elucidated that minor alterations in the light spectrum (in light deficiency conditions) (Figure 3B) can increase in the rate of the adaptation processes of plants. Figure 5 demonstrates that after 30 min of adaptation to various actinic light conditions, Y(II) and Y(NPQ) in plants growing under photoconversion film remained relatively stable with increasing AL intensity to comparably high light intensity (in contrast to plants growing under common film). It can be presumed that plants growing under photoconversion films develop resistance to the inhibitory effects of light. It was shown that plants, which adapted to weak illumination, demonstrated the limited ability to acclimate, and experienced photoinhibition after exposition to high light [85]. Thus, it can be suggested that films containing upconversion luminophores can contribute to the acquisition by plants of properties that allow the plant to more effectively adapt to the ultraviolet and high light.