Reaction of pigment complex in meadow clover leaves to weather conditions and macronutrients

In the field studies of 2018…2019, the influence of macronutrients and weather conditions on pigment complex of leaves of meadow clover (Trifolium pratense L.) Dymkovsky variety was assessed. The study was carried out in grainfallow-grass crop rotation in the conditions of Kirov region. Leaf samples (fully developed second or third leaf from above) were taken in the flowering phase, and the chlorophyll and carotenoids content were measured spectrophotometrically under laboratory conditions. It has been found that the content of pigments in the leaves of meadow clover depended mostly on weather conditions of the year of cultivation. The concentration of green pigments (Chl a+b) in clover leaves was in the range of 15.34...19.05 in the conditions of warmer and dry 2018 and 11.47...14.10 mg/g dry matter in colder and humid year of 2019. Chl a accounted for 9.64...11.36 and 6.67...7.98 mg/g (2018 and 2019, respectively). Colder conditions promoted an increase in the ratio of Chl a associated with light-harvesting complexes (from 69…78 up to 89…96 %). Weight content of carotenoids was 2.69...3.12 and 1.52…1.88 mg/g in 2018 and 2019, respectively, and correlated with the content of a total chlorophyll (r = 0.53…0.82). The weight ratio of chlorophylls a/b (1.54... 1.75 in 2018 and 1.18... 1.47 in 2019) indicates a lack of insolation in the conditions of mutually shading of leaves of the created phytocenosis. However, the weight ratio of the sum of chlorophylls to carotenoids (5.7... 6.7 in 2018 and 6.86... 9.65 in 2019) suggests that this abiotic factor has not led to disorders in the structure of the photosynthetic leaf apparatus. Weather conditions considerably modified influence of fertilizers on pigment synthesis: in 2018, nitrogen fertilizers reduced the content of chlorophylls by 11…22 %, full mineral fertilizer on acid soil background led to decrease in the content of pigments by 6.7…11.7 %. In colder conditions of 2019 nitrogen fertilizers did not influence the content of pigments, full mineral fertilizer increased the content of Chl a by 14.1…17.8 %, carotinoids – by 18.2…25.4 %. In the conditions of 2019 the content of Chl a significantly depended on nitrogen content in leaves (r = 0.52…0.92) and correlated with phosphorus level in the soil: for Chl a – r = 0.74 and 0.54, for Chl b r = 0.73 and 0.75 (acid soil background and soil background with lime application, respectively).