ВЛИЯНИЕ НИЗКОЙ НОЧНОЙ ТЕМПЕРАТУРЫ ВОЗДУХА НА ФЛУКТУИРУЮЩУЮ АСИММЕТРИЮ ЛИСТОВЫХ ПЛАСТИН ЧЕРЕМУХИ ОБЫКНОВЕННОЙ

The foliation process in a tree is influenced by temperature, illumination, atmospheric CO2 level, and air humidity. These factors affect the rate of transpiration. According to the Global Carbon Budget at COP29/, global greenhouse gas emissions could be 2,5% higher in 2024 than in 2023, contributing to a significant increase in atmospheric temperatures. An early start to the growing season is known to result in plant damage in the event of spring frosts. An early spring in Central and Northern Europe in 2018 contributed to increased vegetation growth and increased summer drought. The night temperature fluctuations cause inhibition of growth of both stems and leaf blades and affect the formation of their morphological structures. It is known that positive night temperatures stimulate the consumption of nutrients for respiration and promote metabolism, increasing the biomass of leaf blade tissue. Low (even negative) temperatures at night lead to weakening of respiration, and often to damage the leaves of many woody plants.

The fluctuating asymmetry (FA) is a minor fluctuation in the difference in the values ​​of bilaterally symmetrical structures, including metric features. FA is considered an indicator of developmental instability. According to Valkam Ya. and Kozlov M.V. (2001), the coldest summer periods of 1993-2000 on the Kola Peninsula caused a decrease in the developmental stability of mountain birch (Betula pubescens subsp. czerepanovii (N.I. Orlova, Hamet-Ahti), while the temperature factor was no less significant than the anthropogenic pollution factor

Bird cherry (Prunus padus L.) is not the most valid bioindicator of anthropogenic pollution of the environment compared to other tree species; its use requires improvement of the methodology for assessing the stability of development using FA indices

The previous studies show that in northern populations of the Kola Peninsula, the shape of the bird cherry leaf blades varies to a greater extent than their asymmetry. Moreover, northern populations did not show increased fluctuating asymmetry

We used digitized herbarium collected in 2021-2024 in Elektrostal, Moscow Region. Ten leaves from five trees of approximately the same age but with different leaf blade sizes were examined. The width of the left and the right halves of each leaf blade was measured three times using a TPSDIG2 digitizer. The day and night temperatures in May were obtained from the GOSMETEO archive. To determine temperature variations, the difference between day and night date (average daily air temperature) was found and the variation coefficient of these values ​​was determined.

The fluctuating asymmetry was found in a two-factor ANOVA for the significance of the interaction of the factors "leaf × side". The FA10 index was obtained for each population, the probability level p was adjusted using the Bonferroni method, i.e. the least significant index was assigned the level p = 0,05. Directional asymmetry was tested by the null hypothesis H0: L = R in a two-factor ANOVA for the significance of the factor "side". The normality of the samples was tested by the Shapiro-Wilk test using an online calculator. The significance level in the methods of probability statistics was α = 0,95.

The test for normality of temperature data distribution did not reveal any deviations (Shapiro test p> 0,05).

The greatest width of leaf blades was noted in 2023 and 2024. The directional asymmetry was present in leaf collections of 2022 and 2023 with a high significance of the "side" factor (p<<0,05).

Allometric correlation between the value of the trait and FA was not carried out. A statistically significant difference was obtained for May night temperatures in the period 2021-2024. The lowest average monthly temperature in May was noted in 2022 (6,2°C) and 2024 (6,7°C) (Fig. 1).

Figure 1 - Results of one-way ANOVA

Note: nighttime temperature values ​​(OY axis) were statistically different in May 2021-2024 (p = 0,001). Leaves collected in 2022 and 2024 showed a significant FA index (highlighted with an asterisk)

DOI:10.60797/jbg.2024.26.8.1

The coefficients of variation of nighttime air temperatures by years: 2021 – CV = 0,36; 2022 – CV = 0,50; 2023 – CV = 0,58; 2024 – CV = 0,67. The high variance in the distribution of nighttime temperatures data were also noted: in 2024 (s2 = 19,83), the lowest in 2022 (s2 = 9,85). The negative skew in 2022 indicated a shift towards low temperatures. The study revealed the influence of night temperature fluctuations on the fluctuating asymmetry of the leaves. Bird cherry, like all plants, possess a reaction norm. It is a frost-resistant species. However, the temperature difference from +13°C (May 1) to -1°C (May 4) in 2024 should be considered a serious factor that led to the fluctuation in the formation of leaf blades, an increase in FA and, as a consequence, a change in the developmental stability.

The climate change on Earth is leading to higher night temperatures in some regions, such as tropical forests. Thermomorphogenesis of plants is associated with increased respiration at night

We classify the past frosts as the radiation frosts, typical for nighttime, which appear as a result of the passage of an anticyclone from the north. As a result, there was a strong supercooling of the soil's surface. Such weather anomalies were caused by the movement of cold masses due to the unusual movement of cyclones: to the west and to the east of Moscow. This contributed to the drawing in of cold air from the territories of the Far North.

Similar frosts recorded in Germany in 2011 showed a high percentage of damage to deciduous trees against the background of a shift in phenological dates to earlier dates in the context of global warming

According to Hufkens K. et al., post-leaf frosts will become more common with climate change and may affect both the composition of European forests and ecosystem productivity