Evaluation of arbuscular mycorrhiza colonization and photosynthetic pigment content in Haloxylon ammodendron var. aphyllum under arid conditions

Abstract

Introduction. Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with the root systems of many plants, including trees and shrubs, enhancing growth, productivity, and protection against biotic and abiotic stresses. However, data on AMF distribution and community dynamics remain limited, and the adaptive mechanisms of Haloxylon ammodendron var. aphyllum to arid conditions in relation to rhizosphere endophytes, particularly regarding photosynthetic pigment dynamics in its assimilative shoots, require further investigation. Purpose of the research. Evaluation of AMF colonization intensity in the root system and photosynthetic pigment content in the green shoots of H. ammodendron var. aphyllum growing in the Astrakhan region before and during drought. Materials and methods. The content of photosynthetic pigments in the assimilative shoots of H. ammodendron var. aphyllum was determined spectrophotometrically in acetone extracts, calculating the concentrations of chlorophylls a and b and carotenoids, as well as their ratios. Colonization of the root system by arbuscular mycorrhizal fungi was assessed after staining root segments with trypan blue, followed by microscopy and calculation of standard parameters (F%, M%, m%, a%, A%) according to the Trouvelot method. Research results and discussion. The study found that in H. ammodendron var. aphyllum under drought conditions from May to July, the content of chlorophylls a and b decreased by 2–3 times, and the ratio of total chlorophylls to carotenoids decreased by 23%, indicating a decline in photosynthetic apparatus activity. Parameters of AMF root colonization also decreased: mycorrhizal frequency by 13%, root and fragment colonization intensity by 3.6 times, and arbuscule abundance by 6 and 4.5 times. Correlation analysis revealed multidirectional relationships between pigments and mycorrhization parameters: in May, a negative correlation was found between arbuscule abundance and chlorophyll b (r = -0.78); in June, positive correlations were observed with root system colonization intensity; in July, positive correlations were found between mycorrhizal frequency and chlorophyll a (r = 0.76), carotenoids (r = 0.75), and total chlorophylls (r = 0.70), along with a negative correlation between intensity of colonization in the mycorrhizal root fragments and the chlorophylls ratio (r = -0.67). Conclusion. The study revealed that in H. ammodendron var. aphyllum under drought conditions, by July there was a significant decrease in the content of photosynthetic pigments and the intensity of AMF root colonization, with maximum values observed in May. Correlation analysis revealed significant relationships between the parameters under study, indicating the presence of mutualistic interactions and reflecting the species-specific nature of the plant's adaptive responses to drought stress.