Which habitat element has the critical impact on photosynthetic pigments, carbohydrates, and antioxidant defense in epiphytic mosses?

Mosses, as an essential component of the Hyrcanian Forest ecosystem, are influenced by various ecological factors. The current study aimed to investigate the role of habitat elements on the concentration of photosynthetic pigments, carbohydrates, antioxidant compounds, and antioxidative enzymes activity in three native epiphytic moss species from the Neckeraceae family: Forsstroemia remotifolia, Homalia besseri, and Neckera complanata. The mosses were collected from the Hyrcanian Forest in Golestan Province, northern Iran, along three bands of an elevational transect with different climatic conditions. The results revealed that in H. besseri and F. remotifolia the metabolite concentrations and antioxidative enzyme activities were not correlated with elevation or associated climatic factors. Instead, they were strongly influenced by the characteristics of their host trees. Notably, the patterns of change in metabolites including chlorophyll a and b, soluble carbohydrates, proteins, phenols, and the activity of antioxidative enzymes such as superoxide dismutase (SOD) and peroxidase were similar in these two moss species, regardless of whether they were collected from low or high elevations. This similarity may be attributed to their common host tree, Parrotia persica. It appears that the host tree plays a significant role in shaping the mosses’ metabolite profiles particularly through traits such as bark thickness and pH. In contrast, the metabolite composition in N. complanata, including photosynthetic pigments, soluble proteins, flavonols, and SOD activity, was influenced by both the host tree and elevation. Moreover, N. complanata exhibited different responses to host tree features (bark thickness and pH) compared to H. besseri and F. remotifolia. This study concludes that host tree characteristics play a pivotal role in modulating the physiological responses of epiphytic mosses, revealing species-specific sensitivities to elevational gradients. The findings emphasize the intricate interaction between host bark traits and abiotic environmental factors in shaping moss metabolism within the Hyrcanian Forest ecosystem.