The accumulation of toxic elements poses a significant threat to terrestrial ecosystems, with the patterns and influencing factors of this accumulation being complex. However, elevational patterns of toxic elements in montane ecosystems, along with the underlying drivers, have largely been unexplored.

In a study published in Ecological Indicators, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences provided clear insights into the concept that changes in elevational gradients driven by shifts in climate and vegetation play a pivotal role in altering the patterns of toxic elements accumulation in montane ecosystems.

Researchers performed a thorough literature review to analyze prior studies comprehensively, aiming to discern the distribution patterns and determinants of toxic elements across various elevational gradients.

Researchers determined that atmospheric deposition plays a pivotal role in the accumulation of toxic elements along terrestrial altitude gradients. Aerosols, fine particulate matter, and minute toxic substances are carried through the atmosphere from proximate or distant point sources such as industrial chimneys. Notably, atmospheric deposition demonstrates seasonal fluctuations, with elevated deposition rates observed during summer and winter.

Moreover, researchers found that the accumulation patterns of individual toxic elements showed variability. Certain elements displayed an increase in concentration along elevational gradients, whereas others exhibited a decrease. Approximately 10% of the elements presented hump-shaped distributions, while 20% lacked discernible patterns.

Wind-borne, long-transboundary toxic elements could settle on foliage, subsequently accumulating in the soil through mechanisms such as throughfall and litter decomposition. Climatic variations along elevational gradients established a microclimate that augments the cold trapping of these toxic elements in the atmosphere, which notably promoted their wet deposition via precipitation, dew, or frost.

Furthermore, atmospheric deposition, human activities, and precipitation were revealed to be the main factors affecting the accumulation of toxic elements. Seasonal variability, especially between summer and winter, also modulated the deposition rates (both wet and dry) of toxic elements. Researchers pointed out that toxic elements pose significant risks to terrestrial biota and may profoundly affect litter decomposition and nutrient cycling.

“In order to protect the biodiversity, further research on how toxic elements affect ecosystem function as well as the corresponding protective measures is needed,” said XU Guorui from XTBG.

Sources of toxic elements in terrestrial ecosystems. (Image by XU Guorui)