3 June 2024

This is how canopies affect the distribution of soil nutrients


Chinese research analyzed nutrient precipitation dynamics by identifying and quantifying soil enrichment mechanisms in relation to climate and vegetation

by Matteo Cavallito


The aerodynamic characteristics of tree canopies, especially during growth periods, affect the mechanisms of nutrient transport from rainwater to the soil. This is highlighted in a study published in the journal Science China Earth Sciences.

Precipitation, the authors recall in a statement, “deeply couples with nutrient cycling through its interactions with atmospheric deposition and canopy interception, which alters its own chemical properties.” Once precipitated into the soil, these elements affect community structure and the ecosystem as a whole. The mechanisms that affect their transport and impact, however, are still poorly understood.

Rain and nutrients

Scientists from several academic institutions including Zhejiang, Hebei, Sichuan, Yunnan Universities, Beijing Normal University, the Northwest Institute of Eco-Environment and Resources in Lanzhou, and the University of British Columbia in Kelowna, Canada, analyzed a thousand English and Chinese academic papers published in the 21st century. Focusing on the distribution mechanism favored by the interaction between rain and canopies, the authors identified key ions decisive for plant survival.

These include key elements and compounds such as potassium, sodium, calcium, magnesium, ammonium, chloride, nitrate and sulfites. They then calculated their concentrations and leaching coefficients.

“We aimed to synthesize the mechanisms, quantify the enrichments, and identify global patterns of nutrient enrichment in stemflow and throughfall across climate zones, and vegetation types and ecosystems,” the researchers explain.

Canopies primarily impact magnesium and potassium

Canopies, as is well known, intercept and retain some of the precipitation. Water that does not evaporate first flows through canopies and carries nutrients to the soil by dripping in two ways: through leaves and branches or along stems. The results of the study “indicate that stemflow exhibits, on average, 2.1 times greater ion concentration compared to throughfall.”

Specifically, “among the investigated ions, SO2−4 (12.45 and 6.32 mg L−1) for stemflow and throughfall, respectively, and Cl− (9.21 and 4.81 mg L−1) exhibit the highest concentrations in both rainfall redistribution components.”

Potassium ions (13.7 and 5.8 mg) and magnesium (5.6 and 2.8), on the other hand, “have the highest enrichment factors.” In summary, their presence in the soil is determined by the canopy precipitation mechanism to a greater extent in comparison with other elements or compounds.

Climate and humidity are factors to consider

On a global scale, humid regions at any latitude have the lowest ion concentrations and highest enrichment factors. The presence of ions is greatest in cold climates. Finally, “shrubs, conifers, mixed forests, and artificial ecosystems (such as urban and agricultural ecosystems, ed.) demonstrate enrichment factors 1.1 to 3.0 times greater than those of trees, broad- leaved plants, pure forests, and natural ecosystems.”

Future research, the scientists conclude, should also focus on soil moisture. Indeed, analysis of this peculiar factor, they note, would allow for a better understanding of the impact of precipitation redistribution on soil enrichment processes, patterns and nutrient balance in terrestrial ecosystems.