Chlorine in plants and soils of a tropical lower montane forest in Ecuador: Development during two decades

Aims
Cl is a micronutrient mainly supplied via deposition of marine aerosols. We assessed the development of Cl concentrations and stocks in plants and soils of a tropical montane forest far from a downwind ocean during two decades (1998–2019).

Methods
We measured Cl concentrations in solid samples with a new combustion-based method.

Results
The Cl concentrations in leaves of 17 tree species ranged 0.04–1.6 g kg$^{−1}$. Three tree species showed Cl concentrations below the minimum requirement of 0.2 g kg$^{−1}$. Twigs had the largest Cl concentration of all plant compartments (2.1 ± SD1.5 g kg$^{−1}$) and leaves the smallest. The Cl concentrations decreased from litterfall (0.52 ± 0.14) to the soil organic layer (0.12 ± 0.06), within the organic layer from top to bottom and further in the mineral soil (0.02–0.03) reflecting leaching losses and the retention of Cl in soil organic matter. The parent rocks (metamorphic sand to clay stone interlayering) contained 0.44 ± 0.20 g kg$^{−1}$ Cl. The vegetation stored more Cl (28 ± 17 g m$^{−2}$) than the organic layer (2.9 ± 3.1) and mineral soil (fine earth 0–1 m, 22 ± 8.6) together. ... mehrOne meter of rock contained up to 168 g m$^{−2}$ Cl. Wood production took up 0.36 ± 0.24 g m$^{−2}$ yr$^{−1}$ Cl. Litterfall cycled 0.55 ± 0.17 g m$^{−2}$ yr$^{−1}$ Cl representing 86 ± 72% of the standing Cl stock in leaves (0.64 ± 0.50 g m$^{−2}$). The leaching potential of Cl$^−$ from leaves was likely < 10% of the reported Cl$^−$ bulk deposition of 1.2 g m$^{−2}$ yr$^{−1}$. There were no significant temporal trends of Cl concentrations in leaves, litterfall, organic layer, and mineral soil.