Microstructural regulation of seasonal organic nitrate accumulation on pine needle surfaces

This study investigates the microregulatory mechanisms governing seasonal variations in particle-bound organic nitrates (PBONs) accumulation on pine needle surfaces. Using scanning electron microscopy, atomic force microscopy, and high-resolution mass spectrometry across five sites in the Changbai Mountain Nature Reserve, we revealed that seasonal transformations in epicuticular wax properties directly control PBON retention. Winter conditions produced maximum wax thickness (5.82 ± 0.47 μm) and PBON concentrations (142.6 ± 18.3 ng/g), while summer showed minimums for both (2.73 ± 0.55 μm; 56.4 ± 9.7 ng/g). We identified temperature as the dominant environmental factor (r = −0.81) with a previously unreported threshold effect at 4.8 ℃, below which PBON accumulation rates accelerate significantly. Structural equation modeling revealed that seasonal conditions influence PBON accumulation through both direct atmospheric pathways and surface-mediated mechanisms. The findings demonstrate that microstructural changes in sampling surfaces are crucial for interpreting seasonal biomonitoring data and understanding pollutant dynamics in forest ecosystems.