Particulate Matter Fluxes in a Mediterranean Mountain Forest: Interspecific Differences Between Throughfall and Stemflow in Oak and Pine Stands

Abstract

In forested areas, canopies play an important role in the partitioning of rainfall. During this process there is also a redistribution of particulate matter (PM) that is deposited from the atmosphere on vegetative surfaces and transported to soil layers by throughfall and stemflow. We collected samples of rainfall, throughfall, and stemflow from two different forest plots (pine and oak) in a Mediterranean mountainous area and analyzed the amount and size distributions of PM (0.45 μm < PM < 500 μm). The exploration of backward trajectories revealed that PM content varied significantly. This depended on the origin of the air mass, with Atlantic fronts transporting less PM in the atmosphere than North African dust intrusions, which added disproportionate inputs of PM. Overall, throughfall provided the largest proportion of incoming PM under trees, but, at the base of each tree, stemflow led to a localized input of water that was more PM enriched than water through open precipitation or throughfall. Interspecific differences in PM fluxes were noted with pines retaining more PM in their crowns than oaks. Furthermore, the presence of leaves on oak increased the size and the amount of particulates released by throughfall. The PM in stemflow was smaller and rounder than in throughfall. This study adds to our understanding knowledge of the processes that control the deposition and distribution of PM delivered to forest soils, a fraction that is often ignored in studies of nutrient and energy fluxes in ecosystems.

Assessing the efficacy of eDNA metabarcoding for measuring microbial biodiversity within forest ecosystems

“…Take for example the global-scale transport of nearly 40 million tons of dust particulates per year originating in the Bodel´e depression in the Sahara Desert in Africa and ending up in North and South America 106 . This phenomenon, driven by multiple factors including topography, seasonal patterns in global weather and prevailing winds, all of which are influenced by climate change, are known to transport significant amounts of mineral and trace nutrient inputs to the Amazon rainforest in South America 107,108 , and in general, hold important implications for nutrient inputs into forests 109 . Given the overwhelming support of the bioprecipitation hypothesis 70,[110][111][112] , it is likely that sampling Saharan dust, for example, using the eDNA metabarcoding approach set forth here, would yield a treasure trove of microbial community data, and would build upon findings from previous studies 101,113 to provide further insight into global-sale macroecological dynamics of interconnected yet geographically disparate biomes.…”

Throughfall and stemflow are major hydrologic highways for particulate traffic through tree canopies

“…The only estimate known to the authors for annual stemflow particulate flux is for the 0.45–500 µm size fraction (1.5–2.4 kg ha –1 yr –1 ) (Cayuela et al . 2019). The coarse particle contribution to annual stemflow particulate flux is currently unknown (Figure 5).…”

“…As a result of pre-storm conditions, physicochemical factors, and organismal adaptations, some proportion of particulates washes from canopies to the soil in throughfall and stemflow (Cayuela et al 2019). Research simulating the mobilization of nonliving particulates with rainfall indicates that 30-86% of particulates <2.5 µm can be washed from canopy surfaces (Chen et al 2017).…”

“…Mobilization is, however, a complex process, with the likelihood that particulates will be mobilized dependent on atmospheric factors, canopy and particle characteristics, and accumulated particulate mass (Figure 3). Both in controlled experiments and field settings, particulates >2.5 µm represent the largest proportion of particulate mass collected in rinse, throughfall, and stemflow waters (Cayuela et al 2019). Furthermore, most particulates are washed from trees within the first 15 minutes of rainfall, with higher intensity storms being more effective at initiating particulate movement and removal from plant surfaces due to the larger diameter and kinetic energy of rainfall drops (Xu et al 2017).…”

“…Throughfall particulates may influence other nutrient cycles as well (Figure 5): 24-47 kg ha -1 yr -1 of mineral dust (Lequy et al 2014), 7 kg ha -1 yr -1 of radioactive particles when present (Kato et al 2012), and 1 kg ha -1 yr -1 of black C (Figure 5) have been delivered via hydrologic highways from canopy to forest floor in these temperate forest sites. The only estimate known to the authors for annual stemflow particulate flux is for the 0.45-500 µm size fraction (1.5-2.4 kg ha -1 yr -1 ) (Cayuela et al 2019). The coarse particle contribution to annual stemflow particulate flux is currently unknown (Figure 5).…”