Atmospheric deposition of elements and its relevance for nutrient budgets of tropical forests

Abstract

Atmospheric deposition is an important component of the nutrient cycles of terrestrial ecosystems, but field measurements are especially scarce in tropical regions. In this study we analysed 15 months of precipitation chemistry collected in an old growth tropical forest located in French Guiana. We measured nutrient inputs via bulk precipitation and throughfall and used the canopy budget model to estimate nutrient fluxes via canopy exchange and dry deposition. Based on this method we quantified net fluxes of macronutrients and compared their contribution to internal cycling rates via litterfall. Our results suggest that while atmospheric deposition of nitrogen was relatively high (13 kg ha -1 y -1 ), and mainly in organic forms, the N inputs via litterfall were an order of magnitude higher. In contrast to nitrogen, we found that atmospheric deposition of phosphorus (0.5 kg ha -1 y -1 ) supplied up to one third of the annual litterfall input to the forest floor. Most strikingly, combined annual inputs of potassium via atmospheric deposition (14 kg ha -1 y -1 ) and canopy leaching (22 kg ha -1 y -1 ) were three times larger than internal nutrient recycling via litterfall (11 kg ha -1 y -1 ). We conclude that atmospheric deposition of phosphorus and especially potassium may play an important role in sustaining the productivity of this old-growth tropical rainforest.

Impact of Phytophthora agathidicida infection on canopy and forest floor plant nutrient concentrations and fluxes in a kauri‐dominated forest

“…Large buildup of organic matter (up to 2 m close to tree trunks) with resident times of up to 78 years (Silvester & Orchard, 1999) partly explains the lower nutrient return through litterfall. Similar findings have been reported from exotic conifer stands in New Zealand where throughfall reaching the soil under Douglas fir contained twice as much K as litterfall (Will, 1959), while atmospheric deposition plus canopy leaching delivered three times more K to the soil than the internal nutrient recycling via litterfall (van Langenhove et al, 2020). Nutrient input by throughfall and forest floor leachates may be critical in sustaining forest productivity, particularly in ecosystems characterized by low soil nutrient availability, such as kauri forests (Steward & Beveridge, 2010;Verkaik et al, 2006).…”

“…Solution collected underneath the forest floor (forest floor leachate) is often greatly enriched in nutrients compared to bulk precipitation and canopy water fluxes due to the leaching of nutrients from organic matter (Batjes, 1996). Nutrient transfer to the soil by throughfall deposition and forest floor leachates is an important input pathway, particularly in ecosystems where nutrient return through litterfall decomposition is slow (van Langenhove et al, 2020;Will, 1959) and in ecosystems with low soil nutrient availability (Forti & Moreira-Nordermann, 1991;Moslehi et al, 2019;Parker, 1983).…”

Direct foliar uptake of phosphorus from desert dust

“…Despite the spatial heterogeneity of its sources, desert dust is often highly enriched in P, with concentrations far higher than those in most soils (Bristow et al ., 2010; Gross et al ., 2015a). In ecosystems with poor soil P and high rates of dust deposition, yearly dust P inputs can be of the same magnitude as litterfall P inputs (Okin et al ., 2004; Gross et al ., 2015b; Van Langenhove et al ., 2020). Hence, dust deposition may support a large fraction of the ecosystems’ net primary productivity and P demand (Cleveland et al ., 2013; Runyan et al ., 2013; Wang et al ., 2017).…”

Impact of Nutrient Additions on Free‐Living Nitrogen Fixation in Litter and Soil of Two French‐Guianese Lowland Tropical Forests

“…Previous research in French Guiana, especially in Paracou, indicated that soil P stocks and soil extractable P are low (Allié et al., 2015; Sabatier et al., 1997; Soong et al., 2020). Additionally, a recent study of BNF and its drivers in French Guiana identified P as a regulating driver for soil BNF in Paracou, with higher soil P responsible for higher BNF rates (Van Langenhove et al., 2019). That same study, however, did not identify Mo as regulating driver for soil BNF, even though it clearly caused an increase in Nouragues soil BNF rates here (Figure 3a).…”

“…It is highly likely that the addition of P to the litter layer at least partially relieved the P constraints present in the litter, just as suspected by Vitousek and Hobbie (2000) and Reed et al (2013) in their respective studies. The global increase in P deposition (R. Wang et al, 2017), already measurable in French Guiana (Barkley et al, 2019;Van Langenhove et al, 2020), is thus likely to cause increases in litter BNF at our forest sites. As for Mo, the P fertilizer we added in the field contained Mo as a hidden trace element (<0.15 mg/kg), shedding doubt on the validity of our results following P additions (Barron et al, 2009).…”