Experimental addition of marine-derived nutrients affects wildflower traits in a coastal meta-ecosystem

Abstract

Organismal movement can bring individuals, resources and novel interactions across ecosystem boundaries and into recipient habitats, thereby forming meta-ecosystems. For example, Pacific salmon ecosystems receive large marine-derived nitrogen subsidies during annual spawning events, which can have a wide range of effects on aquatic and terrestrial plant species and communities. In this study, we evaluate the effects of cross-ecosystem nutrient subsidies on terrestrial plant growth and reproduction. We conducted a large-scale field experiment with four treatments: (i) addition of a pink salmon ( Oncorhynchus gorbuscha ) carcass, (ii) addition of the drift seaweed rockweed ( Fucus distichus ), (iii) addition of both salmon + rockweed, and (iv) a control. We examined treatment effects on leaf nitrogen and fitness-associated floral traits in four common estuarine wildflower species. We found elevated leaf ∂ 15 N in all plant species and all sampling years in treatments with salmon carcass additions but did not observe any differences in leaf per cent nitrogen. We also observed larger leaf area in two species, a context-dependent increase in floral display area in two species, and a limited increase in plant seed set in response to both salmon carcass treatments. In sum, our study suggests that marine nutrients can affect terrestrial plant growth and reproduction.

Nutrients from spawning salmon influence leaf area, tissue density, and nitrogen‐15 in riparian plant leaves

“…Some prior work in our study region has shown a positive relationship between salmon density and percent nitrogen only in nitrogen indicator species such as salmonberry and false lily‐of‐the‐valley (Hocking & Reynolds, 2011), and other research showed relationships between salmon and percent nitrogen in false azalea and salmonberry using comparisons above and below waterfalls on a limited number of salmon‐bearing rivers (Mathewson & Reimchen, 2003). Conversely, experimental evidence found no relationship between salmon carcass deposition and foliar percent nitrogen in estuarine meadow plants (Dennert et al., 2023). Plant elemental composition can vary due to competition, subsidies, and nutrient limitation (Sterner & Elser, 2002), and we may only observe changes in elemental composition during excess nutrient deposition, resulting in luxury (or excess) consumption of this nutrient (Ågren, 2008; Chapin, 1980).…”

“…Moreover, leaf tissues are more likely to respond to changes in nutrient availability than other above-or belowground tissues (Chapin, 1980;Marschner, 1995). Prior work in the region has also found a relationship between salmon carcass deposition and flowering plant leaf size (Dennert et al, 2023), and work across the Pacific northwest has found a relationship between salmon, tree growth, and forest productivity (Brown et al, 2020;Kieran et al, 2021;Quinn et al, 2018;Reimchen & Arbellay, 2019;Reimchen & Fox, 2013).…”

“…We predicted that plants growing in watersheds with higher salmon density would have higher leaf nitrogen content, both in the marine-derived isotope nitrogen-15 and in their percent nitrogen content (Hocking & Reynolds, 2011Mathewson & Reimchen, 2003;Wilkinson et al, 2005). Next, building on prior work indicating that one of our study species has more leaf stomata in areas of high salmon spawning density (van den Top et al, 2018), we predicted that plants on the banks of salmon-dense watersheds would have an elevated photosynthetic capacity or rate, which would be seen in higher leaf greenness (Brown et al, 2020;Hultine & Marshall, 2000;Kieran et al, 2021) and larger leaf area (Dennert et al, 2023). Larger leaf area may be coupled with a lower leaf mass per area as is commonly seen in fertile soils (Poorter et al, 2009).…”

“…Subsidies from spawning Pacific salmon have been shown to influence a variety of taxa, from plants (Ben‐David et al., 1998 ; Hocking & Reynolds, 2011 ), to aquatic and terrestrial invertebrates (Hocking et al., 2009 , 2013 ), to birds (Christie & Reimchen, 2008 ; Field & Reynolds, 2011 ). The effects of salmon subsidies are varied (reviewed by Walsh et al., 2020 ), ranging from organismal abundance and behavior (Wilcox et al., 2021 ) to community composition (Hurteau et al., 2016 ), phenology (Lisi & Schindler, 2011 ), and even reproductive effort (Dennert et al., 2023 ). Plant communities are particularly affected by nutrient subsidies, as they intersect the abiotic and biotic components of ecosystems.…”

Legacy of salmon-derived nutrients on riparian soil chemistry and soil fertility on the Central Coast of British Columbia, Canada

“…These nutrients permeate stream environments, increasing aquatic nutrient loads (Levi et al, 2013); biofilm and plankton biomass (Collins et al, 2015); and change fish abundance, individual fish biomass, behavior, and spawning success (Swain and Reynolds, 2015;Collins et al, 2016). Salmon presence also affects nearby terrestrial sites by changing plant communities and increasing the abundance of nitrophyllic plant species (Mathewson et al, 2003;Hocking and Reynolds, 2011); increasing plant growth, fruit growth, and other plant traits (Sayer, 2008;Quinn et al, 2018;Siemens et al, 2020;Dennert et al, 2023); and increasing bird diversity and abundance (Christie and Reimchen, 2008;Wagner and Reynolds, 2019). In addition, their carcasses provide food for numerous large mammals such as bears and wolves (Hocking et al, 2009;Reimchen, 2017), small mammals such as mink and river otter (Dolloff, 1993;Ben-David et al, 1997), and insects (Hocking and Reimchen, 2006;Hocking et al, 2009;Reimchen, 2017;Rammell et al, 2021).…”