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 ∂¹⁵N 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.

Keywords: floral traits; marine-derived nutrients; meta-ecosystem; nitrogen; subsidy.

Figure 1.

The four focal plant species: (a) yarrow (Achillea millefolium, Asteraceae), (b) Douglas' aster (Symphyotrichum subspicatum, Asteraceae), (c) common red paintbrush (Castilleja miniata, Orobanchaceae) and (d) silverweed (Potentilla anserina, Rosaceae).

Figure 2.

Leaf δ¹⁵N in relation to the four treatments in the four plant species. Points indicate the raw data overlaid by the modelled least-squares means with 95% confidence intervals in black, averaged across years (N = 629).

Figure 3.

The logarithm of the estimated leaf area (mm²) in relation to the four treatments in the four plant species. Points indicate the raw data in link space overlaid by the modelled least-squares means with 95% confidence intervals in black, averaged across years (N = 2180).

Figure 4.

The logarithm of the estimated floral display area (mm²) in relation to the four treatments in the four plant species. Points indicate the raw data in link space overlaid by the modelled least-squares means with 95% confidence intervals in black, averaged across years (N = 1337).

Figure 5.

Estimated seed set in relation to the four treatments in the four plant species. Points indicate the raw data in link space overlaid by the modelled least-squares means with 95% confidence intervals in black, averaged across years (N = 1458).