Abstract
Abstract Vascular plants and lichens often produce a diversity of carbon‐based secondary compounds (CBSCs) to protect them against biotic and abiotic stresses. These compounds play important but often compound‐specific roles in community and ecosystem processes by affecting herbivore and decomposer activity. However, our understanding of what drives community‐level CBSCs among ecosystems or across environmental gradients is limited. We measured concentrations and compositions of CBSCs for all dominant vascular plant and lichen species present across a 500‐m alpine elevational gradient. These measurements were combined with data on species composition and abundance to obtain whole‐community measures of plant and lichen CBSCs across the gradient. At the whole community level, plant CBSCs had the lowest concentrations while lichen CBSCs had the highest concentrations at the highest elevations. Further, plant CBCSs shifted from those associated with herbivore defence towards those protecting against light and oxidative stress as elevation increased, while lichen CBSCs showed the opposite pattern. Synthesis. Our findings that individual compounds show contrasting responses to the same environmental gradient highlight the importance of studying qualitative as well as quantitative changes in CBSCs. Further, the divergent responses between vascular plants and lichens reveal that in systems where both groups are abundant, they need to be considered simultaneously to better understand how future environmental changes may impact on ecosystem‐level processes. A free Plain Language Summary can be found within the Supporting Information of this article.
Highlights
Both vascular plants and lichens have evolved a high variety of secondary compounds, as defence against herbivores (e.g. Coley et al, 1985; Gauslaa, 2005), pathogens (Witzell & Martín, 2008), oxidative stress and light damage (Close & McArthur, 2002)
We show that responses of plant and lichen carbon-based secondary compounds (CBSCs) to elevation at the whole community level is compound-specific
These compound-specific changes can to some extent be understood from a functional perspective, that is, the shift from those associated with protection against herbivory at lower elevations to those associated with protection from oxidative stress at higher elevations, this pattern was less pronounced for lichens
Summary
Both vascular plants and lichens have evolved a high variety of secondary compounds, as defence against herbivores (e.g. Coley et al, 1985; Gauslaa, 2005), pathogens (Witzell & Martín, 2008), oxidative stress and light damage (Close & McArthur, 2002). | Functional Ecolo gy 331 the predominant type (Coley et al, 1985; Herms & Mattson, 1992). These compounds have after-life effects in senesced litter as they can inhibit decomposer activity and immobilize nitrogen (N) through protein complexation, and reduce plant-available N (Asplund et al, 2013; Fierer et al, 2001). Given the importance of secondary compounds in species-driven ecosystem processes, it is important to understand their effects at the whole community level. Only a few studies have considered community-level measures of secondary compounds and how they may vary among ecosystems or across environmental gradients (Kichenin et al, 2013; Siefert et al, 2015; Sundqvist et al, 2013)
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