Leaf digestibility and litter decomposability are related in a wide range of subarctic plant species and types

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Abstract
Summary: Herbivory and litter decomposition are key controllers of ecosystem carbon and nutrient cycling. We hypothesized that foliar defences of plant species against vertebrate herbivores would reduce leaf digestibility and would subsequently, through ‘afterlife effects’, reduce litter decomposability. We tested this hypothesis by screening 32 subarctic plant species, belonging to eight types in terms of life form and nutrient economy strategy, for (1) leaf digestibility in cow rumen juice; (2) biochemical and structural traits that might explain variation in digestibility; and (3) litter mass loss during simultaneous incubation in an outdoor subarctic litter bed. Interspecific variation in green‐leaf digestibility corresponded significantly with that in litter decomposability; this relationship was strongly driven by overall variation among the eight plant types (r = 0·92). The same relationship was not detectable within plant types in taxonomic relatedness tests. Several biochemical and structural parameters (phenol‐to‐N ratio, lignin‐to‐N ratio) explained a significant part of the variation in leaf digestibility, but again only between and not within plant types. Our results provide further support for the role played by foliar defence in the link between plant and soil via the decomposition pathway. They are also a new example of the potential control of plant functional types over carbon and nutrient dynamics in ecosystems.