Intra-specific leaf trait variability controls leaf decomposition of Vitis vinifera L. cultivars in streams

The decomposition of leaf litter is a key ecological process in stream ecosystems. Leaf traits, variable across species and within species, constitute a prime driver of this process. Vitis vinifera, the most valuable horticultural crop in the world, represent a priviledged opportunity to assess the importance of intra-specific leaf variability on litter decomposition due to its high phenotypical diversity across cultivars. This study aims to assess the importance of leaf trait differences of four Vitis vinifera cultivars (Aragonez, Baga, Bical and Fernao Pires) on mass loss and microbial and detritivore descriptors, in a low order stream. Results indicate that leaf trait variability among cultivars is a main driver of leaf mass loss and microbial decomposers activity. Fungal sporulation rates were reduced in leaves from cultivars more defended by structural defenses—thoughness, higher leaf mass per area and trichomes density. Invertebrates’ structure and density of shredders responded to leaf N concentrations more than leaf structural descriptors. Macroinvertebrates seem to play a crucial role as decomposition facilitators, by accelerating fungal colonization and conidial release, particularly in cultivars endowed with a dense indumentum. Our results indicate that V. vinifera leaf litter is a high-quality substratum that may present narrow intra-specific leaf traits variability, determined by distinct cultivar genetics, which are able to modulate the litter decomposition process in streams. We suggest that further research assessing the effects of vegetation alterations on stream ecosystem functioning should include leaf litter intra-specific dissimilarities that, even when subtle, may propagate from terrestrial to aquatic systems with cascading impacts across the stream food chains.