Abstract
The interaction of shortwave radiation with vegetation drives basic processes of the biosphere, such as primary productivity, species interactions through light competition, and energy fluxes between the atmosphere, vegetation, and soil. Here, we aim to understand the effects of leaf functional trait diversity on canopy light absorption. We focus on the diversity of three key functional traits that influence the light-canopy interaction: leaf area index (LAI), leaf angle distribution (LAD) and leaf optical properties (LOP). We used a 3D radiative transfer model to perform an in-silico biodiversity experiment to study the effects of leaf functional diversity on a light proxy for productivity (the fraction of absorbed photosynthetically active radiation (FAPAR)) and net radiation (shortwave albedo). We found that diverse canopies had lower albedo and higher FAPAR than the average of the corresponding monoculture values. In mixtures, FAPAR was unequally re-distributed between trees with distinct traits: some plant functional types absorbed more light and some plant functional types absorbed less than in monocultures. The net biodiversity effect on absorptance was greater when combining plant functional types with more distinct leaf traits. Our results support the mechanistic understanding of overyielding effects in functionally diverse canopies and may partially explain some of the growth-promoting mechanisms in biodiversity-ecosystem functioning experiments. They can further help to account for biodiversity effects in climate models.
Highlights
Plant functional traits underlie the interaction of plants with their biotic and abiotic environment, and are used to assess the structure, function, and diversity of ecosystems (Bodegom et al, 2014; Cadotte et al, 2011; Garnier et al, 2016; Mokany et al, 2008)
We focus on the diversity of three key functional traits that influence the light-canopy interaction: leaf area index (LAI), leaf angle distribution (LAD) and leaf optical properties (LOP)
We found the highest albedo change for the LAI trait, for the LAD trait (0–4%) and the lowest for the LOP trait (0.2–1.2%) on the natural background (Fig. 3a)
Summary
Plant functional traits underlie the interaction of plants with their biotic and abiotic environment, and are used to assess the structure, function, and diversity of ecosystems (Bodegom et al, 2014; Cadotte et al, 2011; Garnier et al, 2016; Mokany et al, 2008). Most experimental studies have shown that productivity increases with species diversity; mixed communities produce more yield than the average monoculture of the same species (“overyielding” effect (de Wit, 1960)). This relationship arises from interspecific niche complementarity, but the particular mechanisms remain unclear. Previous studies investigating effects of biodiversity on plant-light interactions were mainly based on field experiments and observational studies (Cardinale et al, 2006), and have shown that plant species mixtures (hereafter referred to as “mixtures”) typically absorb more light than monocultures in forest and grassland crop ecosystems (Bauhus et al, 2004; Binkley et al, 1992; Forrester et al, 2012; Gebru, 2015). A process-based physical model with accurate vegetation structure representation that tracks radiative fluxes could allow for directly linking plant functional diversity to the light environment, but to our knowledge, it has not been used so far
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