A novel proxy to examine interspecific phosphorus facilitation between plant species.

Resource complementarity can contribute to enhanced ecosystem functioning in diverse plant communities, but the role of facilitation in the enhanced complementarity is poorly understood. Here, we use leaf manganese concentration ([Mn]) as a proxy for rhizosheath carboxylate concentration to explore novel mechanisms of complementarity mediated by phosphorus (P) facilitation. In pot experiments, we showed that mixtures involving Carex korshinskyi, an efficient P-mobilizing species, exhibited greater biomass and relative complementarity effect than combinations without C. korshinskyi on P-deficient soils. Compared with monocultures, leaf [Mn] and [P] of species that are inefficient at P mobilization increased by 27% and 21% when grown with C. korshinskyi (i.e. interspecific P facilitation via carboxylates) rather than next to another inefficient P-mobilizing species. This experimental result was supported by a meta-analysis including a range of efficient P-mobilizing species. Phosphorus facilitation enhanced the relative complementarity effect in low-P environments, related to a greater change in several facilitated species of their root morphological traits relative to those in monoculture. Using leaf [Mn] as a proxy, we highlight a vital mechanism of interspecific P facilitation via belowground processes and provide evidence for the pivotal role of P facilitation mediated by the plasticity of root traits in biodiversity research.

Mycorrhizal associations change root functionality: a 3D modelling study on competitive interactions between plants for light and nutrients.

Recent studies show that the variation in root functional traits can be explained by a two-dimensional trait framework, containing a 'collaboration' axis in addition to the classical fast-slow 'conservation' axis. This collaboration axis spans from thin and highly branched roots that employ a 'do-it-yourself' strategy to thick and sparsely branched roots that 'outsource' nutrient uptake to symbiotic arbuscular mycorrhizal fungi (AMF). Here, we explore the functionality of this collaboration axis by quantifying how interactions with AMF change the impact of root traits on plant performance. To this end, we developed a novel functional-structural plant (FSP) modelling approach that simulates plants competing for light and nutrients in the presence or absence of AMF. Our simulation results support the notion that in the absence of AMF, plants rely on thin, highly branched roots for their nutrient uptake. The presence of AMF, however, promotes thick, unbranched roots as an alternative strategy for uptake of immobile phosphorus, but not for mobile nitrogen. This provides further support for a root trait framework that accommodates for the interactive effect of roots and AMF. Our modelling study offers unique opportunities to incorporate soil microbial interactions into root functionality as it integrates consequences of belowground trait expression.

Leaf litter quality drives litter mixing effects through complementary resource use among detritivores.

To comprehend the potential consequences of biodiversity loss on the leaf litter decomposition process, a better understanding of its underlying mechanisms is necessary. Here, we hypothesize that positive litter mixture effects occur via complementary resource use, when litter species complement each other in terms of resource quality for detritivores. To investigate this, monocultures and mixtures of two leaf litter species varying in quality were allowed to decompose with and without a single macro-detritivore species (the terrestrial woodlice Oniscus asellus). Resource quality of the mixture was assessed by the mean concentration, the dissimilarity in absolute and relative concentrations, and the covariance between nitrogen (N), phosphorus (P) and calcium (Ca) supply. Our results clearly show that litter mixing effects were driven by differences in their resource quality for detritivores. In particular, complementary supply of N and P was a major driver of litter mixing effects. Interestingly, litter mixing effects caused by the addition of woodlice were predominantly driven by N dissimilarity, whereas in their absence, increased P concentration was the main driver of litter mixing effects. These results show that ultimately, litter diversity effects on decomposition may be driven by complementary resource use of the whole decomposer community (i.e., microbes and macro-detritivores).