Functional composition has stronger impact than species richness on carbon gain and allocation in experimental grasslands.

Christiane Roscher,Olivier Ravel,Tanja Strecker,Gerd Gleixner,Stefan Karlowsky,Perla Mellado-Vázquez,Annette Jesch,Dörte Bachmann,Nina Buchmann,Markus Lange,Arthur Gessler,Jacques Roy,Damien Landais,Alexandru Milcu

doi:10.1371/journal.pone.0204715

Abstract

Numerous experiments have shown positive diversity effects on plant productivity, but little is known about related processes of carbon gain and allocation. We investigated these processes in a controlled environment (Montpellier European Ecotron) applying a continuous 13CO2 label for three weeks to 12 soil-vegetation monoliths originating from a grassland biodiversity experiment (Jena Experiment) and representing two diversity levels (4 and 16 sown species). Plant species richness did not affect community- and species-level 13C abundances neither in total biomass nor in non-structural carbohydrates (NSC). Community-level 13C excess tended to be higher in the 16-species than in the 4-species mixtures. Community-level 13C excess was positively related to canopy leaf nitrogen (N), i.e. leaf N per unit soil surface. At the species level, shoot 13C abundances varied among plant functional groups and were larger in legumes and tall herbs than in grasses and small herbs, and correlated positively with traits as leaf N concentrations, stomatal conductance and shoot height. The 13C abundances in NSC were larger in transport sugars (sucrose, raffinose-family oligosaccharides) than in free glucose, fructose and compounds of the storage pool (starch) suggesting that newly assimilated carbon is to a small portion allocated to storage. Our results emphasize that the functional composition of communities is key in explaining carbon assimilation in grasslands.

Highlights

Over the last years, numerous studies have accumulated evidence that loss of plant species diversity impairs ecosystem functioning [1]
In a previous study we have shown that gross and net ecosystem C uptake rates were higher at increased species richness and that higher leaf area index (LAI) and diversity in leaf nitrogen concentrations were most important in explaining positive diversity effects [27]
Among the terms determining canopy leaf N, i.e. total leaf area, communityweighted means in specific leaf area (SLA) and NLeaf, the relative importance of total leaf area was greatest compared to minor relative importance of Community-weighted trait means (CWM)-NLeaf and CWM-SLA

Summary

Introduction

Numerous studies have accumulated evidence that loss of plant species diversity impairs ecosystem functioning [1]. It has been verified that the effects of increasing plant diversity on the biomass production of individual species are highly variable and range from positive, over neutral to negative effects Leaves in different positions of the canopy have different physiological potentials, which are finely tuned to the prevalent light conditions [11]. This acclimation in photosynthetic capacity involves variation in a range of leaf traits between the bottom and the top of the canopy, such as leaf N concentrations, specific leaf area or stomatal conductance [12,13,14]. Identifying which plant functional traits most affect the species-level carbon gain in mixed plant communities could help to better understand the ecophysiological basis of varying responses of different species or functional groups to plant diversity

Methods

Results

Discussion

Conclusion