Plant diversity enhances production and downward transport of biodegradable dissolved organic matter

Markus Lange,Alexandru Milcu,Christiane Roscher,Liesje Mommer,Janneke Ravenek,Anke Hildebrandt,Nico Eisenhauer,Gerd Gleixner,Natalie J Oram,Odette González Macé,Alexandra Weigelt,Christine Fischer‐Bedtke,Stefan Scheu,Tanja Strecker,Cameron Wagg,Thorsten Dittmar,Vanessa‐Nina Roth,Bernhard Schmid

doi:10.1111/1365-2745.13556

Abstract

Abstract Plant diversity is an important driver of below‐ground ecosystem functions, such as root growth, soil organic matter (SOM) storage and microbial metabolism, mainly by influencing the interactions between plant roots and soil. Dissolved organic matter (DOM), as the most mobile form of SOM, plays a crucial role for a multitude of soil processes that are central for ecosystem functioning. Thus, DOM is likely to be an important mediator of plant diversity effects on soil processes. However, the relationships between plant diversity and DOM have not been studied so far. We investigated the mechanisms underlying plant diversity effects on concentrations of DOM using continuous soil water sampling across 6 years and 62 plant communities in a long‐term grassland biodiversity experiment in Jena, Germany. Furthermore, we investigated plant diversity effects on the molecular properties of DOM in a subset of the samples. Although DOM concentrations were highly variable over the course of the year with highest concentrations in summer and autumn, we found that DOM concentrations consistently increased with plant diversity across seasons. The positive plant diversity effect on DOM concentrations was mainly mediated by increased microbial activity and newly sequestered carbon in topsoil. However, the effect of soil microbial activity on DOM concentrations differed between seasons, indicating DOM consumption in winter and spring, and DOM production in summer and autumn. Furthermore, we found increased contents of small and easily decomposable DOM molecules reaching deeper soil layers with high plant diversity. Synthesis. Our findings suggest that plant diversity enhances the continuous downward transport of DOM in multiple ways. On the one hand, higher plant diversity results in higher DOM concentrations, on the other hand, this DOM is less degraded. This study indicates, for the first time, that higher plant diversity enhances the downward transport of dissolved molecules that likely stimulate soil development in deeper layers and therefore increase soil fertility.

Highlights

The loss of biodiversity (Barnosky et al 2011) has severe consequences for multiple ecosystem functions, such as reduced plant biomass production, soil organic matter (SOM) storage, and soil nutrient provision (Balvanera et al 2006; Hooper et al 2012)
This study demonstrates that Dissolved organic matter (DOM) may be an appropriate proxy to investigate ecosystem functions and functioning
DOM plays a crucial role in a multitude of processes, such as cycling and distributing of nutrients and carbon that are central to ecosystem functioning (Bolan et al 2011; Jansen, Kalbitz & McDowell 2014)

Summary

Introduction

The loss of biodiversity (Barnosky et al 2011) has severe consequences for multiple ecosystem functions, such as reduced plant biomass production, SOM storage, and soil nutrient provision (Balvanera et al 2006; Hooper et al 2012). With higher plant diversity more active soil microbial communities mineralize higher quantities of organic matter (Zak et al 2003; Eisenhauer et al 2010), and thereby provide more plant-available nutrients (Oelmann et al 2011; Hacker et al 2015; Lange et al 2019). These plant-soil interactions mostly occur in the liquid phase of soil (Schimel & Weintraub 2003) and are mediated by dissolved organic molecules, which are detected in DOM. Despite this important function, the role of DOM in the relationship between plant diversity and soil functions has scarcely been addressed

Methods

Results

Discussion

Conclusion