Above and Belowground Relative Yield Total of Clover–Ryegrass Mixtures Exceed One in Wet and Dry Years

Inga Dirks,Catharina Meinen,Juliane Streit

doi:10.3390/agriculture11030206

Abstract

Grassland mixtures hold the potential for increasing biomass and productivity. In a field experiment, monocultures and mixtures of eight white clover (Trifolium repens L.) genotypes and perennial ryegrass (Lolium perenne L.) were analyzed over three years (2015, 2016, and 2018) for their species-specific aboveground and belowground biomass. Roots were analyzed by Fourier transform infrared (FTIR) spectroscopy to identify species-specific root mass, vertical distribution, and belowground relative yield total (RYT). Aboveground biomass decreased strongly from 2015 to 2018. Aboveground and belowground RYT were always significantly higher than one. Aboveground biomass overyielded in 2016 and 2018 compared to monocultures. Monocultures of perennial ryegrass displayed a significantly higher proportion of roots in shallow soil layers than white clover in two of the three examined years. In mixtures, these differences in vertical root distribution between both species were not present and perennial ryegrass, and white clover occupied similar vertical niches in 2015 and 2016. Interestingly, in the dry year 2018, white clover had a higher proportion of roots in shallow soil layers than perennial ryegrass in mixtures.

Highlights

Diverse plant communities use a broader range of belowground resources, such as nutrients and soil moisture
Roots were analyzed by Fourier transform infrared (FTIR) spectroscopy to identify species-specific root mass, vertical distribution, and belowground relative yield total (RYT)
In the dry year 2018, white clover had a higher proportion of roots in shallow soil layers than perennial ryegrass in mixtures

Summary

Introduction

Diverse plant communities use a broader range of belowground resources, such as nutrients and soil moisture. Deep rooting is fundamental for efficient nutrient acquisition and scavenging subsoil water resources [1,2]. Complementarity increases when roots of a given species grow away from zones of intense nutrient competition with neighbors, leading to a segregation of roots of the different species [10,11,12]. Nonlegumes and legumes differ in their competitive ability regarding light, water, and soil resources [13,14]. While nonlegumes often have a higher competitive ability under high N-fertility and are characterized by a higher N-absorption under wet conditions, legumes can be fiercely competitive under high soil P availability [15,16]

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