Root exudation rate as functional trait involved in plant nutrient‐use strategy classification

Abstract

Plants adopt a variety of life history strategies to succeed in the Earth's diverse environments. Using functional traits which are defined as “morphological, biochemical, physiological, or phonological” characteristics measurable at the individual level, plants are classified according to their species’ adaptative strategies, more than their taxonomy, from fast growing plant species to slower‐growing conservative species. These different strategies probably influence the input and output of carbon (C)‐resources, from the assimilation of carbon by photosynthesis to its release in the rhizosphere soil via root exudation. However, while root exudation was known to mediate plant‐microbe interactions in the rhizosphere, it was not used as functional trait until recently. Here, we assess whether root exudate levels are useful plant functional traits in the classification of plant nutrient‐use strategies and classical trait syndromes? For this purpose, we conducted an experiment with six grass species representing along a gradient of plant resource‐use strategies, from conservative species, characterized by low biomass nitrogen (N) concentrations and a long lifespans, to exploitative species, characterized by high rates of photosynthesis and rapid rates of N acquisition. Leaf and root traits were measured for each grass and root exudate rate for each planted soil sample. Classical trait syndromes in plant ecology were found for leaf and root traits, with negative relationships observed between specific leaf area and leaf dry matter content or between specific root length and root dry matter content. However, a new root trait syndrome was also found with root exudation levels correlating with plant resource‐use strategy patterns, specifically, between root exudation rate and root dry matter content. We therefore propose root exudation rate can be used as a key functional trait in plant ecology studies and plant strategy classification.

Changes in root‐exudate‐induced respiration reveal a novel mechanism through which drought affects ecosystem carbon cycling

“…In addition, we found that root exudation per unit root biomass increased with SRL – which was also found in a recent study by Guyonnet et al . ()), although they did not express root exudation per unit root biomass – but root exudation only weakly predicted root‐exudate‐induced respiration at the 2 wk recovery harvest (Fig. S3).…”

Plant root exudation under drought: implications for ecosystem functioning

“…These strategies are reflected in their allocation of resources to root exudates; for instance, the fast‐growing grassland species Glyceria maxima exuded more C than the conservative Carex acuta (Kaštovská et al ., ). More recently, exudation has been proposed to be a functional root trait in its own right (Guyonnet et al ., ) and is also reflective of root traits such as specific root length, being positively correlated with increased C exudation. However, these studies did not take into account the quality (i.e.…”

Relationships between plant traits, soil properties and carbon fluxes differ between monocultures and mixed communities in temperate grassland

“…Leaf and root traits often show coordinated variation in stoichiometry and tissue density ( 5 ) (Freschet et al, ), but traits relating to root morphology can be a secondary, and potentially independent dimension of root trait variation ( 4 ) (Kramer‐Walter et al, ) as we observed in this study (see Figure ). The fast–slow spectrum can drive relative growth rates ( 6, 7, 8 ) (Reich, ; Wright et al, ) and root morphology may drive patterns of C allocation above‐ and below‐ground ( 14 , 15 ) (Guyonnet et al, ; Lange et al, ) and thus collectively standing biomass above‐ and below‐ground, while relative investment of growth above‐ versus below‐ground can drive root to shoot ratios ( 16 ) (Kimball et al, ). The fast–slow leaf spectrum can drive the relative importance of fungal versus bacterial dominated energy channels below‐ground ( 2, 9 ) (Legay et al, ), while patterns of plant C allocation below‐ground in terms of root length and root diameter may impact on root colonization rates and patterns of C exudation with consequences for microbial community structure ( 13 ) (Lange et al, ).…”

“…Furthermore, increasing plant functional trait diversity has been proposed as a potential mechanism by which to increase carbon (C) allocation and storage below-ground (De Deyn, Cornelissen, & Bardgett, 2008). Root traits have been linked with below-ground C inputs (Guyonnet, Cantarel, Simon, & Haichar, 2018), decomposition rates (Freschet, Aerts, & Cornelissen, 2012;Smith, Woodin, Pakeman, Johnson, & Wal, 2014), soil C storage (Lange et al, 2015) and soil physical properties (Gould, Quinton, Weigelt, De Deyn, & Bardgett, 2016), which have wider implications for soil functioning. Despite these advances, there remains considerable uncertainty as to which plant functional traits (aboveground and/or below-ground) best predict soil properties and ecosystem processes.…”