Root exudation as a major competitive fine‐root functional trait of 18 coexisting species in a subtropical forest

Abstract

Root exudation stimulates microbial decomposition and enhances nutrient availability to plants. It remains difficult to measure and predict this carbon flux in natural conditions, especially for mature woody plants. Based on a known conceptual framework of root functional traits coordination, we proposed that root functional traits may predict root exudation. We measured root exudation and other seven root morphological/chemical/physiological traits for 18 coexisting woody species in a deciduous-evergreen mixed forest in subtropical China. Root exudation, respiration, diameter and nitrogen (N) concentration all exhibited significant phylogenetic signals. We found that root exudation positively correlated with competitive traits (root respiration, N concentration) and negatively with a conservative trait (root tissue density). Furthermore, these relationships were independent of phylogenetic signals. A principal component analysis showed that root exudation and morphological traits loaded on two perpendicular axes. Root exudation is a competitive trait in a multidimensional fine-root functional coordination. The metabolic dimension on which root exudation loaded was relatively independent of the morphological dimension, indicating that increasing nutrient availability by root exudation might be a complementary strategy for plant nutrient acquisition. The positive relationship between root exudation and root respiration and N concentration is a promising approach for the future prediction of root exudation.

Root functional traits explain root exudation rate and composition across a range of grassland species

“…Yet, only recently has root exudation been considered a functional trait in its own right, where it has been theoretically central to an exploitative nutrient acquisition strategy within the root Accepted Article economic space, along with competitive traits like high root nitrogen content (Sun et al, 2020).…”

“…Root traits dictate the functional biology of plants; for instance, roots of legumes that recruit nitrogen fixers in the rhizosphere have high root nitrogen content (Roumet et al, 2006). Root functional traits are dynamic and operate on an economic spectrum of resource use, partially informed by the environment in which the plant is growing (Meier et al, 2020;Sun et al, 2020). This root-trait plasticity in the face of changing environmental pressures, over the life-time of the plant, may be central to plant survival and fitness in different environments; for instance by reducing intraspecific resource competition (Valverde-Barrantes et al, 2017).…”

“…This root-trait plasticity in the face of changing environmental pressures, over the life-time of the plant, may be central to plant survival and fitness in different environments; for instance by reducing intraspecific resource competition (Valverde-Barrantes et al, 2017). Root exudation chemistry is no exception, and the exudation of costly metabolites is likely to occur on an economic spectrum, determined by the resource-use strategy of the plant (Miao et al, 2020;Sun et al, 2020). The quantity of metabolites allocated towards root exudates are likely to relate to metabolic activity, and be negatively associated with other, more conservative, plant traits (Bergmann et al, 2020).…”

“…For example, across six grasses of contrasting nutrient use strategies, high levels of root exudation were associated with high specific root length (SRL) and low root dry matter content (RDMC), traits associated with exploitative growth . Interestingly, in woody species high rates of root exudation are found in more active root tissue, so are likely necessary for rapid development; this comes at the cost of structural investment traits, such as root tissue density (Sun et al, 2020).…”

Functional phenomics and genetics of the root economics space in winter wheat using high-throughput phenotyping of respiration and architecture

“…The fraction of newly fixed carbon from photosynthesis allocated to roots can exceed 50%, and this proportion to roots significantly increases under edaphic stress (Lambers et al , 1996; Rachmilevitch et al , 2015). Root system carbon costs can be classified as construction costs, including the structure of the roots and growth respiration, and maintenance costs, primarily respiration and exudation (Mooney, 1972; Sun et al , 2020). For example, in wheat seedlings, 30% of net photosynthesis was measured as root construction and maintenance costs, such as respiration (Sawada, 1970).…”