Grassland root functional parameters vary according to a community‐level resource acquisition–conservation trade‐off

Abstract

Abbreviations CFI = comparative fit index; RLD = root length density; RMSEA = root mean square error of approximation; RTD = root tissue density; SRL = specific root length; SEM = structural equation model. NomenclatureAbstract Questions: The fundamental trade-off between fine root trait attributes related to resource acquisition and conservation is well documented at species and community levels. However, relations remain unclear between this trade-off and community adaptation to environmental factors. As a result we ask: (1) how do fertility changes influence community position along the root acquisition-conservation trade-off; (2) how does root position along the soil profile influence its functional parameter; and (3) do fertility and soil depth have an interactive effect on community root parameters?Location: Native multi-species temperate grassland in the French Massif Central.Methods: We assessed botanical composition and measured community root functional parameters (at plot and soil layer levels) in 16 plots differentiated by the amounts of N and P fertilizers applied over 16 yr and a soil depth gradient. Structural equation models were used to analyse relations among environmental factors, botanical composition and root functional parameters.Results: Botanical composition and plot-level root functional parameters vary according to fertility and soil depth. Communities from low fertility plots display a resource conservation strategy, i.e. high root tissue density, low specific root length (SRL) and low root length density (RLD), while communities from high fertility plots display a resource acquisition strategy, i.e. opposite parameter values. This demonstrates the importance of root resource management strategies in community adaptation to resource acquisition. Roots display different parameter values with soil depth. Roots in the surface horizon have small diameters and high SRL and RLD, suggesting intensive soil exploration and a high nutrient acquisition capacity. Roots in deep horizons have large diameters and low SRL, suggesting high water transport capacity per root length unit. This pattern is affected by plot fertility, i.e. communities from high fertility plots show higher root strategy differentiation with depth than communities from low fertility plots. We hypothesize that this root specialization along the soil profile enables species to be competitive for nutrient uptake in shallow soil layers and water uptake and transport in deep soil layers. Conclusion:Our study provides evidence that fertility and soil depth modified root functional parameters, in agreement with predictions from the economics spectrum theory.

Root traits are related to plant water‐use among rangeland Mediterranean species

“…The decrease in RTD with soil depth, recently identified at the community level (Fort et al . ), could be roots’ adaptation to specific soil conditions in deep soil layers [high water availability, low risk of dehydration and anoxic conditions; (Hodge et al . )].…”

“…; Fort et al . ). This shallow root trait syndrome may allow species to efficiently acquire nutrients (Mommer & Weemstra ) and water during rain pulses (Padilla et al .…”

“…; Fort et al . ). The increase in root diameter with soil depth was associated with a higher stele to root diameter ratio and higher hydraulic conductivity (McElrone et al .…”

“…Root functional traits vary among species and also with soil depth. At the community level, recent studies demonstrate that fine roots (diameter ≤2 mm) at shallow depths generally have a smaller diameter, with longer SRL and RLD, than fine roots at deeper depths (Prieto et al 2015;Fort et al 2016). This shallow root trait syndrome may allow species to efficiently acquire nutrients (Mommer & Weemstra 2012) and water during rain pulses (Padilla et al 2013).…”

Linking reliance on deep soil water to resource economy strategies and abundance among coexisting understorey shrub species in subtropical pine plantations

“…Inconsistent with our hypothesis, we found no significant correlation between shallow fine root economy traits (first‐order root diameter, SRL, RTD) and deep water utilization parameters across species, suggesting independent dimensions of soil resource acquisition between deep and shallow soil. This is consistent with previous studies showing that the form and function of deep fine roots may exhibit some differences from shallow fine roots (Prieto et al ., ; Wang et al ., ; Fort et al ., ). These variations of root traits along the soil profile are likely the result of root specialization to acquire different resources (Fort et al ., ), because nutrient availability often declines, whereas bulk density tends to increase with soil depth (Schenk, ; Ugawa et al ., ).…”