Absorptive roots drive a larger microbial carbon pump efficacy than transport roots in alpine coniferous forests

Abstract

1. Root activity creates a unique microbial hotspot in the rhizosphere and profoundly regulates soil carbon (C) dynamics, but empirical assessments of the soil microbial carbon pump (MCP, the iterative accumulation of necromass after microbial anabolism) and associated ecological consequences on soil C storage based on insight of the rhizosphere are still neglected, especially for different root functional modules.2. We assessed the soil MCP efficacy (i.e. the contribution of microbial necromass to SOC) by investigating the divergent contribution of microbial necromass based on amino sugar extrapolations to soil organic C (SOC) in the rhizosphere of two root functional modules (i.e. absorptive roots and transport roots) and the bulk soil in an alpine coniferous forest.3. The results showed that the MCP efficacy in both rhizosphere and bulk soil was more than 50%, suggesting that microbial necromass plays a key role in SOC formation. More importantly, absorptive roots drove a greater rhizosphere MCP efficacy (56%) than transport roots (51%). 4. Synthesis. These observations suggest that the microbial necromass is a major contributor to SOC storage in both rhizosphere and bulk soil in alpine coniferous forests. The magnitude of the contribution of microbial necromass to rhizosphere SOC depends on root functional differentiation. Our study provides novel and direct empirical evidence for the active soil MCP functions in SOC sequestration from the perspective of the rhizosphere.

Embracing fine‐root system complexity in terrestrial ecosystem modeling

“…In the 2000s, experimental measurements revealed unique morphological, anatomical, chemical, physiological, and demographic properties among root branching orders (e.g., Atucha et al, 2021; Guo et al, 2008; Pregitzer et al, 2002), as well as varying microbial associations with both mycorrhizal fungi and bacteria (e.g., King et al, 2021; Phillips et al, 2013; Sen & Jenik, 1962). These structural differences support functional differentiation within fine‐root systems: only finer and more distal roots in symbiosis with mycorrhizal fungi are responsible for nutrient and water acquisition from soils, while fine roots of higher orders are primarily responsible for transport (e.g., Hishi & Takeda, 2005; McCormack, Dickie, et al, 2015; Wang et al, 2022). This internal heterogeneity within a fine‐root system, and degree of coordination with the aboveground, changes with species and habitat, shaping fine‐root system complexity and forming diverse whole‐plant strategies (e.g., McCormack & Iversen, 2019; McShea & Brandon, 2010; Weigelt et al, 2021).…”

Embracing fine-root system complexity to improve the predictive understanding of ecosystem functioning

“…Within a fine-root system, plants have evolved roots with unique morphological, anatomical, chemical, and physiological features that differ among root branching orders (e.g., Pregitzer et al 2002; Atucha et al 2021 ), as well as varying microbial associations with both mycorrhizal fungi and bacteria (e.g., Sen and Jenik 1962; King et al 2021 ). These structural differences support both functional differentiation and cooperation within fine-root systems; fine roots of higher orders are primarily responsible for transport of water and nutrients to the rest of the plant, while finer and more distal roots in cooperation with mycorrhizal fungi are responsible for nutrient and water absorption (e.g., Hishi & Takeda 2005; McCormack et al 2015a; Wang et al 2022 ). This heterogeneity, and degree of coordination with aboveground plant activities, changes with species and habitat, forming diverse whole-plant strategies across biomes under physical and functional constraints (e.g., McCormack and Iversen 2019; Weigelt et al 2021) .…”