Nitrogen‐mediated effects of elevated CO₂ on intra‐aggregate soil pore structure

Abstract

Soil pore structure has a strong influence on water retention, and is itself influenced by plant and microbial dynamics such as root proliferation and microbial exudation. Although increased nitrogen (N) availability and elevated atmospheric CO concentrations (eCO ) often have interacting effects on root and microbial dynamics, it is unclear whether these biotic effects can translate into altered soil pore structure and water retention. This study was based on a long-term experiment (7 yr at the time of sampling) in which a C pasture grass (Paspalum notatum) was grown on a sandy loam soil while provided factorial additions of N and CO . Through an analysis of soil aggregate fractal properties supported by 3D microtomographic imagery, we found that N fertilization induced an increase in intra-aggregate porosity and a simultaneous shift toward greater accumulation of pore space in larger aggregates. These effects were enhanced by eCO and yielded an increase in water retention at pressure potentials near the wilting point of plants. However, eCO alone induced changes in the opposite direction, with larger aggregates containing less pore space than under control conditions, and water retention decreasing accordingly. Results on biotic factors further suggested that organic matter gains or losses induced the observed structural changes. Based on our results, we postulate that the pore structure of many mineral soils could undergo N-dependent changes as atmospheric CO concentrations rise, having global-scale implications for water balance, carbon storage, and related rhizosphere functions.

Decadal-scale shifts in soil hydraulic properties as induced by altered precipitation

“…Moreover, it is likely that the mechanisms altering pore systems will vary as a function of the environmental setting. As one study showed, the aggregate properties of a sandy soil responded very differently to elevated CO 2 depending on nitrogen availability, likely due to differences in the availability of labile organic matter ( 16 ). It will also be important to determine how malleable soils with different textures and mineral compositions are when acted upon by various climatic drivers.…”

Shifts in microbial communities in soil, rhizosphere and roots of two major crop systems under elevated CO2 and O3

“…There is evidence across diverse ecosystems for elevated CO 2 and/or O 3 effects on: (1) the quantity and quality of roots 12 , 13 , root exudates 14 and leaf litter 15 as inputs to the soil; (2) plant mineral nutrient uptake 16 , 17 , nitrogen fixation by symbiotic bacteria 18 and soil weathering, organic matter decomposition and nutrient acquisition by mycorrhizae 19 – 21 and (3) the extent and location of water use in the soil profile 5 . Consequently, these treatments can modify soil N mineralization, organic content, C storage, respiration 22 , 23 , N 2 O emissions 24 , and even the physical structure 25 with consequences for ecosystem-scale biogeochemistry 11 , 26 – 28 . Despite the recognized importance and sensitivity of the soil and plant microbiome to environmental perturbations 29 , 30 , little is known about the microbe community response and the role of soil microbes in mediating plant and ecosystem responses to eCO 2 and eO 3 .…”

Effects of mowing and fertilization on soil quality in a semiarid grassland of North China

“…Soil physical and chemical properties in semiarid grasslands are sensitive to land use management (Garcia‐Orenes et al, 2016; Liu et al, 2017). For soil physical structure, it is generally considered that nitrogen addition induces an increase in intra‐aggregate porosity and a simultaneous shift toward the greater accumulation of pore space in larger aggregates (Caplan et al, 2017; Chen et al, 2019; Kiani et al, 2017; Liu, Zhang, Liu, Zong, & Yu, 2018). However, nitrogen addition significantly decreased soil aggregate proportions in the present study (Figure 1d).…”

“…Several parameters, including bulk density (BD), porosity, soil moisture, aggregate stability (Caplan et al, 2017; Huang et al, 2020; Liu, Zhang, Liu, Zong, & Yu, 2018; Raiesi & Kabiri, 2016; Su et al, 2018; Sun et al, 2018), pH, total carbon and nitrogen content (Chen et al, 2017; Li, Gao, & Tang, 2016; Liu et al, 2018; Schmidt et al, 2011; Zuber, Behnke, Nafziger, & Villamil, 2017), and microbial carbon and nitrogen content (Gao et al, 2016; Leff et al, 2015; Wang, Zhang, Zhu, Yang, & Li, 2018), can be used to reflect soil properties. However, these indicators individually cannot reflect the complexity of soil structure, due to their interdependence (Raiesi & Kabiri, 2016; Zhao et al, 2017).…”