Earthworms Modulate Impacts of Soil Heterogeneity on Plant Growth at Different Spatial Scales

Abstract

Soil heterogeneity (uneven distribution of soil nutrients and/or other properties) is ubiquitous in nature and can greatly affect plant growth. As earthworm activity can influence nutrient redistribution in the soil, we hypothesize that earthworms may alter the effect of soil heterogeneity on plant growth and this effect may depend on the scale of soil heterogeneity. To test these hypotheses, we grew the clonal grass Leymus chinensis in three soil treatments (heterogeneous large vs. heterogeneous small patch vs. homogeneous soil treatment) with or without earthworms [i.e., Eisenia fetida Savigny (Lumbricidae, epigeic redworm)]. In the heterogeneous treatments, the soil consisted of patches with and without 15N-labeled litter (referred to as high- and low-quality patches, respectively), and in the homogeneous treatment, the soil was an even mixture of the two types of soil patches. Biomass of L. chinensis was significantly higher in the high- than in the low-quality patches, showing the foraging response; this foraging response occurred at both scales and under both earthworm treatments. Compared to the homogeneous treatment, the heterogeneous large patch treatment increased biomass of L. chinensis without earthworms, but decreased it with earthworms. In contrast, biomass of L. chinensis in the heterogeneous small patch treatment did not differ from that in the homogeneous treatment, irrespective of earthworms. Belowground biomass was much greater in the heterogeneous small than in the heterogeneous large patch treatment without earthworms, but it did not differ between these two scale treatments with earthworms. In the heterogeneous treatments, soil 15N was greater in the high- than in the low-quality patches, but this effect became much weaker with than without earthworms, suggesting that earthworm activity homogenized the soil. We conclude that earthworms can change the impact of soil heterogeneity on plant growth via homogenizing the soil, and that this effect of earthworms varies with patch scale. Such scale-dependent interactive effects of soil heterogeneity and earthworms could be a potential mechanism modulating plant community structure and productivity.

Soil heterogeneity in the horizontal distribution of microplastics influences productivity and species composition of plant communities

“…We observed that, in the environment with the spatially heterogeneous distribution of soil microplastics, plant communities produced more root, shoot and total biomass in the soil patches without microplastics (high-quality patches) than in the soil patches with the higher (0.2%) concentration of microplastics (low-quality patches) when the microplastic was EPS and more root biomass when the microplastic was HDPE (Figure 4), demonstrating root and/ or shoot foraging responses (2015;James et al, 2009;Giehl and von Wireń, 2014;Keser et al, 2014). However, such foraging responses at the patch level did not cascade to influence biomass of the plant communities at the whole box level (Figures 2A-C), as also reported in some previous studies testing the effect of spatial heterogeneity in the distribution of other soil factors (Dong et al, 2015;Liu et al, 2017;Xue et al, 2018;Adomako et al, 2021b;Yao et al, 2021).…”

“…Further studies could combine soil microbial and physico-chemical analyses to explore the mechanisms underlying the effect of soil microplastic heterogeneity on community productivity ( Baer et al., 2020 ; Lozano et al., 2021 ; Xue et al., 2021 ; Zhao et al., 2021 ). The impacts of patch scale and patch contrast of soil microplastic heterogeneity should also be considered in future ( Adomako et al., 2021b ; Li et al., 2022 ).…”

“…A large number of studies have assessed the ecological impacts of soil heterogeneity in the horizontal distribution of factors other than microplastics, including nutrients ( Tsunoda et al., 2014 ; Xue et al., 2020 ; Adomako et al., 2021a ; Gao et al., 2021 ), water ( You et al., 2016 ; Wang et al., 2017 ), heavy metals ( Roiloa and Retuerto, 2012 ; Xu and Zhou, 2017 ) and particle size of the soil ( Baer et al., 2005 ; Huang et al., 2013 ; Xue et al., 2016 ). These studies have shown that soil heterogeneity in the distribution of such factors can affect growth, morphology and physiology of individual plants ( Zhou et al., 2012 ; Tsunoda et al., 2014 ; Adomako et al., 2021b ; Si et al., 2021 ), influence dynamics of plant populations ( Hutchings et al., 2003 ; Baer et al., 2020 ), modify intraspecific and interspecific plant-plant interactions ( Liang et al., 2020 ; Xue et al., 2021 ; Hu et al., 2022 ), and change plant community structure and ecosystem function ( Wijesinghe et al., 2005 ; Yao et al., 2021 ). One underlying mechanism is that some plants can grow across patches and allocate more roots and/or shoots in favorable microsites (e.g., high-nutrient patches and patches not contaminated by heavy metals) and less in unfavorable microsites (e.g., low-nutrient patches and patches contaminated by heavy metals), showing foraging responses to increase resource harvesting ( Hutchings et al., 2003 ; Tsunoda et al., 2014 ; Chen et al., 2019 ; Cao et al., 2022 ).…”

A Novel and Non-Invasive Approach to Evaluating Soil Moisture without Soil Disturbances: Contactless Ultrasonic System

“…One concern was that the dataset and experimental designs we used in this study were admittedly limited. Natural soils were inherently heterogeneous, leading to imperative but complex soil moisture dynamics (e.g., [ 68 , 69 , 70 ]). The controlled environments (constant temperature and humidity) used in this study were artificial ways to minimize the effects of uncertain variables that were not in the interest of this study.…”

Temporal–spatial variability of grazing behaviors of yaks and the drivers of their intake on the eastern Qinghai-Tibetan Plateau

“…can affect directly and indirectly the grazing livestock behaviors. Soil spatial heterogeneity strongly influences the growth and physiology of individual plants ( 24 , 25 ), the dynamics of plant populations ( 26 ) and interspecific interactions ( 25 ), and plant community composition ( 27 ). Alternatively, temporal and spatial variations in climatic conditions, such as the inter- and intra-annual variability of precipitation and temperature have also led to significant shifts in the plant community characteristics ( 28 , 29 ).…”