Effects of climate change and land use on the structure and function of earthworm communities
by Qun Liu
Date of Examination:2024-04-30
Date of issue:2024-05-07
Advisor:Prof. Dr. Stefan Scheu
Referee:Prof. Dr. Stefan Scheu
Referee:Dr. Nico Eisenhauer
Persistent Address:
http://dx.doi.org/10.53846/goediss-10480
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Abstract
English
Human activity-induced global change is increasingly threatening biodiversity and composition of species assemblages worldwide, which reduces ecosystem resilience and provokes concerns about ecosystem functions. Over the past decades, studies examining such effects have overwhelmingly focused on aboveground taxa, while our understanding of the effects on soil biodiversity and aboveground-belowground interactions remains comparatively limited. In soil systems, earthworms, as ecosystem engineers, dominate invertebrate biomass in numerous terrestrial ecosystems, and are key drivers of terrestrial ecosystem functions, such as promoting aboveground plant productivity. Simultaneously, they exhibit high sensitive to environmental changes, making them an indicator group in soil quality assessments. Global change factors, particularly climate change and land use change, have been mainly studied in isolation regarding their effects on earthworm communities, thereby the ecosystem functions they drive. Therefore, there is a pressing need for comprehensive quantitative reviews of global change factors on a global scale and exploring the interactive effects of climate change and land use, which give rise to significant uncertainty in projecting effects. In my thesis, I firstly comprehensively assessed the quantitative effects of land-use intensification on earthworms under different land-use types on a global scale using a meta-analysis. Subsequently, in the Global Change Experimental facility (GCEF) - a novel experimental platform to investigate the interactive effects of land use and climate change on ecosystem processes, I conducted one field assessment to evaluate the consequence of climate change for earthworms under different land-use types and one microcosm experiment to investigate how climate change and earthworms affect plant nutrient uptake and productivity in grasslands and croplands. Given the widespread distribution of earthworms and the direct pressure on soils caused by land-use intensification, the meta-analysis (Chapter 2) was used to quantitatively assess the effects of land-use intensification across six land-use types on a global scale. A total of 148 relevant studies conducted between 1990 and 2021 on six continents were selected for our analysis. Results revealed that higher land-use intensity significantly decreased earthworm abundance and biomass at the global scale. However, these negative effects were predominantly based on observations in Asia, Europe, and the Americas. Among different land-use types, we found the most negative impacts of land-use intensification in annual and perennial croplands. Notably, tillage was identified as the most detrimental factor, causing the strongest negative effects in annual cropland systems. Conversely, the study highlighted positive effects in pastures and tree plantations, where the higher intensity of grazing in pastures appears to promote earthworm populations. When looking at earthworm ecological groups, epigeic and anecic earthworms responded more negatively than endogeic earthworms. These findings emphasize the importance of management strategies that are tailored to specific regions and land-use types as well as the need for sustainable management practices in annual and perennial croplands to mitigate the negative effects on earthworms. Reduced tillage, plant residue management, and organic fertilization strategies might be key to support high earthworm populations. These measures form a critical foundation for implementing effective management approaches and contributing more broadly to soil health and ecosystem sustainability. At the same time, the intensification of land-use changes may reduce the resilience of earthworm species to climate change. Therefore, understanding the interactions among global change factors affecting earthworm communities is crucial for predicting and mitigating the consequences of global environmental changes on soil systems. In order to explore the interactive effects of climate change and land use (Chapter 3), the field experiment investigated species diversity, abundance, biomass, and community composition of earthworms across different seasons and years in the GCEF platform. The results show that compared to the two grasslands, species richness, abundance and biomass of earthworms in both croplands were reduced, particularly the abundance of juveniles and Aporrectodea rosea and the biomass of juveniles of A. rosea, Octolasion cyaneum and Lumbricus terrestris. Due to extreme droughts in Central Europe in 2018, 2019, and 2020, earthworm abundance and biomass were low across land-use types, but in grassland they increased in 2021 presumably due to increased moisture conditions. Effects of experimental climate change, intensified management practices, and the interaction between experimental climate change and land use on the abundance and biomass of earthworms were weak. Notably, experimental climate change and land use interactively altered earthworm community composition, with the most pronounced difference between ambient and future climate in croplands than in grasslands. This finding indicates that the community composition of earthworms more sensitively reflects changes in environmental conditions than earthworm abundance and biomass, but the latter two negatively responded to prolonged drought conditions. Our results indicate that grasslands have a higher resilience of earthworm populations to buffer adverse environmental conditions than croplands. Overall, this study provides a comprehensive overview of the response of earthworms to inter-annual climatic change and experimental climate change under different land-use types. These changes in earthworm communities may have significant consequences on ecosystem functions, such as nutrient cycling and plant growth. To delve deeper into the consequences of variations in earthworm communities, the field microcosm experiment (Chapter 4) investigated the effects of climate change and earthworms (anecic - Lumbricus terrestris, endogeic - Allolobophora chlorotica and both together) on plant biomass and stoichiometry in two contrasting land-use types (intensively-used meadow with four forage grass species and conventional farming with winter wheat). I found little evidence for earthworm effects on aboveground biomass. However, future climate increased above- (+40.9%) and belowground biomass (+44.7%) of grass communities, which was mainly driven by production of the dominant Festulolium species during non-summer drought periods, but decreased the aboveground biomass (-36.9%) of winter wheat. Projected climate change and earthworms interactively affected the N content and C:N ratio of grasses. Earthworms enhanced the N content (+1.2%) thereby decreasing the C:N ratio (-4.1%) in grasses, but only under ambient climate conditions. The future climate treatment generally decreased the N content of grasses (aboveground: -1.1%, belowground: -0.15%) and winter wheat (-0.14%), resulting in an increase in C:N ratio of grasses (aboveground: +4.2%, belowground: +6.3%) and wheat (+5.9%). Our results suggest that climate change diminishes the positive effects of earthworms on plant nutrient uptakes due to soil water deficit, especially during summer drought. Overall, the main findings of this thesis reveal that: (1) the global effects of land-use intensification on earthworm communities are dissimilar across land-use types; (2) grasslands support more diverse and resilient earthworm communities to climate change than croplands; (3) climate change can mitigate the positive effects of earthworms on N uptake of forage grasses in grassland, but not in cropland. As a whole, this dissertation contributes insights into the complex and context-dependent nature of the relationships between land use, climate change, earthworm communities, and associated ecosystem functions.
Keywords: land-use intensity, land-use types, ecological groups, croplands, pasture, tillage, grazing, global change, future climate, intensive land use, earthworms, grassland, biomass, stoichiometry, climate change, summer droughts, plant-soil interactions
