jenatron-an-experimental-approach-to-study-effects-plant-history-soil

JenaTron - An Experimental Approach to Study the Effects of Plant History and Soil History on Grassland Ecosystem Functioning

The global loss of biodiversity has motivated many studies that experimentally vary plant species richness and examine the consequences for ecosystem ...

German Centre for integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig

Leipzig University

Widespread evidence shows that local species richness (α-diversity) loss hampers the biomass production and stability of ecosystems. β-Diversity, namely the variation of species compositions among different ecological communities, represents another important biodiversity component, but studies on how it drives ecosystem functioning show mixed results. We argue that to better understand the importance of β-diversity we need to consider it across contexts. We focus on three scenarios that cause gradients in β-diversity: changes in (i) abiotic heterogeneity, (ii) habitat isolation, and (iii) species pool richness. We show that across these scenarios we should not expect universally positive relationships between β-diversity, production, and ecosystem stability. Nevertheless, predictable relationships between β-diversity and ecosystem functioning do exist in specific contexts, and can reconcile seemingly contrasting empirical relationships.

Universal beta-diversity-functioning relationships are neither observed nor expected.

Root-associated fungi could play a role in determining both the positive relationship between plant diversity and productivity in experimental grasslands, and its strengthening over time. This hypothesis assumes that specialized pathogenic and mutualistic fungal communities gradually assemble over time, enhancing plant growth more in species-rich than in species-poor plots. To test this hypothesis, we used high-throughput amplicon sequencing to characterize root-associated fungal communities in experimental grasslands of 1 and 15 years of age with varying levels of plant species richness. Specifically, we tested whether the relationship between fungal communities and plant richness and productivity becomes stronger with the age of the experimental plots. Our results showed that fungal diversity increased with plant diversity, but this relationship weakened rather than strengthened over the two time points. Contrastingly, fungal community composition showed increasing associations with plant diversity over time, suggesting a gradual build-up of specific fungal assemblages. Analyses of different fungal guilds showed that these changes were particularly marked in pathogenic fungi, whose shifts in relative abundance are consistent with the pathogen dilution hypothesis in diverse plant communities. Our results suggest that root-associated fungal pathogens play more specific roles in determining the diversity-productivity relationship than other root-associated plant symbionts.

The structure of root-associated fungal communities is related to the long-term effects of plant diversity on productivity.

Recent studies on root traits have shown that there are two axes explaining trait variation belowground: the collaboration axis with mycorrhizal partners and the conservation ('fast - slow') axis. However, it is yet unknown whether these trait axes affect the assembly of soilborne fungi. We expect saprotrophic fungi to link to the conservation axis of root traits, whereas pathogenic and arbuscular mycorrhizal fungi link to the collaboration axis, but in opposite directions, as arbuscular mycorrhizal fungi might provide pathogen protection. To test these hypotheses, we sequenced rhizosphere fungal communities and measured root traits in monocultures of 25 grassland plant species, differing in age. Within the fungal guilds, we evaluated fungal species richness, relative abundance and community composition. Contrary to our hypotheses, fungal diversity and relative abundance were not strongly related to the root trait axes. However, saprotrophic fungal community composition was affected by the conservation gradient and pathogenic community composition by the collaboration gradient. The rhizosphere AMF community composition did not change along the collaboration gradient, even though the root trait axis was in line with the root mycorrhizal colonization rate. Overall, our results indicate that in the long term, the root trait axes are linked with fungal community composition.

Responses of rhizosphere fungi to the root economics space in grassland monocultures of different age.

Trait-based approaches have been increasingly used to relate plants to soil microbial communities. Using the recently described root economics space as an approach to explain the structure of soil-borne fungal communities, our study in a grassland diversity experiment reveals distinct root trait strategies at the plant community level. In addition to significant effects of plant species richness, we show that the collaboration and conservation gradient are strong drivers of the composition of the different guilds of soil fungi. Saprotrophic fungi are most diverse in species-rich plant communities with 'slow' root traits, whereas plant pathogenic fungi are most diverse and abundant in communities with 'fast' and 'DIY' root traits. Fungal biomass is strongly driven by plant species richness. Our results illustrate that the root economics space and plant species richness jointly determine the effects of plants on soil fungal communities and their potential role in plant fitness and ecosystem functioning.

Plant Species Richness and the Root Economics Space Drive Soil Fungal Communities.

The relationship of plant diversity and several ecosystem functions strengthens over time. This suggests that the restructuring of biotic interactions in the process of a community's assembly and the associated changes in function differ between species-rich and species-poor communities. An important component of these changes is the feedback between plant and soil community history. In this study, we examined the interactive effects of plant richness and community history on the trophic functions of the soil fauna community. We hypothesized that experimental removal of either soil or plant community history would diminish the positive effects of plant richness on the multitrophic functions of the soil food web, compared to mature communities. We tested this hypothesis in a long-term grassland biodiversity experiment by comparing plots across three treatments (without plant history, without plant and soil history, controls with ~20 years of plot-specific community history). We found that the relationship between plant richness and below-ground multitrophic functionality is indeed stronger in communities with shared plant and soil community history. Our findings indicate that anthropogenic disturbance can impact the functioning of the soil community through the loss of plant species but also by preventing feedbacks that develop in the process of community assembly.

Shared community history strengthens plant diversity effects on below-ground multitrophic functioning.

Although the interest in root traits has increased in recent years, we still have limited knowledge of (i) whether functionally different fine roots-absorptive versus transport roots-have similar trait coordination and (ii) how they help to explain plant performance, such as growth. We measured traits of 25 European broadleaved tree species growing in a research arboretum to study (i) the coordination of root traits within absorptive and transport fine roots and (ii) the degree of trait-tree growth relationships. To do so, we combined a suite of morphological and anatomical traits for each of the absorptive and transport roots. Despite remarkable differences in average trait values between absorptive and transport roots, our study shows that trait coordination within absorptive and transport roots is relatively similar. Our results also show that, for the selected traits, tree growth is better explained by absorptive root traits than by transport root traits and is higher in species with thinner roots. The stronger relationship between absorptive roots and tree growth highlights that roots mostly involved with resource absorption are more important in explaining tree growth than transport roots, which are mainly responsible for resource transportation.

Tree growth is better explained by absorptive fine root traits than by transport fine root traits.

The increased positive impact of plant diversity on ecosystem functioning is often attributed to the accumulation of mutualists and dilution of antagonists in diverse plant communities. While increased plant diversity alters traits related to resource acquisition, it remains unclear whether it reduces defence allocation, whether this reduction differs between roots and leaves, or varies among species. To answer these questions, we assessed the effect of plant species richness, plant species identity and their interaction on the expression of 23 physical and chemical leaf and fine root defence traits of 16 plant species in a 19-yr-old biodiversity experiment. Only leaf mass per area, leaf and root dry matter content and root nitrogen, traits associated with both, resource acquisition and defence, responded consistently to species richness. However, species richness promoted a decoupling of these defences in leaves and fine roots, possibly in response to resource limitations in diverse communities. Species-specific responses were rare and related to chemical defence and mutualist collaboration, likely responding to species-specific antagonists' dilution and mutualists' accumulation. Overall, our study suggests that resource limitation in diverse communities might mediate the relationship between plant defence traits and antagonist dilution.

Plant species richness promotes the decoupling of leaf and root defence traits while species-specific responses in physical and chemical defences are rare.

Article	Year
Universal beta-diversity-functioning relationships are neither observed nor expected. Trends in ecology & evolution\| PubMed ID: 36806396	2023
The structure of root-associated fungal communities is related to the long-term effects of plant diversity on productivity. Molecular ecology\| PubMed ID: 37081579	2023
Responses of rhizosphere fungi to the root economics space in grassland monocultures of different age. The New phytologist\| PubMed ID: 37691273	2023
Plant Species Richness and the Root Economics Space Drive Soil Fungal Communities. Ecology letters\| PubMed ID: 39737799	2025
Shared community history strengthens plant diversity effects on below-ground multitrophic functioning. The Journal of animal ecology\| PubMed ID: 39887967	2025
Tree growth is better explained by absorptive fine root traits than by transport fine root traits. Communications biology\| PubMed ID: 40011709	2025
Plant species richness promotes the decoupling of leaf and root defence traits while species-specific responses in physical and chemical defences are rare. The New phytologist\| PubMed ID: 40013369	2025

Justus Hennecke

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