Ecosystems worldwide are under increasing pressure from human activities and environmental change, with complex consequences impacting biodiversity and ecosystem functions. Among these ecosystems, temperate grasslands stand out as both extraordinarily diverse and alarmingly vulnerable. Recent research has illuminated critical ecological thresholds in these grasslands—particularly related to land use intensification—that may dictate their future resilience or decline. Understanding these tipping points is essential to safeguarding the services these ecosystems provide, from carbon sequestration to habitat support for pollinators.
Grasslands occupy a significant portion of the Earth’s terrestrial surface and are hotspots for biodiversity, hosting a vast array of plant species characterized by a spectrum of functional traits. These traits—including leaf morphology, nutrient acquisition strategies, and growth patterns—determine how plants respond to environmental pressures and interact with each other. The capacity of grasslands to maintain ecosystem services depends on the coexistence of diverse species with complementary traits. Yet, intensified agricultural practices, especially nitrogen fertilisation, threaten this delicate balance.
Researchers from leading European institutions undertook an extensive analysis of 150 temperate grassland sites across Germany, which serve as a microcosm for Western European grasslands. These sites, monitored from 2008 to 2020, represent a gradient of land use intensities as managed by local farmers. By integrating extensive field data and advanced trait-based ecological analysis, the research untangled the complex interactions linking species diversity, functional traits, and agricultural inputs.
.adsslot_k5BDlf0PxI{ width:728px !important; height:90px !important; }
@media (max-width:1199px) { .adsslot_k5BDlf0PxI{ width:468px !important; height:60px !important; } }
@media (max-width:767px) { .adsslot_k5BDlf0PxI{ width:320px !important; height:50px !important; } }
ADVERTISEMENT
One of the pivotal findings is the identification of a distinct ecological threshold related to nitrogen fertiliser application. Nitrogen is a vital nutrient for plant growth and is widely applied to enhance agricultural productivity. However, the research reveals that beyond a certain input — approximately 80 kilograms of nitrogen per hectare per year — grassland ecosystems undergo a profound shift in their species composition and functional trait diversity. Before this threshold, fertilisation reduces biodiversity compared to unfertilised, more natural grasslands, but the ecosystem sustains relative stability and productivity.
Crossing this fertilisation boundary triggers an abrupt loss in the ability of species to coexist. The plant community homogenizes, dominated by a reduced number of species with similar traits such as fast growth and efficient nutrient uptake. Particularly, species like ryegrass and common weeds such as dandelion proliferate, outcompeting more diverse and functionally varied species. This homogenization compromises the intricate ecological interactions that ordinarily confer resilience to the ecosystem, rendering it more vulnerable to environmental stresses and less capable of delivering key ecosystem functions.
Moreover, the research highlights a secondary but equally critical threshold beyond which further fertiliser intensification fails to yield additional increases in plant biomass. This plateau signifies a diminishing return on productivity. Instead, excessive nutrient inputs exacerbate nutrient leaching and runoff due to increased water infiltration. Such processes not only degrade soil and water quality but also heighten the susceptibility of grasslands to climate-induced stresses, notably drought events that are projected to rise in frequency and severity under current climate scenarios.
Natural, unfertilised grasslands support a complex assemblage of plants exhibiting a wide array of functional traits—variations in root depth, leaf area, nutrient storage, and growth timing. This functional diversity underpins ecosystem stability by promoting complementary resource use and buffering against environmental fluctuations. Contrastingly, intensively managed grasslands with reduced trait diversity are less capable of adapting to abrupt climatic disturbances, threatening ecosystem services such as carbon sequestration, pollinator habitat provision, and soil nutrient cycling.
The application of functional trait analysis in this study serves as a powerful tool for detecting early warning signs of ecosystem degradation. By quantifying how plant traits respond to incremental changes in management intensity, scientists can pinpoint the tipping points at which ecosystems transition from resilient to vulnerable states. This trait-based framework offers a predictive lens for environmental monitoring that transcends traditional species richness metrics, allowing for more nuanced assessments of ecosystem health.
Importantly, the study’s identification of fertilisation thresholds carries significant implications for sustainable land management policies. Balancing agricultural productivity with biodiversity conservation is a global challenge, particularly in regions where grasslands represent key agricultural landscapes. Limiting nitrogen inputs to levels below the critical threshold could maintain functional trait diversity and ecosystem resilience, ensuring continued delivery of essential ecosystem services.
Beyond grasslands, the conceptual approach of detecting ecological thresholds via trait diversity holds promise for broader application. Freshwater ecosystems threatened by eutrophication, fisheries subjected to overharvesting, forest stands facing fragmentation, and arid environments prone to desertification could all benefit from similar trait-informed management frameworks. Anticipating critical regime shifts before they occur is vital for guiding timely conservation and restoration actions worldwide.
While the study advances understanding of the effects of fertilisation on grassland trait diversity and ecosystem thresholds, ongoing research is required to explore whether degraded ecosystems can undergo partial or full recovery if management practices are adjusted. Understanding reversibility is crucial, as many ecosystems may experience hysteresis effects—where returning to previous states requires substantially different conditions than those causing degradation.
The integration of long-term, large-scale observational data with functional trait analyses exemplifies a rigorous, interdisciplinary approach to ecology. It highlights the necessity of considering multiple scales—from individual plants to landscape-level processes—to capture the complexity of ecosystem responses under anthropogenic influence. Such research endeavors are indispensable in informing sustainable agriculture and biodiversity conservation in the face of accelerating global change.
In summary, this research delivers a compelling case for rethinking grassland management by foregrounding ecological thresholds and functional trait diversity as key indicators. It underscores the perils of excessive nitrogen fertilisation, not only for biodiversity loss but also for diminishing returns in productivity and increased ecosystem vulnerability. By adopting management strategies mindful of these ecological limits, we stand a better chance of preserving grasslands as vibrant, resilient ecosystems that continue to support both human and environmental well-being in an unpredictable future.
Subject of Research: Ecological thresholds and functional trait diversity in temperate grasslands under land use intensification.
Article Title: Thresholds of functional trait diversity driven by land use intensification
News Publication Date: 3-Jun-2025
Web References: https://doi.org/10.1038/s41559-025-02729-0
Image Credits: INRAE – Christophe Maitre
Keywords: ecological thresholds, grasslands, nitrogen fertilisation, functional traits, biodiversity, land use intensification, ecosystem services, resilience, nutrient leaching, climate change impacts
Tags: agricultural practices and ecosystem healthbiodiversity and ecosystem functionscarbon sequestration in ecosystemsecological thresholds in grasslandsfunctional traits of grassland specieshabitat support for pollinatorsimpacts of land use intensificationmonitoring ecological changes in temperate regionsnutrient acquisition strategies in plantsresearch on grassland biodiversityresilience of grassland ecosystemstemperate grassland management