Silent invasion: How microplastics are disrupting land ecosystems

Micro- and nanoplastics (MNPs), plastic particles and fibers sized from nanometers (≥ 1 nm) to micrometers (≤ 5 mm), have emerged as critical environmental pollutants. While their impact on marine ecosystems has been widely studied, research on the effects of microplastics on terrestrial ecosystems remains underdeveloped.

A recent study by researchers from the Xishuangbanna Tropical Botanical Garden at the Chinese Academy of Sciences sheds light on this overlooked issue.

Microplastics in terrestrial ecosystems

Micro- and nanoplastics are ubiquitous in terrestrial ecosystems, bioaccumulating in plants and organisms connected through aboveground (AG) and underground (BG) food webs.

These tiny particles not only impact individual plants but also disrupt multi-trophic interactions, biodiversity patterns, and ecosystem processes.

According to the researchers, MNPs interact with plants and associated AG-BG biota at multiple trophic levels. These interactions include herbivores, pollinators, and mycorrhiza fungi, which are essential for plant health and ecosystem stability.

By transferring across trophic levels, MNPs can harm biodiversity and affect ecosystem multifunctionality.

Microplastic transfer in terrestrial ecosystems

The study identifies several trophic and non-trophic pathways for MNP transfer within and between AG-BG food webs.

These include:

• Leaves to herbivores:
  Herbivores that feed on plant leaves inadvertently ingest MNPs present on the surface of these leaves. This exposes them to potential toxic effects of these tiny particles.
• Flowers to pollinators:
  Pollinators, like bees and butterflies, come into contact with MNPs when they land on flowers to collect nectar or pollen. These interactions can impact pollinator health and their role in pollination.
• Prey to predators:
  Predators consume prey that has already ingested MNPs, leading to the transfer of these plastics up the food chain. This can accumulate and potentially harm predator species.
• Roots to arbuscular mycorrhizal fungi:
  Mycorrhizal fungi, which form symbiotic relationships with plant roots to aid in nutrient absorption, can absorb MNPs present in the soil. This impacts the fungi and their role in plant health.
• Roots to herbivores:
  Soil-dwelling herbivores that feed on plant roots may ingest MNPs present in or around the roots, exposing them to the harmful effects of these plastics.
• Leaf litter to decomposers:
  When leaves containing MNPs decay, decomposer organisms like fungi, bacteria, and invertebrates break them down, absorbing or ingesting the embedded plastics.
• Aboveground litter to belowground decomposers:
  Plant litter from aboveground, such as fallen leaves or flowers, carries MNPs into the soil, where they are processed by belowground decomposers like earthworms and microbes.
• Belowground prey to aboveground predators:
  MNPs present in soil-dwelling prey (like insects or larvae) transfer to aboveground predators (like birds or spiders) when they consume these organisms.
• Belowground larvae to aboveground adults:
  Insects that spend their larval stages underground and then emerge as adults aboveground may carry microplastics they absorbed in their earlier stages into aboveground ecosystems.

These pathways illustrate the complexity of microplastic interactions within ecosystems and highlight their potential to disrupt ecological functions.

Ecotoxicological effects of microplastics

The study emphasizes that MNPs pose ecotoxicological threats across trophic levels.

When plants absorb MNPs, these particles can affect the interactions between plants and organisms, leading to cascading effects in food webs.

The researchers noted significant impacts on biodiversity, ecosystem processes, and multifunctionality. However, the extent of these effects remains uncertain due to limited research.

Call for urgent research and mitigation

The researchers argue that terrestrial ecosystems urgently require more attention to fully assess the ecological impacts of MNPs.

They emphasize the need for research to identify the long-term effects of MNPs on plants and food webs, mitigation strategies to reduce MNP exposure in terrestrial ecosystems, and policies to manage MNP pollution effectively.

Such research will be critical to safeguarding plants and the intricate food webs they support.

Future research directions

To bridge the knowledge gap, researchers recommend focusing on the following areas:

• MNP detection methods: Developing advanced techniques to identify and measure MNPs in terrestrial environments.
• Long-term monitoring: Establishing long-term studies to understand MNP bioaccumulation and ecosystem impacts.
• Mitigation strategies: Designing solutions to reduce MNP exposure, such as improved waste management and soil remediation techniques.

In sum, micro- and nanoplastics have emerged as a hidden threat to terrestrial ecosystems, affecting plants and interconnected AG-BG food webs. The findings emphasize the urgency of expanding research on this topic to mitigate their ecological impact.

This study highlights the interconnected nature of ecosystems and the critical role of plants in maintaining balance. Addressing MNP pollution in terrestrial systems will be vital for protecting biodiversity and ensuring ecosystem sustainability.

The study is published in the journal Trends in Plant Science.

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