Nitrogen Pollution Supercharges Invasive Plant’s Growth Advantage, Study Finds

Every year, human activity dumps staggering quantities of reactive nitrogen into the atmosphere, much of which eventually settles onto soils as fertilizer-like pollution. For ecologists trying to understand why some exotic plants explode across new landscapes while native species retreat, this global shift in soil chemistry has long been a prime suspect. A new field experiment published in the journal Plant and Soil now offers some of the clearest evidence yet that nitrogen enrichment does not merely help invasive plants—it selectively amplifies the very traits that make them formidable competitors in the first place.

The study, led by Jian-Kun Sun, Wei-Wei Feng, Ming-Chao Liu, Ji-Xin Chen, Fa-Zhao Qi, and Yu-Long Feng of Southwest Forestry University and Shenyang Agricultural University in China, focused on a dramatic head-to-head contest between two plants. On one side was Solanum rostratum, an aggressive invader native to North America that has spread widely across China and other regions, armed with spines and a voracious appetite for resources. On the other was Astragalus laxmannii, a native species that shares the same habitats. The researchers grew the two species together in mixed field plots, forcing them to compete directly under different nitrogen regimes, and then measured everything from total biomass to the microscopic economics of their leaves and roots.

The central question was deceptively simple: when soils receive more nitrogen, and when that nitrogen arrives in different chemical forms, do invasive and native species respond in the same way? The answer, according to the data, is a resounding no. Across nearly all treatments, Solanum rostratum outperformed its native neighbor in total biomass, and the gap between the two species widened as nitrogen availability increased. Crucially, the mechanism behind that widening gap was not just faster growth but a coordinated shift in how the invader builds and deploys its tissues.

To understand that mechanism, it helps to think of plants as investors operating under a strict carbon budget. Ecologists describe this through the framework of the plant economics spectrum, a continuum that runs from acquisitive strategies—thin, cheap tissues built for rapid resource capture—to conservative strategies, which favor dense, durable structures that conserve resources over the long term. The leaves and roots of a plant tend to align along this spectrum, and the new study shows that the two species sit at opposite ends of it.

Solanum rostratum displayed the classic acquisitive profile. It had a higher specific leaf area, meaning it constructed more light-intercepting surface per gram of leaf tissue, and a higher net photosynthetic rate, converting sunlight into sugars faster. It also achieved a higher photosynthetic nitrogen-use efficiency, extracting more carbon gain from every unit of nitrogen invested in its photosynthetic machinery. Below ground, the invader paired these leaf traits with a higher specific root length—more foraging root length per unit of root mass—along with thinner roots and lower root tissue density. In other words, it built an inexpensive, high-throughput system for capturing both light and soil nutrients. Astragalus laxmannii, by contrast, showed the conservative syndrome: thicker, denser roots, a higher root-to-shoot ratio, and slower, more frugal resource economics.

The most striking finding emerged when nitrogen was added. For the invader, nitrogen addition pushed its acquisitive traits even further: specific leaf area, photosynthetic rate, photosynthetic nitrogen-use efficiency, and specific root length all increased. For the native species, those same responses were smaller or in some cases statistically indistinguishable from zero. Because the invader could flexibly scale up its resource-capture apparatus while the native could not, the growth difference between the two species grew larger under nitrogen enrichment. Nitrogen pollution, in effect, acted as an amplifier for a pre-existing competitive asymmetry rather than creating one from scratch.

The chemical form of the nitrogen mattered as well. Soils supply inorganic nitrogen primarily in two forms: nitrate and ammonium. Plants expend different amounts of energy assimilating each, and species differ in their preferences and transport capacities. The experiment revealed that adding nitrate was generally more effective at boosting the invader’s performance in some cases, while ammonium additions could more effectively increase biomass for the native Astragalus laxmannii. This detail carries real-world weight, because atmospheric nitrogen deposition changes not just the total amount of nitrogen entering ecosystems but also the relative proportions of nitrate and ammonium that plants encounter. Landscapes receiving nitrate-dominated deposition may therefore be tipping the competitive balance further in favor of invaders with nitrate-hungry, acquisitive physiologies.

Statistical analysis of the trait data confirmed that these leaf and root characteristics were not incidental correlates of the growth difference—they significantly contributed to it. The acquisitive traits of the invader and the conservative traits of the native together explained a substantial portion of why Solanum rostratum accumulated more biomass under competition. This coordinated leaf-root perspective is important because much earlier invasion research focused on leaves alone, treating below-ground economics as a black box. By measuring both organ systems simultaneously, the study demonstrates that invasion success rests on a whole-plant strategy, with roots and leaves working in concert to convert abundant nitrogen into rapid growth.

The findings arrive at a moment of mounting global concern. Nitrogen deposition has intensified dramatically over industrialized and agricultural regions, with East Asia among the most affected areas, and recent global assessments have documented rising impacts of plant invasions on terrestrial ecosystems worldwide. If nitrogen enrichment systematically favors acquisitive invaders over conservative natives, then the two environmental pressures—nutrient pollution and biological invasion—may be reinforcing each other, producing ecosystems that are simultaneously more eutrophic and more dominated by exotic species. That feedback could accelerate the displacement of native flora and erode the biodiversity that underpins ecosystem services.

There are also practical implications for land managers. Controlling invasive plants in nitrogen-enriched landscapes may require more than mechanical removal or herbicide treatment; it may demand interventions that address the underlying soil fertility, such as restoring low-nitrogen conditions, managing fertilizer runoff, or favoring native species with sufficient plasticity to respond to elevated nutrients. The study’s authors suggest that increasing soil nitrogen availability, especially in the form of nitrate, may facilitate invasions of exotic plants characterized by coordinated resource-acquisitive strategies—a conclusion that turns a global pollution problem into a predictive tool for invasion risk. As nitrogen continues to accumulate in soils around the world, the plants best positioned to exploit it may increasingly be the ones we least want.

Subject of Research: How soil nitrogen availability and form influence competitive trait differences between an invasive plant and a native species

Article Title: Increasing soil availability of nitrogen, especially nitrate, amplifies growth advantage associated with acquisitive leaf–root traits in Solanum rostratum compared with co-occurring native species

Article References: Sun, J.-K., Feng, W.-W., Liu, M.-C., Chen, J.-X., Qi, F.-Z., & Feng, Y.-L. (2026). Increasing soil availability of nitrogen, especially nitrate, amplifies growth advantage associated with acquisitive leaf–root traits in Solanum rostratum compared with co-occurring native species. Plant and Soil. https://doi.org/10.1007/s11104-026-09091-5

Image Credits: AI Generated

DOI: 10.1007/s11104-026-09091-5

Keywords: biological invasion, Solanum rostratum, nitrogen deposition, nitrate, ammonium, plant traits, leaf economics, root economics, photosynthetic nitrogen-use efficiency, specific leaf area, specific root length, plant competition