What effect has increasing fertiliser use had on plants over the past century? It’s a difficult research project to start now because, ideally, you’d have started gathering samples over a century ago, and it’s hard to find a time-machine allowing you to start. But not impossible. New research by Kühn, Umazekabiri & colleagues uses specimens from herbaria to track back the use of fertilisers to the 19th century.
A herbarium is a store of catalogued plant tissue, kept for reference. Botanists have been taking samples for a long time, so it’s no surprise that herbaria are excellent places to examine material from across a wide range of time. The problem with chemically analysing these specimens is that the process is usually destructive. That means you’ll be damaging irreplaceable material, and can you be sure that your research technique isn’t going to be surpassed in ten, twenty or fifty years time?
Kühn, Umazekabiri & colleagues have solved this problem by using a non-destructive method to analyse samples. They were able to work out the chemical content of the plant tissue by examining the light it reflects. They examined the plants under light ranging from 350 to 2500 nanometres, which is just into the ultra-violet and quite a way into the infra-red. Different nutrients and compounds in the plant tissues reflect light in different ways, creating a spectral fingerprint of the plant’s chemical makeup.
The analysis of 1270 samples from over 170 years of collection revealed that plant nitrogen content has increased markedly over time, tracking the rise of chemical fertilisers in the 20th century. Farm field plants showed the most rapid changes in nitrogen content, compared to meadow plants, which tallies with modern agriculture being the culprit for the change. They also found that plants’ carbon content had decreased over time. This may be another sign of increased fertilisation pushing plants into faster growth strategies.
This has shifted the balance of nitrogen to phosphorus, which may be a sign of rising nitrogen or declining phosphorus in the soil. This change in balance may have altered the make-up of plant communities, boosting some species and harming others. Kühn, Umazekabiri & colleagues note this result isn’t a big surprise.
A recent study has found that increased nitrogen fertilization in general will result in reduced phosphorus availability in the soil over time, exacerbating the trend. Furthermore, increased soil nutrient availability has been found to primarily and negatively impact the abundance of specialized, small- ranged species, thus establishing a connection to the wider topic of biological conservation. Given that classical monitoring and related studies of plant communities and traits rarely span more than a few decades, evidence on long- term trends in nutrient limitation is, however, limited.
This article adds that greater depth of historical understanding to the other recent studies. The research links changes in plant chemistry to historical fertiliser application records, correlating fertiliser applied per year, with leaf nutrient levels. Thanks to the new methods employed by Kühn, Umazekabiri & colleagues this historical record won’t have been damaged leaving open the possibility of further insights in the future.
Kühn, P., Umazekabiri, R., Römermann, C., Bruelheide, H., & Wesche, K. 2025. Nitrogen content of herbarium specimens from arable fields and mesic meadows reflect the intensifying agricultural management during the 20th century. Journal of Ecology. https://doi.org/10.1111/1365-2745.14474
Cross-posted to Bluesky & Mastodon.
Cover image: Canva.
The post Historic Specimens Reveal a Century of Agricultural Change appeared first on Botany One.
