Nitrogen content of herbarium specimens from arable fields and mesic meadows reflect the intensifying agricultural management during the 20th century

Arable fields and mesic meadows have been affected by intensifying agricultural management and nutrient input during the 20th century, but direct evidence for the long-term impact of intensification on plant nutrient contents remains scarce. Non-destructive novel spectroscopic methods can produce such data from herbarium specimens, making it possible to investigate how contents of leaf nutrient traits, especially nitrogen and phosphorus, changed over the last century, and what role habitat type and management practices play.
We carried out a resurvey study of functional traits in arable field and mesic meadow communities. We used specimens from two German herbaria with a high coverage of their local floras: the Senckenberg Herbarium Görlitz and the Herbarium Haussknecht in Jena. Following specimen information, the same plant species were resampled in the field in 2022 at the same locations. We employed Near-Infrared Spectroscopy to predict leaf nitrogen, phosphorus, and carbon content o..., The dataset consists of metadata, functional trait data, and fertilization data for herbarium specimens and plant specimens sampled in 2022.The herbarium specimens are from the collections of the Herbarium Haussknecht in Jena, Germany (JE), and the Senckenberg Herbarium Görlitz in Görlitz, Germany (GLM). The field specimens were gathered from May to August of 2022, and were press-dried in the same way as the herbarium specimens. Near-Infrared Spectroscopy (NIRS) measurements were taken from both specimen types using an ASD FieldSpec 4 and a contact probe. A subset of the field specimens was selected to create a NIRS calibration dataset, which involved conventional wet lab analyses of the leaf nutrient contents of leaf nitrogen, leaf carbon and leaf phosphorus contents for these specimens. These wet lab measurements were used in conjunction with the NIRS measurements to build partial least squares regression (PLSR) models for each trait. The PLSR models were in turn used to predict the r..., , # Nitrogen content of herbarium specimens from arable fields and mesic meadows reflect the intensifying agricultural management during the 20th century.

[https://doi.org/10.5061/dryad.z34tmpgpw ](https://doi.org/10.5061/dryad.z34tmpgpw)

## Description of the data and file structure

“`Resurvey_analysis_code.R`” is a commentated script for RStudio, which allows the user to load the data, calculate statistics, and create plots.

\"`01_resurvey_combined_table_cleaned.csv`\" is a data table containing data for 1270 herbarium and field specimens of 49 plant species. For each specimen, data on the species and sampling date, the locality description, GPS coordinates (if available) and the collection it is stored in are included. Leaf functional trait values are also included: leaf nitrogen content, leaf phosphorus content, leaf carbon content, and the leaf carbon:nitrogen ratio and the leaf nitrogen:phosphorus ratio were all predicted from NIR spectra using PLSR calibration models.

\"`02_fert...