DOI: 10.5061/dryad.qnk98sfqz
title: Data from: Foliar N content parallels increasing aridity in a Mediterranean-Saharan transition zone: Evidence from regional and global trends

description: Aim Warm deserts are characterized by water shortages and high-temperature
 extremes. A common adaptive strategy in such environments is the
 maximization of photosynthetic capacity, which allows plants to achieve
 positive carbon budgets by taking advantage of short periods of water
 availability and non-inhibitory temperatures. Assuming that photosynthetic
 capacity is approximated by leaf N concentration, we tested the hypothesis
 that environmental aridity is related to an elevated leaf nitrogen
 content. Location 53 locations in the transitional zone spanning the
 Mediterranean and the Sahara Desert in Morocco. The mean maximal
 temperature (Tmax) within the area varied between 35.7 and 43.5 °C, and
 the mean annual precipitation (MAP) was between 12 and 246 mm. Taxon 225
 vascular species representative of local vegetation Methods Leaf samples
 were collected along a regional aridity gradient and preserved in
 herbarium presses. The leaf mass per area (LMA) and N concentrations
 expressed on leaf mass (Nmass) and area (Narea) basis were determined. We
 also obtained LMA and Nmass values for 6711 species from a worldwide
 database for comparative analysis. Results Significant increases in mean
 LMA, Nmass, and Narea accompanied the increase in Tmax and the decrease in
 MAP in woody species and in non-graminoid herbs, but not in graminoids.
 Considering that the climate in our sampling area as a whole was arid, we
 compared the Nmass values of Moroccan plants with those from a worldwide
 database and found that at a common LMA, the Moroccan plants showed on
 average elevated Nmass relative to the global values. Main conclusions
 These two lines of evidence: regional gradient and global comparison
 confirm that hot deserts select for high leaf N content. This result
 predicts the direction of natural selection that will accompany future
 climate warming.
description: <strong>Field sampling</strong> - Plant material was
 collected during two field trips conducted between 9 and 18 June 2011 and
 between 12 and 22 March 2012 at 53 sites located within the state limits
 of Morocco. Site selection was haphazard and was based on the presence of
 relatively undisturbed spontaneous vegetation. One to several species were
 sampled per site. Two aggregate samples consisting of several healthy,
 mature, well-illuminated leaves per species were collected, each from
 several separate individuals. The total number of taxa sampled (sometimes
 identified down to subspecific level but hereafter referred to as species)
 was 225; however, 22 species were sampled from two sites and one from
 three sites. The leaves were carefully placed between sheets of newsprint
 and blotting paper and pressed tightly in a herbarium press. The blotting
 paper was exchanged daily for several days until the material was
 dry. <strong>Sample processing</strong> -
 Samples were transported to the laboratory, where areas of individual leaf
 laminas were measured using a desktop scanner controlled by WinFOLIA
 software (Regent Instruments, Sainte Foy, Quebec, Canada). Typically, 5 or
 10 leaves per sample were used, but in several species, the number was
 lower (2-4). The leaves were then placed in a forced circulation oven at
 65 °C for 72 hours and weighed, and leaf mass-per-area (LMA, g
 m<sup>-2</sup>) was calculated. Leaf material was ground in a
 mill (IKA Labortechnik, Staufen, Germany) and leaf N content per mass
 (N<sub>mass</sub>) was analyzed in an Elemental Combustion
 System CHNS-O 4010 (Costech Instruments, Italy/USA). Leaf N content per
 area (N<sub>area</sub>) was calculated by multiplying
 N<sub>mass</sub> by LMA.
 <strong>Evaluation of the press drying
 technique</strong> - To assess the effect of using desiccated
 material on the accuracy of trait determination, a set of mature leaves
 from diverse species widely varying in shape and structure was collected
 in August 2018 from the grounds of Adam Mickiewicz University campus in
 Poznań, Poland. Thirty-nine species were sampled and the number of leaves
 per species was 14-20. In <em>Picea omorica</em> several
 needles constituted a single sample. The samples were placed in plastic
 bags containing moist paper towels and brought to the laboratory, and the
 areas of fresh leaf laminas were measured with a desktop scanner and
 Winfolia software. Within each species, samples were randomly assigned to
 one of two drying treatments. The first treatment involved immediate
 drying of the leaves in a forced circulation oven at 65 °C for 72 hours.
 For the second treatment, the leaves were placed in herbarium presses, as
 described above. The drying in the presses lasted four weeks. The blotting
 paper was replaced daily during the first week and less frequently
 thereafter. The presses were kept indoors in a well-ventilated spot with
 variable temperatures that on most days exceeded 30 °C. When drying in the
 presses was complete, leaves were again scanned to determine leaf areas
 followed by drying at 65 °C for 72 hours. All dry leaves were weighed and
 LMA was calculated. For N determination, four press-dried and four
 oven-dried leaf samples from each species were ground and analyzed as
 described above.
description: # Data from: Foliar N content parallels increasing aridity in a
 Mediterranean-Saharan transition zone: Evidence from regional and global
 trends
 [https://doi.org/10.5061/dryad.qnk98sfqz](https://doi.org/10.5061/dryad.qnk98sfqz) ## Description of the data and file structure This is the data used in the article 'Foliar N content parallels increasing aridity in a Mediterranean-Saharan transition zone: Evidence from regional and global trends' by Wyka et al.  ### Files and variables #### File: README.md **Description:** This file contains lists of variables for each of the three spreadsheets. #### File: Wyka\_et\_al.\_Morocco Raw data.xlsx **Description:** This data set consists of three spreadsheets entitled 'Morocco raw data', 'Morocco species means', and 'Press drying trial data'. ##### Variables: 1\) The sheet "Morocco raw data" contains location data, taxonomy, climate, and leaf trait measurements of individual leaf samples collected from 53 sites across Morocco. Column headings: **Site name** (working names of the 53 sites assigned by collectors, usually referring to formally named topographic features) **Latitude** of the site (degrees in decimal form) **Longitude** of the site (degrees in decimal form) **MAP** - mean annual precipitation (mm) at the site (30-year average obtained from Wordclim) **MAT** - mean annual temperature (°C) at the site (30-year average obtained from Wordclim) **Tmax** - mean maximal temperature of the warmest month (°C) at the site (30-year average obtained from Wordclim) **Collection date** **Year collected** (2011 or 2012) **Field sample i.d**. - number originally assigned to the sample; between 1 and 558 **Species name** - name verified by Taxonomic Name Resolution Service (https://tnrs.biendata.org/) in Jan-Feb 2024 **Family** - family assignment verified by Taxonomic Name Resolution Service (https://tnrs.biendata.org/)) in Jan-Feb 2024 **Lifeform** - herbaceous (non-graminoid), graminoid or woody; assignment omitted for borderline species (e.g., woody at base) that were not used in life-form specific analyses and are labelled as ‘other’ **LMA** - leaf mass per area (g m-2) **N (mg g-1)** = Nmass (nitrogen concentration per leaf dry mass) **N (g m-2**) = Narea (nitrogen concentration per leaf area unit) 2\) The sheet "**Morocco species means**" contains location data, climate variables, sampling dates, taxonomic information and values of LMA, Nmass, and Narea averaged per species and site. Column headings as in "**Morocco raw data" sheet**. The total number of species in this sheet is 225, but since some occurred at two or three sites, the total number of species by site means is 249. 3\) The sheet "**Press drying trial data**" contains data used in evaluating the effects on trait determination of the leaf drying method (herbarium press drying followed by leaf area determination vs. area determination from fresh leaves followed by oven drying). Column headings: **Sample i.d.** (from 1 to 691, given individually to each leaf or set of leaves for which a single set of traits  was measured) **Species name** **Sample i.d. within species** (numbers 1-20 applied within species) **Drying method** (press vs. oven). Note that leaf samples initially dried in a press were scanned for leaf area determination and later were oven-dried for determination of mass and N content. **Fresh area (cm2)** - Leaf area determined immediately after collection **Dry area (cm2)** - Leaf area determined after drying in a press (note that there are no data for oven-dried leaves) **Dry mass (g)** - leaf mass determined after oven drying of fresh leaves or press-dried leaves **LMAtrue (g m-2)** - Leaf mass per area determined based on fresh leaf area **LMApress (g m-2)** - Leaf mass per area determined using area of press-dried leaves (no data for oven-dried leaves) **Delta area (%)** - area reduction (%) of press-dried leaves relative to the fresh area of the same leaves **Delta LMA (%**) - LMA increase (%) of press dried leaves relative to LMA based on fresh area of the same leaves **N (mg g-1)**  - Nmass (nitrogen concentration per leaf dry mass) **N (g m-2)** - Narea (nitrogen concentration per leaf area unit) Empty cells indicate that the data were not available because of sample mishandling. Cells containing n/a (i.e., not applicable) indicate that the absence of data was intentional as per design. ## Code/software NA ## Access information NA