Shifts in soil and plant functional diversity along an altitudinal gradient in the French Alps

Objectives Altitude integrates changes in environmental conditions that determine shifts in vegetation, including temperature, precipitation, solar radiation and edaphogenetic processes. In turn, vegetation alters soil biophysical properties through litter input, root growth, microbial and macrofaunal interactions. The belowground traits of plant communities modify soil processes in different ways, but it is not known how root traits influence soil biota at the community level. We collected data to investigate how elevation affects belowground community traits and soil microbial and faunal communities. This dataset comprises data from a temperate climate in France and a twin study was performed in a tropical zone in Mexico. Data description The paper describes soil physical and chemical properties, climatic variables, plant community composition and species abundance, plant community traits, soil microbial functional diversity and macrofaunal abundance and diversity. Data are provided for six elevations (1400–2400 m) ranging from montane forest to alpine prairie. We focused on soil biophysical properties beneath three dominant plant species that structure local vegetation. These data are useful for understanding how shifts in vegetation communities affect belowground processes, such as water infiltration, soil aggregation and carbon storage. Data will also help researchers understand how plant communities adjust to a changing climate/environment.


Objective
Elevational gradients can be used as a space-for-time substitution to provide insights into the response of communities to climatic changes and the impact on the local environment [1,2]. In particular, altitude integrates changes in the diverse conditions that determine soil biophysical properties [3], including temperature, soil moisture, solar radiation and input from vegetation [4].
In an attempt to disentangle the mechanisms through which vegetation affects soil biotic and abiotic processes at different elevations, we collated data on the biophysical environment, soil physico-chemical properties, plant community traits, microbial functional diversity and soil macroinvertebrate indicators.
Soil biophysical properties are heavily influenced by input rates and decomposability of organic matter, transport to deeper soil horizons and physical protection in

BMC Research Notes
*Correspondence: alexia.stokes@cirad.fr 1 AMAP, Univ Montpellier, INRAE, IRD, CIRAD, CNRS, 34000 Montpellier, France Full list of author information is available at the end of the article aggregate complexes. Therefore, our dataset includes data from infiltration experiments in the field and the measurement of soil aggregate stability at different depths. Our data also allow researchers to explore the impact of plant communities and soil macroinvertebrates on soil properties and vice-versa. With a particular focus on three plant species that structure local vegetation communities, belowground community-level traits were measured to determine how plant community composition impacts soil biophysics and microbial activity. To our knowledge, this dataset represents the largest freely available collection of data on plant traits and soil variables along a 1000 m elevational gradient in a temperate climate. Methods for each measurement are provided in the data files and supplementary materials ( Table 1).
Five 400 m 2 plots were chosen at each altitude, so that two or three dominant and community-structuring species were present: Picea abies (L.) H. Karst, Vaccinium myrtillus L. and Juniperus communis L. A botanical survey was performed in the plot (Table 1, file 5) and one adult individual of each structuring species was selected. At the limit of the individual's canopy on the downslope side, infiltration tests were performed to estimate water flow through soil [8] and hydraulic conductivity of the quasi-steady phase was calculated ( To investigate the relationships between soil biophysical properties and vegetation, plant community composition was measured in a 1.0 m 2 subplot within each plot and close to each structuring species (  [10] was used to characterize microbial activity and functional diversity on air-dried bulk and rhizospheric samples, through the community level physiological profiles of the soil microbial communities (Table 1, file 11).
Soil macroinvertebrates were hand sorted from each monolith and fixed in 100% ethanol. Macroinvertebrates were identified at the order level, except for earthworms for which morphological diagnoses were combined with DNA barcoding to obtain species level assignations. Invertebrates within each taxa were counted and weighed (Table 1, file 12, [11]).
Roots were hand sorted, washed and sorted into categories according to their diameter and functionality: rhizomes, very coarse roots with diameter > 5 mm, coarse  [27] roots with diameter 2-5 mm and fine roots (< 2 mm). Fine roots were separated into absorptive and transport roots [12]. Two subsamples of roots < 5 mm were scanned and analysed using Winrhizo Pro (Regent Instruments, Canada). Several root traits were measured, including root length density and mass, diameter, specific root length and tissue density (Table 1, file 13, [13]. Chemical traits were measured on absorptive and transport roots ( Table 1, file 13), including nitrogen, carbon content and hydrosoluble compounds, hemicellulose, cellulose and lignin content [14].

Limitations
Although this dataset comprises a large number of field and laboratory data collated from 70 monoliths in 30 plots, long-term climatic data were not available for each of the six altitudinal levels. Therefore we used the Aurelhy model, that estimates climatic data to a resolution of 1 km [7]. As some altitudinal bands were located within 1 km of each other, data will be the same for those plots. Also, datasets refer specifically to three dominant and community-structuring plant species, limiting generalization at larger scales.