Funcitree database

Study Extent

Seasonally-dry savanna in Mali, Nicaragua and Senegal The study was conducted in silvopastoral and agroforestry ecosystems of the western Sahel region. Sampling sites were selected near Louga (15° 37’ N, 16° 13’ W) in northwest Senegal (7 sites), and near Ségou (13° 27’ N, 6° 16’ W) in south-central Mali (8 sites). In this region, rain falls mainly during the monsoon season (June- October), followed by a dry season between November and June (Fig. S1). Louga has a semiarid sub-Canarian climate (Wade, 1997) with a mean temperature of 24.9 ºC and average annual rainfall of 330 mm (1950-2000). Both rain and the warmest temperatures occur mostly during the monsoon season (Edmunds & Gaye, 1994; NOAA, 2015). Ségou has a continental semiarid climate with lower relative humidity than Louga, but has higher mean annual temperature (27.8 ºC) and precipitation (566 mm; NOAA 2015; Fig. S1). Daily maximum temperatures in both areas frequently reach above 50ºC. Soils in Louga and Ségou are highly weathered acidic sands on ancient dunes, inter-dune depressions or plains that typically show low water holding capacity and organic matter content and are particularly poor in phosphorus and other nutrients (Bitchibaly et al., 2012). Relatively shallow groundwater can be found in both Louga and Ségou studied sites. Vegetation of these agroforestry ecosystems is an open savannah with sparse trees and shrubs scattered across a grassland matrix and interspersed with croplands where typical management practices include harvesting of trees and shrubs, grazing and farming (IER, 2010; Konaté, 2010).

Sampling

We sampled leaves and stems from individual trees and shrubs species, including evergreen species that retain a full canopy throughout the year and drought-deciduous species that remain leafless or partially leafless for several months during the dry season. The only exception is Faidherbia albida, a deciduous legume that sheds leaves during the rainy season (Diémé et al., 2018). Plant samples were collected in the early dry season before leaf senescence of deciduous species. Sampled trees and shrubs were healthy-looking and were at least 15 m far apart from each other (ranging between 0.015 and 60 km apart within each country) and with their crowns fully exposed to sunlight.

Method steps

1. From each plant, we sampled two sun-exposed branches from the eastern side of the canopy before dawn. One branch was placed in a sealed plastic bag within a dark hermetic bucket and was used for measuring stem predawn water potential (Ψpd) with a Scholander-type pressure bomb. Leaf thickness (mm), specific leaf area (SLA; m2kg-1), and leaf relative water content (RWC; g g-1) were measured in fully expanded, mature, damage-free fresh leaves. Thickness was measured in three points in each leaf with a digital caliper and the mean value was recorded. The leaf collected to measure RWC was first weighed (fresh weight, Fw), then fully rehydrated overnight in the dark, weighed again (Hw) and then scanned, and leaf area was then measured with ImageJ. Leaves were then oven-dried at 60ºC for 72 h and weighed again (dry weight, Dw). SLA is the one-sided area (leaf area, LA) of the fully rehydrated leaf divided by its dry mass (SLA=LA/DM), while leaf RWC is the difference between fresh and dry leaf weight divided by the difference between fully hydrated and dry leaf weight (i.e., RWC=(Fw-Dw)/(Hw-Dw). Dry leaves were then ground using a ball-mill to determine C and N concentrations (mass based) and δ13C, δ15N and δ18O composition. Leaf Narea (mg cm-2) was calculated as the ratio between leaf Nmass and SLA. From the second branch, we cut a terminal 8-cm leafless woody stem that was immediately placed in a screw-cap polypropylene vial and sealed with Parafilm. Vials were transported in a cooler to the lab within four hours and stored frozen. Xylem water was extracted using cryogenic vacuum distillation (Ehleringer & Osmond, 1989). The oxygen isotopic composition of xylem water (Xylem water δ18O) helps assess the approximate depth of soil water uptake by roots in dryland ecosystems where steep vertical gradients in soil water δ18O develop during rainless periods (Moreno-Gutiérrez et al., 2012). Evaporation from upper soil during hot, dry periods leads to heavy isotopic enrichment of the remaining soil water near the surface that steeply decreases with depth (Allison & Hughes, 1983). Higher xylem water δ18O values indicate uptake of isotopically enriched water from shallower soil layers exposed to intense evaporation, whereas lower xylem water δ18O values indicate utilization of non-enriched water from deeper, less evaporated water sources (Querejeta et al., 2007; Ding et al., 2021). Foliar δ13C can be used to estimate long-term ratios of the intercellular to ambient CO2 values (ci/ca) if the carbon isotope ratio of atmospheric CO2 (δ13Cair) is known (Farquhar et al., 1989). To calculate long-term ci/ca ratios, we first calculated Δ13C as: where δ13Cair is the C isotopic composition of atmospheric CO2 (-8.45‰, Mauna Loa records; http://www.esrl.noaa.gov/gmd/dv/ftpdata.html) and δ13Cleaf is the C isotopic composition of leaf material. Then, from Δ13C values, we calculated ci/ca as: where as is the fractionation factor of gaseous diffusion (4.4‰) and represents effective fractionation due to carboxylation (27‰), estimated empirically (Farquhar et al., 1982). Cryogenic vacuum distillation and stable isotope analyses of leaf and water samples were conducted at the Stable Isotope Ratio Facility for Environmental Research, University of Utah (USA). Leaf N and C concentrations and δ13C, δ15N were measured with an isotope ratio mass spectrometer (Finnigan Mat Delta+ IRMS) coupled to an elemental analyzer (EA, Carlo Erba CHN EA1110). Leaf δ18O was measured with a Finnigan TC/EA IRMS. The δ18O isotopic composition of xylem water was measured using laser water isotope analyser (Picarro L2130i).

Plant taxonomy Kew Garden

1. Plantae
   common name: Plants rank: kingdom

Mali, Senegal, Nicaragua