Results of repeated measures ANOVA on the effect of species and date of sampling (May and September) on the N proficiency (N_prof), N resorption efficiency (NR_eff) and the ¹⁵N abundance of leaf litter.

<p>Significant effects at α = 0.05 are highlighted in bold, n = 5.</p

Seasonal change in the dry weight of branch components.

<p>Average dry weight of the short (SS, round) shoots and the long shoots leaves (LL, triangles) produced in 2002 (solid symbols) and 2003 (open symbols) in three-year-old branches of <i>L. subulatum</i> (A) and <i>L. suffruticosum</i> (B). Values are means ± SE, n = 15.</p

Percentage of labelled (new) N (A) and total amount of labelled (B) and unlabelled N (C) in the canopy of <i>L. subulatum</i> (open symbols) and <i>L. suffruticosum</i> (solid symbols) throughout the experiment.

<p>Data are means ± SE, n = 5.</p

Seasonal dynamics of the nitrogen (N) content in the shoots of study species (g per plant).

<p>N content in the short shoots (whole, including both leaves and stems, SS; round) and the stems of long shoots (LS, triangles) produced in 2002 (solid symbols) and 2003 (open symbols) by <i>L. subulatum</i> (A) and <i>L. suffruticosum</i> (B) is shown. Values are the product of two means (see materials and methods for details on calculations).</p

Main phenological events and seasonal dynamics of nitrogen (N) mass-based concentrations of study species.

<p>Upper bars indicate main phenological events in both species (<i>Lepidium subulatum</i>: black bars; <i>Linum suffruticosum</i>: open bars). Lower panels show N concentrations (mg g⁻¹) of the short shoots (SS, round), main stems (MS, solid squares) and coarse roots (CR, open squares) of <i>L. subulatum</i> (A) and <i>L. suffruticosum</i> (B). Different cohorts of short shoots are denoted by solid (2002) and open (2003) symbols. Values are means ± SE, n = 5. PSG: primary shoot growth; F+FR: flowering and fruiting; LS: Leaf shedding.</p

Distribution of labelled and total N at the end of the experiment (24^th September 2010).

<p>(A) Allocation of new (labelled) N to the main organs of both study species. (B) Distribution (% of total) of N among the main organs of study species. (C) Total amount of N allocated to the main organs of study species at the end of the experiment. Different letters indicate significant differences among fractions after one-way ANOVAs (α = 0.05). Values are means ± SE, n = 5.</p

Results of two-way ANOVAs testing the differences between species and fractions (young branches/main stems/roots) on the percentage of total and labelled N and the total amount of N allocated at the end of the growing season (September 2010).

<p>Significant effects at α = 0.05 are highlighted in bold, n = 5.</p

Plant affinity to extreme soils and foliar sulphur mediate species-specific responses to sheep grazing in gypsum systems

Plants growing on extreme soils have mainly been described in relation to their adaptations to edaphic conditions, although herbivores may also be an important factor in these ecosystems. Gypsum soils occur in drylands often where livestock practices occur. However, it is unknown whether plant traits related to gypsum soil constraints are associated with resistance to herbivory. In order to assess whether gypsumspecialist species might be favoured at higher grazing levels and to detect the traits involved, we evaluated the responses of gypsum specialists vs. generalists to three intensities of livestock pressure. We analysed the relative cover shifts of species along a livestock gradient, and variation in canopy height, canopy area, leaf carbon (C), nitrogen (N), and sulphur (S), specific leaf area (SLA) and leaf dry matter content (LDMC). We found that gypsum-specialists responded by increasing or maintaining their cover at medium and high grazing pressure, whereas most generalists responded by decreasing it. Gypsum-specialists showed higher leaf S than generalists, regardless of grazing intensity. All species showed similar patterns for traits linked to loss of above-ground biomass when grazing increased. Plant affinity to gypsum soils mediates vulnerability to grazing with foliar S possibly being a defence trait.</p

Climatic and edaphic characteristics of study sites.

<p><i>Abbreviations:</i> T  =  Mean annual temperature; P  =  total annual rainfall; SOM  =  soil organic matter; N  =  nitrogen.</p>a<p>M  =  Madrid (Central Spain, Middle Tajo Basin), Z  =  Zaragoza (NE Spain, Middle Ebro Basin).</p><p>Climatic and edaphic characteristics of study sites.</p

Results of PLS regression analyses between FTIR spectra and the C (%), N (mg/g), C/N, Na (mg/g), K (mg/g), Ca (%), Mg (mg/g), P (mg/g), S (%) and Ash (%) concentrations of the samples analysed.

<p>Results of PLS regression analyses between FTIR spectra and the C (%), N (mg/g), C/N, Na (mg/g), K (mg/g), Ca (%), Mg (mg/g), P (mg/g), S (%) and Ash (%) concentrations of the samples analysed.</p