Background and aims It remains uncertain whether a higher toxicity of either NaCl or Na 2 SO 4 in plants is due to an altered toxicity of sodium or a different toxicity of the anions. The aim of this study was to determine the contributions of sodium and the two anions to the different toxicities of chloride and sulfate salinity. The effects of the different salts on physiological parameters, mineral nutrient composition and expression of genes of sulfate transport and assimilation were studied. Methods Seedlings of Brassica rapa L. have been exposed to NaCl, Na 2 SO 4 , KCl and K 2 SO 4 to assess the potential synergistic effect of the anions with the toxic cation sodium, as well as their separate toxicities if accompanied by the non-toxic cation potassium. Biomass production, stomatal resistance and Fv/ fm were measured to determine differences in ionic and osmotic stress caused by the salts. Anion content (HPLC), mineral nutrient composition (ICP-AES) and gene expression of sulfate transporters and sulfur assimilatory enzymes (real-time qPCR) were analyzed. Results Na 2 SO 4 impeded growth to a higher extent than NaCl and was the only salt to decrease Fv/fm. K 2 SO 4 reduced plant growth more than NaCl. Analysis of mineral nutrient contents of plant tissue revealed that differences in sodium accumulation could not explain the increased toxicity of sulfate over chloride salts. Shoot contents of calcium, manganese and phosphorus were decreased more strongly by exposure to Na 2 SO 4 than by NaCl. The expression levels of genes encoding proteins for sulfate transport and assimilation were differently affected by the different salts. While gene expression of primary sulfate uptake at roots was downregulated upon exposure to sulfate salts, presumably to prevent an excessive uptake, genes encoding for the vacuolar sulfate transporter Sultr4;1 were upregulated. Gene expression of ATP sulfurylase was hardly affected by salinity in shoot and roots, the transcript level of 5′adenylylsulfate reductase (APR) was decreased upon

Questions: Are the vegetation structure and soil properties of fallows similar to adjacent species-rich Mediterranean steppe communities 35 years after abandonment? Is there a spontaneous redevelopment towards the original steppe vegetation after reintroduction of the traditional grazing system? Can differences in functional trait composition be identified according to different land-use types? Do traits of selected species affect the ability to recolonize fallow land? Location: Mediterranean steppe of La Crau (Southeastern France). Methods: We conducted 80 vegetation surveys and soil analyses in the steppe and adjacent fallow land in six locations in La Crau in 2015; for three locations, data from 2001 were included. To compare the functional composition of steppe vs fallow land, community-weighted means (CMW) of specific leaf area (SLA), leaf dry matter content (LDMC) and canopy height were calculated. To test whether trait variability is associated with the recolonization success of 12 selected target species, we measured SLA, LDMC, canopy height, plant width and aboveground biomass on eight replicate individuals per site and species.Results: Fallow land was characterized by lower species richness and elevated phosphorus and potassium content in the soil. Comparing vegetation relevés between 2001 and 2015 revealed that the fallows were developing towards steppe vegetation. CWMs of SLA were significantly lower and CWM of LDMC higher in steppe than in fallow land. There was no similarity in trait composition between steppe species that successfully recolonized the fallow-land community, and no evidence that intraspecific trait variability is associated with recolonization success of these species. K E Y W O R D S community trait means, cultivation, dry grassland, grazing, intraspecific trait variability, leaf dry matter content, natural recovery, restoration, specific leaf area | 75 Applied Vegetation Science HELM Et aL.

Tree stem CO2 efflux is an important component of ecosystem carbon fluxes and has been the focus of many studies. While CO2 efflux can easily be measured, a growing number of studies have shown that it is not identical with actual in situ respiration. Complementing measurements of CO2 flux with simultaneous measurements of O2 flux provides an additional proxy for respiration, and the combination of both fluxes can potentially help getting closer to actual measures of respiratory fluxes. To date, however, the technical challenge to measure relatively small changes in O2 concentration against its high atmospheric background has prevented routine O2 measurements in field applications. Here we present a new and low-cost field-tested device for autonomous real-time and quasi-continuous long-term measurements of stem respiration by combining CO2 (NDIR based) and O2 (quenching based) sensors in a tree stem chamber. Our device operates as a cyclic closed system and measures changes in both CO2 and O2 concentration within the chamber over time. The device is battery-powered with a > 1 week power independence and data acquisition is conveniently achieved by an internal logger. Results from both field and laboratory tests document that our sensors provide reproducible measurements of CO2 and O2 exchange fluxes under varying environmental conditions.

Little is known about the sources and age of C respired by tree roots. Previous research in stems identified two functional pools of non-structural carbohydrates (NSC): an "active" pool supplied directly from canopy photo-assimilates supporting metabolism and a "stored" pool used when fresh C supplies are limited. We compared the C isotope composition of water-soluble NSC and respired CO 2 for aspen roots (Populus tremula hybrids) cut off from fresh C supply after stem-girdling or prolonged incubation of excised roots. We used bomb radiocarbon to estimate the time elapsed since C fixation for respired CO 2 , water-soluble NSC and structural α-cellulose. While freshly excised roots (mostly <2.9 mm in diameter) respired CO 2 fixed <1 year previously, the age increased to 1.6-2.9 year within a week after root excision. Freshly excised roots from trees girdled~3 months ago had respiration rates and NSC stocks similar to un-girdled trees but respired older C (~1.2 year). We estimate that over 3 months NSC in girdled roots must be replaced 5-7 times by reserves remobilized from root-external sources.Using a mixing model and observed correlations between Δ 14 C of water-soluble C and α-cellulose, we estimate~30% of C is "active" (~5 mg C g À1 ).