Annual growth of Cassiope tetragona as a proxy for Arctic climate: developing correlative and experimental transfer functions to reconstruct past summer temperature on a millennial time scale

Annual growth of the polar evergreen shrub Cassiope tetragona on Svalbard was evaluated as a proxy for Arctic summer temperatures. Transfer functions were derived from temperature‐growth correlations of shoots and from a temperature‐growth response, obtained from experimental warming using open top chambers (OTC) in high Arctic tundra vegetation at Isdammen approximately 1.5 km southeast of Longyearbyen, Svalbard (78°N, 15 E) and in Longyeardalen, 3 km west of Isdammen from 2004 to 2006. Air temperatures, monitored throughout the summer months, were 1.3 °C higher inside the OTCs than in the control plots. Annual stem growth was measured by tagging stems and leaves, and in the lab with shoots harvested from OTCs and control plots. Annual growth parameters assessed were leaf production, sum of length and weight of individual leaves, and stem length increment derived from leaf scar distances and the distances between wintermarksepta in the stem. Wintermarksepta are formed at the end of the summer growth period when the pith is narrowing and consist of dense and dark tissue ( Fig. 1b ). The variation of annual growth in a 34‐year site chronology (based on Cassiope shoots from the surroundings of the OTCs and control plots) correlated strongly with the mean summer temperature on Svalbard. The number of leaf pairs, leaf length and stem length also increased in the OTC warmed plots in the second and third year of warming. Transfer functions were derived from the temperature‐annual growth correlations from a single shoot from Longyeardalen, from the cross‐dated Isdammen site chronology and from the growth response to experimental warming. Based on leaf scar distances and distances between wintermarksepta of well‐preserved subfossil shoots in arctic tundra soil, annual stem length increase was assessed for the layers of a soil core collected at the Isdammen site. Based on the derived transfer functions summer temperature of the period relating to the 15 cm deep tundra soil core layer, radiocarbon dated at 4230±40 bp , may have been 3.0 °C lower than the present‐day 6.2 °C value. These results indicate that the transfer functions can be used to reconstruct past temperatures, beyond the time range of instrumental temperature and ice core records of Svalbard.

Figure 1 Open in figure viewer PowerPoint (a) Morphology of shoot of Cassiope tetragona collected May 26, 2007, Longyeardalen. Removal of the front row of leaves shows four leaf pairs of the 2006 summer, the leaf primordium for the 2007 growing season and the stem length increase summer 2006. (b) Wintermarksepta, darker colored than the pith tissue, indicating the winterperiod in a longitudinal section of an air‐dried shoot collected August 26, 2006, Longyeardalen.     

AN ECOPHYSIOLOGICAL STUDY OF THE SALT SECRETION OF FOUR HALOPHYTES

Plants of Spartina anglica, Limonium vulgare, Armeria maritima and Glaux maritima were collected in the field and grown on different concentrations of NaCl, KCl and CaCl₂. Salt secretion, ion content, water content and transpiration rates were determined. The highest sodium secretion was found in Spartina anglica , a species from the most saline habitat; and a somewhat lower secretion rate in Limonium vulgare. The lowest rates were found in Glaux maritima and Armeria maritima. The sodium secretion efficiency, i.e. the ability to maintain an unchanged internal sodium content, was highest in Spartina anglica. Spartina anglica is the most successful in the removal of excessively absorbed salt, since it secretes 60% of the absorbed sodium. The values for Limonium vulgare, Glaux maritima and Armeria maritima were 33, 20 and 4% respectively. The species studied differ in the preferential sequence of ion secretion as well as in secretion rate and efficiency. This preferential sequence of ion secretion seems to be similar in members of the same taxonomic group (Plumbaginaceae). The comparability of the secretion parameters is discussed with regard to morphological differences between the species.     

An Ecophysiological Comparison of Measurements of the Diurnal Rhythm of the Leaf Elongation and Changes of the Leaf Thickness of Salt-resistant Dicotyledonae and Monocotyledonae

Rozema, J., Arp, W., van Diggelen, J., Kok, E. and Letschert,J. 1987. An ecophysiological comparison of measurements of thediurnal rhythm of the leaf elongation and changes of the leafthickness of salt-resistant Dicotyledonae and Monocotyledonae.—J.exp. Bot. 38: 442–453. The continuous measurement of leaf elongation and leaf thicknesswith the use of a rotation potentiometer set up revealed a rapidand sensitive reaction of halophytic plants to conditions affectingthe plant's water relations. At increased salinity (450 molm^–3 NaCl) the rate of leaf elongation decreased both inAster tripolium and in Sparlina anghca. Increased shrinkageduring the day and a long period for recovery swelling at nightin leaves of Aster iripolium at increased salinity illustratesthat water shortage is part of the cause of salinity-inducedgrowth reduction. All dicotyledonous species analysed (Aster tripolium, A triplexhastata, A. littoralis, Suaeda maritima and Beta vulgaris) showeda day/night ratio of the leaf elongation rate lower than 1,while this ratio was higher than or equal to 1 in Monocotyledons(Spartina anglica, Juncus gerardii, J. maritimus, Festuca rubrassp. litoralis, Elymus pycnanthus). With the exception of Triglochinmaritima none of the monocotyledonous halophytes tested (Sparlinaanglica, Juncus gerardii, J. maritimus, Festuca rubra ssp. litoralis,Elymus pycnanthus) exhibited a diurnal rhythm of leaf thicknesschanges, such as was observed for all dicotyledonous speciesstudied (Aster tripolium, Atriplex hastata, A. littoralis, Salicorniabrachyslachya, Suaeda maritima, Glaux maritima, Odontites vernassp. serotina). The diurnal pattern of the leaf elongation rateand the leaf thickness changes can be explained by variationof photosynthetic rate and transpiration water losses by stomatalclosure in the dark and opening in the light such as shown forthe dicotyledon species Glaux maritima. This difference betweendicot and monocot species in diurnal variation of the leaf elongationrate and leaf thickness may partly be explained in terms ofthe different position of the growth zone and possibly by adifference in elasticity of the tissue of halophytic monocotyledonsand dicotyledons. The consequences of these differences arediscussed. Key words: Leaf elongation rate, leaf thickness, water relations, salt resistance, Dicotyledonae, Monocotyledonae