Photochemical activity and osmotic adjustment of some halophyte and xerophyte species in different microtopographic conditions

Abstract

The saline area of the Kiskunsag region of Hungary has varied micro-topographic conditions with different plant communities. This study was performed in a dry sandy grassland community (Potentillo arenariae-Festucetum pseudovinae Soo (1938) 1940) and a neighbouring saline sandy grassland community (Lepidio crassifolii-Puccinellietum limosae Soo (1947) 1957). These are located at different elevations and have completely different floristic composition and physiognomy due to the soil characteristics and water availability. We assessed how the different environmental conditions during summer period might alter some physiological traits of two dominant xerophytes of sandy grassland (Achillea collina L., Festuca pseudovina Hack. ex Wiesb.) and two halophytes of saline grassland (Lepidium crassifolium (W. et K.), Puccinellia limosa (Schur) Holmbg.). The relationship between soil water potential and water content showed lower water availability for plants in the saline habitat as the high water soluble sodium content (900–2000 ppm) of this soil type limits water absorption. Both halophyte species in this study exhibited lower K/Na ratio than xerophyte species. Between the two halophytes L. crassifolium can be described as a “leaf/shoot sodium accumulator” species while P. limosa as a “leaf sodium avoider” species. The four species differed in proline accumulation. The salt adapted species had multifold accumulation of proline as compared to species of dry sandy grassland. The three microhabitats differing in total plant cover offered different microenvironmental conditions for L. crassifolium. Proline content was twice higher in leaves of this species in the microhabitats with high soil Na content than in the closed microhabitat. Every species showed a transient reversible decrease of potential photochemical efficiency of PSII (Fv/Fm) at midday during the study period. In the saline habitat the midday depression of Fv/Fm for L. crassifolium was much larger than in case of P. limosa which reflected its higher susceptibility to photoinhibition. In sandy grassland Fv/Fm of A. collina was smaller than that of F. pseudovina. Mesophyll succulence index (Sm) expressing the ratio of water content to chlorophyll content was the highest in L. crassifolium (1.6–2.2 g H2O mg-1 Chl). Sm was low in xerophyte species (0.5–1.1 g H2O mg-1 Chl), and the lowest value was found for the F. pseudovina (0.54 g H2O mg-1 Chl).