Z. Tuba

UV-B tolerance of bryophyte species with different degrees of desiccation tolerance

Abstract We report on the efficiency of the primary photochemistry of photosystem II and potential thylakoid activity (represented by the variable fluorescence decrease ratio) of seven UV-B-treated bryophyte species during exposure and the subsequent recovery period. In Tortula ruralis , a strongly desiccation-tolerant grassland moss, there is no indication of any effects of UV-B irradiation. Desiccation-tolerant forest mosses ( Polytrichum formosum, Mnium hornum ) are only temporarily affected by UV-B radiation or can even be positively affected by it ( Dicranum scoparium ). The protective mechanism of desiccation-sensitive mesic species ( Plagiothecium undulatum, Leucobryum glaucum, Pellia epiphylla ) is rapidly exhausted and they cannot tolerate increased UV-B radiation. These results support our view presented here that desiccation tolerance and UV-B tolerance involve similar defence mechanisms.

Long-term acclimation of plants to elevated CO2 and its interaction with stresses.

Abstract:u2002 Rising atmospheric carbon dioxide (CO2) concentration and air temperature are of major concern when considering the possible effects of global climate change on vegetations. Although production has been found to increase in many cases, other experiments have also indicated increased hazards for plant growth because of the increased frequency of weather extremes, such as droughts, floods, and extreme temperatures. Thus at the same time elevated CO2 and the extreme climatic events, intra‐ and interannual climatic variability alone can be foreseen as an indirect constraint, which separately influences significantly the carbon cycling in ecosystems, too. In the shorter term the effect of CO2 is direct and is mediated by photosynthesis. In the longer term the effects of elevated CO2 became more and more indirect and its effects are mediated by source‐sink interactions within plants, resources (nutrients, water), temperature, microbes, herbivores, and land‐use management practice. In fact, the plants can make use of their general stress coping mechanisms to avoid or compensate possible negative effects of elevated CO2. One has to consider that all the classical abiotic, biotic, and anthropogenic stressors are threatening plant growth and development also under elevated CO2, although at possibly different doses compared to ambient CO2 concentrations. Therefore, the knowledge of the general stress coping, stress avoiding, and tolerance mechanisms is needed to understand the regulation of the plants metabolism under normal and elevated CO2 levels.

Responses of nine bryophyte and one lichen species from different microhabitats to elevated UV-B radiation

Chlorophyll fluorescence parameters (Fv/Fm, RFd) of nine bryophyte and one lichen species were investigated after prolonged exposure to elevated UV-B radiation. The majority of the investigated bryophytes showed a prompt or inducible tolerance to increase UV-B irradiation. Among the investigated species high degree of UV-tolerance coincides with strong desiccation tolerance.

Seasonal accumulation pattern of pinitol and other carbohydrates in Limonium gmelini subsp. hungarica

Summary Concentrations of the main soluble carbohydrates were measured in leaf and root samples of Limonium gmelini subsp. hungarica (Plumbaginaceae), a species native to the Hungarian inland salty areas. Samples were collected between March and October, from plants growing in their natural habitat. D-pinitol was identified as a significant component of the carbohydrate pool. The seasonal changes in the leaf pinitol concentration were dependent on different stress factors such as decrease of soil water content, low temperature, and leaf sodium concentration. A five-fold increase in the shoot D-pinitol values were observed between mid-April (15 μmol g −1 dw −1 ) and August (78 μmol g −1 dw −1 ) concentrations. In the roots, pinitol concentration was relatively low and increased only moderately in the summer. No significant diel changes in the concentration of pinitol were observed except during the time of intensive leaf growth in the spring. The possible functions of pinitol in L. gmelini are discussed.

Changes of chloroplast ultrastructure and carbohydrate level in festuca, achillea and sedum during drought and after recovery.

The changes of chloroplast ultrastructure and carbohydrate level in C(4) sclerophyllous Festuca vaginata, C(3) malacophyllous Achillea ochroleuca and CAM succulent Sedum sexangulare were investigated during naturally induced drought and after subsequent recovery. Chloroplasts of the species show some characteristic changes due to drought: decreased volume, permanent adhesions within the grana, partitions become thinner, lipid droplets increase in number and size. Contraction of the stroma, swelling and blistering of thylakoids are characteristic of Sedum chloroplast and mesophyll chloroplasts of Festuca. Structure of bundle sheath chloroplasts of C(4) Festuca scarcely shows changes during drought and after recovery. During drought and subsequent recovery in the chloroplasts onf Achillea the slightest changes of the stromal and grana lamellae region can be observed. During drought starch grains are characteristic of chloroplasts of Achillea and Sedum; they disappear after recovery. Achillea and Sedum leaves contain more starch during drought than after recovery, while the starch content in Festuca is unchanged. There is more soluble sugar in Festuca and Sedum during drought than after recovery, although the amount of soluble sugar in Achillea is decreased during drought.

Ecophysiology of Homoiochlorophyllous and Poikilochlorophyllous Desiccation-Tolerant Plants and Vegetations

Some vascular angiosperm plants, which are sometimes addressed as “resurrection plants,” can survive severe drought periods and regain full physiological function in the subsequent rainy season. These desiccation-tolerant (DT) plants are poikilohydric and capable of surviving the loss of at least 80–95% of their cell water content for shorter or longer periods. DT plants are important constituents of many ecosystems from the arctic (lichen and moss vegetations) to the tropics (lichen, moss, and mainly vascular/flower vegetations). The inselbergs in the tropics, as habitats ecologically isolated from their surrounding areas, are evolutionary centers of the flowering DT plants and vegetations. DT plants may be subdivided into homoiochlorophyllous (HDT) plants and poikilochlorophyllous (PDT) plants, which are using contrasting strategies to solve the same ecological problem of longer severe dryness. The HDT plants keep their chlorophyll and thylakoids during desiccation, whereas the PDT strategy is bound to desiccoplasts, a unique type of chloroplast, that break down and reconstitute their chlorophylls and thylakoids. The HDT pteridophytes and angiosperms are generally adapted to more rapid alternations of wet and dry periods than the PDT species. The PDT strategy, in turn, has evolved in habitats where the plants remain in the desiccated state for 6–10 months. Under these conditions, it is evidently more advantageous to dismantle the whole photosynthetic apparatus and to reconstitute it after rehydration. This chapter summarizes the recent developments in our understanding of physiology and ecophysiology of HDT and PDT plants and vegetations.

Comparison of CO2 and H2O fluxes over grassland vegetations measured by the eddy-covariance technique and by open system chamber

Measurements of CO2 and H2O fluxes were carried out using two different techniques—eddy-covariance (EC) and open system gas exchange chamber (OC)—during two-years’ period (2003–2004) at three different grassland sites. OC measurements were made during fourteen measurement campaigns. We found good agreement between the OC and EC CO2 flux values (n = 63, r2 = 0.5323, OC FCO2 = −0.6408+0.9508 EC FCO2). The OC FH2O values were consistently lower than those measured by the EC technique, probably caused by the air stream difference inside and outside the chamber. Adjusting flow rate within the chamber to the natural conditions would be necessary in future OC measurements. In comparison with EC, the OC proved to be a good tool for gas exchange measurements in grassland ecosystems.

Winter photosynthetic activity of twenty temperate semi-desert sand grassland species

The winter photosynthetic activity (quantified by net CO(2) assimilation rates and chlorophyll (Chl) a fluorescence parameters) of 20 plant species (including two lichens and two mosses) of a Hungarian temperate semi-desert sand grassland was determined on one occasion per year in 1984, 1989 and 1994. Throughout winter, the overwintering green shoots, leaves or thalli were regularly exposed to below zero temperatures at night and daytime temperatures of 0-5 degrees C. In situ tissue temperature varied between -2.1 and +6.9 degrees C and the photosynthetic photon flux density (PPFD) between 137 and 351 micromol m(-2)s(-1). Under these conditions 18 of the grassland species exhibited photosynthetic CO(2) uptake (range: vascular plants ca. 0.2-3.8 micromol m(-2)s(-1), cryptogams 0.3-2.79 micromol kg(-1)s(-1)) and values of 0.9-5.1 of the Chl fluorescence decrease ratio R(Fd). In 1984, Festuca vaginata and Sedum sexangulare had net CO(2) assimilation at leaf temperatures of -0.85 to -1.2 degrees C. In 1989, all species except Cladonia furcata showed net CO(2) assimilation at tissue temperatures of 0 to +3.3 degrees C, with the highest rates observed in Poa bulbosa and F. vaginata. The latter showed a net CO(2) assimilation saturation at a PPFD of 600 micromol m(-2)s(-1) and a temperature optimum between +5 and +18 degrees C. At the 1994 measurements, the photosynthetic rates were higher at higher tissue water contents. The two mosses and lichens had a net photosynthesis (range: 1.1-2.79 micromol CO(2)kg(-1)s(-1)) at 2 degrees C tissue temperature and at 4-5 degrees C air temperature. Ca. 80% of the vascular grassland plant species maintained a positive C-balance during the coldest periods of winter, with photosynthetic rates of 1.5-3.8 micromol CO(2)m(-2)s(-1). In an extremely warm beginning March of the relatively warm winter of 2006/2007, the dicotyledonous plants had much higher CO(2) assimilation rates on a Chl (range 6-14.9 micromol g(-1)Chl s(-1)) and on a dry weight basis (9-48 micromol kg(-1)dw s(-1)) than in the cold winter of 1994. However, the assimilation rates of the three investigated cryptogams (Tortula and two Cladonia) and the two grasses Festuca and Poa were not affected by this increase. The results indicate that the photosynthetic activity of temperate semi-desert sand grassland species can help somewhat in slowing the general CO(2) rise in winter and function as a potential carbon sink of the investigated semi-desert Hungarian grassland species.

Rearrangement of Photosynthetic Pigment Composition in C4, C3 and CAM Species During Drought and Recovery

The response of C(4), C(3) and CAM species to naturally induced drought and their subsequent recovery are similar. However, there are differences in the degree of the pigment responses, which are related to the differences in the pigment composition of the species. During drought the decrease of the lutein, neoxanthin and chl b content indicates the reduction of the LHC-xanthophyll-proteins, while the considerably increased level of β-carotene, together with the elevated chl a/b ratio, reflect the increased amounts of chl a/β-carotene-pigment-proteins. Moreover, from the pigment data it is concluded that the species seem to possess during drought a higher proportion of pigment-proteins of PSI than pigment-proteins of PS II. These reactions to drought decrease gradually in the direction of C(4)-C(3)-CAM (succulence). The C(4)Festuca vaginata responds with a considerable change in its pigment composition, while this is moderate in CAM Sedum, and C(3)Achillea occupies an intermediate position.

Seasonal CO2-exchange variations of temperate semi-desert grassland in Hungary

CO2 exchange components of a temperate semi-desert sand grassland ecosystem in Hungary were measured 21 times in 2000–2001 using a closed IRGA system. Stand CO2 uptake and release, soil respiration rate (Rs), and micrometeorological values were determined with two types of closed system chambers to investigate the daily courses of gas exchange. The maximum CO2 uptake and release were −3.240 and 1.903 μmol m−2 s−1, respectively, indicating a relatively low carbon sequestration potential. The maximum and the minimum Rs were 1.470 and 0.226 μmol(CO2) m−2 s−1, respectively. Water shortage was probably more effective in decreasing photosynthetic rates than Rs, indicating water supply as the primary driving variable for the sink-source relations in this ecosystem type.