Tibor Kalapos

Effect of soil drying on growth, biomass allocation and leaf gas exchange of two annual grass species

Influence of short-term water stress on plant growth and leaf gas exchange was studied simultaneously in a growth chamber experiment using two annual grass species differing in photosynthetic pathway type, plant architecture and phenology:Triticum aestivum L. cv. Katya-A-1 (C3, a drought resistant wheat cultivar of erect growth) andTragus racemosus (L.) All. (C4, a prostrate weed of warm semiarid areas). At the leaf level, gas exchange rates declined with decreasing soil water potential for both species in such a way that instantaneous photosynthetic water use efficiency (PWUE, mmol CO2 assimilated per mol H2O transpired) increased. At adequate water supply, the C4 grass showed much lower stomatal conductance and higher PWUE than the C3 species, but this difference disappeared at severe water stress when leaf gas exchange rates were similarly reduced for both species. However, by using soil water more sparingly, the C4 species was able to assimilate under non-stressful conditions for a longer time than the C3 wheat did. At the whole-plant level, decreasing water availability substantially reduced the relative growth rate (RGR) ofT. aestivum, while biomass partitioning changed in favour of root growth, so that the plant could exploit the limiting water resource more efficiently. The change in partitioning preceded the overall reduction of RGR and it was associated with increased biomass allocation to roots and less to leaves, as well as with a decrease in specific leaf area. Water saving byT. racemosus sufficiently postponed water stress effects on plant growth occurring only as a moderate reduction in leaf area enlargement. For unstressed vegetative plants, relative growth rate of the C4T. racemosus was only slightly higher than that of the C3T. aestivum, though it was achieved at a much lower water cost. The lack of difference in RGR was probably due to growth conditions being relatively suboptimal for the C4 plant and also to a relatively large investment in stem tissues by the C4T. racemosus. Only 10% of the plant biomass was allocated to roots in the C4 species while this was more than 30% for the C3 wheat cultivar. These results emphasize the importance of water saving and high WUE of C4 plants in maintaining growth under moderate water stress in comparison with C3 species.

Leaf water potential-leaf water deficit relationship for ten species of a semiarid grassland community

The relationship between water potential and relative water content (water content in percentage of full hydration) is a characteristic of plant tissues, that may vary with environmental conditions. It is used here to compare leaf water relations of ten species coexisting in a semiarid grassland community (Festucetum vaginatae danubiale) in Hungary. Three groups of species can be distinguished. In two of these leaf water potential changes only moderately with decreasing leaf water content. These are either short-lived, drought escaping spring plants relying on seasonally favourable water supply (group 1) or xerophytes with very deep root system having access to permanent water resources (group 2, only one species studied here). Xerophytes with moderately deep roots (group 3) display a rapid drop of leaf water potential with increasing leaf water deficit. This generates a steep water potential gradient in the soil-plant continuum that in turn enhances water uptake by roots. There is a positive correlation between the rate of water potential decline and degree of sclerophylly (proportion of dry material in the water-saturated leaf), and both variables show seasonal change in perennial species.

Occurrence and ecological characteristics of C4 dicot and Cyperaceae species in the Hungarian flora

AbstractThe non-graminaceous wild flora of Hungary was screened for C4 plants by using the stable carbon isotope ratio, the leaf anatomy and the photosynthetic carbon dioxide compensation concentration to determine the photosynthetic pathway type. On the whole, 31 C4 species (native or naturalized) were found in the Amaranthaceae, Chenopodiaceae, Cyperaceae, Euphorbiaceae, Portulacaceae and Zygophyllaceae families. Together with the 26 C4 grass species (Poaceae) reported earlier (Kalapos 1991), a total of 57 wild C4 species occur in Hungary, which forms 2.6 % of the countrys angiosperm flora. This figure is somewhat higher than what was expected on climatic grounds, a fact probably due to certain edaphic conditions favouring C4 plant growth. In Hungary, the C4 species are predominantly annuals growing in open habitats such as dry grasslands, inland saline areas, temporarily exposed riverbeds and disturbed sites. In comparison with C3 plants, the C4 species have higher temperature and light preferences, and their phenology lags behind that of the C3 plants. These differences might account for C4 plants being usually excluded from productive biotopes in Hungary, where the C3 canopy may become closed during the growing season before C4 plants can start their ontogenetic development. Ecological properties of C3 and C4 plants differ considerably in the Cyperaceae, but much less in the Chenopodianceae family. Among C4 annuals naturalized aliens are common, most of which colonized hungary in the last two centuries. Increasing preponderance of C4 plants is anticipated in the future as a consequence of possible climate changes and the ever increasing human impact on terrestrial vegetation.

Plasticity of leaf and shoot morphology and leaf photochemistry for Brachypodium pinnatum (L.) Beauv. growing in contrasting microenvironments in a semiarid loess forest-steppe vegetation mosaic

Summary After clearcutting xerothermic oakwoods once natural in semiarid temperate loess regions of Hungary the perennial understorey grass Brachypodium pinnatum(L.) Beauv. may persist through decades and often dominates grasslands maintained by grazing and/or cutting in the place of former oakwoods. This grass also successfully establishes from low- to high-light microenvironments co-ocurring as forest regeneration commences after pasture abandonment. It was assumed that B. pinnatum must possess a high degree of phenotypic plasticity for such an ecological versatility. This assumption was tested by comparing leaf and sho ot morphology and leaf photochemistry in the species’ three typical microenvironments (full shade under oak canopy, half shade near shrubs, and full sun in unshaded grassland) for plants growing in situ and for those reciprocally transplanted between these microhabitats. Aboveground standing crop of B. pinnatum was greatest near shrubs, indicating that in this microhabitat light limitation (typical in oak shade) and water stress (appearing temporarily in the grassland) are ameliorated. Average leaf lifes pan was greatest under oak canopy, while leaf senescence was highest in the grassland. An efficient adjustment to low light was observed both in leaf morphology (specific leaf mass, leaf thickness and bulk tissue density were lowest in oak shade) and in leaf photochemistry (quantum yield of PSII ( ΦPSII), photochemical quenching (qP), and non-photochemical energy dissipation (NPQ) were lower, while PSII antenna efficiency (Fv’/Fm’) was higher for leaves in oak shade than for others). Transplanted plants showed remarkable phenotypic plasticity since after one year of transfer their leaves did not differ in photochemistry and/or morphology from those growing in situ in the new microenvironment. However, transplants appeared to be more sensitive to the high radiation load in the grassland than in situ ones. Our results confirm the high capacity of B. pinnatum for phenotypical adjustment to habitat light environment, that is consistent with the species’ original forest-steppe coenological affi nity and also may contribute to the species’ persistence after deforestation. Nevertheless, temporary water stress associated with hi gh radiation load in the unshaded grassland appear to pose a limitation on the ecological distribution of this species in Central Europe.

Juniper shade enables terricolous lichens and mosses to maintain high photochemical efficiency in a semiarid temperate sand grassland

On a semiarid sand grassland (Festucetum vaginatae) colonised by juniper (Juniperus communis L.) shrubs terricolous lichens and mosses segregate strongly between microhabitats: certain species grow in the open grassland, others almost exclusively in the shade of junipers. The contrasting irradiances of these microhabitats influence much the metabolism of these organisms, and thus affect their small-scale distribution. This was confirmed by determining the efficiency of photochemical energy conversion by measuring chlorophyll a fluorescence parameters. In the open grassland maximum photochemical efficiency of photosystem 2 (PS2, Fv/Fm) declined from the humid spring to the hot and dry summer in all species, and this was caused by an increase in base fluorescence (F0), but not by the decrease in fluorescence maximum (Fm). In summer, mosses and lichens growing in the open grassland generally possessed lower Fv/Fm than cryptogams growing in the shade cast by juniper shrubs. Thus mosses and lichens in the open grassland suffer lasting reduction in photochemical efficiency in summer, which is avoided in the shade of junipers. Juniper shrubs indeed influence the composition and small-scale spatial pattern of sympatric terricolous lichen and moss communities by—among others—providing a shelter against high light in summer.

SOIL RESPIRATION AND ITS MAIN LIMITING FACTORS IN A SEMIARID SAND FOREST-STEPPE ECOSYSTEM - RESULTS OF A CLIMATE SIMULATION EXPERIMENT

Oil rape is a valuable fodder because in early spring and late autumn it produces green forage used for the nutrition of domestic animals. It has been replacing sunflower and soy in colder and wetter regions. It is additionally advantageous because it leaves behind more nitrogen in soil, which is beneficial to other plants in plant rotation. There are some possible ways for the fixation of nitrogen in soil and they are as follows: by the means of oil rape straw ; by relatively long roots ; by the action of nitrogen bacteria, which perform the nitrogen synthesis within their root system, which is the case in some leguminous plants. Oil seed rape is expected to be wider used in crop rotation of West and Middle Europe, Croatia included. Due to this various sorts have been introduced and potential positive impacts have been studied in order to boost the process. This paper presents information on barley and wheat yield in case when they were sown after oil seed rape and corn. The aim of the research is to determine the presence of positive impacts upon the soil with special attention paid to a potential increase of nitrogen content after oil seed rape was grown. The preceding crops had statistically significant effect. Rape yield was significantly higher compared to the one with corn as preceding crops. Very similar results were obtained in 2007.The maize hybrids seed from three different FAO groups (FAO 400, FAO 500 and FAO 600) in four fractions (KO, KP, SO and SP) produced in two climatically different years (extremely dry 2000 and extremely wet 2001) had been different in quality and chemical composition. The effects of year, genetic specifity and seed fraction at the kernel mass, chemical composition (starch, proteins, cellulose, oil and moisture content) and seed vigour have been evaluated. The influence of agroecological conditions during two production years have been exposed at seed chemical composition and vigour indicators (cold test – CT and bulk seed electrical conductivity - EC). The genetic specificity and seed fraction had significant influence at all tested indices, with the exception of the influence of the fraction at the starch content

Plant-derived smoke enhances germination of the invasive common milkweed (Asclepias syriaca L.)

ABSTRACT Common milkweed (Asclepias syriaca L.) has become an invasive weed in Central and Eastern Europe, where human-induced fires have also taken part in forming the landscape. There is growing evidence that plant-derived smoke enhances seed germination, especially for species from fire-prone ecosystems, via the mechanisms of dormancy-breaking, germination stimulation or both. Hence, we hypothesized that smoke promotes seed germination for common milkweed by either or both mechanisms. To test this, germination responses of A. syriaca to the application of aqueous smoke solution (smoke-water) were studied in laboratory. Seeds were either cold stratified (+7°C, 16 days) in tap water (TW), smoke-water (SW) or were not stratified at all, and then were germinated with SW or with TW (encompassing 5 treatments: 0—TW, 0—SW, TW—TW, TW—SW and SW—TW, where the first abbreviation indicates stratification, the second germination condition). In line with our hypothesis, the low (5%) germination of seeds was enhanced by cold stratification with SW at a greater extent (increasing to 52%) than by cold stratification with TW (25%), indicating that SW contributed to dormancy-breaking of seeds for A. syriaca. In contrast, SW did not stimulate germination when it was applied during the germination phase. To our best knowledge, this is the first study demonstrating smokeenhanced germination for common milkweed, which mechanism may help this species to successfully colonize new habitats after fire. As fire frequency is expected to increase in Europe with recent climate change, these results might contribute to a more efficient control of A. syriaca in areas threatened by its invasion.

Plant ecophysiological responses to drought, nocturnal warming and variable climate in the Pannonian sand forest-steppe: Results of a six-year climate manipulation experiment

Abstract The impacts of year-round nocturnal warming or late spring rain exclusion on three plant functional types were studied in a plot-scale climate simulation experiment in a semiarid sand forest-steppe of Central Hungary. Ecophysiological traits were followed through six years for the C3 bunch grass Festuca vaginata, the spreading C4 grass Cynodon dactylon and shrub-sized root suckers of Populus alba. In general, experimental treatments had slighter effects than weather fluctuations yielding extremities did. Populus alba responded to nocturnal warming with developing slenderer leaves. Rain exclusion reduced leaf physiological activity or growth, but only during or just after the treatment, and in certain years. When assessing treatment and background climatic variation effects together, in spring, leaf area growth was consistently stimulated by increasing temperature, but decreased with longer rainless periods for P. alba and F. vaginata. Physiological responses in spring indicated low temperature limitation for C. dactylon, and both low and high temperature control for P. alba. Longer summer droughts reduced leaf gas exchange, particularly for F. vaginata with substantial drop in photochemical activity and chlorophyll content. These results suggest that shallow rooted C3 bunch grasses can be the most susceptible to climatic variation, thus their abundance is expected to decline in the Pannonian forest-steppe. In contrast, plants having deeper roots and clonal integration will probably be less affected by the projected warming and drying climate. C4 photosynthesis or southern geographical distribution may also be beneficial, thus, the abundance of such species is expected to diminish less or even increase.

Within-generation and transgenerational plasticity in growth and regeneration of a subordinate annual grass in a rainfall experiment

Precipitation changes may induce shifts in plant species or life form dominance in ecosystems, making some previously subordinate species abundant. The plasticity of certain plant functional traits of these expanding subordinate species may be one possible mechanism behind their success. In this study, we tested if the subordinate winter annual grass Secale sylvestre shows plasticity in growth and reproduction in response to altered environment associated with field-scale rainfall manipulations (severe drought, moderate drought, and watering) in a semiarid grassland, and whether the maternal environment influences offspring germination or growth in a subsequent pot experiment. Compared to control plots, S. sylvestre plants grew 38% taller, and produced 32% more seeds in severe drought plots, while plants in watered plots were 17% shorter, and had 22% less seeds. Seed mass was greatest in severe drought plots. Plants growing in drought plots had offspring with enhanced juvenile shoot growth compared to the progeny whose mother plants grew in watered plots. These responses are most likely explained by the decreased cover of previously dominant perennial grasses in severe drought plots, which resulted in wetter soil compared to control and watered plots during the peak growth of S. sylvestre. We conclude that the plasticity of this subordinate annual species in response to changing environment may help to gain dominance with recurring droughts that suppress perennial grasses. Our results highlight that exploring both within-generation and transgenerational plasticity of subordinate species may lead to a better prediction of changes in plant species dominance under climate change.

Comparison of Seed Longevity for Thirty Forest, Grassland and Weed Species of the Central European Flora: Results of a Seed Burial Experiment

ABSTRACT We compared seed longevity of herbaceous species in three habitat types differing in stability. We hypothesized that seed longevity is the lowest for forest species (living in stable habitat), the highest for weeds, while species of xerothermic grasslands take an intermediate value. Ten species were selected from each of the three habitats with balanced representation of plant families among habitats. Seeds of the 30 species were deep buried at 65 cm depth, then replicates recovered after 1, 2, 3, 4 and 6 years, and germinated in an unheated greenhouse. Weeds expressed the highest germination rate (36.1% in average) exceeding forest (14.4%) and grassland species (10.2%) which did not differ significantly. The number of species with transient, short-term persistent and long-term persistent seed bank, respectively, was 1, 7 and 2 for grasslands; 1, 3 and 6 for forests; and 0, 1 and 9 for weeds. As expected, weeds possessed the highest seed longevity. Contrary to our assumption, low seed longevity was not the norm among forest understorey species, and seed longevity of xerothermic grassland species was not intermediate but the shortest one. Ecological background of differences between hypotheses and experimental results are discussed. First record on seed bank type is reported here for 12 species: Dianthus pontederae, Digitalis grandiflora, Ferula sadleriana, Hieracium sylvaticum, Inula ensifolia, Jurinea mollis, Lychnis coronaria, Saponaria officinalis, Scorzonera austriaca, Secale sylvestre, Stipa borysthenica, Verbascum lychnitis.