Andrea Mojzes

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.

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.