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

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 smoke-enhanced 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

Ökofiziológiailag plasztikusabbak-e az invázív növények nem invázív rokonaiknál? = Are invasive plants ecophysologically more plastic than their non-invasive relatives?

Az inváziós növények egyre jelentősebb természetvédelmi problémát okoznak. Kutatásainkban a növényi invázió ökofiziológiai hátterét elemeztük. Hipotézisünk volt, hogy az inváziós fajok jelentősebb környezeti heterogenitást élnek meg, mint nem terjedő honos rokonaiknak, így élettani működésük és kapcsolódó morfológiájuk - anatómiájuk szorosabban illeszkedik fenotípusosan a változó környezethez. Mérsékeltövi pázsitfüvekre (Poaceae) szorítkoztunk, az elterjedési területük klimatikus határát megközelítő C4-es fotoszintézisűekre különös tekintettel. Terepi átültetési kísérletekben a lösz erdőspusztai lokális térfoglaló C3-as Brachypodium pinnatum nagyfokú fotokémiai, morfológiai, fenológiai és mikorrhizáltsági plasztikusságot mutatott, a levél anatómiája viszont alig módosult. A fényintenzitás gyors változásaira a C4-es füvek között az inváziósak levél CO2 és H2O gázcseréje érzékenyebben reagált, mint a nem inváziósaké, ahol a vízhasznosítási hatékonyság megőrzése a prioritás. C4-es füveknél a levél morfológia és durva szerkezet gyenge fénnyel szemben plasztikusabb az inváziósaknál, mint a nem inváziósaknál, ám ebben nem maradtak el a C4-es invázósak a C3-asok mögött. A magvak csírázását a hőkezelés C3-as füveknél általában nem serkentette, C4-eseknél legtöbbször igen, de nem volt különbség az invázós alkat szerint. Az inváziós füvek új közösségükben rendszeresen létesítenek ugyan VA mikorrhiza-kapcsolatot, ám ennek intenzitása és hatékonysága elmarad a honos fajokétól. | Here we studied the ecophysiological background of grass invasions. It was hypothesized that invasive species face a greater degree of environmental heterogeneity than their stationary non-invasive relatives, thus invasives should better adjust their physiology and associated morphology and anatomy to variations in the environment. Temperate grasses (Poaceae) were studied, particularly C4 species close to the climatic limit of distribution. In field transplant experiments in a semiarid loess grassland the C3 Brachypodium pinnatum of high capacity for local spread displayed high degree of plasticity in photochemistry, shoot morphology, phenology and VA mycorrhizal association, but leaf anatomy remained invariant. Among C4 grasses leaf CO2 and H2O gas exchange responded sensitively to rapid changes in light intensity for invasives, but less so for non-invasives, with maintenance of high water use efficiency enjoying priority in response. In C4 grasses when developed under moderate light leaf morphology and coarse structure were more plastic for invasives than for non-invasives, and there was no difference in this capacity between C3 and C4 invasive grasses. Heat treatment usually had no effect on the germination of C3 grasses, mostly enhanced that of C4 grasses, but there was no difference according to invasion capacity. Invasive grasses establish VA mycorrhizal symbioses in their new habitat, but the intensity and efficiency of association remains below that of local grasses

Correlation between age basal diameter of Fraxinus Ornus L. in three ecologically contrasting habitats

Manna ash (Fraxinus ornus L.) is a typical deciduous tree of South European distributioin reaching the northern border of its range in the Carpathian Basin. The correlation between age and basal diameter of this tree was analysed in three ecologically contrasting habitats, as follows. (1) Succesional habitat. Abandonedframland with scattered occurrence of manna ash as a colonisong tree of this area. (2) Austrian pine plantation, where manna ash often forms a spontaneous subordinate tree or shrub layer. (3) Cotino-Quercetum pubescentis, the naturla vegetation on south facing calcareous hillslopes in Hungary, where Quercus pubescenes Willd. and Fraxinus ornus codominate in the low canopy. At each sampling site 21 individuals were selected with an even distribution within circumference categories ranging  from 6cm to 60cm. Circumference measurements were made at the base of the trunk, or cores were taken by a driller. Linear regression analysis was applied to test the correlation between age and diameter

Is the positive response of seed germination to plant-derived smoke associated with plant traits?

Relationships between seed germination response to plant-derived smoke and various plant traits (habitat requirements, life form, seed morphology, seed bank type) were analysed for 97 species of the Hungarian flora using published data. It was hypothesized that smoke-responsive species – those displaying enhanced germination in response to smoke – differ from non-responsive species – smoke having an indifferent or inhibitory effect on germination – in habitat requirements and/or certain life history traits. To our knowledge, no such comparison has previously been reported for a European flora. We found that species indicating disturbance and those preferring soils rich or moderately rich in nitrogen were more frequent in the smoke-responsive group (80% and 41%, respectively) than in the non-responsive group, while the non-responsive group contained a high percentage of natural species (i.e. species dominant or characteristic in natural plant communities; 47%) and species indicative of nutrient poor (38%) or (sub)mesotrophic (38%) soils. Annuals or biennials (67%) dominated the smoke-responsive group, whereas in the non-responsive group these short-lived species and perennial herbs were equally abundant (43% each). There was a tendency for higher frequency of long-term persistent seed bank among smoke-responsive species (78%) than in the non-responsive group (54%). These findings suggest that smoke-stimulated germination is associated with only a few specific plant traits for species from a semiarid temperate region of Europe, but highlight the frequent occurrence of smoke-enhanced germination among short-lived, nitrophilous or disturbance tolerant species. These results can contribute to a better understanding of post-fire regeneration of plant communities, and could also be considered during vegetation restoration or weed management