Competition plays an important role in the replacement of native species by alien plants. A greenhouse experiment was conducted to investigate whether the competition pattern of alien Robinia pseudoacacia L. and native Quercus acutissima Carr. is affected by soil sterilization. Physiological traits, such as gas-exchange parameters and chlorophyll (Chl) content, and growth traits, such as the biomass accumulation of the two species, were examined in natural soil or in soil sterilized with benomyl. The results show that native Q. acutissima inhibits the growth of R. pseudoacacia in natural soil. When the two plants coexisted and competed under sterilization treatment, R. pseudoacacia was less inhibited by Q. acutissima and the competition of R. pseudoacacia decreased the growth of Q. acutissima in terms of biomass, Chl a, Chl b, total Chl, and Chl a/b. These results suggest that soil sterilization benefits the growth of R. pseudoacacia and changes the competition pattern by the changed soil biota. Soil sterilization increased the biomass of root nodules, which ultimately benefits the growth of R. pseudoacacia and root nodule bacteria may be important in the dispersal and invasion process of nitrogen-fixing alien plants such as R. pseudoacacia., H. Chen ... [et al.]., and Obsahuje bibliografii
An ecophysiological approach was used to determine if competition can be detected among plants in a recently abandoned old-field and in a native tallgrass prairie in northeastern Kansas. In situ photosynthetic parameters and water potentials (Ψ) of target plants were measured 1-2 d after neighbor (intra- and interspecific) removal as well as 1-4 weeks later, and compared with values for plants with neighbors. Only two of the six study species (four old-field and two prairie species) responded to removal of neighboring plants, and only after several weeks had elapsed. Net photosynthetic rates (PN) and stomatal conductances (gs) of Ambrosia trifida in an old-field increased after removal of both intra- and interspecific neighbors. For Apocynum cannabinum, another old-field species, PN of target plants without neighbors was significantly higher than that of target plants with neighbors. For both these species, values of Ψ were not different between target plants with and without neighbors, suggesting that increased availability of nutrients may have been responsible for the observed ecophysiological responses. Though numerous past studies indicate that competition is a major factor influencing plants in old-field and in prairie communities, the experimental approach used in this study revealed that neighbor removal had only limited effects on ecophysiology of the target plants in either community. and F. Norman, C. E. Martin.
In this study, we questioned whether ground-level ozone (O3) induces hormesis in Japanese larch (Larix kaempferi) and its hybrid F1 (L. gmelinii var. japonica × L. kaempferi). In order to answer the question, we exposed seedlings of both taxa to four O3 treatments [ranging from ≈10 to 60 nmol(O3) mol-1] in open-top chambers for two consecutive growing seasons. We found a hormetic response in maximum photosynthetic rate (PNmax) at 1700 μmol(CO2) mol-1 and maximum rates of carboxylation (Vcmax) and electron transport (Jmax) in both larches. Stimulation of PNmax, Vcmax, and Jmax did not lead to suppressed plant productivity in Japanese larch, which followed a stress-tolerant strategy, but it did lead to suppressed plant productivity in hybrid larch which followed a competitive strategy. These findings are the first to suggest that stimulation of physiological functions by low O3 exposures may have negative consequences for larch reproduction., T. Sugai, D.-G. Kam, E. Agathokleous, M. Watanabe, K. Kita, T. Koike., and Obsahuje bibliografii
Jana Cahlíková, Lubomír Cingl, Ian Levely., Částečně tištěno napříč, Obsahuje bibliografii a bibliografické odkazy, České a anglické resumé, and born digital
Experimental infection of rainbow trout Oncorhynchus mykiss (Walbaum) with the monogenean Discocotyle sagittata (Leuckart, 1842) allowed comparison between trickle and single exposure, two infection modes demonstrated to occur in the wild. Both types of infection resulted in mean larval attachment success around 50%, which was significantly dependent on dose of infective larvae used (P < 0.0001), but was not affected by mode of infection (P = 0.244). Worms recovered from fish exposed to the same number of oncomiracidia but different mode of infection differed in their rate of development. The developmental stage attained by parasites was significantly affected by number of infective larvae used (P = 0.005), and by the interaction between dose and mode of infection (P = 0.026), suggesting competition among attached larvae. Statistical analysis demonstrated that in the early stages of infestation, worm distribution over the gill arches can be explained by the relative amount of water flowing over them. One, two and three months post-infection parasite numbers were comparable (P = 0.805), but their observed distribution gradually decreased in gill arches III and IV and increased in gill arch I, suggesting that parasites migrate after initial attachment. These results reproduce phenomena observed in the field, indicating that the experimental infection system could be employed to study infection dynamics and host-parasite interactions under controlled conditions.