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Ecophysiology of photosynthesis of wetland grasses
MEJDOVÁ, Markéta
The wetland ecosystems play an important role in the global carbon cycle. The individual processes of carbon (C) exchange and sequestration of vegetation are studied using different approaches and methods. Using by the photosynthesis light curves can be determined parameters of photosynthesis (Pmax -maximum rate of photosynthesis, Icomp- compensation point, Rd- dark respiration, - maximum quantum yield) of individual plant species. Knowledge of these parameters will allow us to understand what role plants play in the processes of C exchange and sequestration. The main goal of this work was to determine the parameters of the photosynthesis light curve of dominant plant species in the sedge-grass marsh stand of Mokré louky near to Třeboň town. Further to evaluate whether the investigated plant species differ in individual photosynthetic parameters and whether they are affected by environmental conditions. The work took place during the vegetation period of 2013 at weekly intervals. Vegetation mapping was performed also in 2013 and consequently in 2017. For a comprehensive knowledge of the ecosystem, the production characteristics of the investigated plant species and the determination of the big-leaf parameters of the light curve for whole ecosystem. Estimated carbon uptake by the hypothetical big-leaf was compared with net ecosystem exchange (NEE) measured by eddy-covariance (EC) system. The investigated plant species differed significantly in the Pmax parameter and can be divided into three groups according to it. The first group with the highest average value of Pmax includes Glyceria maxima (18.36 ?mol m-2 s-1) and Acorus calamus (16.61 ?mol m-2 s-1). The second group includes Carex acuta (10.83 ?mol m-2 s-1) and Phalaris arundinacea (9.41 ?mol m-2 s-1). And in the third groups with the lowest average value of Pmax includes Calamagrostis canescens (7.02 ?mol m-2 s-1). Pmax was higher in early summer and then gradually decreased. Higher Rd was observed, for example, at the beginning of the growth season; after the flood and especially at the end of the growing season. The Pmax was significantly affected by water level fluctuations in Phalaris arundinacea and Calamagrostis canescens. The Pmax in Phalaris arundinacea was also significantly affected by the June floods. The conductivity of the stomata did not affect the Pmax parameter, but was significantly affected by the water level in all examined plant species. During vegetation mapping in 2013, the following relative representation of individual plant species was processed: Phalaris arundinacea 35 %, Carex acuta 28.6 %, Glyceria maxima 16.5 %, Acorus calamus 1.2 %, and Calamagrostis canescens 18.7 %. Rate of Pn and NEE had a similar seasonal course (R2=0,859 - 0,998), but Pn reached higher values than NEE measured by EC method.
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Does water stress and interspecific competition contribute to the functional divergence or convergence of wetland plant species?
Műnichová, Radka ; Douda, Jan (advisor) ; Alena, Alena (referee)
This diploma thesis is based on the experiment which took 5 years. In 52 plastic containers were planted four species wetland plants; two species of grasses (Calamagrostis canescens and Deschampsia cespitosa) and two species of sedges (Carex elata and Carex elongata). Three types of water regime were set up with: high, low and fluctuating water level, where the high and low level of water took turns after one year. One year before the data collection the strongest competitor Carex elata was cut out. For the evaluation of the role of water level (environmental stress) and removal of the dominant (competition) we selected two functional trait indicators: specific leaf area (SLA) and leaf dry matter content (LDMC). SLA is an indicator of resource strategies, competitiveness and efficiency of light photosynthesis. Species with high SLA are usually better competitors for light, but tolerate harder the environmental stress. LDMC reflects a plants investment in persistent leaf structures and therefore in nutrient retention. A significant effect of water regime on LDMC was observed in the species Deschampsia cespitosa that had higher average values of LDMC in dry water regime, which is indicating higher investment into persistent leaf structures. And the effect of the dominant removal on SLA, where the values of SLA in the containers without removed dominant were higher. Increased SLA implies increased intensity of competition for light. My diploma thesis supported that specific leaf area and leafdry matter content are important functional indicators different types of stress conditions in wetland communities.
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Interspecific interactions in wetland communities in dependence on water regime: long-term test of stress-gradient hypothesis
Růžičková, Kateřina ; Douda, Jan (advisor) ; Alena, Alena (referee)
The Stress-gradient hypothesis predicates a change of interspecies relations from negative to positive according to the stress gradient. The basic assumption is that the presence of one species (the facilitator) makes the growth of other species easier. In this study was determined based on the 5years experiment, whether the interspecies interactions (i.e. the importance of facilitation and competition) changes according to the hydrological conditions. Three wetland species (Calamagrostis canescens, Carex elongata and Deschampsia cespitosa) were planted in experimental pots with the presence and absence of the dominant species (Carex elata). The hydrological gradient (= the stress gradient) was simulated by three types of hydrological conditions: dry, fluctuating and wet. The success of the species within the specific conditions was correlated with the fitness-related characteristics of the plants including the biomass, the number of ramets and the height of the plants. Following hypotheses were tested: i) at a low intensity of stress (with the wet treatment), the C. elata represents a competitor for other species. On the other hand, at a high intensity of stress (with the dry treatment), the C. elata represents a facilitator, making it easier to the other coexisting species to grow. This presumption was confirmed only with the D. cespitosa, which was more successful under dry treatment with the presence of a dominant species, which facilitated it. With the other two species the change of interspecific relations was not observed and the relationships remained negative. Furthermore the results showed, that in the dry treatment with the presence of a dominant species, there was a lower intensity of competition among the coexisting species. The experiment showed, that the interactions of particular species with dominant species can vary according to the stress gradient. The hydrological gradient also influences the character and intensity of interactions among the species.
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