Štěpán Janeček

Integration in the clonal plant Eriophorum angustifolium : an experiment with a three-member-clonal system in a patchy environment

A clonal plant in heterogeneous environments is usually expected to profit from resource exchange via a clonal network where ramets placed in contrasting environments can specialise so to acquire the most abundant resources. An experiment was designed using the three member clonal system of Eriophorum angustifolium, which consisted of one parent ramet growing in a resource poor environment and two offspring: one was limited in growth by nutrients while the other was light limited; the contrast in availability of limited resources between the offspring ramets was high, medium or none, with the system either connected or severed. The total resource availability was the same in all treatments. We proposed four possible scenarios for the system: offspring ramets will share resources via the deficient parent ramet, and the whole clone will profit from the contrasting environment (scenario 1); offspring ramets will support exclusively the parent ramet, and the whole clone will profit from a homogeneous environment (scenario 2); offspring ramets will stop the export of the limiting resource to the parent ramet, with split and connected treatments not differing (scenario 3); and offspring ramets will exhaust the carbon stored in the biomass of the parental ramet; offspring ramet will profit from connection (scenario 4). In the experiment, the limiting resources were sent to the strongest sink (scenario 2). The parent ramet growing in a deficient environment received the highest support in the treatment where both offspring ramets were growing in the same conditions (no-contrast treatment). Production of new shoots, but not biomass of whole clone, was supported in a homogenous environment. The experiment revealed that multiple stresses might prohibit free exchange of limiting resources via the clonal network and supports the idea that experimental studies on more complex clones are essential for understanding the costs and benefits of clonal growth.

Effect of abandonment and plant classification on carbohydrate reserves of meadow plants

We studied the effect of cessation of management on carbohydrate reserves of plants in meadows with different environmental characteristics and plant composition. We recorded storage carbohydrates and seasonal changes for 40 plant species. We asked whether there are differences in responses of carbohydrate reserves in forbs versus graminoids and in plants storing starch versus plants storing osmotically active carbohydrates. We analysed belowground organs before the meadows were mown and at the end of the vegetation season in mown versus recently abandoned plots. Whereas starch and fructans were widely distributed, raffinose family oligosaccharides were the main carbohydrate reserves of the Lamiaceae and Plantago lanceolata. Properties of carbohydrate reserves differed between forbs and graminoids but no difference was found between plants storing starch versus osmotically active carbohydrates. Graminoids had lower carbohydrate concentrations than forbs. We observed a positive effect of mowing on carbohydrate concentrations of graminoids in the dry, calcium-rich meadow and higher seasonal fluctuations of these values in the acid, wet meadow, suggesting that local factors and/or the species pool affect carbohydrate reserves. Despite local conditions, graminoids represent a distinct functional group in meadows from the point of view of their storage economy. We suggest that as well as growth, storage processes should also be considered for understanding the functioning of meadow plant communities.

Habitat preferences of birds in a montane forest mosaic in the Bamenda Highlands, Cameroon

Although the high species richness and endemism of birds in the Bamenda Highlands has attracted ornithological research for decades, most studies have been restricted to bird communities of continuous montane forests. Instead, we focused on a mosaic landscape with montane forest remnants, where the habitat preferences of birds remain unknown. We performed an assessment of habitat associations of birds in the Bamenda Highlands in the Cameroon Mountains. Using a point count census method, we detected 71 species within the study area. The most abundant species were the Northern Double-collared Sunbird Cynniris reichenowi, the Oriole Finch Linurgus olivaceus, the Common Stonechat Saxicola torquata, the Thick-billed Seed-eater Serinus burtoni, the Black-crowned Waxbill Estrilda nonnula, the Brown-backed Cisticola Cisticola chubbi and the Yellow-breasted Boubou Laniarius atroflavus. Canonical correspondence analysis revealed that the most important environmental gradient structuring the bird community follows the forest coverage. We found that both endemic and non-endemic montane species are more closely associated with montane forest remnants, compared to widespread species. Endemic species are most closely dependent on continuous forest cover. However, some montane species did not show any clear habitat associations and thus can be viewed as local habitat generalists. This study shows that many restricted-range species (including endangered endemics) are able to live in fragmented landscapes, which cover a substantial part of the Bamenda Highlands. Therefore, conservation programmes should focus their action plans on these landscapes.

Effects of long- and short-term management on the functional structure of meadows through species turnover and intraspecific trait variability

The functional structures of communities respond to environmental changes by both species replacement (turnover) and within-species variation (intraspecific trait variability; ITV). Evidence is lacking on the relative importance of these two components, particularly in response to both short- and long-term environmental disturbance. We hypothesized that such short- and long-term perturbations would induce changes in community functional structure primarily via ITV and turnover, respectively. To test this we applied an experimental design across long-term mown and abandoned meadows, with each plot containing a further level of short-term management treatments: mowing, grazing and abandonment. Within each plot, species composition and trait values [height, shoot biomass, and specific leaf area (SLA)] were recorded on up to five individuals per species. Positive covariations between the contribution of species turnover and ITV occurred for height and shoot biomass in response to both short- and long-term management, indicating that species turnover and intraspecific adjustments selected for similar trait values. Positive covariations also occurred for SLA, but only in response to long-term management. The contributions of turnover and ITV changed depending on both the trait and management trajectory. As expected, communities responded to short-term disturbances mostly through changes in intraspecific trait variability, particularly for height and biomass. Interestingly, for SLA they responded to long-term disturbances by both species turnover and intraspecific adjustments. These findings highlight the importance of both ITV and species turnover in adjusting grassland functional trait response to environmental perturbation, and show that the response is trait specific and affected by disturbance regime history.

Generalization versus Specialization in Pollination Systems: Visitors, Thieves, and Pollinators of Hypoestes aristata (Acanthaceae)

Many recent studies have suggested that the majority of animal-pollinated plants have a higher diversity of pollinators than that expected according to their pollination syndrome. This broad generalization, often based on pollination web data, has been challenged by the fact that some floral visitors recorded in pollination webs are ineffective pollinators. To contribute to this debate, and to obtain a contrast between visitors and pollinators, we studied insect and bird visitors to virgin flowers of Hypoestes aristata in the Bamenda Highlands, Cameroon. We observed the flowers and their visitors for 2-h periods and measured the seed production as a metric of reproductive success. We determined the effects of individual visitors using 2 statistical models, single-visit data that were gathered for more frequent visitor species, and frequency data. This approach enabled us to determine the positive as well as neutral or negative impact of visitors on H. aristata’s reproductive success. We found that (i) this plant is not generalized but rather specialized; although we recorded 15 morphotaxa of visitors, only 3 large bee species seemed to be important pollinators; (ii) the carpenter bee Xylocopa cf. inconstans was both the most frequent and the most effective pollinator; (iii) the honey bee Apis mellifera acted as a nectar thief with apparent negative effects on the plant reproduction; and (iv) the close relationship between H. aristata and carpenter bees was in agreement with the large-bee pollination syndrome of this plant. Our results highlight the need for studies detecting the roles of individual visitors. We showed that such an approach is necessary to evaluate the pollination syndrome hypothesis and create relevant evolutionary and ecological hypotheses.

Effects of Fertilization and Competition on Plant Biomass Allocation and Internal Resources: Does Plantago lanceolata Follow the Rules of Economic Theory?

According to economic theory, plants should modify biomass allocation by (1) investing in those organs that obtain the limiting resource (this subset of economic theory is referred to as the optimal partitioning theory – OPT) and by (2) storing easily available resources. Although used often, these predictions are also frequently criticized for contradictory results and methodological problems. We tested the effects of fertilization and competition on biomass allocation and concentrations of internal resources in Plantago lanceolata. To separate the effects of ontogenetic drift from true plasticity, we determined how plant size and plant age influence partitioning of biomass and resources. We also determined how root/shoot ratios are affected when the biomass of generative organs and storage carbohydrates are subtracted from measurements. The results for storage of resources supported economic theory: fertilized plants had higher concentrations of nitrogen than unfertilized plants, and unfertilized plants subjected to competition stored higher concentrations of non-structural carbohydrates than unfertilized plants without competition or fertilized plants with or without competition. Other results, mainly those related to the OPT, were inconsistent with economic theory. Nearly all examined allocations (except for the root/shoot ratio) were affected by both plant size and ontogeny. They also showed true plasticity in their response to competition but usually not in their response to fertilization. Although our experimental plants did not increase leaf biomass when carbon was relatively scarce (in the fertilized treatment), higher foliar nitrogen might have enhanced photosynthesis without biomass investment in leaves. Our results indicate that economic theory and the methodological problems associated with its measurement should be reconsidered.

Carbohydrate storage in meadow plants and its depletion after disturbance: do roots and stem-derived organs differ in their roles?

Storage of carbohydrates in organs protected from disturbance is an important adaptation of plants in disturbed habitats. We carried out a field experiment involving 31 herbaceous plant species in two cultural meadows to find out whether roots or belowground stem-derived organs (stem bases, stem tubers and rhizomes) are the main storage organs, to study how reserves accumulate in individual organs in the long term (growing season) and to ascertain whether meadow abandonment affects the distribution of carbohydrate reserves in plants. We also conducted a 22-day pot experiment with four meadow plant species to determine how removal of roots and aboveground parts affects the use of carbohydrates stored in roots and stem-derived organs in the short term. From the long-term perspective of the field experiment, mowing had a positive effect on the concentration of carbohydrate reserves. From the short-term perspective of the pot experiment, however, the effect on concentration and pools of carbohydrates was negative. In the field experiment, carbohydrate concentrations before winter were generally higher than in mid-season, and more often higher in roots than in stem-derived organs. Roots and stem-derived organs of plants in the pot experiment were depleted similarly after both types of disturbance. Our results indicate a need for including both types of belowground plant organs in future studies of the carbon economy of plants from disturbed habitats.

How to Preserve Plant Samples for Carbohydrate Analysis? Test of Suitable Methods Applicable in Remote Areas

Nonstructural carbohydrates (NSC) are frequently studied both by ecologists and plant physiologists because they serve as fundamental carbon and energy sources in plant metabolism. Because of the rapid enzymatic hydrolysis of NSC after harvest, plants are usually placed into liquid nitrogen until subsequent analyses in the laboratory. Nevertheless, when the research is performed in poorly accessible regions such as high mountains, tropical forests or deserts, the use of heavy containers containing vaporizing liquid nitrogen is problematic for logistical reasons. These places are particularly interesting as they harbor plant species with interesting physiological adaptations. In our study we aimed to develop a suitable storage method for plants intended for NSC analyses, which would require minimal equipment. These demands resulted in the idea of using the first step in NSC analyses – extraction in ethanol. Samples were extracted in 50 % and 96 % boiling or non-boiling ethanol and then stored for one month; they were compared with samples immediately frozen in liquid nitrogen. We discovered that for samples containing starch, fructans, soluble sugars and sugar alcohols, the best pretreatment for subsequent storage is extraction in 50 % or 96 % boiling ethanol. For total nonstructural carbohydrates (TNC) assessment, only extracting with 50 % ethanol without boiling gave very good results. Finally, we developed a method that could be used in any remote place without bulky laboratory equipment.

Biomass and Stored Carbohydrate Compensation after Above-Ground Biomass Removal in a Perennial Herb: Does Environmental Productivity Play a Role?

Many plant species are able to tolerate severe disturbance leading to removal of a substantial portion of the body by resprouting from intact or fragmented organs. Resprouting enables plants to compensate for biomass loss and complete their life cycles. The degree of disturbance tolerance, and hence the ecological advantage of damage tolerance (in contrast to alternative strategies), has been reported to be affected by environmental productivity. In our study, we examined the influence of soil nutrients (as an indicator of environmental productivity) on biomass and stored carbohydrate compensation after removal of aboveground parts in the perennial resprouter Plantago lanceolata. Specifically, we tested and compared the effects of nutrient availability on biomass and carbon storage in damaged and undamaged individuals. Damaged plants of P. lanceolata compensated neither in terms of biomass nor overall carbon storage. However, whereas in the nutrient-poor environment, root total non-structural carbohydrate concentrations (TNC) were similar for damaged and undamaged plants, in the nutrient-rich environment, damaged plants had remarkably higher TNC than undamaged plants. Based on TNC allocation patterns, we conclude that tolerance to disturbance is promoted in more productive environments, where higher photosynthetic efficiency allows for successful replenishment of carbohydrates. Although plants under nutrient-rich conditions did not compensate in terms of biomass or seed production, they entered winter with higher content of carbohydrates, which might result in better performance in the next growing season. This otherwise overlooked compensation mechanism might be responsible for inconsistent results reported from other studies.

Specialization of pollination systems of two co-flowering phenotypically generalized Hypericum species (Hypericaceae) in Cameroon

The degree of specialization in plant–pollinator relationships is probably the most intensively discussed topic of pollination biology. Phenotypically generalized flowers are typically also considered to be generalized ecologically and/or functionally. Our study focuses on visitors to flowers of Hypericum roeperianum and H. revolutum, two closely related co-flowering Afromontane plants with flat flowers, which can be visited by many insects. We collected insect visitors and recorded their behaviour. Both Hypericum species were visited by large numbers of morphospecies and functional groups, which might indicate that they are highly generalized plants. Nevertheless, after including the visitors’ abundance, behaviour and contact with the plants’ reproductive organs, only a single carpenter bee species could be considered an effective pollinator of H. roeperianum, and a few smaller bee species (mainly Apis mellifera and Meliplebeia ogouensis) could be considered as effective pollinators of H. revolutum. Despite the fact that the flowers appear at first glance phenotypically generalized, both species seem to be ecologically and functionally specialized for bee pollination. Our results indicate that even phenotypically generalized flowers can be functionally and ecologically specialized. More precise knowledge of their visitors’ behaviour is crucial for understanding their pollination systems. Our results cast doubts upon the currently leading opinion that generalization prevails in pollination systems, as such conclusions are based mainly on community-wide studies, which usually do not consider the true role of insect visitors.