Vojtěch Lanta

Biodiversity Increases the Resistance of Ecosystem Productivity to Climate Extremes

It remains unclear whether biodiversity buffers ecosystems against climate extremes, which are becoming increasingly frequent worldwide. Early results suggested that the ecosystem productivity of diverse grassland plant communities was more resistant, changing less during drought, and more resilient, recovering more quickly after drought, than that of depauperate communities. However, subsequent experimental tests produced mixed results. Here we use data from 46 experiments that manipulated grassland plant diversity to test whether biodiversity provides resistance during and resilience after climate events. We show that biodiversity increased ecosystem resistance for a broad range of climate events, including wet or dry, moderate or extreme, and brief or prolonged events. Across all studies and climate events, the productivity of low-diversity communities with one or two species changed by approximately 50% during climate events, whereas that of high-diversity communities with 16–32 species was more resistant, changing by only approximately 25%. By a year after each climate event, ecosystem productivity had often fully recovered, or overshot, normal levels of productivity in both high- and low-diversity communities, leading to no detectable dependence of ecosystem resilience on biodiversity. Our results suggest that biodiversity mainly stabilizes ecosystem productivity, and productivity-dependent ecosystem services, by increasing resistance to climate events. Anthropogenic environmental changes that drive biodiversity loss thus seem likely to decrease ecosystem stability, and restoration of biodiversity to increase it, mainly by changing the resistance of ecosystem productivity to climate events.

Potential contribution of natural enemies to patterns of local adaptation in plants.

Genetic differentiation among plant populations and adaptation to local environmental conditions are well documented. However, few studies have examined the potential contribution of plant antagonists, such as insect herbivores and pathogens, to the pattern of local adaptation. Here, a reciprocal transplant experiment was set up at three sites across Europe using two common plant species, Holcus lanatus and Plantago lanceolata. The amount of damage by the main above-ground plant antagonists was measured: a rust fungus infecting Holcus and a specialist beetle feeding on Plantago, both in low-density monoculture plots and in competition with interspecific neighbours. Strong genetic differentiation among provenances in the amount of damage by antagonists in both species was found. Local provenances of Holcus had significantly higher amounts of rust infection than foreign provenances, whereas local provenances of Plantago were significantly less damaged by the specialist beetle than the foreign provenances. The presence of surrounding vegetation affected the amount of damage but had little influence on the ranking of plant provenances. The opposite pattern of population differentiation in resistance to local antagonists in the two species suggests that it will be difficult to predict the consequences of plant translocations for interactions with organisms of higher trophic levels.

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.

Background losses of woody plant foliage to insects show variable relationships with plant functional traits across the globe

Summary Despite a long history of research, we lack a comprehensive understanding of the reasons behind pronounced variation in foliar losses to insects among plant species. Our aim was to test the hypothesis that plant functional traits and/or ecological strategies are good predictors of the background losses of woody plant foliage to insects (i.e. losses occurring when herbivore populations are at their ‘normal’ densities) at the global scale. We conducted a quantitative synthesis of published and original data on foliar losses of 793 species of woody plants belonging to 128 families from ca. 500 localities world-wide, representing tropical, temperate and polar climate zones. The background foliar losses to insects varied among plant life forms, increasing from dwarf shrubs to large trees, and were higher in inherently fast-growing species than in slow-growing species. These patterns supported predictions of both the apparency and growth rate (resource availability) hypotheses for data combined across localities, but only outside the tropics. Foliar losses to insects slightly but significantly increased with specific leaf area (SLA) in all climate zones. No differences were noted in background herbivory between woody plant species with deciduous and evergreen foliage, with different shade tolerance and with different successional status. Synthesis. Factors affecting the distribution of herbivory among species of woody plants differed among the climate zones, and the predictive power of at least some of the theories/hypotheses addressing plant–herbivore interactions at large spatial scales varies among climates and/or biomes. The average background losses of woody plant foliage to insects across localities can be predicted from the inherent growth rate of the plant species, its life form and SLA, although these plant characteristics jointly explain only a minor part of the total variation observed in the primary data.

Effects of disturbance regime on carbohydrate reserves in meadow plants

Plants in unmown meadows are able to store large amounts of carbohydrates. These stores, however, become depleted during winter and/or spring and thus do not differ from levels in mown plots at the peak of the next growing season. It is clear, moreover, that although carbohydrate concentrations at first reflect the carbohydrate mobilization needed for resprouting in response to plant damage and then the refilling of reserves thereby expended, the total carbohydrate amounts are affected by the growth of storage organs. Although concentrations and total amounts of carbohydrates reflect different aspects of plant carbohydrate storage, their concentration might sufficiently describe short-term effects of disturbance.

Sown species richness and realized diversity can influence functioning of plant communities differently

Biodiversity–ecosystem functioning experiments (BEF) typically manipulate sown species richness and composition of experimental communities to study ecosystem functioning as a response to changes in diversity. If sown species richness is taken as a measure of diversity and aboveground biomass production as a measure of community functioning, then this relationship is usually found to be positive. The sown species richness can be considered the equivalent of a local species pool in natural communities. However, in addition to species richness, realized diversity is also an important community diversity component. Realized diversity is affected by environmental filtering and biotic interactions operating within a community. As both sown species richness and the realized diversity in BEF studies (as well as local species pool vs observed realized richness in natural communities) can differ markedly, so can their effects on the community functioning. We tested this assumption using two data sets: data from a short-term pot experiment and data from the long-term Jena biodiversity plot experiment. We considered three possible predictors of community functioning (aboveground biomass production): sown species richness, realized diversity (defined as inverse of Simpson dominance index), and survivor species richness. Sown species richness affected biomass production positively in all cases. Realized diversity as well as survivor species richness had positive effects on biomass in approximately half of cases. When realized diversity or survivor species richness was tested together with sown species richness, their partial effects were none or negative. Our results suggest that we can expect positive diversity–productivity relationship when the local species pool size is the decisive factor determining realized observed diversity; in other cases, the shape of the diversity–functioning relationship may be quite opposite.

Radial Growth and Ring Formation Process in Clonal Plant Eriophorum angustifolium on Post-Mined Peatland in the Šumava Mts., Czech Republic

Eriophorum angustifolium (Cyperaceae) is a pioneer clonal sedge colonizing bare peat surface of harvested peatlands in central Europe. It forms circular patches of densely aggregated ramets, followed by central die-back and ring formation as circles develop. This study experimentally tested the importance of inter-ramet competition, interference with litter, soil nutrient depletion, and architectural constraints for radial clonal spread and ring formation process. Effects of fertilization, litter addition and competition of neighbor ramets on growth and survival of tillers transplanted into four distinct zones within individual circle were detected only in the first zone (green band) with high ramet density. This suggested that both above-ground competition for light and below-ground competition for soil nutrients can play an important role in population dynamics of E. angustifolium. A field study of clonal growth has shown that rhizomes orient preferentially towards the periphery. As the old ramets within the interior of the tussock died due to senescence and inter-ramet competition, disproportionately more ramets are recruited on the periphery, which reduce axillary bud availability within the interior of the tussocks. We also explored the soil nutrient content (NH4-N, NO3-N and PO4-P). High values of NO3-N outside the circles and low values inside patches might partly explain why Eriophorum rhizomes are oriented into open space. High accumulation of phosphorus (PO4-P) in the centre of the patches was attributed to the leaching of phosphorus from decaying Eriophorum plants. We suggest that processes of nutrient foraging and utilization are responsible for development of circular patches of E. angustifolium in the harsh environment of cut-away peatland.

Non-native and native shrubs have differing impacts on species diversity and composition of associated plant communities

The spread of non-native plants has been depicted as a serious threat to biodiversity. However, it remains unclear whether the indigenousness of the invading plant plays a marked role for the ecological consequences of an invasion as few studies have compared the ecological impacts of non-native shrubs with structurally or functionally comparable native shrubs. We studied patches of introduced and native shrubs to assess whether there are general differences in plant species composition or biomass between patches formed by non-native versus native shrubs. The indigenousness of the shrub (non-native vs. native) did not explain the variation in soil nutrients, neither the production of shoot biomass or allocation of growth to different parts of the shoot. The amount of light reaching ground level did not differ between patches of a non-native and a native shrub. However, species richness and biomass of herbaceous plants were lower in patches of non-native than native shrubs and the amount of litter was higher below non-native than native shrubs. Our results suggest that the indigenousness of the patch-forming plant may be an important factor for the diversity and composition of associated herbaceous vegetation. Based on our results, resource availability (light and nutrients) is not a sufficient explanation for the negative effects of non-native shrubs on plant communities. Further research is needed to investigate whether alternative explanations, such as the novelty of the toxic compounds produced by non-native plants, can explain the differences we observed.

Leaf Litter Decomposition of Nonnative Shrub Species in Nonnative and Native Shrub Environments: A Field Experiment with Three Rosaceae Shrubs

Abstract Invasion by nonnative plants may have ecosystem-wide effects, altering the decomposition rate of plant material via changes in litter quality or altered environment (abiotic conditions, associated biotic community), or both. Yet, the relative importance of these factors for decomposition rates is not clear. We studied decomposition using the leaves of related shrub species (nonnative Sorbaria sorbifolia and Rosa rugosa, native Rubus idaeus) with comparable physiognomy but different leaf characteristics and origin (alien vs. native) in patches formed by S. sorbifolia and Rubus idaeus in southwestern Finland. Decomposition of cellulose in the topsoils of the patches was also studied. Using litter bags, we found that S. sorbifolia leaf litter decomposed slowest and Rosa rugosa leaves fastest irrespective of patch type. Topsoils in S. sorbifolia patches were richer in carbon, nitrogen, and calcium than those of Rubus idaeus, but these differences did not affect decomposition rates. Very little decomposition appeared to happen during the winter but during the summer, microclimate had minor but significant effects on decomposition rates. Our results highlight the key role of litter source in the decomposition of plant material. Between-patch differences in abiotic conditions appear to play a minor role relative to litter quality. Nomenclature: False spirea; Sorbaria sorbifolia (L.) A. Braun; rugosa rose; Rosa rugosa Thunb.; red raspberry; Rubus idaeus L. Management Implications: Decomposition of plant material is crucial for nutrient cycling. Invasive woody species may alter decomposition rates by altering litter quality and by altering the environmental conditions below the plants. We compared the leaf decomposition of a native and two nonnative shrubs in environments created by the native and one of the nonnative shrubs to estimate the relative importance of leaf source (species identity) and environment (microclimatic conditions, soil nutrient levels) for leaf decomposition rates. All shrubs belonged to the same family (Rosaceae) and had comparable physiognomy and leaf biomass production, which helped to minimize the influence of confounding factors. Our results demonstrate how the decomposition rate of leaves depends on species-specific differences in the quality of leaves rather than on the minor differences in the environments created by the patch-forming shrubs. The predominant importance of leaf source has been stressed also in some previous studies, suggesting that our conclusions can be generalized to a wider group of woody species. Although our conclusions can be regarded as preliminary rather than conclusive due to the small number of studied species, our results suggest that evaluations based solely on changes in leaf litter quality (and quantity) may capture the essential changes in leaf decomposition rates after an invasion of a nonindigenous plant. However, our results also indicate that species-specific differences in leaf quality prevent generalizations across all species, so the consequences of plant invasions for decomposition rates should be evaluated at the level of plant species.

Niche Separation of two Grass Species along a Moisture Gradient in a Post-Mined Peatland

The natural capacity of peatland ecosystems to regenerate after a disturbance by peat mining is often a long-lasting process. However, some plants have an ability to colonize, stabilize the peat surface and cope with harsh environmental conditions. Here, we studied ecological factors helping to explain niche separation of two grass species Holcus mollis and Deschampsia flexuosa, which have colonized peat deposits soon after the peat extraction ended in a post-mined peatland (South Bohemia, Czech Republic). While H. mollis, a creeping growth-like plant, formed lawns in dry parts of deposits, D. flexuosa, a tussock forming plant, colonized wetter parts. This implies that microhabitat conditions, most importantly soil moisture, may influence niche separation. The diversity of other less abundant vascular plants was the highest in lawns of H. mollis and low in an open vegetation dominated by D. flexuosa. The roots of the two studied grasses were colonized by arbuscular mycorrhizal fungi in a similar rate which suggests that positive associations are essential for plants to set up in harsh conditions of post-mined peatlands.