Showing papers by "Martin Zobel published in 2014"

Fifty thousand years of Arctic vegetation and megafaunal diet

Abstract: Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr bp (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25–15 kyr bp), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr bp, with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe.

Which is a better predictor of plant traits: temperature or precipitation?

Abstract: Question: Are plant traits more closely correlated with mean annual temperature, or with mean annual precipitation? Location: Global. Methods: We quantified the strength of the relationships between temperature and precipitation and 21 plant traits from 447,961 species-site combinations worldwide. We used meta-analysis to provide an overall answer to our question.

Species richness of arbuscular mycorrhizal fungi: associations with grassland plant richness and biomass

Abstract: Summary � Although experiments show a positive association between vascular plant and arbuscular mycorrhizal fungal (AMF) species richness, evidence from natural ecosystems is scarce. Furthermore, there is little knowledge about how AMF richness varies with belowground plant richness and biomass. � We examined relationships among AMF richness, above- and belowground plant richness, and plant root and shoot biomass in a native North American grassland. Root-colonizing AMF richness and belowground plant richness were detected from the same bulk root samples by 454-sequencing of the AMF SSU rRNA and plant trnL genes. � In total we detected 63 AMF taxa. Plant richness was 1.5 times greater belowground than aboveground. AMF richness was significantly positively correlated with plant species richness, and more strongly with below- than aboveground plant richness. Belowground plant richness was positively correlated with belowground plant biomass and total plant biomass, whereas aboveground plant richness was positively correlated only with belowground plant biomass. By contrast, AMF richness was negatively correlated with belowground and total plant biomass.

Predicting species’ maximum dispersal distances from simple plant traits

Abstract: Many studies have shown plant species' dispersal distances to be strongly related to life-history traits, but how well different traits can predict dispersal distances is not yet known. We used cross-validation techniques and a global data set (576 plant species) to measure the predictive power of simple plant traits to estimate species' maximum dispersal distances. Including dispersal syndrome (wind, animal, ant, ballistic, and no special syndrome), growth form (tree, shrub, herb), seed mass, seed release height, and terminal velocity in different combinations as explanatory variables we constructed models to explain variation in measured maximum dispersal distances and evaluated their power to predict maximum dispersal distances. Predictions are more accurate, but also limited to a particular set of species, if data on more specific traits, such as terminal velocity, are available. The best model (R2 = 0.60) included dispersal syndrome, growth form, and terminal velocity as fixed effects. Reasonable predictions of maximum dispersal distance (R2 = 0.53) are also possible when using only the simplest and most commonly measured traits; dispersal syndrome and growth form together with species taxonomy data. We provide a function (dispeRsal) to be run in the software package R. This enables researchers to estimate maximum dispersal distances with confidence intervals for plant species using measured traits as predictors. Easily obtainable trait data, such as dispersal syndrome (inferred from seed morphology) and growth form, enable predictions to be made for a large number of species.

Agricultural policies exacerbate honeybee pollination service supply-demand mismatches across Europe.

Abstract: Declines in insect pollinators across Europe have raised concerns about the supply of pollination services to agriculture. Simultaneously, EU agricultural and biofuel policies have encouraged substantial growth in the cultivated area of insect pollinated crops across the continent. Using data from 41 European countries, this study demonstrates that the recommended number of honeybees required to provide crop pollination across Europe has risen 4.9 times as fast as honeybee stocks between 2005 and 2010. Consequently, honeybee stocks were insufficient to supply >90% of demands in 22 countries studied. These findings raise concerns about the capacity of many countries to cope with major losses of wild pollinators and highlight numerous critical gaps in current understanding of pollination service supplies and demands, pointing to a pressing need for further research into this issue.

Plant and arbuscular mycorrhizal fungal (AMF) communities – which drives which?

Abstract: More than a decade ago, the Driver (arbuscular mycorrhizal fungal partners drive plant communities) and Passenger (AMF community dynamics follows changes in the host plant community) hypotheses were suggested to explain the mutual relationships of plant and AMF communities. We propose one more hypothesis: the Habitat hypothesis, which postulates that both plant and AMF communities follow changes in abiotic conditions. The null hypothesis for all three working hypotheses can be called the Independence hypothesis, which proposes that plant and AMF communities are unrelated. We investigate the assumptions of these hypotheses and the available evidence in support of them. We suggest that community dynamics during secondary succession, including those related to land-use changes, may be explained by the Driver hypothesis, while the dynamics of plant and AMF communities during primary succession may be explained by the Passenger hypothesis. Within-region co-variation of successionally stable plant and AMF communities may be explained by the Habitat hypothesis, while the Independence hypothesis may explain global patterns of plant and AMF communities. These suggestions are tentative, and more evidence from both descriptive and experimental studies is required to assess them. In particular, comparative information is needed about dispersal limitation of plant and AMF communities in dynamic landscapes.

Soil nutrient content influences the abundance of soil microbes but not plant biomass at the small-scale.

Abstract: Small-scale heterogeneity of abiotic and biotic factors is expected to play a crucial role in species coexistence. It is known that plants are able to concentrate their root biomass into areas with high nutrient content and also acquire nutrients via symbiotic microorganisms such as arbuscular mycorrhizal (AM) fungi. At the same time, little is known about the small-scale distribution of soil nutrients, microbes and plant biomass occurring in the same area. We examined small-scale temporal and spatial variation as well as covariation of soil nutrients, microbial biomass (using soil fatty acid biomarker content) and above- and belowground biomass of herbaceous plants in a natural herb-rich boreonemoral spruce forest. The abundance of AM fungi and bacteria decreased during the plant growing season while soil nutrient content rather increased. The abundance of all microbes studied also varied in space and was affected by soil nutrient content. In particular, the abundance of AM fungi was negatively related to soil phosphorus and positively influenced by soil nitrogen content. Neither shoot nor root biomass of herbaceous plants showed any significant relationship with variation in soil nutrient content or the abundance of soil microbes. Our study suggests that plants can compensate for low soil phosphorus concentration via interactions with soil microbes, most probably due to a more efficient symbiosis with AM fungi. This compensation results in relatively constant plant biomass despite variation in soil phosphorous content and in the abundance of AM fungi. Hence, it is crucial to consider both soil nutrient content and the abundance of soil microbes when exploring the mechanisms driving vegetation patterns.

Seed bank and its restoration potential in Estonian flooded meadows

Abstract: Questions What is the overall restoration potential of the persistent soil seed bank of abandoned flooded meadows? To what degree does the share of typical flooded meadow species in the soil seed bank change during secondary succession from traditionally managed hayfields to stages overgrown by woody vegetation? Location Flooded meadows in Alam-Pedja Nature Reserve, central Estonia (26°14′ E, 58°33′ N). Methods The species composition of above-ground vegetation and the persistent soil seed bank were investigated with PerMANOVA and non-metric multidimensional scaling in mown, 25-yr abandoned and 50-yr abandoned sedge and tall forb meadows subjected to annual flooding. Particular attention was given to typical flooded meadow species in the persistent soil seed bank. General linear models and non-parametric tests were used to assess successional trends in seed bank richness, density, similarity to target vegetation and percentage of flooded meadow species to assess the restoration potential of the soil seed bank. Results The cessation of traditional management has led to considerable changes in both above-ground and seed bank communities, differences between successional stages being more pronounced in the soil seed bank. The density of the seed bank was higher in abandoned meadows. Diversity in the vegetation and soil seed bank was lowest in the 25-yr abandoned tall forb meadows. Although the soil seed bank similarity to above-ground mown meadows (locally defined target vegetation) was relatively low across different successional stages, the proportion of flooded meadow species in the seed bank remained high – even after 50-yr abandonment, on average 42% of emerged seeds from sedge meadow and 34% from tall forb meadow were typical flooded meadow species. Conclusions Abandoned floodplain meadows in central Estonia still contain a relatively large grassland community species pool, including a large and effective soil seed bank. The soil seed bank could thus play an important role in the restoration of abandoned and overgrown meadow communities. Targeted experiments addressing the optimal techniques for activating the soil seed bank in flooded meadow soil are needed.

Spatially-explicit estimation of geographical representation in large-scale species distribution datasets.

Abstract: Much ecological research relies on existing multispecies distribution datasets. Such datasets, however, can vary considerably in quality, extent, resolution or taxonomic coverage. We provide a framework for a spatially-explicit evaluation of geographical representation within large-scale species distribution datasets, using the comparison of an occurrence atlas with a range atlas dataset as a working example. Specifically, we compared occurrence maps for 3773 taxa from the widely-used Atlas Florae Europaeae (AFE) with digitised range maps for 2049 taxa of the lesser-known Atlas of North European Vascular Plants. We calculated the level of agreement at a 50-km spatial resolution using average latitudinal and longitudinal species range, and area of occupancy. Agreement in species distribution was calculated and mapped using Jaccard similarity index and a reduced major axis (RMA) regression analysis of species richness between the entire atlases (5221 taxa in total) and between co-occurring species (601 taxa). We found no difference in distribution ranges or in the area of occupancy frequency distribution, indicating that atlases were sufficiently overlapping for a valid comparison. The similarity index map showed high levels of agreement for central, western, and northern Europe. The RMA regression confirmed that geographical representation of AFE was low in areas with a sparse data recording history (e.g., Russia, Belarus and the Ukraine). For co-occurring species in south-eastern Europe, however, the Atlas of North European Vascular Plants showed remarkably higher richness estimations. Geographical representation of atlas data can be much more heterogeneous than often assumed. Level of agreement between datasets can be used to evaluate geographical representation within datasets. Merging atlases into a single dataset is worthwhile in spite of methodological differences, and helps to fill gaps in our knowledge of species distribution ranges. Species distribution dataset mergers, such as the one exemplified here, can serve as a baseline towards comprehensive species distribution datasets.

Vegetation patterns and their underlying processes: where are we now?

Abstract: This Special Feature of the Journal of Vegetation Science contains ten contributions from the 56th Symposium of the International Association for Vegetation Science (IAVS), which was held in Tartu, Estonia, 26–30 Jun 2013, and focused on processes underlying vegetation patterns. These contributions give an overview of recent advances in vegetation science, with topics ranging from the introduction of new methods and ideas to comprehensive analysis of vegetation patterns on a global scale. The focus of these Special Feature contributions indicates that vegetation science is becoming more global, more complex and more interdisciplinary. It is likely that progress in methods and accumulation of data have led vegetation science into a ‘new era of discovery’.