Small herbivores and abiotic heterogeneity promote trait variation of a saltmarsh plant in local communities

Intraspecific trait variation (ITV) enables plants to respond to global changes. However, causes for ITV, especially from biotic components such as herbivory, are not well understood. We explored whether small vertebrate herbivores (hares and geese) impact ITV of a dominant clonal plant (Elytrigia atherica) in local communities. Moreover, we looked at the relative importance of their direct (e.g., selective grazing) and indirect effects (altering genotypic richness/diversity and abiotic environment) on ITV. We used exclosures at two successional stages in a Dutch saltmarsh, where grazing pressure at the early successional stage was ca. 1.5 times higher than that of the intermediate successional stage. We measured key functional traits of E. atherica including height, aboveground biomass, flowering (flower or not), specific leaf area, and leaf dry matter content in local communities (1 m × 1 m plots) inside and outside the exclosures. We determined genotypic richness and diversity of each plant using molecular markers. We further measured abiotic variations in topography and clay thickness (a proxy for soil total nitrogen). Structural equation models revealed that small herbivores significantly promoted ITV in height and flowering at the early successional stage, while they marginally promoted ITV in height at the intermediate successional stage. Moreover, the direct effects of herbivores played a major role in promoting ITV. Small herbivores decreased genotypic diversity at the intermediate successional stage, but genotypic richness and diversity did not impact ITV. Small herbivores did not alter topographic variation and variation in clay thickness, but these variations increased ITV in all traits at the early successional stage. Small herbivores may not only impact trait means in plants as studies have shown but also their ITV.

Aboveground forest biomass varies across continents, ecological zones and successional stages: refined IPCC default values for tropical and subtropical forests

For monitoring and reporting forest carbon stocks and fluxes, many countries in the tropics and subtropics rely on default values of forest aboveground biomass (AGB) from the Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas (GHG) Inventories. Default IPCC forest AGB values originated from 2006, and are relatively crude estimates of average values per continent and ecological zone. The 2006 default values were based on limited plot data available at the time, methods for their derivation were not fully clear, and no distinction between successional stages was made. As part of the 2019 Refinement to the 2006 IPCC Guidelines for GHG Inventories, we updated the default AGB values for tropical and subtropical forests based on AGB data from >25,000 plots in natural forests and a global AGB map where no plot data were available. We calculated refined AGB default values per continent, ecological zone, and successional stage, and provided a measure of uncertainty. AGB in tropical and subtropical forests varies by an order of magnitude across continents, ecological zones, and successional stage. Our refined default values generally reflect the climatic gradients in the tropics, with more AGB in wetter areas. AGB is generally higher in old-growth than in secondary forests, and higher in older secondary (regrowth >20 years old and degraded/logged forests) than in young secondary forests (≤20 years old). While refined default values for tropical old-growth forest are largely similar to the previous 2006 default values, the new default values are 4.0 to 7.7-fold lower for young secondary forests. Thus, the refined values will strongly alter estimated carbon stocks and fluxes, and emphasize the critical importance of old-growth forest conservation. We provide a reproducible approach to facilitate future refinements and encourage targeted efforts to establish permanent plots in areas with data gaps.

Closed-Canopy Tropical Forests of Hainan, (China) Are Resilient against Invasive Herbs and Shrubs

The successful establishment of many plants in tropical forests often depends on species-specific adaptations related to light availability and forest successional stage. Species that are present in early successional stages generally do not occur in later successional stages. In this study, we documented the diversity, distribution, and abundance of terrestrial invasive plants across the (sub)tropical island of Hainan, China, and tested the germination of specific invasive plants in forested environments. In 97 transects positioned randomly across the island, we found nine invasive herb and shrub species were present in all human-modified habitats but not in intact forest interiors. In separate forest-specific transects, we documented a sharp drop in the abundance of invasive plants >5 m into the forest. High numbers of invasive plant seeds germinated from the soil seed bank sampled at the forest edge, but very few seeds germinated from soil sampled any distance into the forest. Finally, in experiments with four focal invasive plant species, overall germination rates were low; and much lower in shaded sites compared to full gap sites. In conclusion, our findings demonstrated that invasive herbs and shrubs do not yet form a serious threat to native species in the closed-canopy forests of Hainan.

Manipulation of phyllosphere bacterial communities reversibly alters the plant microbiome and leaf traits in the field

Bacterial communities in the phyllosphere are shaped by host genotype and phenotype and spatio-temporal variation of the environment. In turn, bacteria have the potential for altering the plant phenotype. Field experiments can help to estimate bacterial effects on plant functional traits under natural conditions. We used a transplantation approach of culturable bacterial communities to explore how manipulation of leaf-associated microbial communities in two different successional stages within a glacier foreland can influence microbial composition and functional plant traits. Our study documents successional stage-specific variations in the composition of foliar bacterial communities and shifts therein throughout a season and between years. We show that cultured bacteria transferred between plant communities can alter diversity and composition of the microbiome on plant community level as well as species-specific functional plant traits of two selected plant species within one growing season. Furthermore, our results demonstrate a strong resilience of plant-associated bacterial communities and of plants in response to bacterial invaders. Our study illustrates that inoculation experiments in the field with naturally occurring microbial communities of wild plants are suited to investigate complex interactions between microbial communities, the environment, and plant traits.

SUCCESSION DYNAMICS OF NATIVE SPRUCE FORESTS OF DIFFERENT AGES IN EUROPEAN RUSSIA

Relevance. The article discusses various options for assigning forest biogeocenoses to a certain dynamic position in the successional field of their development. The proposed method for dynamic assessment of the position of forest creates the possibility of assessing the total movement of tree volumes in the age generations of the age range of the forest biogeocenosis the possibility of analyzing the past changes in the age structure of the biogeocenosis and predicting its future development for a very distant future. Material and methods. The objects of research are native virgin spruce biogeocenoses of different ages in the northern taiga of the Kandalaksha forestry enterprise of the Nyamozersky forestry of the Murmansk region, the Severodvinsky forestry enterprise of the Arkhangelsk region; middle taiga spruce forests of the Vepssky forest reserve, Leningrad region. and the tract “Atleka” of the Andomsky forestry of the Vologda region; southern taiga spruce forests of the Kologrivsky forest reserve Kostroma region and the Central Forest Biosphere Reserve in the Tver region. The author studied the features of the structures of the age series of spruce forests, the most typical and productive types of growing conditions for spruce. Results and conclusions. All represented forest communities have different ratios of the number and volume of trees in the age generations of the age series and, as a consequence, different positions in the successional dynamics of development. Wood-destroying fungi of the biotrophic complex, as an endogenous structure of the forest community, actively participates in the dynamic processes of its development at all stages of its successional movement. The infection of trees by fungi of this complex increases from the last generations to the first to the maximum values in the oldest trees of the first generation. The dynamic position of the indigenous virgin forest community of different ages can be described with a wider range of assessments of the dynamics of its development in retrospect and perspective in terms of the ratio of quantitative and volumetric indicators of age generations of age series than in terms of the current structure of the age series. When assessing the successional stage of the forest community, it is necessary to take into account the quantity (volumes) and structure of the deadwood.

Bridging Microbial Functional Traits With Localized Process Rates at Soil Interfaces

In this review, we introduce microbially-mediated soil processes, players, their functional traits, and their links to processes at biogeochemical interfaces [e.g., rhizosphere, detritusphere, (bio)-pores, and aggregate surfaces]. A conceptual view emphasizes the central role of the rhizosphere in interactions with other biogeochemical interfaces, considering biotic and abiotic dynamic drivers. We discuss the applicability of three groups of traits based on microbial physiology, activity state, and genomic functional traits to reflect microbial growth in soil. The sensitivity and credibility of modern molecular approaches to estimate microbial-specific growth rates require further development. A link between functional traits determined by physiological (e.g., respiration, biomarkers) and genomic (e.g., genome size, number of ribosomal gene copies per genome, expression of catabolic versus biosynthetic genes) approaches is strongly affected by environmental conditions such as carbon, nutrient availability, and ecosystem type. Therefore, we address the role of soil physico-chemical conditions and trophic interactions as drivers of microbially-mediated soil processes at relevant scales for process localization. The strengths and weaknesses of current approaches (destructive, non-destructive, and predictive) for assessing process localization and the corresponding estimates of process rates are linked to the challenges for modeling microbially-mediated processes in heterogeneous soil microhabitats. Finally, we introduce a conceptual self-regulatory mechanism based on the flexible structure of active microbial communities. Microbial taxa best suited to each successional stage of substrate decomposition become dominant and alter the community structure. The rates of decomposition of organic compounds, therefore, are dependent on the functional traits of dominant taxa and microbial strategies, which are selected and driven by the local environment.

The vegetation of rich fens (Sphagno warnstorfii-Tomentypnion nitentis) at the southeastern margins of their European range

Question: Rich fens of the Sphagno warnstorfii-Tomentypnion nitentis alliance require a specific combination of base richness and climate to occur. Their rarity at the southeastern margins of their European range has previously prevented rigorous vegetation classification. We asked how many associations may be delimited here and whether some of them are restricted to the high Balkan Mountains showing high endemicity. Study area: Entire territories of Bulgaria and Romania. Methods: We compiled all available vegetation-plot records, including some hitherto unprocessed data. We classified them by both divisive (modified TWINSPAN) and agglomerative (beta-flexible clustering) numerical classification method, with OPTIMCLASS1 applied to set the number of clusters. A semi-supervised approach (k-means) was additionally applied to confirm the classification of Southern-Carpathian (Romania) rich fens, where some Balkan taxa occur. Differences in base richness and elevation were tested by one-way ANOVA with Tukey’s pairwise test. Results: Three associations were delimited and all three occur in Bulgaria, from where only one association had been previously reported. Two associations characterised by Sphagnum contortum and Balkan and Southern-European species occur in Bulgaria, but not in Romania, one at lower elevations around 1,200 m, and one at higher elevations around 2,000 m where pH is lower. One lower-elevation (around 1,300 m) association with S. warnstorfii and S. teres is shared between Romania, Bulgaria and Central Europe. Conclusions: We have described a new high-mountain association, with two subassociations that differ by successional stage and dominant peat moss species (S. contortum and S. warnstorfii, respectively). These subassociations could be reconsidered when more data from other Balkan countries are available. Rich fens in southeastern Europe are rare, have a diverse vegetation, and are deserving of the further attention of nature conservation authorities and vegetation scientists. Taxonomic reference: The nomenclature was harmonized following The Euro+Med PlantBase (Euro+Med 2021) for vascular plants and Hill et al. (2006) for bryophytes, except of Angelica pancicii that is accepted as a separate taxon in Bulgaria (Andreev et al. 1992; Delipavlov et al. 2003). Critical taxa, not always reliably differentiated in the field and in literary sources, were merged to aggregates: Alchemilla vulgaris agg. (all Alchemilla species), Anthoxanthum odoratum agg. (A. alpinum, A. odoratum), Molinia caerulea agg. (M. arundinacea subsp. arundinacea, M. arundinacea subsp. freyi, M. caerulea), Palustriella commutata agg. (P. commutata, P. falcata), Plagiomnium affine agg. (P. affine, P. elatum, P. ellipticum), Sphagnum palustre agg. (S. centrale, S. palustre). Syntaxonomic reference: Peterka et al. (2017) for alliances.

Quantifying functional increases across a large-scale wetland restoration chronosequence

Over 300,000 ha of forested wetlands have undergone restoration within the Mississippi Alluvial Valley region. Restored forest successional stage varies, providing opportunities to document wetland functional increases across a large-scale restoration chronosequence using the Hydrogeomorphic (HGM) approach. Results from >600 restored study sites spanning a 25-year chronosequence indicate that: 1) wetland functional assessment variables increased toward reference conditions; 2) restored wetlands generally follow expected recovery trajectories; and 3) wetland functions display significant improvements across the restoration chronosequence. A functional lag between restored areas and mature reference wetlands persists in most instances. However, a subset of restored sites have attained mature reference wetland conditions in areas approaching or exceeding tree diameter and canopy closure thresholds. Study results highlight the importance of site selection and the benefits of evaluating a suite of wetland functions in order to identify appropriate restoration success milestones and design monitoring programs. For example, wetland functions associated with detention of precipitation (a largely physical process) rapidly increased under post restoration conditions, while improvements in wetland habitat functions (associated with forest establishment and maturation) required additional time. As the wetland science community transitions towards larger scale restoration efforts, effectively quantifying restoration functional improvements will become increasingly important.

Vegetation responses to past volcanic disturbances at the Araucaria araucana forest-steppe ecotone in northern Patagonia

Aims Volcanic eruptions play an important role in vegetation dynamics and its historical range of variability. However, large events are infrequent and eruptions with significant imprint in today vegetation occurred far in the past, limiting our understanding of ecological process. Volcanoes in southern Andes have been active during the last 10 ka, and support unique ecosystems such as the Araucaria-Nothofagus forest as part of the Valdivian Temperate Rainforest Hotspot. Araucaria is an endangered species, strongly fragmented and well adapted to disturbances. Yet it was suggested that volcanism might have increased the fragmentation of its populations. To provide an insight into the vegetation responses to past volcanic disturbances, a paleoecological study was conducted to assess the role of volcanic disturbance on the vegetation dynamics and if the current fragmentation has been caused by volcanism. Location Araucaria forest-steppe ecotone in northern Patagonia. Methods Pollen and tephra analysis from a sedimentary record. Results During the last 9 kyr, 39 tephrafall buried the vegetation around Lake Relem, more frequently between 4-2 ka. The vegetation was sensitive to small tephrafall but seldom caused significant changes. However, the large eruption of Sollipulli-Alpehue (~3 ka) might change the environmental conditions affecting severely the forest and grassland, as suggested by the pollen record. Ephedra dominated early successional stage, perhaps facilitating Nothofagus regeneration recovering original condition after ~500 years. Slight increase of pollen percentage from Araucaria and Nothofagus obliqua-type could be indicative of sparse biological legacies distributed in the landscape. The analysis showed that vegetation resisted without permanent changes, recovering relatively fast after the large eruption. Conclusion The relative stability of Araucaria pollen in the study area after several tephrafall suggests no change in its past geographical distribution at the current forest-steppe ecotone, thus I found no evidence that volcanic eruptions would have affected its current conservation status.