Michael J. Gundale’s research while affiliated with Swedish University of Agricultural Sciences and other places

There has been much recent interest in understanding how abiotic factors such as light, nutrients, and soil moisture affect the composition and biomass of lichen communities. Meanwhile, whether and how ground layer vegetation such as bryophytes and shrubs also influence lichen communities have received much less attention, particularly regarding how these effects vary across environmental gradients. In this study, we used a long‐term (19‐year) biodiversity manipulation experiment to assess the importance of feather moss and ericaceous dwarf shrub removals on the composition and diversity (assessed via metabarcoding) and biomass (assessed via PLFA markers) of terricolous lichen communities along a 5000‐year boreal forest post‐fire chronosequence in northern Sweden. Overall, our results showed that shrub removals had a greater impact than moss removals on the biomass and composition of lichen communities. Shrub removals increased lichen alpha‐diversity while decreasing lichen beta‐diversity. This is mainly because, although the number of lichen species increased in the absence of shrubs, lichen communities were strongly dominated by Cladonia spp. However, the effects of shrub removals were context‐dependent, with greater effects observed in older ecosystems. Our results highlight that shrubs had a greater impact than moss in shaping terricolous lichen communities in boreal forests, with increasing effects from young ecosystems to older ones. We conclude that the foreseen expansion of vascular plants such as ericaceous shrubs into high latitude regions will probably have negative consequences on lichen cover, but that these effects will be dependent on the environmental context.

Trees are an important carbon sink as they accumulate biomass through photosynthesis¹. Identifying tree species that grow fast is therefore commonly considered to be essential for effective climate change mitigation through forest planting. Although species characteristics are key information for plantation design and forest management, field studies often fail to detect clear relationships between species functional traits and tree growth². Here, by consolidating four independent datasets and classifying the acquisitive and conservative species based on their functional trait values, we show that acquisitive tree species, which are supposedly fast-growing species, generally grow slowly in field conditions. This discrepancy between the current paradigm and field observations is explained by the interactions with environmental conditions that influence growth. Acquisitive species require moist mild climates and fertile soils, conditions that are generally not met in the field. By contrast, conservative species, which are supposedly slow-growing species, show generally higher realized growth due to their ability to tolerate unfavourable environmental conditions. In general, conservative tree species grow more steadily than acquisitive tree species in non-tropical forests. We recommend planting acquisitive tree species in areas where they can realize their fast-growing potential. In other regions, where environmental stress is higher, conservative tree species have a larger potential to fix carbon in their biomass.

Inter-continental study systems are crucial for testing ecological hypotheses, such as the widely cited Enemy Release Hypothesis (ERH), which seeks to explain the superior performance of plant species when they are introduced to new regions. Pinus contorta (lodgepole pine), native to North America, has been extensively introduced to Europe and the Southern Hemisphere, making it an ideal tree species for studying invasion hypotheses from a biogeographical perspective. We compared foliar fungal communities, especially pathogens, of P. contorta across two native–introduced region pairs (NIRPs): a northern NIRP (from Canada to Sweden) and a southern NIRP (from the USA to Patagonia), while also examining the differences between source plantations and invasion fronts within Patagonia. P. contorta underwent significant fungal community shifts and experienced pathogen release during its large-scale introduction from North America to Sweden and Patagonia. The fungal richness and relative abundance changes were more pronounced for the southern NIRP pair, where no closely related tree species to P. contorta are present in Patagonia. In Sweden, the presence of the phylogenetically related P. sylvestris and its associated local fungal community appears to play a role in influencing the foliar fungal communities associated with introduced P. contorta. In Patagonia, the incomplete co-invasion of fungal taxa from the USA emerges as a principal driver of the observed variability in fungal community composition and pathogen release following the introduction of P. contorta. In Patagonia, fungal community composition differences between source plantations and invasion fronts provided insufficient evidence that pathogen release occurs at this local scale. Integrating both biogeographical and phylogenetic perspectives, our study suggests that priority effects of local fungi appear to be a dominant community assembly process when introduction is done in a phylogenetically similar community; whereas, co-invasion of fungal communities is the dominant process in phylogenetically distant communities.

The existence of trait coordination in roots and leaves has recently been debated, with studies reaching opposing conclusions. Here, we assessed trait coordination across twelve boreal tree species. We show that there is only partial evidence for above-belowground coordination for “fast-slow” economic traits across boreal tree species, i.e., while N content in leaves and roots were positively correlated, as well as dry matter content, root dry matter content and leaf N had no significant relationship. For resource acquisition traits (i.e. related to light capture and nutrient uptake) we did not find strong evidence for trait coordination, as specific root length and specific leaf area were not positively correlated. We further show that site only explained between 0 and 7% of the total trait variation, while within-site variation contributed substantially to the total trait variation for a large number of traits (1.6–96%), and more so for morphological root traits than leaf traits. This likely influences the strength of above-belowground trait coordination found across species in our study. Understanding sources of trait variation and above-belowground trait relationships can contribute to improving global and regional C cycling models. However, fine-scale environmental variability should be accounted for given its importance for driving trait variation.

This chapter serves as a review of the general mechanisms through which biochar influences nutrient availability to plants, and provides an evaluation of the effect biochar has on nutrient cycling and specific transformations for several key plant nutrients. We explore some of the knowns and unknowns regarding how biochar influences soil nutrient transformations, which are likely to have both short- and long-term impacts on plant productivity in forest and agricultural landscapes. We specifically focus on the influence of biochar additions to soil on transformations of N, P, S, and micronutrients, Cu, Fe, Mn, and Zn. , and explore the implications for modification of these cycles in terms of plant availability of nutrients and their long-term budgets across a range of ecosystems.

Background and aims Plant-soil feedbacks (PSFs) play an important role in mediating plant species coexistence, community dynamics and ecosystem functioning. Soil biota (e.g. mutualists, pathogens), nutrient availability and secondary chemicals can drive the strength and direction of PSFs, but the variations and context-dependence of their effects remain unclear. Methods We used a phylogenetically controlled meta-analysis of 57 PSF studies across 166 plant species to explore whether and how these drivers affect individual PSFs (the performance of a species on conspecific versus heterospecific soils) and pairwise PSFs (indicating whether feedbacks promote stable or unstable species coexistence) under various intrinsic, environmental and experimental contexts. Results Mutualists led to stronger positive individual and pairwise PSFs across various intrinsic and external contexts. However, PSFs became more negative when whole biota was present, with stronger negative effects on native species compared to exotic species and the most negative effects on plants experiencing interspecific competition. Manipulations of pathogens, nutrient availability and secondary chemicals had overall minimal influence on both types of PSFs, but the effect of nutrient availability on pairwise PSFs increased with increasing phylogenetic distance between species. Conclusion Our study suggests that soil biota is an important driver of PSFs and that plant origin and competitive context should be considered when predicting the role of soil biota in driving PSFs. Finally, we propose several directions for the next generation of PSF experiments towards a better understanding of the relative importance and interactions of different PSF drivers.

In European forests, most tree species form symbioses with ectomycorrhizal (EM) and arbuscular mycorrhizal (AM) fungi. The EM fungi are classified into different morphological types based on the development and structure of their extraradical mycelium. These structures could be root extensions that help trees to acquire nutrients. However, the relationship between these morphological traits and functions involved in soil nutrient foraging is still under debate. We described the composition of mycorrhizal fungal communities under 23 tree species in a wide range of climates and humus forms in Europe and investigated the exploratory types of EM fungi. We assessed the response of this tree extended phenotype to humus forms, as an indicator of the functioning and quality of forest soils. We found a significant relationship between the relative proportion of the two broad categories of EM exploration types (short- or long-distance) and the humus form, showing a greater proportion of long-distance types in the least dynamic soils. As past land-use and host tree species are significant factors structuring fungal communities, we showed this relationship was modulated by host trait (gymnosperms versus angiosperms), soil depth and past land use (farmland or forest). We propose that this potential functional trait of EM fungi be used in future studies to improve predictive models of forest soil functioning and tree adaptation to environmental nutrient conditions.

It is often speculated that non-native invasive species undergo rapid changes in their phenotypic properties (i.e., traits) that provide adaptive advantage in their new environment. However, few studies have directly compared traits of invasive non-native species with their native counterparts to reveal whether such phenotypic changes occur, and which stages of initial introduction and subsequent invasion contribute to these shifts. We studied trait variation of an invasive tree, Pinus contorta, which is native to northwestern North America and invasive in the Patagonia region of South America (i.e., Argentina and Chile). Commercial plantations of P. contorta were introduced extensively in Patagonia from the 1970s onward, from an unknown seed origin within the Pacific Northwest, USA, where three sub-species are found, including subsp. contorta, latifolia, and murrayana. We employed a home-versus-away study approach, where we compared mean growth, defense, and reproduction trait values, and mean within-stand trait variation (Coefficient of Variation, CV) of Patagonia plantations, with the three native sub-species. We further compared mean traits, and trait CVs between invasive P. contorta and the Patagonia plantations from which they escaped. Patagonia plantations shared the most similar mean trait values with subsp. latifolia and murrayana, suggesting possible source populations. However, both mean trait values and trait CVs of Patagonia plantations differed from all three native sub-species, indicating potential founder effects, population bottlenecks, and/or plastic responses to their new environment that occurred during or after introduction. We also found evidence for selective change during invasion; however, these differences did not suggest growth traits were prioritized over defense traits, which was inconsistent with hypotheses that invaders exhibit an evolutionary trade-off between defense traits and growth traits. Our study highlights that processes occurring both at first introduction and establishment, as well as the subsequent invasion phase can influence the phenotype of successful invaders.