Looking to the past to understand the future: linking evolutionary modes of response with functional and life history traits in variable environments

Interactive effects of nitrogen deposition and climate change on a globally rare forest geophyte

Nitrogen (N) deposition and climate change are both known to threaten global biodiversity. However, we still have a limited understanding of how interactions between these global change drivers affect individuals and populations of specialist species, such as geophytes, within their natural habitat. We explored possible interactive effects of N, drought, and warming on population vitality (mean leaf length, leaf density, flowering probability) and morpho-physiological traits (e.g., leaf and bulb size, N allocation to leaves and bulbs) of the globally rare forest geophyte Gagea spathacea (Liliaceae) in deciduous forests of northern Germany by applying experimental N addition across a climate gradient over a 5-year period. Mean leaf growth and leaf density were not affected by N addition but were enhanced by warmer and drier conditions in the months before leaf emergence. N addition increased N allocation of individual plants towards their subterranean bulbs. Importantly, effects of N addition on morpho-physiological traits depended on warming and drought, with N-fertilized plants showing increased leaf length and decreased specific leaf and bulb N concentration after drier autumns and warmer winters. This indicates that N deposition may partially compensate for increased N demands during warming-induced growth, although this growth-promoting interaction effect is not (yet) reflected in population vitality. Our results highlight the importance of considering multiple global environmental change drivers and a whole plant perspective (above- and belowground traits) to predict long-term growth responses of (endangered) forest spring geophytes and to develop adapted long-term protection strategies.

Shifts in native tree species distributions in Europe under climate change

Key European tree species are expected to contract their ranges under changing climate, thus there is a need to assess range shifts for other native tree species that could fill their forest niche. Recent studies have focused on economically important species, revealing a wide range of shifts in their distribution worldwide and highlighting several pathways for potential future changes. We aimed to quantify changes in projected ranges and threat levels by the years 2041-60 and 2061-80, for 20 European temperate forest tree species under four climate change scenarios. We compared ten standard stock tree species with ten alternative stock species, that are less frequent and less preferred by managers. We combined distribution data from several sources for each tree species and developed species distribution models using MaxEnt and seven bioclimatic variables. We applied these models to projections of future climate from four global circulation models, under four Shared Socioeconomic Pathways and for near and middle terms: 2041-60 and 2061-80. We also assessed the relationships between predicted range contraction and their functional traits. Analysis of MaxEnt models divided the studied tree species into three groups: non-threatened (Sorbus torminalis, Ulmus minor, Tilia platyphyllos, Acer pseudoplatanus, Prunus avium, and Carpinus betulus), partially threatened (U. laevis, Betula pendula, Quercus robur, Q. petraea, A. platanoides, Fagus sylvatica, Fraxinus excelsior, T. cordata, Alnus glutinosa, and U. glabra), and the most threatened (Abies alba, Larix decidua, Picea abies, and Pinus sylvestris). For the last group, almost half of the range contraction will occur earlier (2041-2060) compared to our previous predictions (2061-2080). The proportion of range contraction decreased with increasing specific leaf area, leaf area, leaf nitrogen content, seed mass, and specific stem density while it increased with increasing height. Our study provides novel predictions of shifts in climatic optima under the most recent climate change scenarios, which would be useful for evidence-based conservation and management of European forests. The near-term predicted threats to the main standard stock tree species call for intensified preparation for incoming changes. We recommend splitting the silvicultural risks over a wider range of tree species, also including alternative stock species.

Temporal variability and predictability predict alpine plant community composition and distribution patterns

One of the most reliable features of natural systems is that they change through time. Theory predicts that temporally fluctuating conditions shape community composition, species distribution patterns, and life history variation, yet features of temporal variability are rarely incorporated into studies of species-environment associations. In this study, we evaluated how two components of temporal environmental variation-variability and predictability-impact plant community composition and species distribution patterns in the alpine tundra of the Southern Rocky Mountains in Colorado (USA). Using the Sensor Network Array at the Niwot Ridge Long-Term Ecological Research site, we used in situ, high-resolution temporal measurements of soil moisture and temperature from 13 locations ("nodes") distributed throughout an alpine catchment to characterize the annual mean, variability, and predictability in these variables in each of four consecutive years. We combined these data with annual vegetation surveys at each node to evaluate whether variability over short (within-day) and seasonal (2- to 4-month) timescales could predict patterns in plant community composition, species distributions, and species abundances better than models that considered average annual conditions alone. We found that metrics for variability and predictability in soil moisture and soil temperature, at both daily and seasonal timescales, improved our ability to explain spatial variation in alpine plant community composition. Daily variability in soil moisture and temperature, along with seasonal predictability in soil moisture, was particularly important in predicting community composition and species occurrences. These results indicate that the magnitude and patterns of fluctuations in soil moisture and temperature are important predictors of community composition and plant distribution patterns in alpine plant communities. More broadly, these results highlight that components of temporal change provide important niche axes that can partition species with different growth and life history strategies along environmental gradients in heterogeneous landscapes.

Spatiotemporal variation in ecophysiological traits align with high resolution niche modelling in the short-range banded ironstone endemic Aluta quadrata

Defining plant ecophysiological responses across natural distributions enables a greater understanding of the niche that plants occupy. Much of the foundational knowledge of species' ecology and responses to environmental change across their distribution is often lacking, particularly for rare and threatened species, exacerbating management and conservation challenges. Combining high-resolution species distribution models (SDMs) with ecophysiological monitoring characterized the spatiotemporal variation in both plant traits and their interactions with their surrounding environment for the range-restricted Aluta quadrata Rye & Trudgen, and a common, co-occurring generalist, Eremophila latrobei subsp. glabra (L.S.Sm.) Chinnock., from the semi-arid Pilbara and Gascoyne region in northwest Western Australia. The plants reflected differences in gas exchange, plant health and plant water relations at sites with contrasting suitability from the SDM, with higher performance measured in the SDM-predicted high-suitability site. Seasonal differences demonstrated the highest variation across ecophysiological traits in both species, with higher performance in the austral wet season across all levels of habitat suitability. The results of this study allow us to effectively describe how plant performance in A. quadrata is distributed across the landscape in contrast to a common, widespread co-occurring species and demonstrate a level of confidence in the habitat suitability modelling derived from the SDM in predicting plant function determined through intensive ecophysiology monitoring programmes. In addition, the findings also provide a baseline approach for future conservation actions, as well as to explore the mechanisms underpinning the short-range endemism arid zone systems.

A novel type of neighbour perception elicits reproductive plasticity in an annual plant with a mixed mating system

Plants display various forms of phenotypic plasticity in anticipation of changing conditions, many of which are influenced by information obtained from neighbouring plants. Here, we tested the hypothesis that cleistogamic Lamium amplexicaule plants can adaptively modify production of chasmogamous (CH) and cleistogamous (CL) flowers based on the perception of conspecific neighbours. The production and proportion of CH and CL flowers was examined in individual L. amplexicaule grown at varying densities or treated with root leachates from plants grown at different densities. When growing at high density or treated with root leachates from high-density pots, L. amplexicaule increased production of more expensive, potentially outcrossing CH flowers. In contrast, single plants or plants treated with root leachates from empty pots or single-source plants predominantly developed cheaper, self-pollinated CL flowers. The results demonstrate a novel root-based neighbour-perception modality that enables plants to adaptively adjust production of CH and CL flowers in response to the presence of potential reproductive partners. Further research is needed to explore the broader ecological implications of this novel interplant cueing on reproductive bet-hedging and plasticity in natural settings, as well as to identify the involved cues and their mode of operation.

Same, same, but different: dissimilarities in the hydrothermal germination performance of range-restricted endemics emerge despite microclimatic similarities

Seed germination responses for most narrow-range endemic species are poorly understood, imperilling their conservation management in the face of warming and drying terrestrial ecosystems. We quantified the realized microclimatic niches and the hydrothermal germination thresholds in four threatened taxa (Tetratheca erubescens, Tetratheca harperi, Tetratheca paynterae subsp. paynterae and Tetratheca aphylla subsp. aphylla) that are restricted to individual Banded Ironstone Formations in Western Australia. While T. aphylla subsp. aphylla largely failed to germinate in our trials, all other species demonstrated extended hydrothermal time accumulation (186-500°C MPa days), cool minimum temperatures (7.8-8.5°C), but broad base water potential thresholds (-2.46 to -5.41 MPa) under which germination occurred. These slow germination dynamics are suggestive of cool and wet winter months, where soil moisture is retained to a greater capacity in local microsites where these species occur, rather than the warmer and drier conditions in the surrounding arid environment. Hydrothermal time-to-event modelling showed that each species occupied unique hydrothermal germination niches, which correspond with the microclimatic differences the species are exposed to. Our results provide a baseline understanding for environmental and germination thresholds that govern the recruitment, and ultimately the population structure and persistence, of these short-range endemic plants. In addition, our results can aid future conservation, as well as restoration actions such as translocation to bolster population numbers and to mitigate against losses due to anthropogenic disturbance and global environmental change.