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Under unfavourable conditions, clonal plants benefit from physiological integration among ramets, sharing resources and information. Clonal integration can buffer against environmental changes and lets the plant clone work as a 'macro' organism. Molecular signals that regulate this phenomenon are completely unknown in marine plants.Here we present a first comprehensive study providing insights into the metabolic role of different types of ramets (i.e. apical vs. vertical) in the foundation species Posidonia oceanica. Plants were exposed to 80% diminishing irradiance level (LL) in a controlled mesocosm system. Subsequent multiscale variations in whole transcriptome expression, global DNA methylation level, photo‐physiology, morphology and fitness‐related traits, were explored at different exposure times. We tested the hypothesis that vertical shoots (the 'vassals') can provide vital resources to apical shoots (the 'kings') under energy shortage, thus safeguarding the whole clone survival.Whole transcriptome analysis of leaves and shoot‐apical meristems (SAMs) emphasized signatures of molecular integration among ramets, which strongly correlated with higher organization‐level responses. In both shoots types, the exposure to LL resulted in a growth slowdown throughout the experiment, which started from immediate signals in SAMs. In apical shoots, this was linked to an acclimative response, where they were suffering a mild stress condition, while in vertical ones it fell in a more severe stress response. Yet, they suffered from sugar starvation and showed a clear cellular stress response in terms of protein refolding and DNA repair mechanisms. Several epigenetic mechanisms modulated the observed gene‐expression patterns and the cross‐talk between DNA methylation and the cellular energetic status appeared to regulate shoot metabolism under LL.Synthesis. Our results demonstrate a high level of specialization of integrated ramets within seagrass clones and a 'division of labour' under adverse conditions. Vertical shoots appear to do 'most of the job' especially in terms of resource providing, whereas activated functions in apical shoots were restricted to few important processes, according to an 'energy‐saving' strategy. The response of vertical shoots could be seen as a 'sacrificing response' allowing the survival of 'the king' that is key for ensuring propagation and population maintenance, and for the colonization of new environments. [ABSTRACT FROM AUTHOR]

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For clonal plants, the role of sexual reproduction in the maintenance of populations can vary widely. Some species are dependent on repeated seedling recruitment. For other species, interactions between adults and seedlings within existing populations can affect seedling survival and limit sexual reproduction in existing populations. Genetic studies of seagrass populations increasingly suggest sexual reproduction is important for the resilience and stability of their populations, but as of yet little observational data support these findings. Because seagrass populations provide important ecosystem services and are threatened with increasing anthropogenic impacts, understanding their reliance on sexual reproduction is evolutionarily and ecologically important.The goals of this study were to determine (a) whether seedlings of a marine angiosperm, Zostera marina, establish and recruit within existing Z. marina meadows and (b) whether interactions between seedlings and surrounding adult shoots influence the survival of established seedlings. To meet these goals, surveys estimated seedling establishment and tracked seedling survival within multiple populations. Manipulative experiments then tested the impact of neighbouring adult shoots on seedling survival and the overall trajectory of experimental plots with and without sexual reproduction.A 3‐year survey identified established seedlings within Z. marina meadows each year. Additionally, concurrent seed addition experiments indicated seed supply could influence seedling establishment rates. A survey tracking the survival of tagged seedlings, as well as the height and density of surrounding adult shoots, showed adult shoots may negatively impact seedling survival. Experiments then demonstrated that seedlings without neighbouring shoots survived longer than those with neighbouring shoots. Lastly, two transplant garden experiments comparing the survival of plots with and without seeds highlighted that seedling recruitment is likely most important to maintain bottom cover where disturbances generate gaps in the adult population.Synthesis. This study demonstrates that seedlings do establish within existing seagrass meadows, and that some survive to recruit into the adult population. Competition with existing vegetation, however, can be a factor compromising seedling survival. Sexual reproduction may thus most likely occur in, and be most important for, clonal plant populations that experience seasonal disturbance. [ABSTRACT FROM AUTHOR]

Halophyte distributions on saltmarshes are strongly related to elevation in the tidal frame. However, collinearity between elevation, the consequent inundation regime, and sediment waterlogging/redox potential obscures the proximate causes of distribution patterns. We sought to distinguish the effects of elevation per se from those of waterlogging by manipulating microtopography.We experimentally manipulated elevation by ±15 cm at locations that spanned the elevation ranges of three saltmarshes recently reactivated by managed coastal realignment. Experimental plots were initially cleared of any vegetation. Elevation and sediment redox potential were determined for each plot. We planted five perennial species (Armeria maritima, Atriplex portulacoides, Limonium vulgare, Plantago maritima and Triglochin maritima) in half of the plots, recording survival over 4 years, and monitored natural colonization of the other plots.Overall, redox potential increased with elevation. Sediments were more oxidizing in raised plots and more reducing in lowered plots. Redox reductions in lowered plots were in line with those that would be predicted from the overall redox/elevation relationship, but increases in raised plots were greater than predicted from elevation alone.Plant colonization and survival was poorer in lowered plots and, for most species, improved in raised plots. This poorer colonization and survival can, in part, be attributed to the concomitant alterations in redox potential and elevation in the tidal frame, but microtopographic manipulation also had substantial independent effects on plant performance, including on the survival of all planted species and the colonization of Puccinellia maritima, Salicornia europaea agg. and Tripolium pannonicum.Synthesis. Microtopography can have effects on sediment chemistry and plant performance similar in magnitude to those of overall tidal elevation. Understanding how its effects modulate the relationship between tidal elevation, redox and other environmental conditions helps clarify the abiotic factors that fundamentally determine halophyte colonization and survival. These results support the use of topographic manipulation to enhance the diversity of created saltmarshes. [ABSTRACT FROM AUTHOR]

Coastal ecosystems provide critical storm and flood protection but are rapidly degrading worldwide, making their restoration urgent. We evaluated whether successional facilitation, where pioneers facilitate climax species, could be leveraged to accelerate coastal dune revegetation. A survey spanning 270 km of Southeast U.S. coastline revealed that Panicum amarum (bitter panicum) supported higher plant richness than Uniola paniculata (sea oats) and that sea oat cover was 230% greater on mature dunes than disturbed dunes, suggesting bitter panicum functions as a pioneer and sea oats as a climax species. A reciprocal transplant experiment confirmed this interpretation: bitter panicum stem production and height fell by 37% and >20 cm, respectively, when planted proximate to sea oats versus in isolation, whereas sea oats produced 38% more and >12 cm taller stems when planted proximate to bitter panicum versus in isolation. A second experiment evaluating the density‐dependence of this facilitative interaction revealed that sea oats transplanted into low densities of bitter panicum grew >15% taller than isolated and high‐density treatments. However, within 7 months, wave inundation eliminated over 60% of propagules in both experiments. To explore foredune inundation frequency and its implications for dune revegetation, we applied empirical wave runup models at 101 locations throughout Volusia County, Florida. While disturbance frequency varied seasonally and annually, sites with low dune crests and steep beach slopes experienced frequent inundation (>50 events/year). Given the interactions between geomorphology and vegetation success, we present a decision matrix to guide managers in determining optimal revegetation methods tailored to project goals and site conditions. [ABSTRACT FROM AUTHOR]

Transformers are widely used deep learning architectures. Existing transformers are mostly designed for sequences (texts or time series), images or videos, and graphs. This paper proposes a novel transformer model for massive (up to a million) point samples in continuous space. Such data are ubiquitous in environment sciences (e.g., sensor observations), numerical simulations (e.g., particle-laden flow, astrophysics), and location-based services (e.g., POIs and trajectories). However, designing a transformer for massive spatial points is non-trivial due to several challenges, including implicit long-range and multi-scale dependency on irregular points in continuous space, a non-uniform point distribution, the potential high computational costs of calculating all-pair attention across massive points, and the risks of over-confident predictions due to varying point density. To address these challenges, we propose a new hierarchical spatial transformer model, which includes multi-resolution representation learning within a quad-tree hierarchy and efficient spatial attention via coarse approximation. We also design an uncertainty quantification branch to estimate prediction confidence related to input feature noise and point sparsity. We provide a theoretical analysis of computational time complexity and memory costs. Extensive experiments on both real-world and synthetic datasets show that our method outperforms multiple baselines in prediction accuracy and our model can scale up to one million points on one NVIDIA A100 GPU. The code is available at https://github.com/spatialdatasciencegroup/HST.

Ecosystems worldwide depend on habitat-forming foundation species that often facilitate themselves with increasing density and patch size, while also engaging in facultative mutualisms. Anthropogenic global change (e.g., climate change, eutrophication, overharvest, land-use change), however, is causing rapid declines of foundation species-structured ecosystems, often typified by sudden collapse. Although disruption of obligate mutualisms involving foundation species is known to precipitate collapse (e.g., coral bleaching), how facultative mutualisms (i.e., context-dependent, nonbinding reciprocal interactions) affect ecosystem resilience is uncertain. Here, we synthesize recent advancements and combine these with model analyses supported by real-world examples, to propose that facultative mutualisms may pose a double-edged sword for foundation species. We suggest that by amplifying self-facilitative feedbacks by foundation species, facultative mutualisms can increase foundation species' resistance to stress from anthropogenic impact. Simultaneously, however, mutualism dependency can generate or exacerbate bistability, implying a potential for sudden collapse when the mutualism's buffering capacity is exceeded, while recovery requires conditions to improve beyond the initial collapse point (hysteresis). Thus, our work emphasizes the importance of acknowledging facultative mutualisms for conservation and restoration of foundation species-structured ecosystems, but highlights the potential risk of relying on mutualisms in the face of global change. We argue that significant caveats remain regarding the determination of these feedbacks, and suggest empirical manipulation across stress gradients as a way forward to identify related nonlinear responses., Competing Interests: The authors declare no conflict of interest., (© 2020 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)