Plant lifespan has important evolutionary, physiological, and ecological implications related to population persistence, community stability, and resilience to ongoing environmental change impacts. Although biologists have long puzzled over the extraordinary variation in plant lifespan and its causes, our understanding of interspecific variability in plant lifespan and the key internal and external factors influencing longevity remains limited. Here, we demonstrate the concurrent impacts of environmental, morphological, physiological, and anatomical constraints on interspecific variation in longevity among >300 vascular dicot plant species naturally occurring at an elevation gradient (2800-6150 m) in the western Himalayas. First, we show that plant longevity is largely related to species’ habitat preferences. Ecologically stressful habitats such as alpine and subnival host long-lived species, while productive ruderal and wetland habitats contain a higher proportion of short-lived species. Second, longevity is influenced by growth form. Small-statured cushion plants with compact canopies and deep roots, most found on cold and infertile alpine and subnival soils, had a higher chance of achieving longevity. Third, plant traits reflecting plant adaptations to stress and disturbance modulate interspecific differences in plant longevity. Importantly, we show that longevity and growth are negatively correlated. Slow-growing plants are those that have a higher chance of reaching a maximum age. Finally, changes in plant carbon, nitrogen, and phosphorus content in root and leaf tissue were significantly associated with variations in longevity. We discuss the link between the longevity and productivity and stability of studied Himalayan ecosystems and the intrinsic growth dynamics and physiological constraints under increasing environmental pressure.

Like many top consumers, parasites can regulate feeding of their prey via trait-mediated means. If parasites modify the feeding behavior of ecologically important grazers, they may have cascading effects on the structure and functioning of whole plant communities. The extent to which parasites can influence plant communities in this way is largely dependent on the strength of their behavioral alteration, their prevalence in host grazers, and the density of those hosts. Recent experiments and comparative surveys in southeastern USA salt marshes revealed that common larval trematode parasites suppress the per capita grazing impacts of the marsh periwinkle (Littoraria irrorata), generating a trophic cascade that protects foundational marsh plants from drought-associated overgrazing. Here, we conducted a field manipulation wherein we modified grazer host density while holding infection prevalence constant at an ecologically relevant level (20%) to determine whether the indirect, facilitative effects of parasites on marsh plants varied with the density of grazers. We found that parasites had significant positive impacts on marsh net primary productivity at moderate densities of snails (≥50 snails/ 0.5 m2), but that the positive effects of parasites were negligible at lower densities. Our results confirm the findings of previous studies that parasites can protect marsh plants from overgrazing at sufficiently high prevalence, but show that their ability to do so depends on host density.

Snowpack dynamics have a major influence on wildlife movement ecology and predator-prey interactions. Specific snow properties such as density, hardness, and depth determine how much an animal sinks into the snowpack, which in turn drives both the energetic cost of locomotion and predation risk. Here, we quantified the relationships between 15 field-measured snow variables and snow track sink depths for widely distributed predators (bobcats [Lynx rufus], coyotes [Canis latrans], wolves [C. lupus]) and sympatric ungulate prey (caribou [Rangifer tarandus], white-tailed deer [Odocoileus virginianus], mule deer [O. hemionus], and moose [Alces alces]) in interior Alaska and northern Washington, USA. We first used generalized additive models to identify which snow metrics best predicted sink depths for each species and across all species. For species occurring in both sites, we then tested whether the snow metric-sink depth relationship differed across regions. Finally, we used breakpoint regression to identify thresholds for the best-performing predictor of sink depth for each species (i.e., values wherein tracks do not appreciably sink into the snow). Near-surface (0-10cm) snow density was the strongest predictor of sink depth across species. This relationship varied slightly by region for wolves and moose but did not differ for coyotes. Thresholds of support occurred at snow densities of 230 kg/m3 for coyotes, 280 kg/m3 for bobcats, 290 kg/m3 for wolves, 340 kg/m3 for deer, 440 kg/m3 for caribou, and 550 kg/m3 for moose. Together, these critical thresholds define the bounds of “danger zones,” the range of snow density in which carnivores have a comparative movement advantage over ungulates. These results can be used to link predator-prey relationships with spatially explicit snow modeling outputs and projected future changes in snow density. As climate change rapidly reshapes snowpack dynamics, these danger zones provide a useful framework to anticipate likely winners and losers of future winter conditions.

Root traits and functioning: from individual plants to ecosystemsFine roots, the most distal portions of the root system, are responsible for the uptake of water and nutrients by plants, represent the main type of plant tissue contributing to soil organic matter accrual, and are key drivers of mineral weathering and soil microbial dynamics (Bardgett et al. 2014). Despite the overwhelming importance of fine root traits for plant and plant community functioning and biogeochemical cycles, basic information about their ecology is lacking, particularly compared to the wealth of information developed for leaves and stems. Testing hypotheses on how root traits underlie these ecosystem processes has been particularly hampered due to (1) a paucity of systematically collected data and (2) the complexity of the relationships between root traits and root, plant and ecosystem functioning. Nonetheless, the development of the field of root ecology in the last two decades has been outstanding, in particular in the compilation of belowground trait datasets (Iversen et al. 2017), methodological root ecological handbooks (Freschet et al. 2021b), novel conceptual frameworks to describe root trait diversity (Bergmann et al. 2020), its connection with belowground plant and community function (Bardgett et al. 2014, Freschet et al. 2021a), species’ distributions (Laughlin et al. 2021), and scaling up traits from the individual root to the ecosystem level (McCormack et al. 2017). The papers that feature in this Special Issue on Root traits and functioning: from individual plants to ecosystems cover different climate regions, taxonomic and spatial scales, and a diversity of traits (Table 1) and form perfect examples of this upward moment of the belowground component in plant ecology.