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Anthropogenic activities are increasing nutrient inputs to ecosystems worldwide, with consequences for global carbon and nutrient cycles. Recent meta-analyses show that aboveground primary production is often co-limited by multiple nutrients; however, little is known about how root production responds to changes in nutrient availability. At twenty-nine grassland sites on four continents, we quantified shallow root biomass responses to nitrogen (N), phosphorus (P) and potassium plus micronutrient enrichment and compared below- and aboveground responses. We hypothesized that optimal allocation theory would predict context dependence in root biomass responses to nutrient enrichment, given variation among sites in the resources limiting to plant growth (specifically light versus nutrients). Consistent with the predictions of optimal allocation theory, the proportion of total biomass belowground declined with N or P addition, due to increased biomass aboveground (for N and P) and decreased biomass belowground (N, particularly in sites with low canopy light penetration). Absolute root biomass increased with N addition where light was abundant at the soil surface, but declined in sites where the grassland canopy intercepted a large proportion of incoming light. These results demonstrate that belowground responses to changes in resource supply can differ strongly from aboveground responses, which could significantly modify predictions of future rates of nutrient cycling and carbon sequestration. Our results also highlight how optimal allocation theory developed for individual plants may help predict belowground biomass responses to nutrient enrichment at the ecosystem scale across wide climatic and environmental gradients.

Shifts in plant species phenology (the timing of life-history events such as flowering) have been observed worldwide in concert with rising global temperatures. While most species display earlier phenology with warming, there is large variation among, and even within, species in phenological sensitivity to rising temperatures. Other indirect effects of climate change, such as shifting species composition and altered species interactions, may also be contributing to shifting plant phenology. Here, we describe how experimental warming and the presence of a range-expanding species, sagebrush (Artemisia rothrockii), interact to influence the flowering phenology (day of first and peak flowering) and production (number of flowers) of an alpine cushion plant, Trifolium andersonii, in California's White Mountains. Both first flowering and peak flowering were strongly accelerated by warming, but not when sagebrush was present. Warming significantly increased flower production of T. andersonii, but less so in the presence of sagebrush. A shading treatment delayed phenology and lowered flower production, suggesting that shading may be the mechanism by which sagebrush presence delayed flowering of the understory species. This study demonstrates that species interactions can modify phenological responses to climate change, and suggests that indirect effects of rising temperatures arising from shifting species ranges and altered species interactions may even exceed the direct effects of rising temperatures on phenology.

Summary Analogous to the spread of non‐native species, shifts in native species’ ranges resulting from climate and land use change are also creating new combinations of species in many ecosystems. These native range shifts may be facilitated by similar mechanisms that provide advantages for non‐native species and may also have comparable impacts on the ecosystems they invade. Soil biota, in particular bacteria and fungi, are important regulators of plant community composition and below‐ground ecosystem function. Compared to non‐native plant invasions, there have been relatively few studies examining how soil biota influence – or are influenced by – native species range shifts. Here, we examined how a native range‐expanding sagebrush species (Artemisia rothrockii) affects below‐ground abiotic conditions and microbial community structure and function using next‐generation sequencing coupled with other biotic and abiotic soil analyses. We utilized a range‐expansion gradient, together with a shrub removal experiment and structural equation models, to determine the direct and indirect drivers of these interconnected processes. Sagebrush colonization increased bacterial and archaeal richness and diversity and altered community composition across the expansion gradient. Soil organic C and N and soil moisture increased with sagebrush presence; however, results varied across the expansion gradient. We found no relationship between sagebrush and soil pH; however, pH strongly influenced microbial richness and diversity. Microbial (substrate‐induced) respiration was influenced by soil organic N, as well as microbial diversity and functional group relative abundances, highlighting direct and indirect effects of sagebrush on microbial community structure and function. Microbial community composition of soils after 4 years of sagebrush removal was more similar to communities in shrub interspaces than underneath shrubs, suggesting microbial community resilience. Synthesis. Our results suggest that native range expansions can have important impacts on soil biological communities, soil chemistry and hydrology which can further impact below‐ground ecosystem processes such as nutrient cycling and litter decomposition. The combination of high‐throughput sequencing and structural equation modelling used here offers an exciting yet underutilized approach to understanding how both native and non‐native species’ range expansions may affect the structure and function of soil ecosystems. Our results suggest that native range expansions can have important impacts on soil biological communities, soil chemistry and hydrology which can further impact below‐ground ecosystem processes such as nutrient cycling and litter decomposition. The combination of high‐throughput sequencing and structural equation modelling used here offers an exciting yet underutilized approach to understanding how both native and non‐native species’ range expansions may affect the structure and function of soil ecosystems.

Question: Have there been shifts in abundance and distribution of alpine and sub-alpine plant species along an elevational gradient in an arid North American mountain range during the last half-century? Location: Elevational gradient in the White Mountains, California, USA (37°30′ N, 118°10′ W). Methods: We conducted a 49-yr re-survey of plant species distribution and abundance in areas originally surveyed in 1961. Species abundance data were collected along line transects between elevations of 2900 and 4000 m. We evaluated the degree of plant community shift over time across elevations; specifically, we expected species ranges to shift upward such that species peak abundances would be observed higher in elevation in 2010 than in 1961. To address this expectation we conducted a permutational multivariate linear model analysis with elevation, soil type and year as factors. We further performed single-species analyses to evaluate how focal species contributed to the multivariate community-level shifts between 2010 and 1961, and how these varied across elevations and soil types. Growing season climate data (June 1 through October 31) collected between 1961 and 2010 were analysed to quantify the change in annual mean temperature and precipitation at this site. Results: We found that Artemisia rothrockii increased in abundance at the upper reaches of its distribution between the 2010 and 1961 surveys. Additionally, we recorded significant declines in abundances in the lower elevation ranges of three alpine cushion plants: Trifolium andersonii, Phlox condensata and Eriogonum ovalifolium. These shifts coincided with a 0.98 °C increase in mean growing season temperatures and a 53 mm decrease in mean annual precipitation between 1961 and 2010. Conclusions: These results suggest that rising temperatures and decreasing precipitation are negatively impacting alpine plant species while promoting expansion of sub-alpine species, possibly signalling the transition of this alpine plant community to sagebrush steppe.

Anthropogenic warming’s effects on phenology across environmental and temporal gradients are well recognized. Long-term phenological monitoring data are often limited in duration and geographic scope, but recent efforts to digitize herbaria collections make it possible to reliably reconstruct historic flowering phenology across broad geographic scales and multiple species, lending to an increased understanding of community response to climate change. In this study, we examined collection dates (1901 to 2015) of 8540 flowering specimens from 39 native species in the Pacific Northwest (PNW) region of North America. We hypothesized that flowering phenology would be sensitive to temperature but that sensitivity would vary depending on blooming season and geographic range position. As expected, we found that early-season bloomers are more sensitive to temperature than later-season bloomers. Sensitivity to temperature was significantly greater at low elevations and in the maritime (western) portion of the PNW than at higher elevations and in the eastern interior, respectively. The elevational and longitudinal effects on flowering sensitivity reflect spring “arriving” earlier at low elevations and in the maritime portion of the PNW. These results demonstrate that phenological responses to warming vary substantially across climatically diverse regions, warranting careful and nuanced consideration of climate warming’s effects on plant phenology.

1. Predicting species responses to climate change involves understanding both the direct effects of environmental change, as well as indirect effects mediated by altered interspecific interactions. Indirect effects may be particularly important for understanding native species responses in systems invaded by highly competitive exotic species. For instance, Mediterranean climate regions are predicted to experience more frequent drought, and are increasingly invaded by exotic annual plants. For native shrubs in these regions, seedling establishment is episodic, and associated with high rainfall years. However, exotic annual plants also often increase in abundance with high rainfall, suggesting competition from exotic annual species could alter the relationship between rainfall and shrub seedling establishment. Theories such as the stress gradient hypothesis predict competition intensity should increase with resource supply, but there have been few evaluations of competitive interactions across experimental gradients of soil moisture availability. 2. Here we examined how competition from an exotic annual influenced native shrub establishment, across an experimental soil moisture gradient. Seedlings of two native shrub species (Encelia californica and Eriogonum fasciculatum) were grown with and without an exotic grass competitor (Avena fatua) across eight water availability levels, and monitored for growth and survival. These species are common and abundant in the Mediterranean climate region of coastal Southern California, where climate change projections include long-term drought for the coming decades. 3. Without competition, shrub seedlings achieved higher growth and survival at high water availability levels. However, when grown in competition with the exotic grass, shrub seedlings had higher growth and/or survival under relatively dry conditions, suggesting competition can modify and even reverse species responses to changing rainfall patterns, compared to predictions made in the absence of competitors. The exotic grass strongly reduced soil nitrate and water availability when it was planted with the native shrub seedlings, and the exotic grass responded with positive but saturating growth with increasing levels of water addition. 4. Synthesis. This experiment demonstrates that competition from invasive species can alter native species responses to climate change; consistent with ecological theories predicting a positive association between the supply of limiting resources and the intensity of competition.

Rapid climate warming is altering Arctic and alpine tundra ecosystem structure and function, including shifts in plant phenology. While the advancement of green up and flowering are well-documented, it remains unclear whether all phenophases, particularly those later in the season, will shift in unison or respond divergently to warming. Here, we present the largest synthesis to our knowledge of experimental warming effects on tundra plant phenology from the International Tundra Experiment. We examine the effect of warming on a suite of season-wide plant phenophases. Results challenge the expectation that all phenophases will advance in unison to warming. Instead, we find that experimental warming caused: (1) larger phenological shifts in reproductive versus vegetative phenophases and (2) advanced reproductive phenophases and green up but delayed leaf senescence which translated to a lengthening of the growing season by approximately 3%. Patterns were consistent across sites, plant species and over time. The advancement of reproductive seasons and lengthening of growing seasons may have significant consequences for trophic interactions and ecosystem function across the tundra.

Background Oropharyngeal squamous cell carcinoma (OPSCC) is the only subgroup of head neck cancer that presents with an increased incidence. Gender-specific studies in other cancer entities have revealed differences in treatment response and prognosis. However, only limited data in OPSCC according to gender and human papillomavirus (HPV) status exist. Therefore, we aimed to investigate sex-specific differences in OPSCC and how these may be distributed in relation to HPV and other risk factors. Methods This retrospective, bicentric study included 1629 patients with OPSCC diagnosed between 1992 and 2020. We formed subgroups based on TNM status, American Joint Cancer Committee 8 th edition (AJCC8), HPV status, treatment modality (surgery (± radio(chemo)therapy (RCT) vs. definitive RCT) and patient-related risk factors and investigated gender differences and their impact on patients survival via descriptive-,uni- and multivariate analysis. Results With the exception of alcohol abuse, no significant differences were found in risk factors between men and women. Females presented with better OS than males in the subgroup T1-2, N + , independent of risk factors ( p  = 0.008). Males demonstrated significant stratification through all AJCC8 stages (all p  < 0.050). In contrast, women were lacking significance between stage II and III ( p  = 0.992). With regard to therapy (surgery (± R(C)T) – vs. definitive RCT) women treated with surgery had better OS than men in the whole cohort ( p  = 0.008). Similar results were detected in the HPV-negative OPSCC sub-cohort ( p  = 0.042) and in high-risk groups (AJCC8 stage III and IV with M0, p  = 0.003). Conclusion Sex-specific differences in OPSCC represent a health disparity, particularly according to staging and treatment, which need to be addressed in future studies.

Questions: Shrub expansion into alpine ecosystems worldwide raises important questions regarding the influence of shrub encroachment on alpine species diversity. The stress gradient hypothesis (SGH) predicts interactions will be competitive when resources are plentiful and the environment is benign, but that facilitative interactions will dominate when conditions are stressful. We asked how Artemisia rothrockii (sagebrush) encroachment in an arid mountain range is affecting alpine plant species there and how the plant community responds to the experimental removal of sagebrush at three sites along an elevational gradient. Location: The White Mountains, California, USA (37°30′N, 118°10′W). Methods: A shrub removal experiment was established at three elevations (2,900, 3,100 and 3,750 m) to evaluate how sagebrush interacts with alpine and sub-alpine plant communities. Results: The study sites experienced a strong drought over the 4 yrs of the experiment and plant cover declined overall. However, in the sagebrush removal treatment, cover of co-occurring species increased at both the high-elevation and low-elevation sites, with no differences observed at the mid-elevation site. Conclusions: We observed the greatest inhibitory effects of sagebrush at high and low elevations, where plants experience the largest temperature and moisture stress, respectively, and no evidence of facilitation anywhere along the elevational gradient. These results demonstrate that while sagebrush has important influences on herbaceous species composition in the White Mountains, they are inconsistent with the classic predictions of the SGH.