Wenbo Luo

Invasive plant species present a growing ecological and economic challenge, and often adapt rapidly to their novel environments through complex demographic and evolutionary processes. Invasion genomics offers powerful tools to disentangle these processes, but most studies rely on geographically narrow sampling across native and non‐native ranges. Erigeron canadensis is a cosmopolitan weed native to North America that has successfully invaded diverse climates worldwide. We used double‐digest restriction site‐associated DNA sequencing (ddRADseq) to investigate the genetic diversity and structure of 280 E. canadensis populations across the Northern Hemisphere. We found that native and non‐native populations maintained comparable genetic diversity. Population structure analyses revealed four genetic clusters that were mainly differentiated along latitudinal and aridity gradients. However, one cluster was strongly overrepresented in the non‐native compared to the native range. In the native range, genetic differentiation was shaped by spatial and environmental gradients, while in non‐native regions human‐mediated dispersal and repeated introductions disrupted environmentally driven genetic structure. Migration network analyses revealed limited intercontinental connectivity and a possible role of long‐distance dispersal in within‐range expansions. Genomic offset analyses showed that genotype‐environment mismatches in non‐native populations associated with reduced growth and reproduction. Together, our results indicate that the invasion dynamics of E. canadensis were driven by multiple introductions, population admixture, and lineage sorting, while some genotypes contributed disproportionately to the spread of this invader. The presence of apparent maladaptation suggests that even long‐established invaders may still be evolving in response to their novel environment, raising concerns about potential future expansions.

Exotic invasions by a single plant species have been well researched, but multi-species invasions are also common and are studied much less. In a greenhouse experiment, we studied co-invasions with two native species and three invasive species which co-occur in grasslands in the northern Rocky Mountains in a greenhouse experiment. Without competition from native neighbors and for all species combined, the biomass of two-invader mixtures was greater than the monoculture means when different species pairs were combined, generating a synergistic non-additive positive effect of co-invasions on total biomass. However, this increase in biomass with co-invasion did not correspond with a greater cumulative competitive effect, across all species combined, on native species or a cumulative competitive response to native species. However, when explored as separate species combinations, two pairs of the invasive species increased their competitive effects relative to their monocultures and one pair increased biomass and also increased their competitive response, or tolerance, to natives. Different combinations of co-invading species had strikingly different effects. Potentilla recta facilitated the growth of both of the other invasive species it was paired with, whereas Centaurea stoebe suppressed the growth of both species it was paired with. Our results suggest that even weak invaders might amplify synergistic effects when paired with stronger invasive species. This indicates that early management of emerging invaders prior to intense co-invasion scenarios may be important.

Plant–soil feedbacks (PSFs) have strong effects on plant community diversity and composition, but we know less about how the abiotic environment alters PSFs. In the context of the stress‐gradient hypothesis (SGH), we predicted less negative PSFs in alpine versus prairie systems and tested this with three alpine and four prairie species and soil from three elevational gradients in western Montana, USA. All species were smaller when grown in prairie soil than in alpine soil, and sterilization of soil increased the growth only of alpine species in prairie soil. Training prairie soil with conspecifics decreased the biomass of both alpine and prairie species, but training alpine soil had no effect. PSFs were three times more negative when plants were grown in low‐elevation prairie soils than in alpine soils. Consistent with the original ideas for the SGH, the frequency of positive PSFs was higher in alpine soil than in prairie soil, and the frequency of negative PSFs was higher in prairie soil than in alpine soil. Our results suggest that alpine species may escape more intense negative PSFs at lower elevations and that PSFs will not limit the upward movement of plant species as temperatures warm.

Soil microbial carbon use efficiency (CUE) is the ratio of carbon allocated to microbial growth to that taken up by microorganisms. Soil microbial CUE affects terrestrial ecosystem processes such as greenhouse gas emissions, carbon turnover, and sequestration, which is an important indicator of changes in the terrestrial carbon cycle. Firstly, we summarized the three methods of soil microbial CUE, stoichiometric modeling, ¹³C glucose tracing, and ¹⁸O water tracing, and compared the advantages and limitations of the three methods. Then, we analyzed the single or combined effects of different environmental factors on soil microbial CUE in grassland ecosystems, forest ecosystems, and wetland ecosystems. Finally, we suggested that future research should focus on the following aspects: the influence of management patterns on CUE (such as grazing and the prohibition of grazing in grassland ecosystems, forest gap, and thinning in forest ecosystems); effects of the strategies of microorganisms for adapting to environmental changes on CUE; effects of anaerobic metabolic pathways, especially in wetland ecosystems; and effects of microbial taxonomic level. This study contributes to the investigation of the microbial mechanisms of carbon cycling in terrestrial ecosystems to mitigate the impacts of climate change.

Exotic invasive plant species commonly outcompete native species. However, a great deal of the evidence for this comes from experiments conducted on an uneven playing field—in substrates containing soil biota from the non-native ranges of the exotics, which should give them a competitive advantage. In competition experiments with nine pairs of non-native invasive versus native species in neutral substrates composed of sterilized soil, we found that the competitive effect of invasive species on natives was approximately five times greater than the reverse, and gram-per-gram competitive effects of invasives on natives were almost two times that of the natives on invasives. The effect of plant size on competitive outcomes was complex. The size of invasive species correlated with their effects on natives but not with their tolerance to competition from natives. The size of natives was not correlated with either aspect of competitive ability. This is important since the tolerance of invaders to competition from natives is thought to be essential for successful invasion. Our results also suggest that assumptions about size-based evidence for the evolution of competitive ability in non-native ranges is reasonable, and that even without the advantage gained from escaping soil biota, invaders still win.

Soil microbial carbon use efficiency (CUE) refers to the efficiency of microorganisms in converting absorbed carbon into their own biomass carbon. Soil microbial CUE is a key parameter to understanding the soil carbon cycle. Biotic and abiotic factors are widely considered to be important factors influencing CUE. However, the related underlying mechanisms remain unclear. This review elaborates on the concept of soil microbial CUE and the various approaches used for its measurement. We reviewed the effects of various abiotic factors, such as temperature, soil moisture, pH, nutrient addition, and substrate type, and biotic factors, such as microbial community structure and diversity, on CUE. Finally, we discussed the focus areas that future studies need to further explore. We hope this review can provide a comprehensive understanding of the factors impacting soil microbial CUE, which is a fundamental step to improving soil carbon storage capacity.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Snow depth may have a complex influence on carbon cycling in winter. Here we set up a field experiment to investigate how different snow depths (0 cm, 60 cm, 90 cm) influenced carbon dioxide (CO₂) in a wetland. The mean ± standard error of CO₂ emissions under snow addition treatments (60 cm and 90 cm snow depths) were 0.92 ± 0.16 g·cm⁻²·s⁻¹ and 0.53 ± 0.16 g·cm⁻²·s⁻¹, respectively, compared with snow removal treatment (0 cm snow depth), 0.11 ± 0.05 g·cm⁻²·s⁻¹. In general, snow addition increased CO₂ fluxes significantly. As snow depths increased, microbial biomass carbon (MBC) and bacterial diversities increased drastically. More important, the community of bacteria differed under different treatments. Firmicutes, which can resist dehydration and extremely low temperatures, was widely distributed in the snow removal treatment, where it sustained soil biochemical processes. Overall, our study indicates that snow cover counteracts the negative effects on soil microbial activities caused by low temperatures and could play a critical role in winter carbon cycling in wetlands.