Plant community diversity alters the response of ecosystem multifunctionality to multiple global change factors.

Biodiversity is considered important to the mitigation of global change impacts on ecosystem multifunctionality in terrestrial ecosystems. However, potential mechanisms through which biodiversity maintains ecosystem multifunctionality under global change remain unclear. We grew 132 plant communities with two levels of plant diversity, crossed with treatments based on 10 global change factors (nitrogen deposition, soil salinity, drought, plant invasion, simulated grazing, oil pollution, plastics pollution, antibiotics pollution, heavy metal pollution, and pesticide pollution). All global change factors negatively impacted ecosystem multifunctionality, but negative impacts were stronger in high compared with low diversity plant communities. We explored potential mechanisms for this unexpected result, finding that the inhibition of selection effects (i.e., selection for plant species associated with high ecosystem functioning) contributed to sensitivity of ecosystem multifunctionality to global change. Specifically, global change factors decreased the abundance of novel functional plants (i.e., legumes) in high but not low diversity plant communities. The negative impacts of global change on ecosystem multifunctionality were also mediated by increased relative abundance of fungal plant pathogens (identified from metabarcoding of soil samples) and their negative relationship with the abundance of novel functional plants. Taken together, our experiment highlights the importance of protecting high diversity plant communities and legumes, and managing fungal pathogens, to the maintenance of ecosystem multifunctionality in the face of complex global change.

Puke or poop? Comparison of regurgitate and faecal samples to infer alpine grasshopper (Paprides nitidus Hutton) diet in experimental plant communities.

Characterising plant-herbivore interactions is important to understanding the processes that influence community structure and ecosystem functioning. Traditional methods used to identify plant-herbivore interactions are being superseded by non-destructive molecular approaches that can infer interactions with greater resolution and accuracy from environmental DNA (e.g. faeces and regurgitate). However, few studies have compared the success of using different sample types and whether they provide similar or contrasting information about species' diet. Here we compared the success of DNA amplification and host plant species identification using restriction fragment length polymorphism (RFLP) applied to faecal and regurgitate samples collected from alpine grasshoppers Paprides nitidus Hutton during a grassland community mesocosm experiment. We found that DNA amplification success was 23% and 86% higher for faecal than regurgitate samples from female and male grasshoppers, respectively. In contrast, successful host plant identification using RFLP was 9% higher for regurgitate than faecal samples. The mean number of host plant species identified per sample (1.40) did not differ between sample types or grasshopper sexes. Of the 136 paired faecal-regurgitate samples, just 41% and 74% produced exactly or partially matching host plant identifications, respectively, indicating that different sample types provided complementary information about herbivore diet. Some plant species were more likely to be identified from faecal samples than expected by chance, and we found that this identification bias skewed towards plant species with higher investment in leaf tissue. We conclude that multiple sample types may be required to fully characterise an invertebrate herbivore species' diet.

A network perspective for sustainable agroecosystems.

Nature-based management aims to improve sustainable agroecosystem production, but its efficacy has been variable. We argue that nature-based agroecosystem management could be significantly improved by explicitly considering and manipulating the underlying networks of species interactions. A network perspective can link species interactions to ecosystem functioning and stability, identify influential species and interactions, and suggest optimal management approaches. Recent advances in predicting the network roles of species from their functional traits could allow direct manipulation of network architecture through additions or removals of species with targeted traits. Combined with improved understanding of the structure and dynamics of networks across spatial and temporal scales and interaction types, including social-ecological, applying these tools to nature-based management can contribute to sustainable agroecosystems.

Exotic plants accumulate and share herbivores yet dominate communities via rapid growth.

Herbivores may facilitate or impede exotic plant invasion, depending on their direct and indirect interactions with exotic plants relative to co-occurring natives. However, previous studies investigating direct effects have mostly used pairwise native-exotic comparisons with few enemies, reached conflicting conclusions, and largely overlooked indirect interactions such as apparent competition. Here, we ask whether native and exotic plants differ in their interactions with invertebrate herbivores. We manipulate and measure plant-herbivore and plant-soil biota interactions in 160 experimental mesocosm communities to test several invasion hypotheses. We find that compared with natives, exotic plants support higher herbivore diversity and biomass, and experience larger proportional biomass reductions from herbivory, regardless of whether specialist soil biota are present. Yet, exotics consistently dominate community biomass, likely due to their fast growth rates rather than strong potential to exert apparent competition on neighbors. We conclude that polyphagous invertebrate herbivores are unlikely to play significant direct or indirect roles in mediating plant invasions, especially for fast-growing exotic plants.

Soil sample pooling generates no consistent inference bias: a meta-analysis of 71 plant-soil feedback experiments.

There is current debate on how soil sample pooling affects the measurement of plant-soil feedbacks. Several studies have suggested that pooling soil samples among experimental units reduces variance and can bias estimates of plant-soil feedbacks. However, it is unclear whether pooling has resulted in systematic mismeasurement of plant-soil feedbacks in the literature. Using data from 71 experiments, we tested whether pairwise plant-soil feedback direction, magnitude and variance differed among soil pooling treatments. We also tested whether pooling has altered our understanding of abiotic and biotic drivers that influence pairwise plant-soil feedbacks. Pooling of soil samples among experimental units was used in 42% of examined experiments. Contrary to predictions, pooling did not affect mean pairwise plant-soil feedback effect size or within-experiment variance. Accounting for soil sample pooling also did not significantly alter our understanding of the drivers of pairwise plant-soil feedbacks. We conclude that there is no evidence that soil sample pooling systematically biases estimates of plant-soil feedback direction, magnitude, variance or drivers across many studies. Given the debate of whether to pool soil samples, researchers should be aware of potential criticisms and carefully consider how experimental design and soil pooling methods influence interpretation of experiments.

Using Network Theory to Understand and Predict Biological Invasions.

Understanding and predicting biological invasions is challenging because of the complexity of many interacting players. A holistic approach is needed with the potential to simultaneously consider all relevant effects and effectors. Using networks to describe the relevant anthropogenic and ecological factors, from community-level to global scales, promises advances in understanding aspects of invasion from propagule pressure, through establishment, spread, and ecological impact of invaders. These insights could lead to development of new tools for prevention and management of invasions that are based on species' network characteristics and use of networks to predict the ecological effects of invaders. Here, we review the findings from network ecology that show the most promise for invasion biology and identify pressing needs for future research.

Intraspecific variation in indirect plant-soil feedbacks influences a wetland plant invasion.

Plant-soil feedbacks (PSFs) influence plant competition via direct interactions with pathogens and mutualists or indirectly via apparent competition/mutualisms (i.e., spillover to co-occurring plants) and soil legacy effects. It is currently unknown how intraspecific variation in PSFs interacts with the environment (e.g., nutrient availability) to influence competition between native and invasive plants. We conducted a fully crossed multi-factor greenhouse experiment to determine the effects of Phragmites australis rhizosphere soil biota, interspecific competition, and nutrient availability on biomass of replicate populations from one native and two invasive lineages of common reed (P. australis) and a single lineage of native smooth cordgrass (Spartina alterniflora). Harmful soil biota consistently dominated PSFs involving all three P. australis lineages, reducing biomass by 10%. Indirect PSFs (i.e., soil biota spillover) from the two invasive P. australis lineages reduced S. alterniflora biomass by 7%, whereas PSFs from the native P. australis lineage increased S. alterniflora biomass by 6%. Interestingly, interspecific competition and PSFs interacted to weaken their respective impacts on S. alterniflora, whereas they exerted synergistic negative effects on P. australis. Phragmites australis soil biota decreased S. alterniflora biomass when grown alone (i.e., a soil legacy), but increased S. alterniflora biomass when grown with P. australis, suggesting that P. australis recruits harmful generalist soil biota or facilitates S. alterniflora via spillover (i.e., apparent mutualism). Soil biota also reduced interspecific competition impacts on S. alterniflora, although it remained competitively inferior to P. australis across all treatments. Competitive interactions and responses to nutrients did not differ among P. australis lineages, indicating that interspecific competition and nutrient deposition may not be key drivers of P. australis invasion in North America. Although soil biota, interspecific competition, and nutrient availability appear to have no direct impact on the success of invasive P. australis lineages in North America, intraspecific lineage variation in indirect spillover and soil legacies from P. australis occur and may have important implications for co-occurring native species and restoration of invaded habitats. Our study integrates multiple factors linked to plant invasions, highlighting that indirect interactions are likely commonplace in influencing plant community dynamics and invasion success and impacts.

Lineage overwhelms environmental conditions in determining rhizosphere bacterial community structure in a cosmopolitan invasive plant.

Plant-microbe interactions play crucial roles in species invasions but are rarely investigated at the intraspecific level. Here, we study these interactions in three lineages of a globally distributed plant, Phragmites australis. We use field surveys and a common garden experiment to analyze bacterial communities in the rhizosphere of P. australis stands from native, introduced, and Gulf lineages to determine lineage-specific controls on rhizosphere bacteria. We show that within-lineage bacterial communities are similar, but are distinct among lineages, which is consistent with our results in a complementary common garden experiment. Introduced P. australis rhizosphere bacterial communities have lower abundances of pathways involved in antimicrobial biosynthesis and degradation, suggesting a lower exposure to enemy attack than native and Gulf lineages. However, lineage and not rhizosphere bacterial communities dictate individual plant growth in the common garden experiment. We conclude that lineage is crucial for determination of both rhizosphere bacterial communities and plant fitness.Environmental factors often outweigh host heritable factors in structuring host-associated microbiomes. Here, Bowen et al. show that host lineage is crucial for determination of rhizosphere bacterial communities in Phragmites australis, a globally distributed invasive plant.

Biogeography of a plant invasion: plant-herbivore interactions.

Theory predicts that native plant species should exhibit latitudinal gradients in the strength of their interactions with herbivores. We hypothesize that if an invasive plant species exhibits a different latitudinal gradient in response to herbivores (e.g., a nonparallel gradient), it can create large-scale heterogeneities in community resistance/susceptibility to the invasive species. We conducted a study of latitudinal variation in the strength of herbivory and defenses of native genotypes of Phragmites australis in North America (NA) and Europe (EU) and European invasive genotypes in NA. Within NA, we tested whether (1) invasive genotypes are better defended and suffer less herbivory than co-occurring native genotypes, (2) herbivory and defenses of native P. australis decreases with increasing latitude; and (3) invasive genotypes exhibit either no latitudinal gradient, or a nonparallel latitudinal gradient in herbivory and defenses compared to native genotypes. For the European genotypes, we tested two additional hypotheses: (4) defenses, nutritional condition, and herbivory would differ between the native (EU) and invasive ranges (NA) and (5) latitudinal gradients in defenses and herbivory would be similar between ranges. Within NA, chewing damage, internal stem-feeding incidence, and aphid abundance were 650%, 300%, and 70% lower, respectively, on invasive than native P. australis genotypes. Genotypes in NA also differed in nutritional condition (percent N, C:N ratio), but there was little support for invasive genotypes being better defended than native genotypes. For the European genotypes, herbivory was significantly lower in the invaded than native range, supporting the enemy-release hypothesis. Defense levels (leaf toughness and total phenolics) and tissue percent C and percent N were higher in the invaded than native range for European genotypes. Overall, latitudinal gradients in P. australis nutritional condition, defenses, and herbivory were common. Interestingly, chewing damage and stem-feeder incidence decreased with latitude for native P. australis genotypes in NA and EU, but no latitudinal gradients in response to herbivores were evident for invasive genotypes in NA. Nonparallel latitudinal gradients in herbivory between invasive and native P. australis suggest that the community may be more susceptible to invasion at lower than at higher latitudes. Our study points to the need for invasion biology to include a biogeographic perspective.

Development of an efficient trapping system for New Zealand flower thrips, Thrips obscuratus.

BACKGROUND: New Zealand flower thrips (NZFT), Thrips obscuratus (Crawford), is an economic pest of various horticultural crops in New Zealand and is recognised as a quarantine pest globally. Two chemical attractants (ethyl nicotinate and 6-pentyl-2H-pyran-2-one), three dispensers, three trap designs and four trap heights were investigated to determine the most effective method for monitoring NZFT. Phenology of NZFT at two locations was compared. RESULTS: 6-Pentyl-2H-pyran-2-one in a polyethylene bag dispenser was the most attractive lure formulation and exhibited high stability in release rate trials. There was no difference in NZFT catch between vertical-panel and cross-panel traps, but both caught significantly more than delta traps. However, both types of panel trap had unacceptably high by-catch of native insects. Catch of thrips increased with height from 0 to 3 m. Phenology of NZFT showed similar population trends at both locations, but with a timing difference of around 50 days. CONCLUSIONS: Delta traps containing 6-pentyl-2H-pyran-2-one in a polyethylene bag at 2 m above the ground is the recommended method for monitoring NZFT, significantly improving the sensitivity, accuracy and labour input compared with prior methods. Long-term monitoring of NZFT could lead to more accurate economic damage thresholds and timing for when to apply insecticides. © 2014 Society of Chemical Industry.