Nitrogen addition affects floral and vegetative traits, reproduction, and pollinator performance in Capsicum annuum L.

BACKGROUND AND AIMS: It has been demonstrated that nitrogen (N) addition alters flower morphology, floral rewards and pollinator performance. However, little is known about the effects of N addition on plant reproduction, including fruit set and seed set during selfing and outcrossing, floral and vegetative traits, and pollinator performance. We hypothesized that N addition would influence fruit set, seed set in selfed and outcrossed flowers, the relationship between vegetative and flower traits, and pollinator performance. METHODS: A 2-year pot experiment was conducted in which Capsicum annuum was exposed to three levels of relatively short-term N supply, i.e. 0 g m-2 (no N addition, as a control), 4 g m-2 (4N) and 16 g m-2 (16N), which are equivalent to about 0-, 1- and 4-fold of the peak local N deposition. We measured flower rewards, flower morphology, flowering phenology, as well as pollinator visitation rate, fruit set and seed set by self- and outcross-fertilization of C. annuum. RESULTS: The four levels of N addition increased plant biomass, biomass allocation to flowers, flower size, stigma-anther separation, nectar production and pollen production, resulting in an increase in pollinator visitation and fruit set. Nevertheless, the control and 16 levels of N addition reduced plant biomass, biomass allocation to flowers, flower size and stigma-anther separation, and nectar and pollen production, and consequently decreased pollinator visitation and fruit set. Exclusion of pollinators and hand-pollination experiments revealed that low levels of N addition were associated with high seed set in outcrossed flowers; however, this trend was reversed in flowers grown in the control and 16N treatments. CONCLUSION: Our results suggest that an optimal level of 4N can enhance the correlation between flower traits, pollinator performance and plant reproduction. Our findings cast new light on the underlying mechanisms of plant-pollinator interactions and plant adaptation to nitrogen deposition.

Environmental DNA metabarcoding reveals the impacts of anthropogenic pollution on multitrophic aquatic communities across an urban river of western China.

Anthropogenic activities are intensively affecting the structure and function of biological communities in river ecosystems. The effects of anthropogenic pollution on single-trophic community have been widely explored, but their effects on the structures and co-occurrence patterns of multitrophic communities remain largely unknown. In this study, we collected 13 water samples from the Neijiang River in Chengdu City of China, and identified totally 2352 bacterial, 207 algal, 204 macroinvertebrate, and 33 fish species based on the eDNA metabarcoding to systematically investigate the responses of multitrophic communities to environmental stressors. We observed significant variations in bacterial, algal, and macroinvertebrate community structures (except fish) with the pollution levels in the river. Network analyses indicated a more intensive interspecific co-occurrence pattern at high pollution level. Although taxonomic diversity of the multitrophic communities varied insignificantly, phylogenetic diversities of fish and algae showed significantly positive and negative associations with the pollution levels, respectively. We demonstrated the primary role of environmental filtering in driving the structures of bacteria, algae, and macroinvertebrates, while the fish was more controlled by dispersal limitation. Nitrogen was identified as the most important factor impacting the multitrophic community, where bacterial composition was mostly associated with NO3--N, algal spatial differentiation with TN, and macroinvertebrate and fish with NH4+-N. Further partial least-squares path model confirmed more important effect of environmental variables on the relative abundance of bacteria and algae, while macroinvertebrate and fish communities were directly driven by the algae-mediated pathway in the food web. Our study highlighted the necessity of integrated consideration of multitrophic biodiversity for riverine pollution management, and emphasized the importance of controlling nitrogen inputs targeting a healthy ecosystem.

Antibiotic profiles and their relationships with multitrophic aquatic communities in an urban river.

Antibiotics have garnered worldwide attention due to their omnipresence and detrimental effects on aquatic organisms, yet their potential relationships with multitrophic aquatic communities in natural rivers remain largely unknown. Here, we examined 107 antibiotics in water and sediment from an urban river in Chengdu, Sichuan province (China). The bacterial, algal, macroinvertebrates, and fish communities were synchronously measured based on the environmental DNA (eDNA) metabarcoding approach, and their relationships with antibiotics were further investigated. The results showed that the total antibiotic concentrations ranged from 1.12 to 377 ng/L and from 7.95 to 145 ng/g in water and sediment, respectively. Significant seasonal variations in the concentrations and compositions of antibiotics in water were observed. eDNA metabarcoding revealed great compositional variations of bacterial, algal, macroinvertebrates, and fish communities along the river, and antibiotics had significant negative relationships with the community diversities of aquatic organisms (p < 0.05) except for fish. Meanwhile, significant negative correlations were observed between antibiotic concentrations and the relative abundances of essential metabolism pathways of bacteria, e.g., energy metabolism (p < 0.05), carbohydrate metabolism (p < 0.05), and lipid metabolism (p < 0.01). Moreover, antibiotics demonstrated greater effects on the function of bacterial community compared with environmental variables. The findings highlight the significance of eDNA metabarcoding approach in revealing the relationships between aquatic communities and antibiotics, and call for further studies on the effects of antibiotics on multitrophic aquatic communities in natural waters.