Invasion stage and competition intensity co-drive reproductive strategies of native and invasive saltmarsh plants: Evidence from field data.

Biological invasion poses a significant threat to biodiversity conservation and also results in substantial economic loss including the excessive cost of management to control it. Still, its impact on plant sexual reproduction strategies remains underexplored in natural settings. We conducted a field experiment on native Phragmites australis and invasive Spartina alterniflora in Bohai Bay and assessed plant size (aboveground biomass and height) and sexual reproduction (ear biomass, reproductive allocation, etc.) in conjunction with water and soil properties. The results showed that during the early stage of invasion, the two species declined in size and sexual reproduction, with S. alterniflora showing a lesser decline than P. australis. However, in the late stage of invasion, S. alterniflora maintained its plant size by reducing its investment in sexual reproduction. Moreover, significant reproductive allometries were demonstrated by S. alterniflora under different competition intensities. P. australis displayed heightened sensitivity to water properties and soil non-resource conditions, while S. alterniflora adapted its inherent traits and environmental tolerance. S. alterniflora allocated more resources to thriving as an individual, while P. australis prioritized reproduction by increasing seed production. Overall, this study revealed the reproductive strategies that invasive and native species employ in response to competition and environmental factors, thereby offering crucial insights for conservation and management efforts.

Nitrogen addition and drought affect nitrogen uptake patterns and biomass production of four urban greening tree species in North China.

Nitrogen (N) is an essential nutrient element limiting plant growth and production, and plant N uptake capacity varies with environmental change. Recently, global climate changes such as N deposition and drought have important impacts on the terrestrial ecosystems, especially for urban greening trees. However, it's still unclear how N deposition and drought affect plant N uptake and biomass production and the underlying relationship between them. Therefore, we conducted a 15N isotope labeling experiment on four common tree species of urban green spaces in North China, including Pinus tabulaeformnis, Fraxinus chinensis, Juniperus chinensis, and Rhus typhina in pots. Three N addition treatments (0, 3.5, and 10.5 gN m -2 year -1; "no", "low", and "high" N treatments, respectively) and two water addition treatments (300 and 600 mm year-1; "drought" and "normal water", respectively) were set up in a greenhouse. Our results showed that N and drought significantly affected tree biomass production and N uptake rates, and the relationship between them depended on the species specificity. Trees could transform their N uptake preference to adapt to the changing environment, from ammonium to nitrate or vice versa, which was also reflected in total biomass. Furthermore, the variation of N uptake patterns was also related to distinct functional traits, including aboveground (specific leaf area and leaf dry matter content) or belowground (specific root length, specific root area, and root tissue density) traits. There was a transformation of plant resource acquisitive strategy in a high N and drought environment. In general, there were tight connections among N uptake rates, functional traits, and biomass production of each target species. This finding comes up with a new strategy that tree species can modify their functional traits and plasticity of the N uptake forms for survival and growth in the context of high N deposition and drought.

Transformation of Plant to Resource Acquisition Under High Nitrogen Addition Will Reduce Green Roof Ecosystem Functioning.

Ecosystem engineering, such as green roof, provides numerous key ecosystem functions dependent on both plants and environmental changes. In the recent years, global nitrogen (N) deposition has become a hot topic with the intensification of anthropogenic disturbance. However, the response of green roof ecosystems to N deposition is still not clear. To explore the effects of N addition on plant ecological strategy and ecosystem functioning (biomass), we conducted a 3-month N addition simulation experiment using 12 common green roof species from different growth forms on an extensive green roof in Tianjin, China. The experiment included three different N addition treatments (0, 3.5, and 10.5 gN m-2 year-1). We found that plants with the resource-acquisitive strategy were more suitable to survive in a high N environment, since both aboveground and belowground traits exhibited synergistic effects. Moreover, N addition indirectly decreased plant biomass, indicating that ecosystem functioning was impaired. We highlight that there is a trade-off between the survival of green roof species and keeping the ecosystem functioning well in the future N deposition. Meanwhile, these findings also provide insights into how green roof species respond to global climate change and offer important information for better managing and protecting similar ecosystem engineering in the background of high N deposition.