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Since wetland construction projects are becoming more commonplace, meaningful follow-up studies are needed to evaluate how these systems change over time. To that end, the objective of our study was to examine the temporal changes in plant community composition and water chemistry in two constructed wetlands. We investigated two wetland sites that were constructed in 2003 in northern Otsego County, NY, a county that is largely dominated by agriculture. Site 1 was previously an active cow pasture and site 2 was previously a wet meadow surrounded by agricultural fields. No active plant introduction was made during the construction; however, both sites were located in areas with many remnant wetlands and were connected to through-flowing streams. In 2004 (Year 1) and 2010 (Year 7), the plant community composition and nitrogen retention were assessed. We found that both sites experienced site-wide declines in plant species richness, including the loss of upland and facultative upland species and the unanticipated loss of facultative wetland and some obligate species. We propose that high water levels, which, at their maximum depth were >1.5 m deeper than in Year 1, maintained by landowners in the years after the initial survey, may have been responsible for the unexpected loss of wetland species. We also found that site 1 exhibited considerable nitrogen retention in both Year 1 and Year 7; however, N concentrations were low at site 2 in both years.

Spatial variation in plant diversity has been attributed to heterogeneity in resource availability for many ecosystems. However, urbanization has resulted in entire landscapes that are now occupied by plant communities wholly created by humans, in which diversity may reflect social, economic, and cultural influences in addition to those recognized by traditional ecological theory. Here we use data from a probability-based survey to explore the variation in plant diversity across a large metropolitan area using spatial statistical analyses that incorporate biotic, abiotic, and human variables. Our prediction for the city was that land use, along with distance from urban center, would replace the dominantly geomorphic controls on spatial variation in plant diversity in the surrounding undeveloped Sonoran desert. However, in addition to elevation and current and former land use, family income and housing age best explained the observed variation in plant diversity across the city. We conclude that a functional relationship, which we term the "luxury effect," may link human resource abundance (wealth) and plant diversity in urban ecosystems. This connection may be influenced by education, institutional control, and culture, and merits further study.

The quantitative role of the canopy size of nurse shrubs on microenvironment and native tree establishment in degraded tropical lands has been seldom studied. In a 21-month field experiment, we aimed to test the effect of a native shrub with different canopy sizes on the early establishment of native trees as part of the effort of forest restoration in tropical China. We examined the microenvironment, and the seedling establishment and growth of two native trees: Castanopsis fissa and Syzygium hancei in both open space (OS) microsite and microsite under the canopy of the native pioneer shrub Rhodomyrtus tomentosa. Shrub microsite was further divided into large canopy (LC), and medium canopy (MC) microsite, based on the shrub leaf area indices. Results showed that relative to OS, LC had higher soil nutrient concentration and water content, and lower photosynthetic active radiation (PAR), while MC had lower PAR and higher soil exchangeable Mg, K, and Ca. Survival and growth were mostly enhanced, while water stress and photoinhibition reduced for C. fissa seedlings in MC and S. hancei seedlings in LC. It is found that the beneficial effects of the native shrub on seedling establishment and growth result mostly from the improvement in nutrient and water availabilities, the reduction in plant stress caused by harsh summer light, and the specific ecological requirements of different tree species. We suggest that different canopy sizes of native shrub R. tomentosa may be explored to target different native trees and hence promote forest restoration in degraded tropical ecosystems. [ABSTRACT FROM AUTHOR]

Background and aims: The impacts of atmospheric nitrogen (N) deposition on terrestrial ecosystem processes remain controversial, mostly because of the uncertainty regarding the fates of deposited N. We conducted a 16-week simulated deposition study to experimentally trace N in a greenhouse plant-soil system. Methods: Using a two-way factorial design, we added (NH)SO solution twice a week to pots containing different soil organic matter (SOM) content and with or without a live plant ( Salix dasyclados). The recoveries of N in soil, plant biomass, and leaching solution were quantified. Results: We found most N was retained in soil (18.0-59.2%), with significantly more N recovered from high-SOM soils than from low-SOM soils. Plant presence significantly increased N retention in soil. Plant biomass accounted for 10-20% of the N input, with proportionally more N assimilated when plants were grown in low-SOM soils. Leaching loss of N was relatively low (10-17%). Conclusion: Our study suggests that SOM content and plant presence significantly affect the fates of deposited N. Indeed, N would be preferentially retained in soils with high SOM content and live plant, while plants would assimilate more deposited N when grown in low SOM soils. Global biogeochemical models thus need to incorporate such soil-specific N retention and plant N assimilation. [ABSTRACT FROM AUTHOR]