Long-term nitrogen addition alters peatland plant community structure and nutrient resorption efficiency

As an elemental carbon (C) and nitrogen (N) pool in the world, peatlands are very sensitive to environmental changes. Under global warming, the increase in available N affects the dynamic changes of plant community structure and nutrients in a permafrost peatland. This study was based on a long-term in situ N addition experiment that had been conducted for 9 years. It utilized the peatland in the permafrost area of Great Hing'an Mountain as the research object to analyze the effects of N addition on the growth characteristics, community structure, and nutrient dynamics of peatland plants. The N inputs were N1: 6 g N m^-2·year^-1, N2: 12 g N m^-2·year^-1 and N3: 24 g N m^-2·year^-1, respectively. Our results showed that the adding N can affect the plant community structure of peatland by affecting the plant growth characteristics. The diversity and richness of plant species in the peatland decreased as the concentration of added N increased. The long-term N addition can reduce the N limitation of plants to some extent. Still, it could further aggravate their phosphorus (P) limitation, resulting in the joint limitation of N and P or the complete limitation by P. The N resorption efficiency decreased with the increase of N addition level. The P resorption efficiency of different plants had varied responses to the changes in the N nutrient environment. Our study clarified the impact of long-term N addition on the plant community structure and nutrient dynamics of peatland in a permafrost area and provided an important theoretical basis to accurately evaluate the carbon and nitrogen balance of peatland in a permafrost area owing to future climate change.

Impact of wastewater discharge on the plant diversity, community structure and heavy metal pollution of range plants in eastern Saudi Arabia

The main objectives of this study were to determine the floristic composition of the vegetation cover and to find the effects of wastewater pollution on the plant community structure in eastern Saudi Arabia. 28 stands which were distributed among polluted and unpolluted sites, were chosen for this study. A total of 42 plant species were recorded (14 in the polluted and 28 in the unpolluted sites). The recorded plants comprised of 13 perennial plant species and 29 annual plant species. Seven vegetation communities were determined using TWINSPAN and DCA classification and ordination techniques. Three in the polluted sites, two in the unpolluted sites and the remaining two were mixed communities. The (Sarcopoterium spinosum – Pistacia len‐tiscus) community in the polluted sites, had the highest values of soil moisture, salinity, sulphate, calcium and potassium. On the other hand, Juniperus phoenicea – Olea europaea community in the unpolluted site, had the lowest value of organic matter, salinity and magnesium. In respect of genetic diversity, the community of Foeniculum vulgare - Nicotiana glauca in the unpolluted site, was the most diverse, while Ricinus communis - Chrysanthemum coronarium in the polluted sites was the least one. Both soil and wastewater heavy metal analysis indicated that Pb, Cd, Cr, Cu and Ni concentrations in the polluted sites were significantly higher than those in the unpolluted ones. The impact of wastewater discharge led to the appearance of new invasive plant species that may significantly affect plant diversity and community structure in eastern Saudi Arabia. Finally wastewater discharge in open rangelands could adversely affect the growth of plant species in the rangelands and thus adversely affect plant community structure and diversity.

Tree species richness and diversity predicts the magnitude of urban heat island mitigation effects of greenspaces

The Urban Heat Island Effect (UHIE) is a widely recognised phenomenon that profoundly affects the quality of life for urban citizens. Urban greenspace can help mitigate the UHIE, but the characteristics that determine the extent to which any given greenspace can cool an urban area are not well understood. A key characteristic is likely to be the properties of trees that are found in a greenspace. Here, we explore the sensitivity of the strength of the cooling effect to tree community structure for greenspaces in Changzhou, China. Land surface temperatures were retrieved from Landsat 7 ETM+ and Landsat 8 TIRS and were used to evaluate the temperature drop amplitude (TDA) and cooling range (CR) of 15 greenspaces across each of the four seasons. Tree community structure of the greenspaces was investigated using 156 sample plots across the 15 greenspaces. We found that a number of plant community structure indicators of greenspaces have a significant impact on the strength of the cooling effect. The Shannon-Wiener diversity index, tree species richness and tree canopy coverage of greenspaces are all positively correlated with the magnitude of the temperature drop amplitude, with the strength of their influence varying seasonally. We also find that mean crown width is positively correlated with cooling range in summer and autumn, while greenspace tree density is negatively correlated with cooling range in winter. Our findings improve understanding of the relationship between plant community structure and the cooling effect of greenspaces. In particular, we highlight the important role that tree species diversity provides for mitigating the UHIE, and suggest that if planners wish to improve the role of urban greenspaces in cooling cities, they should include a higher diversity of trees species.

Phytoremediation ability of naturally growing plant species on the electroplating wastewater-contaminated site

The presence of heavy metal in soil and water resources has serious impact on human health. The study was designed to examine the phytoremediation ability of plant species that are growing naturally on the Zn-contaminated site. For the study, six plant species and their rhizospheric soil as well as non-rhizospheric soil samples were collected from different parts of the industrial sites for chemical and biological characterization. Visual observations and highest importance value index (IVI) through biodiversity study revealed potential plants as effective ecological tools for the restoration of the contaminated site. Among the plants, almost all were the most efficient in accumulating Fe, Mn, Cu and Zn in its shoots and roots, while Cynodon dactylon, Chloris virgata and Desmostachya bipinnata were found to be stabilizing Cr, Pb and Cd (bioconcentration factor in root = 7.95, 6.28 and 1.98 as well as translocation factor = 0.48, 0.46 and 0.78), respectively. Thus, the results of this study showed that the naturally growing plant species have phytoremediation potential to remediate the electroplating wastewater-contaminated site. These plant species are successful phytoremediators with their efficient metal stabilizing and well-evolved tolerance to heavy metal toxicity.