Changes in ecological stoichiometry and nutrient resorption in Castanopsis hystrix plantations along an urbanization gradient in the lower subtropics

The stoichiometry of carbon,nitrogen and phosphorous in plants can reflect the interactions between plants and their environment.The interplay between plant nutrients,climatic factors,and soil properties and the underlying regulatory mechanisms are pillars of ecology but remain underexplored.In this study of plant C-N-P stoichiometry and nutrient resorption in Castanopsis hystrix groves in three cities(Guangzhou,Zhongshan,and Lechang)that represent an urban-rural gradient in Guangdong Province,South China,we explored potential relationships among NO_(2) concentrations,diameter at breast height(DBH),and resident human population.Mean annual temperature,mean annual precipitation,insolation duration per year,and the human resident population differed significantly among the three cities.Soil C-N-P was always highest in suburban Lechang,and the concentration of NO_(2) was highest in urban Guanghzou(55.33±0.67μg m^(-3))and positively correlated with the resident population and leaf N:P.Our findings suggest that C-N-P stoichiometry of C.hystrix was better explained by NO_(2)than by soil C-N-P stoichiometry and that nutrient resorption was better explained by leaf nutrients and DBH than by NO_(2) and soil stoichiometry.Our study supports the hypothesis that rapid urbanization influences NO_(2) concentrations and microclimate,which may jointly change the stoichiometry of plant nutrients in the forest ecosystems.

Impacts on Bats by a Supertyphoon vs.Ordinary Typhoons along a Habitat Urbanization Gradient

Two major human-caused threats to ecosystems are habitat modification and the increasing frequency and intensity of extreme weather events.To study the combined effect of these threats,the authors used acoustic monitoring of bats along a habitat modification gradient on the island of Okinawa,Japan.During the observation period,the island experienced numerous typhoons and one supertyphoon.Native bat species remained active even at high wind speeds(up to 30 m/s in some cases).Milder typhoons had no observable effect on bat populations,with activity levels fully recovering within a few hours or days.The super typhoon also did not seem to affect bats in fully or partially forested habitats but caused their local disappearance at the urban site,which they have not re-colonized three years after the event.Notably,bats that disappeared at the urban site were species roosting in well-protected places such as caves and concrete structures.In all cases,the biomass of small flying insects and the acoustic activity of insects recovered within days after extreme weather events.Thus,the striking difference between habitats in supertyphoon effects on bats cannot be explained by the super typhoon directly killing bats,destroying their roosting sites,or decreasing the abundance of their prey.The results underscore the importance of preserving natural habitats in areas particularly affected by changing climate and show that the survival of species and ecosystems during the numerous episodes of climate change in the Earth’s history does not necessarily mean their ability to survive the accelerating climate change of our time.

Effects of Urbanization,Soil Property and Vegetation Configuration on Soil Infiltration of Urban Forest in Changchun,Northeast China

Urban forest soil infiltration, affected by various factors, is closely related with surface runoff. This paper studied the effect of urban forest types, vegetation configuration and soil properties on soil infiltration. In our study, 191 typical plots were sampled in Changchun City, China to investigate the soil infiltration characteristics of urban forest and its influencing factors. Our results showed that the steady infiltration rates of urban forest soil were highly variable. High variations in the final infiltration rates were observed for different vegetation patterns and compaction degrees. Trees with shrubs and grasses had the highest infiltration rate and trees with bare land had the lowest infiltration rate. In addition, our results showed that the soil infiltration rate decreased with an increase in the bulk density and with a reduction in the soil organic matter content and non-capillary porosity. The soil infiltration rate also had significantly positive relationships with the total porosity and saturated soil water content. Urban soil compaction contributed to low soil infiltration rates. To increase the infiltration rate and water storage volume of urban forest soil, proper techniques to minimize and mitigate soil compaction should be used. These findings can provide useful information for urban planners about how to maximize the water volume of urban forest soil and decrease urban instantaneous flooding.

Effects of Forest Type and Urbanization on Carbon Storage of Urban Forests in Changchun, Northeast China

Rapid urbanization has led to dramatic changes in urban forest structures and functions, and consequently affects carbon(C) storage in cities. In this study, field surveys were combined with high resolution images to investigate the variability of C storage of urban forests in Changchun, Northeast China. The main objectives of this study were to quantify the C storage of urban forests in Changchun City, Northeast China and understand the effects of forest type and urbanization on C storage of urban forests. The results showed that the mean C density and the total C storage of urban forests in Changchun were 4.41 kg/m2 and 4.74 × 108 kg, respectively. There were significant differences in C density among urban forest types. Landscape and relaxation forest(LF) had the highest C density with 5.41 kg/m2, while production and management forest(PF) had the lowest C density with 1.46 kg/m2. These differences demonstrate that urban forest type is an important factor needed to be considered when the C storage is accurately estimated. Further findings revealed significant differences in different gradients of urbanization, and the mean C density decreased from the first ring(6.99 kg/m2) to the fourth ring(2.87 kg/m2). The total C storage increased from the first ring to the third ring. These results indicate that C storage by urban forests will be significantly changed during the process of urbanization. The results can provide insights for decision-makers and urban planners to better understand the effects of forest type and urbanization on C storage of urban forests in Changchun, and make better management plans for urban forests.

Urban avifauna distribution explained by road noise in an Eastern European city

In Eastern Europe,efforts are being made for road infrastructure development,as this area has not yet reached the level of that in the West.Road noise negatively affects birds,especially in urban habitats.Therefore,seven green spaces from an Eastern European city were monitored,which were selected according to the urbanization gradient and the hydrographic peculiarities of the area.The correlation between species richness and human population density,urban mobility,or road noise was verified.These three factors together explained over 99%of species richness distribution in habitats and during study periods.Road noise was the strongest predictor and the most negative influencer of bird species.These correlations were higher when we also considered the variability of species in habitats over time,instead of the total species richness of a habitat,as it expresses more accurately the impact of noise on the presence of species.The presence of species has decreased from one habitat to another along the urbanization gradient,from the edge of the city to the center,both in the case of terrestrial and aquatic green spaces.The most central park differed significantly from the other terrestrial green spaces in the city.At the same time,no significant differences were registered between the aquatic habitats or the rest of the terrestrial habitats.The ideal mitigation measure in this case would be that there are no roads in the immediate vicinity of green spaces.Still,if this is not possible(as in the case of all the existing green spaces in a city),we discuss/recommend placing noise barriers at the edge of green spaces or high-speed roads.

Urbanization reduces resource use efficiency of phytoplankton community by altering the environment and decreasing biodiversity

Urbanization often exerts multiple effects on aquatic and terrestrial organisms,including changes in biodiversity,species composition and ecosystem functions.However,the impacts of urbanization on river phytoplankton in subtropical urbanizing watersheds remain largely unknown.Here,we explored the effects of urbanization on phytoplankton community structure(i.e.,biomass,community composition and diversity)and function(i.e.,resource use efficiency)in a subtropical river at watershed scale in southeast China over 6 years.A total of 318 phytoplankton species belonging into 120 genera and 7 phyla were identified from 108 samples.Bacillariophyta biomass showed an increasing trend with increasing urbanization level.The phytoplankton community shifted from Chlorophyta dominance in rural upstream waters to Bacillariophyta dominance in urbanized downstream waters.Furthermore,phytoplankton diversity and resource use efficiency(RUE=phytoplankton biomass/total phosphorus)were significantly decreased with increasing urbanization level from upstream to downstream.Phytoplankton RUE exhibited a significant positive correlation with species richness,but a negative correlation with phytoplankton evenness.The variation in environmental factors(turbidity,total nitrogen,NH_(4)^(+)-N,total phosphorus,PO_(4)^(3-)-P and percentage urbanized area)was significantly correlated with phytoplankton diversity and RUE.Overall,our results revealed the influence of urbanization on phytoplankton community structure and ecosystem function was due to its altering the environmental conditions.Therefore,human-driven urbanization may play crucial roles in shaping the structure and function of phytoplankton communities in subtropical rivers,and the mechanism of this process can provide important information for freshwater sustainable uses,watershed management and conservation.

Heavy metal gradients from rural to urban lakes in central China

Background:Limited information is available on heavy metal patterns in lakes under rapid watershed urbanization,especially considering a large spatial gradient with a long linear distance and great variations in topographic relief.To fill this gap,we studied concentrations of a series of heavy metals in both water and sediments from 20 lakes along a rural to urban gradient in central China,and we aimed to understand the effects of urban processes on heavy metal dynamics in lake ecosystems.Studied lakes were divided into five groups:A(rural reservoir group),B(rural commercial fishing group),C(urban park group),D(urban recreational fishing group),and E(urban commercial fishing group).An inductively coupled plasma optical emission spectrometer(ICP-OES)and an inductively coupled plasma-mass spectrometer(ICP-MS)were used to analyze the heavy metals in water and sediments.Results:An increasing trend of most heavy metals in water from rural to urban lakes was observed.Concentrations of cadmium(Cd),cobalt(Co),lead(Pb),chromium(Cr),arsenic(As),nickel(Ni),magnesium(Mn),iron(Fe),and aluminum(Al)in water were significantly lower in rural group A than those in other groups.Arsenic in sediments of rural group A was lower than those in other groups.No other heavy metal element in sediments was significantly different among groups.The enrichment factor analysis of selected heavy metals showed there were different degrees of enrichments of heavy metals in sediments.The potential ecological risk index showed a low level for heavy metals in sediments of all studied lakes.Conclusions:Results indicated that urban processes could have an impact on heavy metals in lake water.The sources of heavy metals in sediments were more likely from anthropogenic activities.These results could enhance our understanding of metal dynamics in lake ecosystems under urbanization and could help prevent heavy metal pollutions and promote sustainable management of urban ecosystems.

Urban-induced changes in tree leaf litter accelerate decomposition

Introduction:The role of urban areas in the global carbon cycle has so far not been studied conclusively.Locally,urbanization might affect decomposition within urban boundaries.So far,only few studies have examined the effects of the level of urbanization on decomposition.This study addresses the influence of the level of urbanization on decomposition processes.It explores whether potential influences are exerted through leaf litter quality alterations or through direct effects of decomposition site’s level of urbanization.Leaf litter of five different tree species was sampled at urban and periurban sites.Decomposition of this litter was analyzed in three different experiments:a climate chamber incubation,a reciprocal litterbag transplant at urban and periurban sites,and a common garden litterbag transplant.Results:Decomposition site’s level of urbanization did not show a significant effect.However,in all species,when significant differences were observed,leaf litter of urban origin decomposed significantly faster than leaf litter of periurban origin.This effect was observed in all three experiments.In the reciprocal litter transplant experiment,62%±3%mass loss in litter of urban origin compared to 53%±3%in litter of periurban origin was observed.The difference was not as pronounced in the other two experiments,with 94%±1%mass loss of litter originating in urban habitats compared to 92%±1%mass loss of litter originating in periurban habitats in the common garden experiment and 225±13 mg CO2 released from litter originating in urban habitats compared to 200±13 mg CO2 released from litter originating in periurban habitats in the climate chamber incubation.Conclusions:We conclude that the level of urbanization affects decomposition indirectly through alterations in leaf litter quality even over short urban to periurban distances.