Urban land cover type determines the sensitivity of carbon dioxide fluxes to precipitation in Phoenix, Arizona

Urban CO2 imprints on carbon isotope and growth of Chinese pine in the Beijing metropolitan region

Rapid urbanization has occurred globally and resulted in increasing CO₂ emissions from urban areas. Compared to natural forests, urban forests are subject to higher atmospheric CO₂ concentrations in view of strong urban-periurban-rural gradients of CO₂ emissions. However, relevant insights in the CO₂-associated urban imprints on the physiology and growth of regional forests remain lacking. By sampling foliage and tree rings of Chinese pine (Pinus tabuliformis) in the Beijing metropolitan region, China, we explored whether and how urban CO₂ emissions affect stable carbon isotope ratios (δ¹³C) and tree growth spatially and/or temporally. The results indicate a significant decrease in foliar δ¹³C values towards the urban center and this pattern was mainly explained by the urban-periurban-rural gradients of CO₂ emissions as surrogated by trunk road density. Tree-ring δ¹³C values showed a significant decrease over last four decades and this trend was mainly explained by rising levels of CO₂ and secondarily mediated by the variations of aridity index during growing season. Moreover, annual basal area increment of Chinese pine was significantly accelerated during last two decades, being mainly driven by increasing CO₂ emissions and secondarily mediated by climate variations. These findings reveal significant CO₂-associated imprints of urbanization on plant growth and provide empirical evidences of significant CO₂-induced alteration of carbon cycles in urban forests.

Monitoring of hourly carbon dioxide concentration under different land use types in arid ecosystem

Air pollution is a major factor affecting human life and living quality in arid and semiarid regions. This study was conducted in the Al-Ahsa district in the Eastern part of Saudi Arabia to measure carbon dioxide (CO₂) concentration over different land-use types. Initially, the study's land use/land cover (LULC) was classified using the spectral characteristics of Landsat-8 data. Then, sensors were placed in five sites of different LULC types to detect CO₂, air temperature, and relative humidity. The Friedman test was used to compare CO₂ concentration among the five sites. Five LULC types were identified over the study area: date palm, cropland, bare land, urban land, and water. The results indicated that CO₂ concentration showed a maximum mean value of 577 ppm recorded from a site dominated by urban lands. During the peak time of human transportation, a maximum value of 659 ppm was detected. The CO₂ concentration mean values detected for the other LULC types showed 535, 515, and 484 ppm for the bare land, cropland, and date palm, respectively. This study's sensors and procedures helped provide information over relatively small areas. However, modelling CO₂ fluctuations with time for LULC changes might improve management and sustainability.

Carbon Sequestration in Turfgrass–Soil Systems

Plants are key components of the terrestrial ecosystem carbon cycle. Atmospheric CO₂ is assimilated through photosynthesis and stored in plant biomass and in the soil. The use of turfgrass is expanding due to the increasing human population and urbanization. In this review, we summarize recent carbon sequestration research in turfgrass and compare turfgrass systems to other plant systems. The soil organic carbon (SOC) stored in turfgrass systems is comparable to that in other natural and agricultural systems. Turfgrass systems are generally carbon-neutral or carbon sinks, with the exception of intensively managed areas, such as golf course greens and athletic fields. Turfgrass used in other areas, such as golf course fairways and roughs, parks, and home lawns, has the potential to contribute to carbon sequestration if proper management practices are implemented. High management inputs can increase the biomass productivity of turfgrass but do not guarantee higher SOC compared to low management inputs. Additionally, choosing the appropriate turfgrass species that are well adapted to the local climate and tolerant to stresses can maximize CO₂ assimilation and biomass productivity, although other factors, such as soil respiration, can considerably affect SOC. Future research is needed to document the complete carbon footprint, as well as to identify best management practices and appropriate turfgrass species to enhance carbon sequestration in turfgrass systems.

Direct observations of CO2 emission reductions due to COVID-19 lockdown across European urban districts

The measures taken to contain the spread of COVID-19 in 2020 included restrictions of people's mobility and reductions in economic activities. These drastic changes in daily life, enforced through national lockdowns, led to abrupt reductions of anthropogenic CO₂ emissions in urbanized areas all over the world. To examine the effect of social restrictions on local emissions of CO₂, we analysed district level CO₂ fluxes measured by the eddy-covariance technique from 13 stations in 11 European cities. The data span several years before the pandemic until October 2020 (six months after the pandemic began in Europe). All sites showed a reduction in CO₂ emissions during the national lockdowns. The magnitude of these reductions varies in time and space, from city to city as well as between different areas of the same city. We found that, during the first lockdowns, urban CO₂ emissions were cut with respect to the same period in previous years by 5% to 87% across the analysed districts, mainly as a result of limitations on mobility. However, as the restrictions were lifted in the following months, emissions quickly rebounded to their pre-COVID levels in the majority of sites.