Green infrastructure influences soil health: Biological divergence one year after installation

Unveiling the overlooked microbial niches thriving on building exteriors

Rapid urbanization in the Asia-Pacific region is expected to place two-thirds of its population in concrete-dominated urban landscapes by 2050. While diverse architectural facades define the unique appearance of these urban systems. There remains a significant gap in our understanding of the composition, assembly, and ecological potential of microbial communities on building exteriors. Here, we examined bacterial and protistan communities on building surfaces along an urbanization gradient (urban, suburban and rural regions), investigating their spatial patterns and the driving factors behind their presence. A total of 55 bacterial and protist phyla were identified. The bacterial community was predominantly composed of Proteobacteria (33.7% to 67.5%). The protistan community exhibited a prevalence of Opisthokonta and Archaeplastida (17.5% to 82.1% and 1.8% to 61.2%, respectively). The composition and functionality of bacterial communities exhibited spatial patterns correlated with urbanization. In urban buildings, factors such as facade type, light exposure, and building height had comparatively less impact on bacterial composition compared to suburban and rural areas. The highest bacterial diversity and lowest Weighted Average Community Identity (WACI) were observed on suburban buildings, followed by rural buildings. In contrast, protists did not show spatial distribution characteristics related to facade type, light exposure, building height and urbanization level. The distinct spatial patterns of protists were primarily shaped by community diffusion and the bottom-up regulation exerted by bacterial communities. Together, our findings suggest that building exteriors serve as attachment points for local microbial metacommunities, offering unique habitats where bacteria and protists exhibit independent adaptive strategies closely tied to the overall ecological potential of the community.

Characteristics of nitrogen distribution and its response to microecosystem changes in green infrastructure with different woody plants

With the acceleration of urbanization, N pollution in rainfall runoff has become the primary cause of eutrophication. In order to control N pollution in rainfall runoff, green infrastructure (GI) has been widely implemented. However, little is known about the process through which plants, especially woody plants, affect N distribution and the microecosystem in GI. Limited information suggests that woody plants mainly affect N distribution and alter the microecosystem through the influence of their roots. Therefore, laboratory tests were conducted to investigate the roles of the taproot plant Sophora japonica and the fibrous root plant Malus baccata and the resultant changes at the microecosystem level regarding N removal in a column-scale GI. After one year of growth, analysis of the morphological traits of the roots revealed that the average root length and diameter of S. japonica were approximately 2.3 and 1.8 times greater than those of M. baccata, respectively. An investigation of microbial diversity revealed that in comparison to the control GI system without plants, the GI systems with S. japonica and M. baccata hosted 45.68% and 59.88% more Actinobacteria, respectively. Further, the soil urease (S-UE) activities in the GI systems with S. japonica and M. baccata were 13.6% and 98.8% higher than that in the control, respectively, and the soil acid protease (S-ALPT) activities were 20.5% and 25.4% higher than that in the control, respectively. Compared to the control and the S. japonica GI system, the NH₃-N content in the soil of the M. baccata GI was 94.4% and 15.2% lower, respectively, and the NO₃-N content was 57.3% and 12.7% lower, respectively. The M. baccata GI system had the lowest NH₃-N and NO₃-N contents because it was most abundant in Actinobacteria and Arthrobacter and had the highest S-UE and S-ALPT activities. The results may be useful for improving N removal in GI containing different woody plants, and by extension for improving control of N pollution from rainfall runoff.

Towards circular economy: Sustainable soil additives from natural waste fibres to improve water retention and soil fertility

Human activity is accompanied by the introduction of excessive amounts of artificial materials, including geosynthetics, into the environment, causing global environmental pollution. Moreover, climate change continues to negatively affect global water resources. With the intensification of environmental problems, material reusability and water consumption limitations have been proposed. This study replaced synthetic soil additives with biodegradable materials and analysed the potential and sustainable processing of natural fibrous materials, which form problematic waste. Waste fibres are the basis of innovative soil water storage technologies in the form of biodegradable and water-absorbing geocomposites (BioWAG). We analysed the influence of BioWAGs on plant vegetation and the environment through a three-year field experiment. Furthermore, biomass increases, drought effect reductions, and biodegradation mechanisms were analysed. Natural waste fibres had a positive influence, as they released easily accessible nutrients into the soil during biodegradation. BioWAGs had a positive influence on the biometric parameters of grass, increasing biomass growth by 430 %. Our results indicated that this is an effective method of waste fibre management that offers the possibility to manufacture innovative, environmentally friendly materials in compliance with the objectives of circular economy and the expectations of users.

Greening the city: Thriving for biodiversity and sustainability

Urban population and urbanisation are increasing rapidly, mainly in developing countries, usually at the expense of green and blue areas. This trend will decrease the ecosystems' capacity to supply ecosystem services (ES) and threaten human wellbeing. Therefore, it is key to establish greening policies in urbanising areas, which are essential to improve the liveability of cities. Restoring and developing green and blue infrastructures using nature-based solutions is vital to improving urban biodiversity and urban ecosystems. Healthy urban ecosystems have a high capacity to supply regulating (e.g., air, noise, climate and water regulation), provisioning (e.g., food, medicinal plants, biomass) and cultural (e.g., recreation, landscape aesthetics, social cohesion) ES. This multifunctionality can provide diverse environmental, social and economic benefits to urban residents, hence contributing to the sustainability of urban areas. However, urban green and blue areas are also associated with ecosystem disservices (e.g., plant allergies or poisoning, emission of biogenic volatile organic compounds, unpleasant smells), tradeoffs (e.g., increased water consumption, wildfire risk, associated management costs) and implementation barriers (e.g., political motivation, lack of knowledge, time and workload). Overall, the SI published 8 articles from different parts of the world, such as China, the USA, Italy or Spain, focused on important aspects of greening the city (e.g., green roofs, green walls, green infrastructures, sustainable mobility).

Sensitivity of soil hydrogen uptake to natural and managed moisture dynamics in a semiarid urban ecosystem

The North American Monsoon season (June-September) in the Sonoran Desert brings thunderstorms and heavy rainfall. These rains bring cooler temperature and account for roughly half of the annual precipitation making them important for biogeochemical processes. The intensity of the monsoon rains also increase flooding in urban areas and rely on green infrastructure (GI) stormwater management techniques such as water harvesting and urban rain gardens to capture runoff. The combination of increased water availability during the monsoon and water management provide a broad moisture regime for testing responses in microbial metabolism to natural and managed soil moisture pulses in drylands. Soil microbes rely on atmospheric hydrogen (H₂) as an important energy source in arid and semiarid landscapes with low soil moisture and carbon availability. Unlike mesic ecosystems, transient water availability in arid and semiarid ecosystems has been identified as a key limiting driver of microbe-mediated H₂ uptake. We measured soil H₂ uptake in rain gardens exposed to three commonly used water harvesting practices during the monsoon season in Tucson AZ, USA. In situ static chamber measurements were used to calculate H₂ uptake in each of the three water harvesting treatments passive (stormwater runoff), active (stored rooftop runoff), and greywater (used laundry water) compared to an unaltered control treatment to assess the effects of water management practices on soil microbial activity. In addition, soils were collected from each treatment and brought to the lab for an incubation experiment manipulating the soil moisture to three levels capturing the range observed from field samples. H₂ fluxes from all treatments ranged between -0.72 nmol m^-2 s^-1 and -3.98 nmol m^-2 s^-1 over the monsoon season. Soil H₂ uptake in the greywater treatment was on average 53% greater than the other treatments during pre-monsoon, suggesting that the increased frequency and availability of water in the greywater treatment resulted in higher H₂ uptake during the dry season. H₂ uptake was significantly correlated with soil moisture (r = -0.393, p = 0.001, df = 62) and temperature (r = 0.345, p = 0.005, df = 62). Our findings suggest that GI managed residential soils can maintain low levels of H₂ uptake during dry periods, unlike unmanaged systems. The more continuous H₂ uptake associated with GI may help reduce the impacts of drought on H₂ cycling in semiarid urban ecosystems.