As aquatic-terrestrial ecotones, riparian zones are hotspots not only for denitrification but also for nitrous oxide (N2O) emission. Due to the potential role of nosZ II in N2O mitigation, emerging ...studies in terrestrial ecosystems have taken this newly reported N2O-reducer into account. However, our knowledge about the interactions between denitrification activities and both N2O-producers and reducers (especially for nosZ II) in aquatic ecosystems remains limited. In this study, we investigated spatiotemporal distributions of in situ N2O flux, potential N2O production rate, and potential denitrification rate, as well as of the related genes in a riparian zone of Baiyangdian Lake. Real-time quantitative PCR (qPCR) and high-throughput sequencing targeted functional genes were used to analyze the denitrifier communities. Results showed that great differences in microbial activities and abundances were observed between sites and seasons. Waterward sediments (constantly flooded area) had the lowest N2O production potential in both seasons. Not only the environmental factors (moisture content, NH4+ content and TOM) but also the community structure of N2O-producers and N2O-reducers (nirK/nirS and nosZ II/nosZ I ratios) could affect the potential N2O production rate. The abundance of the four functional genes in the winter was higher than in the summer, and the values all peaked at the occasionally flooded area in the winter. The dissimilarity in community composition was mainly driven by moisture content. Altogether, we propose that the N2O production potential was largely regulated by the community structure of N2O-producers and N2O-reducers in riparian zones. Increasing the constantly flooded area and reducing the occasionally flooded area of lake ecosystems may help reduce the level of denitrifier-produced N2O.
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•The constantly flooded area had lower N2O production potential than other areas.•Denitrifying community structure determined the N2O production potential.•Moisture content was the main driver for dissimilarity in community composition.•nosZ II had a higher diversity in the riparian zone than in other environments.
As aquatic-terrestrial ecotones, riparian zones are hotspots not only for denitrification but also for nitrous oxide (N
O) emission. Due to the potential role of nosZ II in N
O mitigation, emerging ...studies in terrestrial ecosystems have taken this newly reported N
O-reducer into account. However, our knowledge about the interactions between denitrification activities and both N
O-producers and reducers (especially for nosZ II) in aquatic ecosystems remains limited. In this study, we investigated spatiotemporal distributions of in situ N
O flux, potential N
O production rate, and potential denitrification rate, as well as of the related genes in a riparian zone of Baiyangdian Lake. Real-time quantitative PCR (qPCR) and high-throughput sequencing targeted functional genes were used to analyze the denitrifier communities. Results showed that great differences in microbial activities and abundances were observed between sites and seasons. Waterward sediments (constantly flooded area) had the lowest N
O production potential in both seasons. Not only the environmental factors (moisture content, NH
content and TOM) but also the community structure of N
O-producers and N
O-reducers (nirK/nirS and nosZ II/nosZ I ratios) could affect the potential N
O production rate. The abundance of the four functional genes in the winter was higher than in the summer, and the values all peaked at the occasionally flooded area in the winter. The dissimilarity in community composition was mainly driven by moisture content. Altogether, we propose that the N
O production potential was largely regulated by the community structure of N
O-producers and N
O-reducers in riparian zones. Increasing the constantly flooded area and reducing the occasionally flooded area of lake ecosystems may help reduce the level of denitrifier-produced N
O.
Tourism along river basins benefits both tourists and the economy, but its management necessitates trade-offs between nature-based recreation and ecological functioning. Despite ecosystem services ...being helpful in managing environmental challenges, there are limited data on the impact of tourism activities on ecosystem functioning across different river types globally. This study investigates how people's recreational activities and values affect ecosystem functioning in high-order rivers. The original field data were collected from 308 transects along the main river and tributaries of the Three Gorges Dam Reservoir in China during 2019. Kruskal-Wallis tests (p < 0.01) revealed that the ecosystem functioning indices were significantly higher than the recreational activity and value indices around the rivers and that ecosystem functioning was highest around tributaries. The critical variables of ecotourism activities and ecosystem functioning identified by principal component analysis accounted for 66.49% of the total variance. The Pearson correlation coefficient strengths among tourism and ecosystem functioning parameters were correlated mildly to moderately, but they exhibited positive and negative connections with a range of r = -0.27 to 0.37 (p < 0.05). Furthermore, the distribution patterns of these parameters that were determined by hierarchical cluster analysis were diverse for both the main river and its tributaries. The findings suggest that the development and enforcement of zoning may be necessary for the long-term use of natural resources by all sectors of society. Therefore, it is imperative to raise public awareness and urge governments to adopt more progressive ecotourism policies.
•Ecosystem functioning outscore riverside recreational activities.•Indicators of tourism activity have mild to moderate effects on ecological indicators.•Both the main river and its tributaries show varied tourism responses.•Stream tourism requires innovative management planning.
Hydrologic pulsing and revegetation strongly affect both denitrification rate and denitrifier communities in riparian zones, yet how they drive the shifts in the denitrifying bacterial community and ...consequently alter denitrification remains unclear. In this study, we investigated denitrification rate and denitrifier community structure and their abundance in different hydrological pulsing phases and vegetation types (tree, shrub, and herb) in the water-level-fluctuate-zone of the Three Gorges Reservoir, China. Results revealed that hydrologic pulsing greatly affected denitrification rate possibly by regulating the soil NO3−-N concentration, with higher denitrification rate in the reflooding phase in tree soils than that in the saturated and drying phases. Hydrologic pulsing also significantly regulated the abundance and structure of denitrifier communities in herb soils by altering soil temperature, moisture, and NH4+-N. As expected, vegetation types affected the denitrifier communities by altering soil texture, pH, temperature, moisture, soil organic C, and C:N ratio, with higher abundance of nirS genes and higher diversity of nirS and nirK genes in herb soils. However, there was no significant relationship between denitrification rate and denitrifier communities, indicating that hydrologic pulsing regulated denitrification rate primarily by changing soil environmental factors rather than community composition or abundance of denitrifiers. Our results suggest that tree and herb plantations would potentially improve water quality in the riparian zone and adjacent rivers by increasing denitrification rate and abundance of denitrifiers, respectively.
•Hydrologic pulsing impacted denitrification and denitrifying communities.•Herb increased abundance of nirS and diversities of nirS and nirK genes.•Soil pH, temperature, moisture, C and N significantly correlated to nirS and nirK.•Soil NO3−-N was possibly a better predictor of denitrification than nirK or nirS.
As a potent atmospheric greenhouse gas and a major source of ozone depletion, nitrous oxide (N2O) emission has been given increasing attention in aquatic systems, particularly at the ...aquatic-terrestrial interfaces, such as riparian zones. However, the microbial mechanisms regulating N2O emission in riparian zones remain unknown. Here, we measured the contributions of denitrification and ammonium oxidation to N2O emission along with the abundance and community structure of nirK-, nirS-, nosZ I- and nosZ II-harbouring bacteria in both surface sediments (0–10 cm) and overlying water along a lake riparian zone (including nearshore sites and offshore sites). Overall, the nearshore sites of the riparian zones emitted less N2O than the offshore sites. Nearshore N2O emission was dominated by denitrification with a high N2O reduction rate, whereas offshore N2O emission was driven by ammonium oxidation. Furthermore, N2O derived from ammonium oxidation was influenced by the NH4+-N content, and denitrification N2O was modulated by denitrifier communities. The N2O-producing community was dominated by nirS-harbouring bacteria, while the N2O-reducing community was dominated by nosZ I-harbouring bacteria. The relative abundance of Hydrogenophilales from nirS-denitrifiers and Chloroflexi unclassified from nosZ II-type communities influenced the N2O produced by denitrification, according to high-throughput sequencing analysis. Additionally, we also found lower levels of N2O production per unit volume in overlying water, which were 3–4 orders of magnitude less than in the surface sediment. Overall, we propose that using riparian zones can be an effective management tool for N2O mitigation by enhancing the N2O reduction process of denitrification and decreasing ammonium oxidation.
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•Riparian zones were not hotspots for N2O emission.•Denitrification and nitrification separately dominated N2O production at nearshore and offshore sites.•Nearshore sites had higher potential of N2O reduction by denitrification.•NH4+-N content was the key factor impacting ammonium oxidation and N2O emission.•Surface sediment rather than water column was the main contributor to N2O in riparian zone.
Dissimilatory nitrate reduction to ammonium (DNRA), an important intermediate process in the N-cycle, links N-compound oxidation and reduction processes. Hence, the oxic-anoxic interface would be the ...hotspot of the DNRA process. In freshwater ecosystems, the riparian zone is the most typical carrier of the oxic-anoxic interface. Here we report spatio-temporal evidence of a higher abundance and rate of DNRA in the riparian zone than in the open water sediments based on molecular and 15N isotopic-tracing technologies, hence signifying a hotspot for the DNRA process. These abudance and rates were significantly higher than those in open water sediments. 15N isotopic paring technology revealed that the DNRA hotspot promoted higher rates of N-compound oxidation (NO2−), reduction (NO3− and DNRA), and N2 production (anammox and denitrification) in the riparian zone than those in open water sediment. However, high-through sequencing analysis showed that the DNRA bacteria in the riparian zone and openwater sediments were insignificantly different. Network and correlation analysis showed that the DNRA abundance and rates were significantly positively correlated with TOM, TC/NH4+, and TC/NO2−, but not with the dominant genera (Anaeromyxobacter, Lacunisphaera, and Sorangium), which played different roles on the connection in the respective community networks. The DNRA process in the riparian zone could be driven mainly by the related environmental biogeochemical characteristics induced by anthropogenic changes, followed by microbial processes. This result provides valuable information for the management of riparian zones because anthropogenic changes in the riparian water table are expected to increase, inducing consequent changes in the reduction from NO3− to NH4+.
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•DNRA hotspot occurs in the riparian zone of various wetlands worldwide.•DNRA hotspot was positively correlated with TOM and C:N ratio, rather than the dominant genera.•There are different key genera in similar community structure between DNRA hotspot and non-hotspot.•As an important intermediate process, DNRA hotspot promoted higher N-cycling rates.•NO2− oxidation and NO3− reduction circulate nutrients (NO3−) and energies for DNRA hotspot.
Large water conservancy project can strongly alter the plant community composition, however, how these changes can potentially affect ecosystem carbon (C) and nitrogen (N) dynamics is not fully ...understood. Here, we investigated natural 13C and 15N abundance of C3 and C4 plants and soil in different fractions labile C (LC) and N (LN), recalcitrant C (RC) and N (RN)from 6 sites with two elevations (flooding zone, 145–175 m, area with revegetation due to flooding, N = 6); and unflooding zone, >175 m with original plant as a control, N = 3) in riparian zones of the Three Gorges Reservoir, China. The dominant species were the C4 plants in the upstream including Changshou (CS), Fuling (FL) and Zhongxian (ZX) and the C3 plants in the downstream in unflooding zone including Wanzhou (WZ) Badong (BD), and Zigui (ZG). C4 plant in flooding zone was significant decreased by mean 25% compared with unflooding zone in the upstream but significantly increased the by mean 59% in the downstream. The 13C isotopic differences between soil and plant (Δδ13C) was lower than zero in both flooding and unflooding in the upstream, but was only lower than zero in flooding zone in the downstream. The proportion of C3-derived C in soil organic carbon pool (average 74.64%) was lower for the flooding zone compared to the unflooding zone (average 87.26%) in most sites, while the proportion of C3-derived C in LC (average 44.38%) was decreased in the flooding zone compared to the unflooding zone (69.52%) in the downstream. Additionally, the δ15N values of soil were higher than plant community in most sites, and were strongly associated with soil C and N pool content, as well as soil pH. Overall, our results revealed that soil C accumulation was primarily determined by C3 plant in situ and new C input by existing dominant C4 plant, whereas soil N dynamics was predictably dependent on soil relative C and N availability in response to flooding at regional scale.
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•Anti-seasonal flooding increased the C4 plant percentage in the whole region.•The δ13C-soil was closed to δ13C value of C3 plant in all sites.•The increased proportion of C4-derived C in soil was found in labile fraction.•The δ15N-soil was associated with soil C and N availability and soil pH.•Different patterns of soil C and N dynamics in response to flooding
Springbox capped springs divert water for livestock and threaten spring conservation in the Great Basin. Springbox restoration is used to increase water availability at riparian zones and wet ...meadows. The purpose of our study was to compare six restoration methods used to increase soil moisture. We used a BACI design to compare percent soil moisture before and after restoration at 24 spring sites in Northwestern Nevada, U.S.A. Percent soil moisture was measured at 5-, 15-, 30-, and 45-cm depths during spring and summer months. Year 2017 was wetter than 2016 causing an increase in percent soil moisture in all restoration treatments. Empty springbox cases, cases filled with sand, and caseless gravel-filled springs produced the greatest increase in percent soil moisture at all depths. We recommend sand-filled casings because these funnel water to the surface while sand prevents casing collapse. We recommend sand over gravel because sand is easier to displace as water flows to the surface. The ratio of δ18O/d16O suggests that springs are fed by shallow groundwater derived from recent precipitation. Inter-annual reductions in precipitation driven by climate change may be the ultimate force determining the preservation of Great Basin spring ecosystems.
•Springbox restoration can recover ecohydrologic processes and riparian communities.•We compared five methods for recovering modified springs.•Sand filled or empty containers lead to higher soil moisture at all depths.•Results assist in improving spring management during a changing climate.
The increased nitrogen (N) fertilizer usage caused substantial nitrate (NO3−) leaching into groundwater and eutrophication in downstream aquatic systems. Riparian zones positioned as the link ...interfaces of terrestrial and aquatic environments are effective in NO3− removal. However, the microbial mechanisms regulating NO3− reduction in riparian zones are still unclear. In this study, four microbial NO3− reduction processes were explored in fine-scale riparian soil horizons by isotopic tracing technique, qPCR of functional gene, high-throughput amplicon sequencing, and phylogenetic molecular ecological network analysis. Interestingly, anaerobic ammonium oxidation (anammox) contributed to NO3− removal of up to 48.2% only in waterward sediments but not in landward soil. Denitrification was still the most significant contributor to NO3− reduction (32.0–91.8%) and N-losses (51.7–100%). Additionally, dissimilatory nitrate reduction to ammonium (DNRA) played a key role in NO3− reduction (4.4–67.5%) and was even comparable to denitrification. Community structure analysis of denitrifying, anammox, and DNRA bacterial communities targeting the related functional gene showed that spatial heterogeneity played a greater role than both temporal and soil type (rhizosphere and non-rhizosphere soil) variability in microbial community structuring. Denitrification and DNRA communities were diverse, and their activities did not depend on gene abundance but were significantly related to organic matter, suggesting that gene abundance alone was insufficient in assessing their activity in riparian zones. Based on networks, DNRA plays a keystone role among the microbial NO3− reducers. As the last line of defense in the interception of terrestrial NO3−, these findings contribute to our understanding of NO3− removal mechanisms in riparian zones, and could potentially be exploited to reduce the diffusion of NO3− pollution.
•Denitrification dominated NO3− reduction and N-losses in riparian zones.•DNRA is a keystone in the community of microbial dissimilatory NO3− reducers.•Denitrification and DNRA rates depend on organic matter and not on gene abundance.•Anammox only contributed to NO3− removal in waterward sediment, not in landward soil.•Denitrifying anaerobic methane oxidation was absent in the riparian zone.
•Afforestation significantly lowered soil C, N, and available P contents.•Afforestation significantly lowered microbial biomass and enzyme activities.•Microbial N and P and enzymatic C activities ...decreased with increasing soil depth.•Microbial biomass and nutrients explained 82% of the variation in enzyme activities.•Short-term afforestation may reduce soil functions such as C storage and N fertility.
Afforestation strongly influences soil microbial traits, especially microbial biomass and enzyme activity. However, the magnitude and direction of soil microbial traits and their controls following afforestation remain unclear. Here, we examined microbial carbon (C), nitrogen (N), and phosphorus (P) biomass and activities of the most common enzymes involved in C (α-1,4-glucosidase, β-1,4-glucosidase, β-D-1,4-cellobiohydrolase, and β-1,4-xylosidase), N (β-1,4-N-acetyl-glucosaminidase and l-leucine aminopeptidase), and P (alkaline phosphatase) cycling under a 15-year-old forest stands (Morus alba, Salix bablyonica, and a mix of the two species) and adjacent croplands along the riparian zone of the upper Yangtze River of China. Unexpectedly, we found that the 15-year afforestation significantly lowered the contents of total C and N, available P, and NO3– compared to the adjacent cropland soils. The microbial biomass C, N, and P contents were also approximately 14–60%, 34–88%, and 9–89% lower, respectively, in the afforested soils than in the adjacent cropland soils across afforestation types and soil depths. Correspondingly, enzymatic C and N activities were 71–90% and 54–75% lower, respectively, under the S. bablyonica stands across soil depths, whereas enzymatic P activity was 39–72% lower in the afforested soils than in the adjacent cropland soils across afforestation types and depths. Reduced microbial biomass and enzymatic activities after afforestation were attributed to the decreased total C and nutrients in the afforested soils than in the adjacent cropland soils, likely due to high plant uptake nutrients and low soil organic matter inputs during the early stages of forest development. Overall, afforestation with plantations of Morus alba or Salix bablyonica species may reduce soil functions such as C storage and N fertility, suggesting that large-scale afforestation using these species should not be prioritized to restore soil functions within a short period.
