scholarly journals In-depth analysis of N2O fluxes in tropical forest soils of the Congo Basin combining isotope and functional gene analysis

2021 ◽  
Author(s):  
Nora Gallarotti ◽  
Matti Barthel ◽  
Elizabeth Verhoeven ◽  
Engil Isadora Pujol Pereira ◽  
Marijn Bauters ◽  
...  
Keyword(s):  
Tropical Forest ◽  
Tropical Forests ◽  
Forest Soils ◽  
Stratospheric Ozone ◽  
Microbial Reduction ◽  
Functional Gene ◽  
Congo Basin ◽  
N Losses ◽  
Depth Analysis ◽  
Gaseous N Losses

AbstractPrimary tropical forests generally exhibit large gaseous nitrogen (N) losses, occurring as nitric oxide (NO), nitrous oxide (N2O) or elemental nitrogen (N2). The release of N2O is of particular concern due to its high global warming potential and destruction of stratospheric ozone. Tropical forest soils are predicted to be among the largest natural sources of N2O; however, despite being the world’s second-largest rainforest, measurements of gaseous N-losses from forest soils of the Congo Basin are scarce. In addition, long-term studies investigating N2O fluxes from different forest ecosystem types (lowland and montane forests) are scarce. In this study we show that fluxes measured in the Congo Basin were lower than fluxes measured in the Neotropics, and in the tropical forests of Australia and South East Asia. In addition, we show that despite different climatic conditions, average annual N2O fluxes in the Congo Basin’s lowland forests (0.97 ± 0.53 kg N ha−1 year−1) were comparable to those in its montane forest (0.88 ± 0.97 kg N ha−1 year−1). Measurements of soil pore air N2O isotope data at multiple depths suggests that a microbial reduction of N2O to N2 within the soil may account for the observed low surface N2O fluxes and low soil pore N2O concentrations. The potential for microbial reduction is corroborated by a significant abundance and expression of the gene nosZ in soil samples from both study sites. Although isotopic and functional gene analyses indicate an enzymatic potential for complete denitrification, combined gaseous N-losses (N2O, N2) are unlikely to account for the missing N-sink in these forests. Other N-losses such as NO, N2 via Feammox or hydrological particulate organic nitrogen export could play an important role in soils of the Congo Basin and should be the focus of future research.

scholarly journals Well-Aerated Southern Appalachian Forest Soils Demonstrate Significant Potential for Gaseous Nitrogen Loss

Forests ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 1155
Author(s):  
Peter Baas ◽  
Jennifer D. Knoepp ◽  
Jacqueline E. Mohan
Keyword(s):  
Forest Soils ◽  
Nitrogen Loss ◽  
Elevation Gradient ◽  
High Elevation ◽  
N Cycling ◽  
N Losses ◽  
Northern Hardwood ◽  
Southern Appalachian ◽  
Nitrifier Denitrification ◽  
Gaseous N Losses

Understanding the dominant soil nitrogen (N) cycling processes in southern Appalachian forests is crucial for predicting ecosystem responses to changing N deposition and climate. The role of anaerobic nitrogen cycling processes in well-aerated soils has long been questioned, and recent N cycling research suggests it needs to be re-evaluated. We assessed gross and potential rates of soil N cycling processes, including mineralization, nitrification, denitrification, nitrifier denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) in sites representing a vegetation and elevation gradient in the U.S. Department of Agriculture (USDA) Forest Service Experimental Forest, Coweeta Hydrologic Laboratory in southwestern North Carolina, USA. N cycling processes varied among sites, with gross mineralization and nitrification being greatest in high-elevation northern hardwood forests. Gaseous N losses via nitrifier denitrification were common in all ecosystems but were greatest in northern hardwood. Ecosystem N retention via DNRA (nitrification-produced NO3 reduced to NH4) ranged from 2% to 20% of the total nitrification and was highest in the mixed-oak forest. Our results suggest the potential for gaseous N losses through anaerobic processes (nitrifier denitrification) are prevalent in well-aerated forest soils and may play a key role in ecosystem N cycling.

scholarly journals Estimation of N20 and NO emission from a tropical highland forest in Rwanda

Afrika Focus ◽  
2013 ◽  
Vol 26 (2) ◽  
pp. 133-141
Author(s):  
Nasrin Gharahi Ghehi
Keyword(s):  
Climate Change ◽  
Nitrous Oxide ◽  
Tropical Forest ◽  
Forest Soils ◽  
Land Surface ◽  
Stratospheric Ozone ◽  
No Emission ◽  
Tropical Forest Soil ◽  
Broad Subject ◽  
No Emissions

The research of this work fits within the broad subject of greenhouse gas emissions and climate change. More specifically, this work focuses on the contribution of tropical forest soils to the atmospheric N20 and NO budgets. Nitrous oxide has a global warming potential of 310 relative to CO2 and is one of the main greenhouse gases covered by the United Nations Framework Convention on Climate Change (UNFCCC). Nitrous oxide also plays a key role in modulating the stratospheric ozone layer. Tropical forest soils are considered to be the largest natural source of N20. Additionally, they can produce considerable amounts of NO. Estimates of the contribution of tropical rainforest ecosystems, which cover u50 x ro6 ha of the global land surface, to atmospheric N20 and NO have a high uncertainty. Despite the fact that tropical forest soils are considered to be a key source of N20 and NO2 only a relatively small number of detailed studies investigating the temporal and spatial variability of the N20 and NO soil-atmosphere exchange are available, particularly for Africa. Therefore the general objective of this research was to improve N20 and NO emission predictions from tropical forest. The research has been carried out in the Nyungwe forest in Rwanda for which a large number of legacy data are available. The results of this thesis led to (i) a better understanding of the N20 and NO source strength of a central African tropical forest soil, (ii) improved NO and N2O emission estimates from a central African tropical highland forest and more insight into the importance of soil properties controlling N20 and NO emissions and (iii) a better insight in those parameters that preferentially should be monitored to allow better global simulations of N20 and NO emissions from tropical forests.

scholarly journals Anoxic conditions maintained high phosphorus sorption in humid tropical forest soils

2019 ◽  
Author(s):  
Yang Lin ◽  
Avner Gross ◽  
Christine S. O'Connell ◽  
Whendee L. Silver
Keyword(s):  
Tropical Forest ◽  
Tropical Forests ◽  
Sorption Capacity ◽  
Forest Soils ◽  
Soil Minerals ◽  
Anoxic Conditions ◽  
Soil P ◽  
P Sorption ◽  
Reducing Conditions ◽  
Humid Tropical Forest

Abstract. The strong phosphorus (P) sorption capacity of iron (Fe) and aluminum (Al) minerals in highly weathered, acidic soils of humid tropical forests is generally assumed to be an important driver of P limitation to plants and microbial activity in these ecosystems. Humid tropical forest soils often experience fluctuating redox conditions that reduce Fe and raise pH. It is commonly thought that Fe reduction generally decreases the capacity and strength of P sorption. Here we examined the effects of 14-day oxic and anoxic incubations on soil P sorption dynamics in humid tropical forest soils from Puerto Rico. Contrary to the conventional belief, soil P sorption capacity did not decrease under anoxic conditions, suggesting that soil minerals remain strong P sinks even under reducing conditions. Sorption of P occurred very rapidly in these soils, with at least 60 % of the added P disappearing from the solution within six hours. Estimated P sorption capacities were one order of magnitude higher than the soil total P contents. However, the strength of P sorption under reducing conditions was weaker, as indicated by the increased solubility of sorbed P in NaHCO3 solution. Our results show that highly weathered soil minerals can retain P even under anoxic conditions, where it might otherwise be susceptible to leaching. Anoxic events can also potentially increase P bioavailability by decreasing the strength, rather than the capacity, of P sorption. These results improve our understanding of the redox effects on biogeochemical cycling in tropical forests.

scholarly journals Inter-comparison and assessment of gridded climate products over tropical forests during the 2015/2016 El Niño

2018 ◽  
Vol 373 (1760) ◽  
pp. 20170406 ◽  
Author(s):  
C. Burton ◽  
S. Rifai ◽  
Y. Malhi
Keyword(s):  
Southeast Asia ◽  
Tropical Forest ◽  
Tropical Forests ◽  
Air Temperature ◽  
El Niño ◽  
El Nino ◽  
Congo Basin ◽  
Wide Range ◽  
Spatio Temporal ◽  
The Impact

To understand the impacts of extreme climate events, it is first necessary to understand the spatio-temporal characteristics of the event. Gridded climate products are frequently used to describe climate patterns but have been shown to perform poorly over data-sparse regions such as tropical forests. Often, they are uncritically employed in a wide range of studies linking tropical forest processes to large-scale climate variability. Here, we conduct an inter-comparison and assessment of near-surface air temperature fields supplied by four state-of-the-art reanalysis products, along with precipitation estimates supplied by four merged satellite-gauge rainfall products. Firstly, spatio-temporal patterns of temperature and precipitation anomalies during the 2015–2016 El Niño are shown for each product to characterize the impact of the El Niño on the tropical forest biomes of Equatorial Africa, Southeast Asia and South America. Using meteorological station data, a two-stage assessment is then conducted to determine which products most reliably model tropical climates during the 2015–2016 El Niño, and which perform best over the longer-term satellite observation period (1980–2016). Results suggest that eastern Amazonia, parts of the Congo Basin and mainland Southeast Asia all experienced significant monthly mean temperature anomalies during the El Niño, while northeastern Amazonia, eastern Borneo and southern New Guinea experienced significant precipitation deficits. Our results suggest ERA-Interim and MERRA2 are the most reliable air temperature datasets, while TRMM 3B42 V7 and CHIRPS v2.0 are the best-performing rainfall datasets. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

scholarly journals Anoxic conditions maintained high phosphorus sorption in humid tropical forest soils

2020 ◽  
Vol 17 (1) ◽  
pp. 89-101 ◽  
Author(s):  
Yang Lin ◽  
Avner Gross ◽  
Christine S. O'Connell ◽  
Whendee L. Silver
Keyword(s):  
Tropical Forest ◽  
Tropical Forests ◽  
Sorption Capacity ◽  
Forest Soils ◽  
Soil Minerals ◽  
Anoxic Conditions ◽  
Soil P ◽  
P Sorption ◽  
Reducing Conditions ◽  
Humid Tropical Forest

Abstract. The strong phosphorus (P) sorption capacity of iron (Fe) and aluminum (Al) minerals in highly weathered, acidic soils of humid tropical forests is generally assumed to be an important driver of P limitation to plants and microbial activity in these ecosystems. Humid tropical forest soils often experience fluctuating redox conditions that reduce Fe and raise pH. It is commonly thought that Fe reduction generally decreases the capacity and strength of P sorption. Here we examined the effects of 14 d oxic and anoxic incubations on soil P sorption dynamics in humid tropical forest soils from Puerto Rico. Contrary to the conventional belief, soil P sorption capacity did not decrease under anoxic conditions, suggesting that soil minerals remain strong P sinks even under reducing conditions. Sorption of P occurred very rapidly in these soils, with at least 60 % of the added P disappearing from the solution within 6 h. Estimated P sorption capacities were much higher, often by an order of magnitude, than the soil total P contents. However, the strength of P sorption under reducing conditions was weaker, as indicated by the increased solubility of sorbed P in NaHCO3 solution. Our results show that highly weathered soil minerals can retain P even under anoxic conditions, where it might otherwise be susceptible to leaching. Anoxic events can also potentially increase P bioavailability by decreasing the strength, rather than the capacity, of P sorption. These results improve our understanding of the redox effects on biogeochemical cycling in tropical forests.

scholarly journals Tropical forest soils serve as substantial and persistent methane sinks

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jun-Fu Zhao ◽  
Shu-Shi Peng ◽  
Meng-Ping Chen ◽  
Guan-Ze Wang ◽  
Yi-Bin Cui ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Seasonal Variation ◽  
Tropical Forest ◽  
Tropical Forests ◽  
Forest Soils ◽  
Forest Site ◽  
Methane Uptake ◽  
Global Soil ◽  
Methane Fluxes ◽  
Methane Sink

AbstractAlthough tropical forest soils contributed substantially global soil methane uptake, observations on soil methane fluxes in tropical forests are still sparse, especially in Southeast Asia, leading to large uncertainty in the estimation of global soil methane uptake. Here, we conducted two-year (from Sep, 2016 to Sep, 2018) measurements of soil methane fluxes in a lowland tropical forest site in Hainan island, China. At this tropical forest site, soils were substantial methane sink, and average annual soil methane uptake was estimated at 2.00 kg CH4-C ha−1 yr−1. The seasonality of soil methane uptake showed strong methane uptake in the dry season (−1.00 nmol m−2 s−1) and almost neutral or weak soil methane uptake in the wet season (−0.24 nmol m−2 s−1). The peak soil methane uptake rate was observed as −1.43 nmol m−2 s−1 in February, 2018, the driest and coolest month during the past 24 months. Soil moisture was the dominant controller of methane fluxes, and could explain 94% seasonal variation of soil methane fluxes. Soil temperature could not enhance the explanation of seasonal variation of soil methane fluxes on the top of soil moisture. A positive relationship between soil methane uptake and soil respiration was also detected, which might indicate co-variation in activities of methanotroph and roots and/or microbes for soil heterotrophic respiration. Our study highlights that tropical forests in this region acted as a methane sink.

scholarly journals Long-Term Nitrogen Addition Decreases Soil Carbon Mineralization in an N-Rich Primary Tropical Forest

Forests ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 734
Author(s):  
Xiankai Lu ◽  
Qinggong Mao ◽  
Zhuohang Wang ◽  
Taiki Mori ◽  
Jiangming Mo ◽  
...  
Keyword(s):  
Microbial Biomass ◽  
Organic Carbon ◽  
Tropical Forest ◽  
Soil Carbon ◽  
Tropical Forests ◽  
Carbon Mineralization ◽  
N Deposition ◽  
Soil Carbon Mineralization ◽  
N Additions

Anthropogenic elevated nitrogen (N) deposition has an accelerated terrestrial N cycle, shaping soil carbon dynamics and storage through altering soil organic carbon mineralization processes. However, it remains unclear how long-term high N deposition affects soil carbon mineralization in tropical forests. To address this question, we established a long-term N deposition experiment in an N-rich lowland tropical forest of Southern China with N additions such as NH4NO3 of 0 (Control), 50 (Low-N), 100 (Medium-N) and 150 (High-N) kg N ha−1 yr−1, and laboratory incubation experiment, used to explore the response of soil carbon mineralization to the N additions therein. The results showed that 15 years of N additions significantly decreased soil carbon mineralization rates. During the incubation period from the 14th day to 56th day, the average decreases in soil CO2 emission rates were 18%, 33% and 47% in the low-N, medium-N and high-N treatments, respectively, compared with the Control. These negative effects were primarily aroused by the reduced soil microbial biomass and modified microbial functions (e.g., a decrease in bacteria relative abundance), which could be attributed to N-addition-induced soil acidification and potential phosphorus limitation in this forest. We further found that N additions greatly increased soil-dissolved organic carbon (DOC), and there were significantly negative relationships between microbial biomass and soil DOC, indicating that microbial consumption on soil-soluble carbon pool may decrease. These results suggests that long-term N deposition can increase soil carbon stability and benefit carbon sequestration through decreased carbon mineralization in N-rich tropical forests. This study can help us understand how microbes control soil carbon cycling and carbon sink in the tropics under both elevated N deposition and carbon dioxide in the future.

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