scholarly journals Nutrient limitations regulate soil greenhouse gas fluxes from tropical forests: evidence from an ecosystem-scale nutrient manipulation experiment in Uganda

2021 ◽  
Author(s):  
Joseph Tamale ◽  
Roman Hüppi ◽  
Marco Griepentrog ◽  
Laban Frank Turyagyenda ◽  
Matti Barthel ◽  
...  

Abstract. Tropical forests contribute significantly to the emission and uptake of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). However, studies on the soil environmental controls of greenhouse gases (GHGs) from African tropical forest ecosystems are still rare. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes in a tropical forest in northwestern Uganda. Therefore, a large-scale nutrient manipulation experiment (NME) based on 40 m × 40 m plots with different nutrient addition treatments (nitrogen (N), phosphorus (P), N + P, and control) was established. Soil CO2, CH4, and N2O fluxes were measured monthly using permanently installed static chambers for 14 months. Total soil CO2 fluxes were partitioned into autotrophic and heterotrophic components through a root trenching treatment. In addition, soil temperature, soil water content, and mineral N were measured in parallel to GHG fluxes. N addition (N, N + P) resulted in significantly higher N2O fluxes in the transitory phase (0–28 days after fertilization, p 

SOIL ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 433-451
Author(s):  
Joseph Tamale ◽  
Roman Hüppi ◽  
Marco Griepentrog ◽  
Laban Frank Turyagyenda ◽  
Matti Barthel ◽  
...  

Abstract. Soil macronutrient availability is one of the abiotic controls that alters the exchange of greenhouse gases (GHGs) between the soil and the atmosphere in tropical forests. However, evidence on the macronutrient regulation of soil GHG fluxes from central African tropical forests is still lacking, limiting our understanding of how these biomes could respond to potential future increases in nitrogen (N) and phosphorus (P) deposition. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes from a Ugandan tropical forest reserve in the context of increasing N and P deposition. Therefore, a large-scale nutrient manipulation experiment (NME), based on 40 m×40 m plots with different nutrient addition treatments (N, P, N + P, and control), was established in the Budongo Central Forest Reserve. Soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes were measured monthly, using permanently installed static chambers, for 14 months. Total soil CO2 fluxes were partitioned into autotrophic and heterotrophic components through a root trenching treatment. In addition, soil temperature, soil water content, and nitrates were measured in parallel to GHG fluxes. N addition (N and N + P) resulted in significantly higher N2O fluxes in the transitory phase (0–28 d after fertilization; p<0.01) because N fertilization likely increased soil N beyond the microbial immobilization and plant nutritional demands, leaving the excess to be nitrified or denitrified. Prolonged N fertilization, however, did not elicit a significant response in background (measured more than 28 d after fertilization) N2O fluxes. P fertilization marginally and significantly increased transitory (p=0.05) and background (p=0.01) CH4 consumption, probably because it enhanced methanotrophic activity. The addition of N and P (N + P) resulted in larger CO2 fluxes in the transitory phase (p=0.01), suggesting a possible co-limitation of both N and P on soil respiration. Heterotrophic (microbial) CO2 effluxes were significantly higher than the autotrophic (root) CO2 effluxes (p<0.01) across all treatment plots, with microbes contributing about two-thirds of the total soil CO2 effluxes. However, neither heterotrophic nor autotrophic respiration significantly differed between treatments. The results from this study suggest that the feedback of tropical forests to the global soil GHG budget could be disproportionately altered by increases in N and P availability over these biomes.


2021 ◽  
Author(s):  
Joseph Tamale ◽  
Roman Hüppi ◽  
Marco Griepentrog ◽  
Laban Frank Turyagyenda ◽  
Matti Barthel ◽  
...  

&lt;p&gt;The exchange of the climate-relevant greenhouse gases (GHGs) at the soil-atmospheric interface is regulated by both abiotic and biotic controls. However, evidence on nutrient limitations of soil GHG fluxes from African tropical forest ecosystems is still rare. Therefore, an ecosystem-scale nutrient manipulation experiment (NME) consisting of nitrogen (N), phosphorus (P), N + P, and control treatments was set up in a tropical forest in northwestern Uganda. Soil carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;), methane (CH&lt;sub&gt;4&lt;/sub&gt;), and nitrous oxide (N&lt;sub&gt;2&lt;/sub&gt;O) fluxes were measured monthly using static vented chambers for 14 months. A root trenching treatment was also done in all the experimental plots in order to disentangle the contribution of root and microbial respiration to total soil CO&lt;sub&gt;2&lt;/sub&gt; effluxes. In parallel to soil GHG flux measurements, soil temperature, soil moisture, and mineral N were determined. Lifting the N limitation on the soil nitrifiers and denitrifiers through N fertilization significantly increased N&lt;sub&gt;2&lt;/sub&gt;O fluxes in N, and N + P addition plots in the transitory phase (0-28 days after N fertilization, p &lt; 0.01). However, sustained N fertilization did not significantly affect background (measured more than 28 days after fertilization) N&lt;sub&gt;2&lt;/sub&gt;O fluxes. Alleviation of the P limitation on soil methanotrophs through P fertilization marginally and significantly increased CH&lt;sub&gt;4&lt;/sub&gt; consumption in the transitory (p = 0.052) and background (p = 0.010) phases, respectively. Simultaneous addition of N and P (N + P) significantly affected transitory soil CO&lt;sub&gt;2&lt;/sub&gt; effluxes (p = 0.010), suggesting a possible co-limitation of N and P on soil respiration. Microbial CO&lt;sub&gt;2&lt;/sub&gt; effluxes were significantly larger than root CO&lt;sub&gt;2&lt;/sub&gt; effluxes (p &lt; 0.001) across all treatment plots so was the contribution of microbial respiration to the total soil CO&lt;sub&gt;2&lt;/sub&gt; effluxes (about 70 %, p &lt; 0.001). Despite the fact that soil respiration was affected through N + P fertilization, neither heterotrophic nor autotrophic respiration significantly differed in either the N + P or the other treatments. Overall, the study findings suggest that the contribution of tropical forests to the global soil GHG budget could be altered by changes in N and P availability in these biomes.&lt;/p&gt;&lt;p&gt;Key words: Soil greenhouse gas fluxes, nutrient manipulation experiment, soil nutrient limitation, and Ugandan tropical pristine forest.&lt;/p&gt;


Ecosystems ◽  
2018 ◽  
Vol 21 (7) ◽  
pp. 1445-1458 ◽  
Author(s):  
Elodie A. Courtois ◽  
Clément Stahl ◽  
Joke Van den Berge ◽  
Laëtitia Bréchet ◽  
Leandro Van Langenhove ◽  
...  

2021 ◽  
Author(s):  
Warren Daniel ◽  
Clément Stahl ◽  
Benoît Burban ◽  
Jean-Yves Goret ◽  
Jocelyn Cazal ◽  
...  

&lt;p&gt;Tropical forests are the most productive terrestrial ecosystems, global centres of biodiversity and important participants in the global carbon and water cycles. The Amazon, which is the most extensive tropical forest, can contain more than 600 trees (diameter at breast height above 10 cm) and up to 200 tree species in only one hectare of forest. In upland forest, tropical soils are known to be a methane (CH&lt;sub&gt;4&lt;/sub&gt;) sink and a weak source of nitrous oxide (N&lt;sub&gt;2&lt;/sub&gt;O), which are both major greenhouse gases (GHG). Most of researches on GHG fluxes have been conducted on the soil compartment but recent works reported that tree stems of some tropical forests can be a substantial source of CH&lt;sub&gt;4&lt;/sub&gt; and, a to lesser extend of N&lt;sub&gt;2&lt;/sub&gt;O. Tropical tree stems can act as conduits of soil-produced GHG but biophysical mechanisms controlling GHG fluxes and differences among tree species are not yet fully understood.&lt;/p&gt;&lt;p&gt;In order to quantify CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O fluxes of different tropical tree species, we took gas samples in 101 mature tree stems of twelve species with the manual chamber technique during the wet season 2020, in a French Guiana forest. Tree species were selected because of their abundance and their habitat preference. We chose trees belonging to two contrasted forest habitats, the hill-top and hill-bottom, which are respectively characterized by aerobic conditions and seasonal anaerobic conditions. Simultaneously with sampling GHG, we measured bark moisture and tree diameter. Four tree species were found in both habitats whereas the eight others were only present in one of these two habitats.&lt;/p&gt;&lt;p&gt;Among the 101 tree stems, 78.6% were net sources of CH&lt;sub&gt;4&lt;/sub&gt; with a greater proportion in hill-bottom than hill-top. Overall, stem CH&lt;sub&gt;4&lt;/sub&gt; fluxes were significantly and positively correlated with the wood density (&amp;#967;&lt;sup&gt;2&lt;/sup&gt; = 28.0; p &lt; 0.01; N = 75) but neither with the habitat, bark moisture or tree size. We found a significant effect of the tree species on stem CH&lt;sub&gt;4&lt;/sub&gt; fluxes (F = 3.7, p &lt; 0.001) but no interactions between the tree species and habitats.&lt;/p&gt;&lt;p&gt;Among 43.0% of the stem N&lt;sub&gt;2&lt;/sub&gt;O fluxes that were different from zero, half were from trees that were net sources of N&lt;sub&gt;2&lt;/sub&gt;O mainly located in hill-top. Stem N&lt;sub&gt;2&lt;/sub&gt;O fluxes are not significantly correlated with habitat, as also with the tree size, wood density or bark moisture. Unlike stem CH&lt;sub&gt;4&lt;/sub&gt; fluxes, tree species did not significantly influence stem N&lt;sub&gt;2&lt;/sub&gt;O fluxes.&lt;/p&gt;&lt;p&gt;Our study revealed that, in tropical forest, spatial variations in GHG fluxes would not only depend on soil water conditions, but also on tree species. Specific tree traits such as the wood density can favour stem CH&lt;sub&gt;4&lt;/sub&gt; emissions by providing more or less effective pore space for CH&lt;sub&gt;4&lt;/sub&gt; diffusion but seems to have a limited influence on stem N&lt;sub&gt;2&lt;/sub&gt;O fluxes maybe because of the lower diffusive and ebullitive transport of N&lt;sub&gt;2&lt;/sub&gt;O compared to CH&lt;sub&gt;4&lt;/sub&gt;. Further investigation linking tree species traits and tree GHG fluxes are, however, necessary to elucidate the processes and mechanisms behind tree CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O exchanges.&lt;/p&gt;


1996 ◽  
Vol 23 (3) ◽  
pp. 235-248 ◽  
Author(s):  
Oliver L. Phillips

SummaryAnalyzing permanent plot data from 40 tropical forest sites, Phillips and Gentry (1994) found that there has been a significant tendency for tree turnover – as measured by tree mortality and recruitment – to increase since the 1950s. The dataset is now substantially improved, and includes 67 mature forest sites with turnover data representing most of the major tropical forest regions of the world. This paper presents an updated and expanded analysis of the latest data, and confirms that tree turnover has increased in mature tropical forest plots. Several artifactual explanations have been suggested but none are supported by the available data, suggesting that surviving mature tropical forests have been recently affected by large-scale anthropogenic or natural change. The effects of increased turnover may include impacts on future global atmosphere, climate, and biodiversity. Better understanding of the ecological changes in mature tropical forests depends on progress in two critical research areas – a ground-based monitoring network of long-term, fully identified tropical forest plots, and controlled manipulation of atmospheric conditions in forest experiments. Research activity in both areas needs to be substantially increased if we are to understand and predict the complex interactions between tropical forest ecology and global environmental change.


Author(s):  
Stephan Kambach ◽  
Richard Condit ◽  
Salomón Aguilar ◽  
Helge Bruelheide ◽  
Sarayudh Bunyavejchewin ◽  
...  

All species must balance their allocation to growth, survival and recruitment. Among trees, evolution has resulted in different strategies of partitioning resources to these key demographic processes, i.e. demographic trade-offs. It is unclear whether the same demographic trade-offs structure tropical forests worldwide. Here, we used data from 13 large-scale and long-term tropical forest plots to estimate the principal trade-offs in growth, survival, recruitment, and tree stature at each site. For ten sites, two trade-offs appeared repeatedly. One trade-off showed a negative relationship between growth and survival, i.e. the well-known fast−slow continuum. The second trade-off distinguished between tall-statured species and species with high recruitment rates, i.e. a stature−recruitment trade-off. Thus, the fast-slow continuum and tree stature are two independent dimensions structuring most tropical tree communities. Our discovery of the consistency of demographic trade-offs and strategies across forest types in three continents substantially improves our ability to predict tropical forest dynamics worldwide.


Author(s):  
Carlos Eduardo Frickmann Young

Tropical forests are among the most biodiverse areas on Earth. They contribute to ecosystem functions, including regulating water flow and maintaining one of the most important carbon sinks on the planet, and provide resources for important economic activities, such as timber and nontimber products and fish and other food. Rainforests are not empty of human population and are sites of ethnically and culturally diverse cultures that are responsible for many human languages and dialects. They also provide resources for important economic activities, such as timber and nontimber products. However, tropical deforestation caused by the expansion of agricultural activities and unsustainable logging continues at very high levels. The causes of forest loss vary by region. Livestock is the main driver in the Amazon, but commercial plantations (soybeans, sugar cane, and other tradable crops) also have an impact on deforestation, in many cases associated with violent conflicts over land tenure. In Southeast Asia, logging motivated by the tropical timber trade plays an important role, although palm oil plantations are an increasing cause of deforestation. In Africa, large-scale agricultural and industrial activities are less important, and the most critical factor is the expansion of subsistence and small-scale agriculture. However, trade-oriented activities, such as cocoa and coffee plantations in West Africa and logging in Central Africa, are becoming increasingly important. Public policies have a strong influence on these changes in land use, from traditional community-based livelihood practices to for-profit livestock, cultivation, and timber extraction. Investments in infrastructure, tax and credit incentives, and institutional structures to stimulate migration and deforestation represent economic incentives that lead to deforestation. Poor governance and a lack of resources and political will to protect the traditional rights of the population and environmental resources are another cause of the continuous reduction of tropical forests. Consequently, deforestation prevents the expansion of economic activities that could be established without threats to the remnants of native forest. There are also negative social consequences for the local population, which suffers from the degradation of the natural resources on which their production is based, and is hampered by air pollution caused by forest fires. In some situations, a vicious cycle is created between poverty and deforestation, since the expansion of the agricultural frontier reduces the forest areas where traditional communities once operated, but without generating job opportunities. New approaches are required to reverse this paradigm and to lay the foundation for a sustainable economy based on the provision of ecosystem services provided by tropical forests. These include (a) better governance and public management capacity, (b) incentives for economic activities compatible with the preservation of the tropical forest, and (c) large-scale adoption of economic instruments to support biodiversity and ecosystem services. Public policies are necessary to correct market failures and incorporate the values of ecosystem services in the land use decision process. In addition to penalties for predatory actions, incentives are needed for activities that support forest preservation, so the forest is worth retaining rather than clearing. Improving governance capacity, combining advanced science and technology with traditional knowledge, and improving the management of existing activities can also help to ensure sustainable development in tropical forest regions.


2020 ◽  
Author(s):  
Andrew Nottingham ◽  
Alexander W. Cheesman ◽  
Terhi Ruitta ◽  
Christopher E. Doughty ◽  
elizabeth telford ◽  
...  

•Tropical forests are the most productive terrestrial ecosystem, fixing around 41 Pg of carbon from the atmosphere each year. A substantial portion of this carbon is allocated belowground to roots and root-associated microorganisms. However, there have been very few empirical studies on the dynamics of this transfer, especially in tropical forests where the response is mediated by high plant diversity.•We used a large-scale girdling experiment to halt the belowground transfer of recent photosynthates in a lowland tropical forest in Borneo. By girdling 209 large trees in a 0.48 ha plot, we determined: i) the contribution of recent photosynthate to root-rhizosphere respiration and; ii) the relationships among the disruption of this belowground carbon supply, tree species composition and mortality.•Soil CO2 emissions declined markedly (36 ± 5%) over ~50 days following girdling in three of six monitored subplots. In the other three subplots there was either a marginal decline or no response of soil CO2 emissions to girdling. The decrease in soil CO2 efflux was higher in subplots with greater dominance of Dipterocarpaceae.•Mortality of the 209 trees was 62% after 370 days, with large variation among species. There was particularly high mortality for Dipterocarpaceae species. Whilst species with functional traits associated with faster growth rates (including lower wood density) had a higher risk of mortality post-girdle treatment.•Overall, our results indicate a strong coupling of belowground carbon allocation and root-rhizosphere respiration in this tropical forest but with high spatial variation driven by differences in plant community composition, with a closer above-belowground coupling in forest dominated by Dipterocarpaceae. Our findings highlight the implications of the diverse species composition of tropical forests in affecting the dynamics of belowground carbon transfer and its release to the atmosphere.


Author(s):  
Stephan Kambach ◽  
Richard Condit ◽  
Salomón Aguilar ◽  
Helge Bruelheide ◽  
Sarayudh Bunyavejchewin ◽  
...  

All species must balance their allocation to growth, survival and recruitment. Among trees, evolution has resulted in different strategies of partitioning resources to these key demographic processes, i.e. demographic trade-offs. It is unclear whether the same demographic trade-offs structure tropical forests worldwide. Here, we used data from 13 large-scale and long-term tropical forest plots to estimate the principal trade-offs in growth, survival, recruitment, and tree stature at each site. For ten sites, two trade-offs appeared repeatedly. One trade-off showed a negative relationship between growth and survival, i.e. the well-known fast−slow continuum. The second trade-off distinguished between tall-statured species and species with high recruitment rates, i.e. a stature−recruitment trade-off. Thus, the fast-slow continuum and tree stature are two independent dimensions structuring most tropical tree communities. Our discovery of the consistency of demographic trade-offs and strategies across forest types in three continents substantially improves our ability to predict tropical forest dynamics worldwide.


Forests ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1135
Author(s):  
Chuying Guo ◽  
Leiming Zhang ◽  
Shenggong Li ◽  
Qingkang Li ◽  
Guanhua Dai

Soils in mid-high latitudes are under the great impact of freeze–thaw cycling. However, insufficient research on soil CO2, CH4, and N2O fluxes during the spring freeze–thaw (SFT) period has led to great uncertainties in estimating soil greenhouse gas (GHG) fluxes. The present study was conducted in a temperate broad-leaved Korean pine mixed forest in Northeastern China, where soils experience an apparent freeze–thaw effect in spring. The temporal variations and impact factors of soil GHG fluxes were measured during the SFT period and growing season (GS) using the static-chamber method. The results show that the soil acted as a source of atmospheric CO2 and N2O and a sink of atmospheric CH4 during the whole observation period. Soil CO2 emission and CH4 uptake were lower during the SFT period than those during the GS, whereas N2O emissions were more than six times higher during the SFT period than that during the GS. The responses of soil GHG fluxes to soil temperature (Ts) and soil moisture during the SFT and GS periods differed. During the SFT period, soil CO2 and CH4 fluxes were mainly affected by the volumetric water content (VWC) and Ts, respectively, whereas soil N2O flux was influenced jointly by Ts and VWC. The dominant controlling factor for CO2 was Ts during the GS, whereas CH4 and N2O were mainly regulated by VWC. Soil CO2 and N2O fluxes accounted for 97.3% and 3.1% of the total 100-year global warming potential (GWP100) respectively, with CH4 flux offsetting 0.4% of the total GWP100. The results highlight the importance of environmental variations to soil N2O pulse during the SFT period and the difference of soil GHG fluxes between the SFT and GS periods, which contribute to predicting the forest soil GHG fluxes and their global warming potential under global climate change.


Sign in / Sign up

Export Citation Format

Share Document