Nitrogen flux patterns through Oxisols and Ultisols in tropical forests of Cameroon, Central Africa

Abstract

We lack an understanding of nitrogen (N) cycles in tropical forests of Africa, although the environmental conditions in this region, such as soil type, vegetation, and climate, are distinct when compared with other tropical forests. Herein, we simultaneously quantified N fluxes through precipitation, throughfall, and 0-, 15-, and 30-cm soil solutions, as well as litterfall, in two forests with different soil acidity (Ultisols at the MV village (exchangeable Al 3+ in 0-30 cm, 126 kmol c ha -1 ) and Oxisols at the AD village (exchangeable Al 3+ in 0-30 cm, 59.8 kmol c ha -1 )) over 2 years in Cameroon. The N fluxes to the O horizon via litterfall plus throughfall were similar for both sites (MV and AD, 243 and 273 kg N ha -1 yr -1 , respectively). Those values were remarkably large relative to other tropical forests, reflecting the dominance of legumes in this region. The total dissolved N flux from the O horizon at the MV was 28 kg N ha -1 yr -1 , while it was 127 kg N ha -1 yr -1 mainly as NO 3 --N (~80%) at the AD. The distinctly different pattern of N cycles could be caused by stronger soil acidity at the MV, which was considered to promote a superficial root mat formation in the O horizon despite the marked dry season (fine root biomass in the O horizon and its proportion to the 1-m-soil profile: 1.5 Mg ha -1 and 31% at the MV; 0.3 Mg ha -1 and 9% at the AD). Combined with the published data for N fluxes in tropical forests, we have shown that Oxisols, in combination with N-fixing species, have large N fluxes from the O horizon; meanwhile, Ultisols do not have large fluxes because of plant uptake through the root mat in the O horizon. Consequently, our results suggest that soil type can be a major factor influencing the pattern of N fluxes from the O horizon via the effects of soil acidity, thereby determining the contrasting plant-soil N cycles in the tropical forests of Africa. ARTICLE HISTORY

Effects of 3-year cultivation on the soil nutrient status in a tropical forest and savanna of Central Africa, as determined by the microbial responses to substrate addition

“…The FOR site is a mature, old forest (more than 50 years old), and the Crop-F site is a maize field that was planted 3 years after allowing a site near (<100 m) the FOR site to fallow. The FOR was dominated by N-fixing trees (Albizia zygia and so on), which is typical of this area according to our previous study (Shibata et al 2017). The SAV site is a grassland savanna, where the dominant vegetation is Chromolaena odorata, and the Crop-S site is a maize field that was planted 3 years after allowing a site near (<50 m) the SAV site to fallow.…”

Impacto ambiental del vertimiento de aguas servidas en aglomerados urbanos ilegales del municipio de Villavicencio, Colombia

“…Los parámetros fisicoquímicos se encuentran directamente relacionados con la salud del suelo y desem- peñan un rol esencial en el desarrollo de la microbiota y mesofauna edáfica, y con esto, la cobertura vegetal que regula el sistema (Agegnehu y Amede, 2017, Gómez-Sagasti et al, 2012, Muñoz-Rojas, 2018. Estudios muestran que los suelos del lugar presentan de forma natural parámetros relevantes en el funcionamiento, entre los cuales se destacan el pH (4,2-5,5), CE (50 µS cm −1 ), concentración de MO (1,2-1,7 %) y nitrógeno (1600 mg kg −1 ) y CIC (124 meq-g 100 g −1 ) (Eurípides, Peñuela, Yacomeloy Orduz-Rodríguez, 2018, Fernandes et al, 2018, Jamioy, Menjivar y Rubiano, 2015, Nunes et al, 2017, Shibata et al, 2017. Estos parámetros pueden verse afectados fuertemente ante actividades antrópicas, como agricultura, ganadería, pastoreo, contaminación y malas prácticas, que pueden llegar a inestabilizar los procesos de regulación, generando pérdida de servicios ecosistémicos y problemáticas ambientales, lo cual afecta finalmente a la sociedad (Gómez-Sagasti et al, 2012, Castro-Garzón, Torres-Flórez y Gallardo-Lichaa, 2020.…”

A comparison of lignin-degrading enzyme activities in forest floor layers across a global climatic gradient

“…These findings can be interpreted as control of enzyme activity and dominant fungal communities by Table 2 Chemical properties of the organic layers in the boreal, temperate, and tropical forests studied. Data sources of C/N ratio are Gower et al (1997) for Sites 1-3, Nakane et al (1997) for Sites 3-5, Megonigal et al (1997) for Site 6, Yasuda et al (2012) and Fujii et al (2019) for Sites 7-8, Fujii et al (2008) for Site 9, Inagaki et al (2012) for Sites 10-11, Fujii et al (2011) for Sites 12-14, Shibata et al (2017) for Sites 15-16, Fioretto et al (2007), Maisto et al (2013), and Criquet et al (2000) for Site 17, and Fujii et al (2013b) for Sites 18-20. L (litter), F (fermented), H (humified), and FH (mixture of F and H layers) corresponds to Oi, Oe, Oa, and Oea horizons in soil taxonomy, respectively (Soil survey staff, 2014).…”

“…sites information areGower et al (1997) for Sites 1-3,Nakane et al (1997) for Sites 3-5,Megonigal et al (1997) for Site 6,Yasuda et al (2012) andFujii et al (2019) for Sites 7-8,Fujii et al (2008) for Site 9,Inagaki et al (2012) for Sites 10-11,Fujii et al (2011) for Sites 12-14,Shibata et al (2017) for Sites 15-16,Criquet et al (2002) for Site 17, andFujii et al (2013b) for Sites 18-20.…”