Respiration From a Tropical Forest Ecosystem: Partitioning of Sources and Low Carbon Use Efficiency

Abstract

Abstract. Understanding how tropical forest carbon balance will respond to global change requires knowledge of individual heterotrophic and autotrophic respiratory sources, together with factors that control respiratory variability. We measured leaf, live wood, and soil respiration, along with additional environmental factors over a 1-yr period in a Central Amazon terra firme forest. Scaling these fluxes to the ecosystem, and combining our data with results from other studies, we estimated an average total ecosystem respiration (R eco ) of 7.8 mol·m Ϫ2 ·s Ϫ1. Average estimates (per unit ground area) for leaf, wood, soil, total heterotrophic, and total autotrophic respiration were 2.6, 1.1, 3.2, 5.6, and 2.2 mol·m Ϫ2 ·s Ϫ1 , respectively. Comparing autotrophic respiration with net primary production (NPP) estimates indicated that only ϳ30% of carbon assimilated in photosynthesis was used to construct new tissues, with the remaining 70% being respired back to the atmosphere as autotrophic respiration. This low ecosystem carbon use efficiency (CUE) differs considerably from the relatively constant CUE of ϳ0.5 found for temperate forests. Our R eco estimate was comparable to the above-canopy flux (F ac ) from eddy covariance during defined sustained high turbulence conditions (when presumably F ac ϭ R eco ) of 8.4 (95% CI ϭ 7.5-9.4). Multiple regression analysis demonstrated that ϳ50% of the nighttime variability in F ac was accounted for by friction velocity (u*, a measure of turbulence) variables. After accounting for u* variability, mean F ac varied significantly with seasonal and daily changes in precipitation. A seasonal increase in precipitation resulted in a decrease in F ac , similar to our soil respiration response to moisture. The effect of daily changes in precipitation was complex: precipitation after a dry period resulted in a large increase in F ac , whereas additional precipitation after a rainy period had little effect. This response was similar to that of surface litter (coarse and fine), where respiration is greatly reduced when moisture is limiting, but increases markedly and quickly saturates with an increase in moisture.

Arbuscular mycorrhizal mycelial respiration in a moist tropical forest

“…Tropical forests not only fix more C through photosynthesis than any other terrestrial ecosystem (Melillo et al, 1993), they also release more through respiration, over half of which is released from soils (Chambers et al, 2004). Soils in global tropical forests release c. 24 Pg C yr )1 into the atmosphere in soil CO 2 efflux (Raich et al, 2002).…”

Quantificação das emissões de CO2 pelo solo em áreas sob diferentes estádios de restauração no domínio da mata atlântica

“…Essa correlação significativa, entre a umidade e a respiração do solo, foi observada por diversos autores, que justificaram o fato da regulação da atividade microbiana ser feita pela umidade, em decorrência das reações químicas de decomposição da matéria orgânica. 10,23,36 Quando acontece o aumento da umidade do solo, ocorre o aumento as atividades de degradação da matéria orgânica pelos microrganismos. 36 Entretanto, baixos teores de água no solo afetam a difusão de solutos, enquanto solos saturados afetam a difusão de oxigênio.…”

“…Os valores de respiração do solo registrados, durante a execução deste projeto, apresentaram valores similares aos obtidos em experimentos conduzidos no interior de São Paulo na cultura da cana de açúcar após colheita, [22][23][24] e menores que os registrados em áreas florestais na Amazônia. 18,20,21 Observou-se uma relação importante com a umidade do solo.…”

“…19 No Brasil, estudos em ambientes florestais foram realizados especialmente no bioma Amazônico, e taxas de emissão de CO 2 da ordem de 4 a 6 mmol CO 2 m -2 s -1 foram medidas por diversos autores. [20][21][22][23] Nessas áreas foram encontradas relações significativas entre as emissões de CO 2 e a umidade do solo, condicionando a existência de fluxos de carbono maiores para a atmosfera durante a estação chuvosa, indicando que a umidade e a temperatura do solo seriam os principais condicionadores da respiração do solo na área. 24 No estado de São Paulo não existem registros das taxas de emissão em áreas florestais, especialmente naquelas situadas no bioma da Mata Atlântica, e os levantamentos realizados foram exclusivamente em áreas de cultivo de cana de açúcar, sendo observadas variações nas emissões devido à topografia e aos tipos de manejo empregados.…”

Response of CO2 fluxes and productivity to water availability in two contrasting ecosystems in northern Benin (West Africa)

“…Error bars are 95 % confidence intervals and very low for g c and w during the dry periods rather than during the wet one. Moreover, the AR that depends mainly on the growth vegetation (Chambers et al 2004) may be significantly affected by the drier conditions. Indeed, during dry periods (lack of rain, soil, and air drought conditions), the vegetation growth was reduced due mainly to the senescence and desiccation processes leading to the reduced density of the active leaves, but in different proportions according to the ecosystem types (savannah or forest).…”