Influence of drainage status on soil and water chemistry, litter decomposition and soil respiration in central Amazonian forests on sandy soils

Abstract

Central Amazonian rainforest landscape supports a mosaic of tall terra firme rainforest and ecotone campinarana, riparian and campina forests, reflecting topography-induced variations in soil, nutrient and drainage conditions. Spatial and temporal variations in litter decomposition, soil and groundwater chemistry and soil CO 2 respiration were studied in forests on sandy soils, whereas drought sensitivity of poorly-drained valley soils was investigated in an artificial drainage experiment. Slightly changes in litter decomposition or water chemistry were observed as a consequence of artificial drainage. Riparian plots did experience higher litter decomposition rates than campina forest. In response to a permanent lowering of the groundwater level from 0.1 m to 0.3 m depth in the drainage plot, topsoil carbon and nitrogen contents decreased substantially. Soil CO 2 respiration decreased from 3.7±0.6 µmol m -2 s -1 before drainage to 2.5±0.2 and 0.8±0.1 µmol m -2 s -1 eight and 11 months after drainage, respectively. Soil respiration in the control plot remained constant at 3.7±0.6 µmol m -2 s -1 . The above suggests that more frequent droughts may affect topsoil carbon and nitrogen content and soil respiration rates in the riparian ecosystem, and may induce a transition to less diverse campinarana or short-statured campina forest that covers areas with strongly-leached sandy soil.Keywords: Amazon rainforest; Drought experiment; Campina; Soil Nutrients; CO 2 Efflux.Influência da drenagem na química do solo e da água, na decomposição da serapilheira e na respiração do solo em floresta de solo arenoso na Amazônia central RESUMO A floresta Amazônica central possui um mosaico de floresta tropical de terra firme, ecotones de campinarana, florestas ripárias e ecossistema de campina, que reflete a variação induzida pela topografia sobre as condições de solo, nutrientes e drenagem. Foram estudadas em florestas em solo arenoso as variações espacial e temporal da decomposição da liteira, ZANCHI, F. B.; WATERLOO, M. J.; DOLMAN, A. J.; GROENENDIJK, M.; KESSELMEIER, J.; KRUIJT, B.; BOLSON, M. A.; LUIZÃO, F. J.; MANZI, A. O. Influence of drainage status on soil and water chemistry, litter decomposition and soil respiration in central Amazonian forests on sandy soils. Ambi-Agua, Taubaté, v. 6, n. 1, p. 6-29, 2011 . (doi:10.4136/ambi-agua.170) 7 química do solo e da água do solo, e a respiração do solo, uma vez que a sensibilidade à seca estava sendo investigada em solos de vale pobremente drenado com um experimento de drenagem controlada. Pequenas mudanças foram observadas na decomposição da liteira e na química da água do solo devido à drenagem artificial. A floresta ripária experimentou maior taxa de decomposição do que o ecossistema de campina. Em resposta ao permanente rebaixamento do nível do lençol freático de 0.1 m para 0.3 m de profundidade, promovido pelo experimento de drenagem, o carbono e nitrogênio do solo superficial diminuíram substancialmente. A respiração do solo diminuiu de 3.7±0.6 µmol m -2 s -1 antes ...

Does soil moisture overrule temperature dependence of soil respiration in Mediterranean riparian forests?

“…Pacific et al (2008) showed that the soil CO 2 concentrations were significantly higher in the riparian zone as a result of higher soil moisture. In contrast, Zanchi et al (2011) found lower SR in plots after drainage, and suggested that the low C and N content in the topsoil near the river, where most of the soil CO 2 respiration is produced, could partially explain that low SR. The discrepancy of these two studies could be associated with the different drainage regimes as the poorly drained plots imply the anaerobic inhibition of SR.…”

“…Additionally, landscape position and topography not only altered the availability of soil water but also affected the annual range of soil moisture. This was shown in Zanchi et al (2011), studying riparian SR in Amazonia. They indicated that riparian soil is very sensitive to the changes of water-flooding regimes.…”

Understory host plant and insect gall diversity changes across topographic habitats differing in nutrient and water stress in the Brazilian Amazon rainforest

“…This finding suggests that insect galls are favored in stressful environments, since slopes are comparatively the most stressful habitat within Amazonian terra firme forests. Slope habitats have the lowest levels of water and nutrients compared to the other habitats studied (Zanchi et al 2011). A study by Luizão et al (2004) indicated that slope and plateau habitats presentes higher nitrogen levels in their living leaves, litter and soil upper layer than that observed in the valleys, while carbon concentration in the vegetation samples did not vary among these habitats, therefore resulting in a high C:N ratio in valley habitat.…”

“…The water table is at greater depths in the plateaus, and approaches the surface towards the bottom of the valleys (Tomasella et al 2007;Zanchi et al 2011). Likewise, there is an increasing content of sand in the soil from plateau to valleys, with a corresponding decrease in clay content.…”

“…Valleys, on the other hand, exhibit the highest sand content and have a superficial water table with low drainage and nutrient retention, lower plant biomass and trees with lower canopies of 20 to 35 m. In this work, we also considered as "transition" the sloping areas between plateaus and slopes. These areas show intermediate conditions of clay content, soil drainage and plant species composition when compared to the plateaus and the slopes (Luizão et al 2004;Zanchi et al 2011). The steepness of the terrain is approximately 6 and 14 times greater in the slope habitat than in plateaus and valleys, respectively (Table 1).…”