Physical, chemical, and biological properties of soil under soybean cultivation and at an adjacent rainforest in Amazonia

Land-use change in the Amazon basin has occurred at an accelerated pace during the last decade, and it is important that the effects induced by these changes on soil properties are better understood. This study investigated the chemical, physical, and biological properties of soil in a field under cultivation of soy and rice, and at an adjacent primary rain forest. Increases in soil bulk density, exchangeable cations and pH were observed in the soy field soil. In the primary forest, soil microbial biomass and basal respiration rates were higher, and the microbial community was metabolically more efficient. The sum of basal respiration across the A, AB and BA horizons on a mass per area basis ranged from 7.31 to 10.05 Mg CO2-C ha-1yr-1, thus yielding estimates for total soil respiration between 9.6 and 15.5 Mg CO2-C ha-1yr-1across sites and seasons. These estimates are in good agreement with literature values for Amazonian ecosystems. The estimates of heterotrophic respiration made in this study help to further constrain the estimates of autotrophic soil respiration and will be useful for monitoring the effects of future land-use in Amazonian ecosystems.

近十年来，亚马孙盆地（Amazon Basin）的土地利用变化呈加速态势，深入解析此类变化对土壤性质的影响机制具有重要学术价值。本研究系统调研了大豆与水稻种植农田，以及毗邻的原生雨林的土壤化学、物理与生物学性质。研究发现，大豆种植农田的土壤容重（soil bulk density）、交换性阳离子（exchangeable cations）与pH值均有所升高；而原生雨林的土壤微生物生物量（soil microbial biomass）与基础呼吸速率（basal respiration rates）更高，且微生物群落的代谢效率更优。以单位面积质量为基准，A、AB与BA土壤发生层的基础呼吸总量介于7.31至10.05 Mg CO₂-C ha⁻¹yr⁻¹之间，由此估算得到的不同样地与季节条件下总土壤呼吸量介于9.6至15.5 Mg CO₂-C ha⁻¹yr⁻¹之间。该估算结果与亚马孙生态系统（Amazonian ecosystems）的已有文献报道值吻合度较高。本研究得到的异养呼吸（heterotrophic respiration）估算结果，有助于进一步限定自养土壤呼吸（autotrophic soil respiration）的估算范围，同时可为监测亚马孙生态系统未来土地利用变化的影响提供有力支撑。