Brando Paulo M, Nepstad Daniel C, Davidson Eric A, Trumbore Susan E, Ray David, Camargo Plínio
Instituto de Pesquisa Ambiental da Amazônia (IPAM), Avenida Rui Barbosa, 136, 68005-080 Santarém, Pará, Brazil.
Philos Trans R Soc Lond B Biol Sci. 2008 May 27;363(1498):1839-48. doi: 10.1098/rstb.2007.0031.
The Amazon Basin experiences severe droughts that may become more common in the future. Little is known of the effects of such droughts on Amazon forest productivity and carbon allocation. We tested the prediction that severe drought decreases litterfall and wood production but potentially has multiple cancelling effects on belowground production within a 7-year partial throughfall exclusion experiment. We simulated an approximately 35-41% reduction in effective rainfall from 2000 through 2004 in a 1ha plot and compared forest response with a similar control plot. Wood production was the most sensitive component of above-ground net primary productivity (ANPP) to drought, declining by 13% the first year and up to 62% thereafter. Litterfall declined only in the third year of drought, with a maximum difference of 23% below the control plot. Soil CO2 efflux and its 14C signature showed no significant treatment response, suggesting similar amounts and sources of belowground production. ANPP was similar between plots in 2000 and declined to a low of 41% below the control plot during the subsequent treatment years, rebounding to only a 10% difference during the first post-treatment year. Live aboveground carbon declined by 32.5Mgha-1 through the effects of drought on ANPP and tree mortality. Results of this unreplicated, long-term, large-scale ecosystem manipulation experiment demonstrate that multi-year severe drought can substantially reduce Amazon forest carbon stocks.
亚马逊盆地经历着严重干旱，且这种干旱在未来可能会变得更加常见。对于此类干旱对亚马逊森林生产力和碳分配的影响，人们知之甚少。在一项为期7年的部分穿透雨排除实验中，我们检验了这样一个预测：严重干旱会减少凋落物产量和木材产量，但可能会对地下生产产生多种抵消作用。我们在一块1公顷的样地中模拟了2000年至2004年有效降雨量约减少35%-41%的情况，并将森林的反应与一块类似的对照样地进行了比较。木材产量是地上净初级生产力（ANPP）中对干旱最敏感的组成部分，第一年下降了13%，此后高达62%。凋落物产量仅在干旱的第三年下降，与对照样地相比最大差值为23%。土壤二氧化碳通量及其14C特征未显示出显著的处理反应，这表明地下生产的数量和来源相似。2000年各块样地的ANPP相似，在随后的处理年份中降至比对照样地低41%的低点，在处理后的第一年反弹至仅相差10%。由于干旱对ANPP和树木死亡率的影响，地上现存碳减少了32.5Mgha-1。这项未重复的、长期的、大规模的生态系统操纵实验结果表明，多年严重干旱会大幅减少亚马逊森林的碳储量。
