Nicholas School of the Environment, Duke University, Durham, North Carolina, 27708, USA.
Department of Biology, Duke University, Durham, North Carolina, 27708, USA.
Ecology. 2018 Oct;99(10):2363-2373. doi: 10.1002/ecy.2478. Epub 2018 Aug 22.
Reductions in acid precipitation across North America and Europe have been linked to substantial declines of soil organic carbon (SOC) stocks in temperate forests, but the mechanisms underlying these declines remain poorly understood. As forests recover from acid precipitation, soil pH and calcium fertility are both expected to increase, and these changes in soil chemistry may drive altered SOC dynamics. Here, we performed a year-long pot experiment on acid-impacted soils to test the independent and interactive effects of increased soil pH and Ca fertility on SOC solubility, microbial activity and sugar maple (Acer saccharum) sapling growth. We found that microbial respiration and SOC solubility was strongly stimulated by increased soil pH, but only in the presence of plants. In planted pots, a soil pH increase of 0.76 units increased soil respiration by 19% in the organic soil horizon and 38% in the mineral soil horizon, whereas in unplanted pots, soil pH had no effect on microbial respiration. While increased soil pH enhanced plant-mediated heterotrophic respiration, it had no effect on plant growth. By contrast, soil Ca enrichment increased the relative growth rate of plants by 22%, but had no impact on microbial respiration. Our results suggest that, in terms of ecosystem carbon balance, losses of SOC due to increasing soil pH may offset potential gains in primary productivity due to enhanced Ca fertility as ecosystems recover from acid precipitation.
北美洲和欧洲的酸沉降减少与温带森林土壤有机碳（SOC）储量的大量减少有关，但这些减少的机制仍知之甚少。随着森林从酸沉降中恢复，土壤 pH 值和钙肥力预计都会增加，而这些土壤化学变化可能会导致 SOC 动态的改变。在这里，我们在受酸影响的土壤上进行了为期一年的盆栽实验，以测试土壤 pH 值和 Ca 肥力增加对 SOC 溶解度、微生物活性和糖枫（Acer saccharum）幼苗生长的独立和交互影响。我们发现，土壤 pH 值的增加强烈刺激了微生物呼吸和 SOC 溶解度，但只有在有植物存在的情况下才会如此。在种植盆中，土壤 pH 值增加 0.76 个单位会使有机土壤层的土壤呼吸增加 19%，使矿物土壤层的土壤呼吸增加 38%，而在未种植盆中，土壤 pH 值对微生物呼吸没有影响。虽然土壤 pH 值的增加增强了植物介导的异养呼吸，但对植物生长没有影响。相比之下，土壤 Ca 富集使植物的相对生长率增加了 22%，但对微生物呼吸没有影响。我们的研究结果表明，就生态系统碳平衡而言，由于土壤 pH 值的增加而导致的 SOC 损失可能会抵消由于 Ca 肥力增强而导致的初级生产力增加对生态系统从酸沉降中恢复的影响。
