University Program in Ecology, Duke University, Campus Box 90338, Durham, North Carolina 27708, USA.
Ecol Appl. 2012 Jan;22(1):76-86. doi: 10.1890/10-2210.1.
Afforestation, the conversion of unforested lands to forests, is a tool for sequestering anthropogenic carbon dioxide into plant biomass. However, in addition to altering biomass, afforestation can have substantial effects on soil organic carbon (SOC) pools, some of which have much longer turnover times than plant biomass. An increasing body of evidence suggests that the effect of afforestation on SOC may depend on mean annual precipitation (MAP). The goal of this study was to test how labile and bulk pools of SOC and total soil nitrogen (TN) change with afforestation across a rainfall gradient of 600-1500 mm in the Rio de la Plata grasslands of Argentina and Uruguay. The sites were all former grasslands planted with Eucalyptus spp. Overall, we found that afforestation increased (up to 1012 kg C x ha(-1) x yr(-1)) or decreased (as much as 1294 kg C x ha(-1) x yr(-1)) SOC pools in this region and that these changes were significantly related to MAP. Drier sites gained, and wetter sites lost, SOC and TN (r2 = 0.59, P = 0.003; and r2 = 0.57, P = 0.004, respectively). Labile C and N in microbial biomass and extractable soil pools followed similar patterns to bulk SOC and TN. Interestingly, drier sites gained more SOC and TN as plantations aged, while losses reversed as plantations aged in wet sites, suggesting that plantation age in addition to precipitation is a critical driver of changes in soil organic matter with afforestation. This new evidence implies that longer intervals between harvests for plantations could improve SOC storage, ameliorating the negative trends found in humid sites. Our results suggest that the value of afforestation as a carbon sequestration tool should be considered in the context of precipitation and age of the forest stand.
造林，即将无林地转化为森林，是将人为产生的二氧化碳封存到植物生物量中的一种手段。然而，造林除了改变生物量外，还会对土壤有机碳（SOC）储量产生重大影响，其中一些的周转时间比植物生物量长得多。越来越多的证据表明，造林对 SOC 的影响可能取决于年平均降水量（MAP）。本研究的目的是检验在阿根廷和乌拉圭的拉普拉塔草原的降水梯度为 600-1500mm 的范围内，造林如何改变 SOC 的易变和总量库以及总土壤氮（TN）。这些地点均为曾经的草地，现种植桉树属植物。总体而言，我们发现造林在该地区增加（高达 1012kg C x ha(-1) x yr(-1)）或减少（多达 1294kg C x ha(-1) x yr(-1)）SOC 储量，这些变化与 MAP 显著相关。较干燥的地点 SOC 和 TN 增加（r2 = 0.59，P = 0.003；r2 = 0.57，P = 0.004），较潮湿的地点 SOC 和 TN 减少。微生物生物量和可提取土壤库中的易变 C 和 N 遵循与 SOC 和 TN 类似的模式。有趣的是，较干燥的地点随着人工林的老化，SOC 和 TN 的增加量更大，而在较潮湿的地点，随着人工林的老化，损失量出现反转，这表明除降水外，人工林的年龄也是造林过程中土壤有机质变化的关键驱动因素。这一新证据表明，人工林的收获间隔时间更长可能会提高 SOC 储存，从而改善在潮湿地点发现的负面趋势。我们的研究结果表明，在考虑降水和森林林龄的情况下，造林作为碳封存工具的价值应该得到重视。
