Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK.
Department of Biological Sciences, Clemson University, Clemson, SC, USA.
Sci Total Environ. 2019 Dec 20;697:133987. doi: 10.1016/j.scitotenv.2019.133987. Epub 2019 Aug 19.
Reducing atmospheric CO is an international priority. One way to assist stabilising and reducing CO is to promote secondary tropical forest regrowth on abandoned agricultural land. However, relationships between above- and belowground carbon stocks with secondary forest age and specific soil nutrients remain unclear. Current global estimates for CO uptake and sequestration in secondary tropical forests focus on aboveground biomass and are parameterised using relatively coarse metrics of soil fertility. Here, we estimate total carbon stocks across a chronosequence of regenerating secondary forest stands (40-120 years old) in Panama, and assess the relationships between both above- and belowground carbon stocks with stand age and specific soil nutrients. We estimated carbon stocks in aboveground biomass, necromass, root biomass, and soil. We found that the two largest carbon pools - aboveground biomass and soil - have distinct relationships with stand age and soil fertility. Aboveground biomass contained ~61-97 Mg C ha (24-39% total carbon stocks) and significantly increased with stand age, but showed no relationship with soil nutrients. Soil carbon stocks contained ~128-206 Mg C ha (52-70% total stocks) and were unrelated to stand age, but were positively related to soil nitrogen. Root biomass carbon stocks tracked patterns exhibited by aboveground biomass. Necromass carbon stocks did not increase with stand age, but stocks were held in larger pieces of deadwood in older stands. Comparing our estimates to published data from younger and older secondary forests in the surrounding landscape, we show that soil carbon recovers within 40 years of forest regeneration, but aboveground biomass carbon stocks continue to increase past 100 years. Above- and belowground carbon stocks appear to be decoupled in secondary tropical forests. Paired measures of above- and belowground carbon stocks are necessary to reduce uncertainty in large-scale models of atmospheric CO uptake and storage by secondary forests.
减少大气中的二氧化碳是国际优先事项。协助稳定和减少二氧化碳的一种方法是促进废弃农业地上的次生热带森林再生。然而，次生林年龄和特定土壤养分与地上和地下碳储量之间的关系尚不清楚。目前，全球对次生热带森林 CO 吸收和固存的估计主要集中在地上生物量上，并使用相对较粗的土壤肥力指标进行参数化。在这里，我们估计了巴拿马再生次生林演替序列（40-120 年）中整个碳储量，并评估了地上和地下碳储量与林龄和特定土壤养分之间的关系。我们估计了地上生物量、枯落物量、根系生物量和土壤中的碳储量。我们发现，两个最大的碳库 - 地上生物量和土壤 - 与林龄和土壤肥力有明显的关系。地上生物量含有约 61-97 Mg C ha（总碳储量的 24-39%），并且随着林龄的增加而显著增加，但与土壤养分无关。土壤碳储量含有约 128-206 Mg C ha（总储量的 52-70%），与林龄无关，但与土壤氮呈正相关。根系生物量碳储量与地上生物量表现出的模式相吻合。枯落物碳储量随林龄的增加而增加，但在较老的林分中，枯落物碳储量以较大的死木碎片形式存在。将我们的估计与周围景观中较年轻和较老的次生林的已发表数据进行比较，我们表明，土壤碳在森林再生后 40 年内得到恢复，但地上生物量碳储量在 100 年后仍继续增加。次生热带森林中的地上和地下碳储量似乎是脱钩的。地上和地下碳储量的配对测量对于减少大气 CO 吸收和储存的大规模模型中的不确定性是必要的。
