易分解有机碳对不同恢复年限森林土壤激发效应的影响

土壤有机碳库作为陆地生态系统最大的碳库,其微小的改变都将引起大气CO_2浓度的急剧改变。易分解有机碳的输入可以通过正/负激发效应加快/减缓土壤有机碳(SOC)的矿化,并最终影响土壤碳平衡。以长汀县不同恢复年限森林(裸地、5年、15年、30年马尾松林以及天然林)土壤为研究对象,通过室内培养向土壤中添加~(13)C标记葡萄糖研究易分解有机碳输入对不同恢复阶段森林土壤激发效应的影响。研究结果表明,易分解有机碳输入引起的土壤激发效应的方向和强度因不同恢复阶段而异。易分解有机碳输入的初期对各恢复阶段森林土壤均产生正的激发效应,然而随着时间的推移,15年、30年马尾松林以及天然林相继出现负的激发效应。从整个培养期(59 d)来看,易分解有机碳的输入促进了裸地与5年生马尾松林土壤有机碳的矿化,有机碳的矿化量分别提高了131%±27%与25%±5%;但是减缓了15年生马尾松林土壤有机碳的矿化,使其矿化量减少了10%±1%;然而,易分解有机碳输入对30年生马尾松林及天然林土壤有机碳的矿化则无明显影响。土壤累积激发碳量与葡萄糖添加前后土壤氮素的改变百分比呈显著正相关关系(R~2=0.44,P0.05),表明易分解有机碳输入诱导的土壤激发效应受土壤氮素可利用性的调控,土壤微生物需要通过分解原有土壤有机碳释放的氮素来满足自身的需求。

Effects of labile organic carbon input on the priming effect along an ecological restoration gradient

The soil organic carbon (SOC) pool is the largest carbon pool in terrestrial ecosystems, and a small change in the pool will result in a great change in atmospheric CO₂ concentration. The input of labile organic carbon will accelerate or mitigate the mineralization of SOC through a positive or negative priming effect and eventually affect soil carbon balance. In the present study, we sampled forest soils at different restoration years from Changting County, Fujian Province, and added ¹³C-labeled glucose to those soils to investigate the impact of labile organic carbon input on the priming effect. The results showed that the direction and magnitude of the priming effect induced by the input of labile organic carbon were dependent on the restoration age. A positive priming effect was observed immediately after the application of labile organic carbon. However, a shift from positive priming effect to negative effect occurred in the 15- and 30-year-old Pinus massoniana forests as well as natural forest with time. Throughout the experiment (59 days), the input of labile organic carbon accelerated the mineralization of SOC in the bare soil and 5-year-old Pinus massoniana forest. The amount of SOC-derived CO₂ emissions increased by about 131% ±27% and 25% ±5%, respectively. However, the input of labile organic carbon declined by about 10% ±1% of SOC mineralization in the 15-year-old Pinus massoniana forest, and it had no significant effects on SOC mineralization in the 30-year-old Pinus massoniana forest and natural forest. The cumulative priming effect was positive correlated with the cumulative percent change in soil available N due to glucose addition during the 59 days of incubation. This indicates that the priming effect induced by the labile organic carbon input is governed by soil N availability, and microbes increased SOC mineralization to meet the N requirement.