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近期，西安交通大学研究首先显示，造林和再造林对土壤碳的长期影响具有明显差异。全球尺度上，造林相对于非森林基线平均使土壤碳储量增加54%，且这种正效应可持续至少100年，说明从退化地、农田或草地向森林转变后，长期凋落物、根系输入和土壤团聚体稳定化可持续推动土壤碳积累。再造林则使土壤碳平均恢复到原始森林水平的约82%，并在前三十年快速接近原始森林状态，估计恢复拐点约为30年；但在更老林分中，相对恢复效应减弱。这并不一定表示土壤碳下降，而更可能意味着早期恢复速度快，随后因碳输入趋缓、分解和微生物呼吸抵消增加，进一步接近原始森林状态变得更慢（图1）。图1 全球造林与再造林样点分布及土壤碳长期变化趋势
显示，无论造林还是再造林，土壤碳储量都是预测土壤微生物生物量变化的最重要变量；在控制气候、地理和土壤环境因子后，这种正相关仍然存在。这说明，土壤碳积累不仅是气候减缓收益，也为土壤微生物提供底物和栖息环境，从而推动“碳储存—地下生命”共同恢复（图2）。
图2 造林与再造林过程中土壤碳储量与微生物生物量的协同变化
不同前期土地利用和气候背景显著改变造林收益。对于造林而言，退化土地上的土壤碳和微生物生物量增幅最大，因为这些土地通常植被稀疏、有机碳输入低、微生物资源敏感性强，森林建立后更容易带来明显改善。相比之下，草地造林只带来边际土壤碳收益，且没有检测到微生物生物量显著变化；树种方面，混交林并未在土壤碳和微生物响应上稳定优于单一树种，说明混交林的地下生态收益具有明显情境依赖性，不能简单认为“混交一定更好”。气候区差异进一步说明，森林种植不应采用“一刀切”策略。造林在寒冷的北方地区土壤碳和微生物响应最弱，可能因为低温限制地下发育，也因为将天然非森林生态系统转为森林并不一定适宜；再造林在热带地区的土壤碳和微生物恢复最弱，反映出原始热带森林复杂地下系统一旦丧失后很难完全重建。干旱区在造林和再造林中都表现出较大地下收益，但研究团队提醒，水分受限地区造林可能带来地下水消耗等权衡。环境机制分析显示，低初始土壤有机碳地区具有更大提升空间，较高土壤pH有利于土壤碳和微生物恢复，而气候、土壤和种植属性通过影响土壤碳变化进一步影响微生物生物量（图3）。
图3 环境因子对造林和再造林土壤碳与微生物响应的影响
全球空间预测进一步揭示了造林和再造林的潜在优先区域。随机森林模型显示，造林在全球尺度上具有明显长期地下收益，尤其是在退化或边际土地上；而再造林在大面积区域也具有较强恢复潜力。北欧和俄罗斯等北方地区造林收益相对有限，但再造林恢复潜力更强，提示在曾经为森林的北方系统中“重新造林”可能比盲目扩张森林更适合。相反，亚马逊、东南亚和热带非洲等热带地区再造林恢复较弱，进一步凸显保护完整热带森林的重要性：与其在破坏后尝试重建复杂地下碳库和微生物系统，不如优先避免原始森林丧失。作者也强调，这些地图适合识别广义空间格局，而局地造林实践还需要综合考虑水资源、土地利用和生物多样性等多重生态权衡，尤其不鼓励在高价值草地、农田或其他生态重要系统中盲目种树（图4）。
图4 全球造林与再造林土壤碳—微生物协同响应空间格局
文献信息：
Meng, Z., Wu, Y., Eisenhauer, N. et al. Afforestation and reforestation support coupled gains in soil life and carbon storage worldwide. Nat Ecol Evol (2026).
扩展阅读
Forest planting is widely promoted as a nature-based climate solution for mitigating anthropogenic carbon (C) emissions. Whether different planting strategies lead to similar trajectories in C storage and how these affect soil microbial growth are poorly understood. Here we compile data on 1,158 paired afforestation/reforestation and reference sites across six continents. We find that afforestation has the potential to support greater soil microbial biomass and larger topsoil C storage across stand development spanning up to a century. Reforestation is associated with substantial recovery of soil C storage and soil microbial biomass, with both approaching original forest levels during the first three decades, but these gains are not sustained in older stands. Soil C and microbial biomass responses are generally coupled across prior land uses, climatic zones and planted tree species, with greater gains on degraded lands. Overall, our work provides evidence that afforestation and reforestation could contribute to soil C storage and support soil microbial growth under global change, offering critical insights for refining nature-based climate solutions.
Forest planting has emerged as an important land-based strategy that is expected to support soil life and carbon (C) sequestration, contributing to achieving a quarter of the emission reductions pledged under the Paris Agreement1,2,3. As the United Nations Decade on Ecosystem Restoration gets underway, ~291 million hectares of planted forests have been established globally; the Bonn Challenge and similar initiatives plan hundreds of millions more hectares and require billions of dollars in investment to deliver far-reaching benefits for the environment and human well-being4,5,6,7. These ambitious initiatives include both afforestation, which establishes forests on previously non-forest land, and reforestation, which reestablishes forests on previously forested land following clearing or disturbance8,9,10. Although both strategies are widely promoted within restoration and climate agendas, the magnitude and persistence of their consequences should not be assumed to be equivalent. The buildup of new soil C may also be closely intertwined with changes in soil microbes, the most abundant and diverse life forms on the planet11. Given that afforestation and reforestation begin from fundamentally different ecological states and legacies, they may differ in their capacity to build soil C stocks and microbial biomass through stand development. Clarifying these differences is essential for delivering predictable outcomes from new forest plantations and for prioritizing practices with the greatest net benefits. Three major uncertainties limit our ability to predict how afforestation and reforestation support soil C sequestration and microbial biomass. First, experiments and observational studies have shown that forest planting can substantially affect soil C storage and microbial properties12,13,14,15. However, existing evidence has rarely been synthesized in a framework that explicitly distinguishes afforestation from reforestation, despite their distinct ecological starting points and developmental trajectories. More specifically, although previous global and regional studies have addressed soil C responses to afforestation16,17 and, in some cases, reforestation-related transitions9,14,15, the inconsistent definition of reforestation has hindered direct comparison among studies and limited a more explicit evaluation of its role in climate change mitigation. Second, although short-term and local responses of soil C storage to forest planting are well documented, we still lack a comprehensive global synthesis of the long-term soil C responses of afforestation and reforestation across environmental gradients13,18,19. Lastly, the biological consequences of these planting strategies remain poorly understood. Soil microbes are increasingly recognized as central to belowground recovery during the restoration of degraded lands20,21,22,23. Yet how afforestation and reforestation influence the soil microbial biomass during the buildup and persistence of soil C storage remains poorly quantified. Resolving these uncertainties is essential for evaluating the long-term effectiveness of forest planting in meeting global climate targets and advancing ecosystem conservation and restoration. Here we compiled a global database of 1,158 paired afforestation/reforestation and reference sites to investigate the responses of soil C storage and microbial biomass to forest planting. The dataset spans six continents and up to a century of stand development while encompassing diverse prior land uses, climate zones and planted tree categories (Fig. 1a). Our synthesis integrated data on both soil C storage and soil microbial biomass-related measures, including microbial biomass indices, fungal and bacterial phospholipid fatty acids (PLFAs) and taxon-specific abundance measures. Specifically, we aim to address four key questions: (1) To what extent do afforestation and reforestation sustain soil C sequestration over stand development extending to a century? (2) How are changes in soil C storage linked to soil microbial biomass across global environmental gradients? (3) How do these responses vary across ecosystem conversion contexts, climatic zones and planted tree categories? (4) Using machine-learning analyses, what broad spatial patterns of predicted soil C and microbial responses emerge at the global scale?
来源：西安交通大学、期刊官网
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