Phillips Claire L, Wang Ruying, Mattox Clint, Trammell Tara L E, Young Joseph, Kowalewski Alec
USDA-Agricultural Research Service, Northwest Sustainable Agroecosystems Research Unit, P.O. Box 64621, Pullman, WA 99164, United States of America.
Department of Horticulture, Oregon State University, Corvallis, OR 97331, United States of America.
Sci Total Environ. 2023 Feb 1;858(Pt 3):159974. doi: 10.1016/j.scitotenv.2022.159974. Epub 2022 Nov 5.
Managed turfgrass is a common component of urban landscapes that is expanding under current land use trends. Previous studies have reported high rates of soil carbon sequestration in turfgrass, but no systematic review has summarized these rates nor evaluated how they change as turfgrass ages. Here we conducted a meta-analysis of soil carbon sequestration rates from 63 studies globally, comprised mostly of C3 grass species in the U.S., including 24 chronosequence studies that evaluated carbon changes over 75 years or longer. We showed that turfgrass established within the last ten years had a positive mean soil C sequestration rate of 5.3 Mg CO ha yr (95% CI = 3.7-6.2), which is higher than rates reported for several soil conservation practices. Areas converted to turfgrass from forests were an exception, sometimes lost soil carbon, and had a cross-study mean sequestration rate that did not differ from 0. In some locations, soil C accumulated linearly with turfgrass age over several decades, but the major trend was for soil C accumulation rates to decline through time, reaching a cross-study mean sequestration rate that was not different from 0 at 50 years. We show that fitting soil C timeseries with a mechanistically derived function rather than purely empirical functions did not alter these conclusions, nor did employing equivalent soil mass versus fixed-depth carbon stock accounting. We conducted a partial greenhouse gas budget that estimated emissions from mowing, N-fertilizer production, and soil NO emissions. When N fertilizer was applied, average maintenance emissions offset 32% of C sequestration in recently established turfgrass. Potential emission removals by turfgrass can be maximized with reduced-input management. Management decisions that avoid losing accrued soil C-both when turfgrass is first established and when it is eventually replaced with other land-uses-will also help maximize turfgrass C sequestration potential.
人工管理的草坪草是城市景观的常见组成部分，且在当前土地利用趋势下不断扩展。以往研究报道了草坪草土壤碳固存率较高，但尚无系统综述总结这些速率，也未评估其随草坪草年龄的变化情况。在此，我们对全球63项研究的土壤碳固存率进行了荟萃分析，这些研究大多涉及美国的C3草种，其中包括24项年代序列研究，评估了75年或更长时间内的碳变化。我们发现，过去十年内建立的草坪草土壤碳平均固存率为5.3 Mg CO₂ ha⁻¹ yr⁻¹（95%置信区间 = 3.7 - 6.2），高于多项土壤保护措施报告的速率。从森林转变为草坪草的区域是个例外，有时会损失土壤碳，且跨研究平均固存率与0无差异。在某些地点，土壤碳在几十年内随草坪草年龄呈线性积累，但主要趋势是土壤碳积累速率随时间下降，在50年时达到与0无差异的跨研究平均固存率。我们表明，用机械推导函数而非纯经验函数拟合土壤碳时间序列不会改变这些结论，采用等效土壤质量与固定深度碳储量核算方法也不会改变。我们进行了部分温室气体预算，估算了修剪、氮肥生产和土壤一氧化氮排放的排放量。施用氮肥时，平均维护排放量抵消了新建立草坪草碳固存的32%。通过减少投入管理可使草坪草的潜在排放清除最大化。避免在草坪草刚建立时以及最终被其他土地利用方式取代时损失累积土壤碳的管理决策，也将有助于最大化草坪草的碳固存潜力。
