College of Land Science and Technology, China Agricultural University, Beijing 100193, China; Key Laboratory of Arable Land Conservation (North China), Ministry of Agriculture and Rural Affairs, Beijing 100193, China; State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi 712100, China.
School of Forestry, Northern Arizona University, Flagstaff, AZ 86011, USA.
Sci Total Environ. 2020 Nov 1;741:140425. doi: 10.1016/j.scitotenv.2020.140425. Epub 2020 Jun 22.
Land surface albedo measures the degree to which the sun's radiation is absorbed or reflected, and thus can be highly influential in global climate trends, local weather phenomena, and biological processes. As an extensive living cover in drylands, biocrusts cover substantial land surface but their potential influences on surface albedo and energy balance are underdocumented, and its temporal dynamic is virtually unknown. We continuously measured the surface albedo, land-surface energy balance, temperature and moisture of moss-biocrust covered soil and bare soil for two years, and measured the surface color and roughness of the two land cover types. Our results showed that the surface albedo of the biocrusts was 43.4% lower than that of the bare soil, due to the increased darkness (43.7%) and roughness (90.4%) together with increased moisture (20.7%) of the biocrust layer. Through time, the albedo of the biocrusts were negatively and linearly related with surface soil temperature or moisture, which resulted in lower albedo in summer and higher albedo in other seasons. As a result of decreased albedo, biocrusts decreased outgoing short-wave radiation by 44.8% in comparison to the bare soil, and consequently they increased net short-wave radiation by 11.4% and net all-wave solar radiation by 22.9% However, the increased energy absorption by the biocrusts did not consistently increase soil temperature; instead, soil temperature increased by up to 9.3 °C under dry conditions but decreased by as much as 11.4 °C under wet conditions, resulting in a net cooling. This indicates that the temperature regimes of the biocrust-covered soil were not determined only by albedo, but also by modification of soil thermal properties by biocrusts. Because biocrusts are highly responsive to land use, it appears that altered albedo and energy balance may be one of the ways in which human activity can impact climate and weather.
陆地表面反照率衡量的是太阳辐射被吸收或反射的程度，因此它在全球气候趋势、局部天气现象和生物过程中具有重要影响。作为干旱地区广泛存在的生物覆盖层，生物结皮覆盖了大量的地表，但它们对地表反照率和能量平衡的潜在影响尚未被充分记录，其时间动态实际上也不为人知。我们连续两年对苔藓生物结皮覆盖的土壤和裸土的地表反照率、地表能量平衡、温度和湿度进行了测量，并对两种土地覆盖类型的地表颜色和粗糙度进行了测量。结果表明，生物结皮的地表反照率比裸土低 43.4%，这是由于生物结皮层的黑暗度（43.7%）和粗糙度（90.4%）增加以及湿度（20.7%）增加所致。随着时间的推移，生物结皮的反照率与地表土壤温度或湿度呈负线性相关，导致夏季反照率较低，其他季节反照率较高。由于反照率降低，生物结皮与裸土相比减少了 44.8%的出射短波辐射，因此增加了 11.4%的净短波辐射和 22.9%的净全波太阳辐射。然而，生物结皮增加的能量吸收并没有持续增加土壤温度；相反，在干燥条件下，土壤温度最高可增加 9.3°C，但在潮湿条件下，土壤温度最多可降低 11.4°C，从而导致净冷却。这表明，生物结皮覆盖土壤的温度状况不仅取决于反照率，还取决于生物结皮对土壤热性质的改变。由于生物结皮对土地利用高度敏感，因此改变的反照率和能量平衡可能是人类活动影响气候和天气的方式之一。
