Turbulent Heat Exchange and Partitioning and Its Environmental Controls between the Atmosphere and an Alpine Potentilla Fruticosa Shrublands over the Qinghai- Tibetan Plateau

doi:10.3969/j.issn.1000-6362.2020.02.002

Abstract

Abstract: The turbulent heat flux plays important role in micro-climate environment and vegetation phenology but its temporal patterns and partitioning characteristics and associated environmental controls remain unclear in alpine shrublands, which is one of the most important vegetation types on the Qinghai-Tibetan Plateau. The continuous turbulent heat flux and routine environmental variables measured by the eddy covariance techniques were analyzed to quantify the exchange and partitioning of sensible heat flux and latent heat flux over an alpine Potentilla fruticosa shrublands on the northeastern Qinghai-Tibetan Plateau. The results showed that (1) the averaged diurnal variations of turbulent heat exchange both exhibited unimodal patterns, peaking at about 13：30 over the whole year-round period. The diurnal heat flux was dominated by sensible heat flux during non-growth season (November to next April) and the beginning and end of growth season (May and October), while by latent heat flux in mid-growth season from June to September; (2) The daily sensible heat flux exhibited a bimodal seasonal pattern, with the largest peak and the second peak appearing in mid-April and beginning October, respectively. The daily latent heat flux presented a unimodal seasonal pattern with a maximum in end July; (3) The diurnal and daily variations of turbulent heat flux were both mainly controlled by solar shortwave radiation; (4) Bowen ratio showed a U-shape seasonal change, while decoupling coefficient, evaporation ratio exhibited a bell-shape seasonal variation. These partitioning indices were controlled by soil temperature during non-growth season and enhanced vegetation index in growth season, respectively. These results revealed that the turbulent heat exchange was determined by solar radiation while the partitioning between sensible heat flux and latent heat flux was regulated by underlying surface temperature and plant coverage in the alpine shrublands.

Key words: Latent heat flux, Sensible heat flux, Eddy covariance technique, Bowen ratio, Decoupling coefficient

ZHANG Fa-wei, HAN Yun, LI Hong-qin, LI Ying-nian, CAO Guang-min, ZHOU Hua-kun. Turbulent Heat Exchange and Partitioning and Its Environmental Controls between the Atmosphere and an Alpine Potentilla Fruticosa Shrublands over the Qinghai- Tibetan Plateau[J]. Chinese Journal of Agrometeorology, 2020, 41(02): 76-85.

References

[1] 冯松,汤懋苍,王冬梅.青藏高原是我国气候变化启动区的新证据[J].科学通报,1998,43(6):633-636. Feng S,Tang M C,Wang D M.New evidence of Tibetan Plateau is the start area of climate change in China[J].Chinese Science Bulletin,1998,43(6):633-636.(in Chinese) [2] Zheng D,Zhang Q S,Wu S H.Mountain geoecology and sustainable development of the Tibetan Plateau[M].Dordercht, the Netherlands: Kluwer Academic,2000. [3] Li H Q,Zhu J B,Zhang F W,et al.Growth stage-dependant variability in water vapor and CO2 exchanges over a humid alpine shrubland on the northeastern Qinghai-Tibetan Plateau [J].Agricultural and Forest Meteorology,2019,268:55-62. [4] Li H Q,Zhang F W,Li Y N,et al.Seasonal and interannual variations of ecosystem photosynthetic features in an alpine dwarf shrubland on the Qinghai-Tibetan Plateau,China[J]. Photosynthetica,2014,52(3):321-331. [5] Li H Q,Zhang F W,Li Y N,et al.Seasonal and inter-annual variations in CO2 fluxes over 10 years in an alpine shrubland on the Qinghai-Tibetan Plateau,China[J].Agricultural and Forest Meteorology,2016,228-229:95-103. [6] Li H Q,Zhang F W,Wang W Y,et al.The strongest EI Ni?o event stimulated ecosystem respiration,not evapotranspiration, over a humid alpine meadow on the Qinghai-Tibetan Plateau [J].Ecological Indicators,2018, 91:562-569. [7] Li Y N,Sun X M,Zhao X Q,et al.Seasonal variations and mechanism for environmental control of NEE of CO2 concerning the Potentilla fruticosa in alpine shrub meadow of Qinghai-Tibet Plateau[J].Science in China Series D-Earth Sciences,2006,49(Supply 2):163-173. [8] 葛怡情,闫玉龙,梁艳,等.模拟降水氮沉降对藏北高寒草甸土壤呼吸的影响[J].中国农业气象,2019,40(4):214-221. Ge Y Q,Yan Y L,Liang Y,et al.The effects of nitrogen deposition on soil respiration in an alpine meadow in northern Tibet[J].Chinese Journal of Agrometeorology,2019,40(4):214- 221.(in Chinese) [9] Chapin F S,Matson P A,Mooney H A.Principles of terrestrial ecosystem ecology[M].Seconded,New York,USA:Springer- Verlag,2011:142-145. [10] Zeng Z Z,Peng L Q,Piao S L.Response of terrestrial evapotranspiration to Earth's greening[J].Current Opinion in Environmental Sustainability,2018,33:9-25. [11] Zeng Z Z,Piao S L,Li L Z X,et al.Climate mitigation from vegetation biophysical feedbacks during the past three decades[J].Nature Climate Change,2017,7:432-436. [12] Shen M G,Piao S L,Jeong S,et al.Evaporative cooling over the Tibetan Plateau induced by vegetation growth[J]. Proceedings of the National Academy of Sciences of the United States of America,2015,112(30):9299-9304. [13] 秦孟晟,郝璐,郑箐舟,等.秦淮河流域土地利用/覆被变化对蒸散量变化的贡献[J].中国农业气象,2019,40(5):269-283. Qin M S,Hao L,Zheng Q Z,et al.Contributions of land use/cover change to the change of evapotranspiration in Qinhuai River Basin[J].Chinese Journal of Agrometeorology,2019,40(5):269-283.(in Chinese) [14] Hu Z M,Yu G R,Fu Y L,et al.Effects of vegetation control on ecosystem water use efficiency within and among four grassland ecosystems in China[J].Global Change Biology, 2008,14(7):1609-1619. [15] 张法伟,王军邦,林丽,等.高寒草甸非生长季土壤表层水汽传输阻抗的变化特征和水热驱动[J].中国农业气象,2017, 38(2):96-103. Zhang F W,Wang J B,Lin L,et al.Temporal variations of soil surface resistance to vapor transfer and its quantitative relationship between soil temperature and soil moisture during non-growing season on an alpine meadow[J].Chinese Journal of Agrometeorology,2017,38(2):96-103.(in Chinese) [16] Gu S,Tang Y H,Cui X Y,et al.Energy exchange between the atmosphere and a meadow ecosystem on the Qinghai- Tibetan Plateau[J].Agricultural and Forest Meteorology, 2005,129(3):175-185. [17] Zhang F W,Li H Q,Li Y N,et al.Surface energy partitioning in alpine swamp meadow in the Qinghai Tibetan Plateau[J]. Pratacultural Science,2008,25(4):14-23. [18] McFadden J P,Eugster W,Chapin F S.A regional study of the controls on water vapor and CO2 exchange in arctic tundra[J].Ecology,2003,84(10):2762-2776. [19] Wilson K B,Baldocchi D D,Aubinet M,et al.Energy partitioning between latent and sensible heat flux during the warm season at FLUXNET sites[J].Water Resources Research, 2002,38(12):1294. [20] Zhu G F,Lu L,Su Y H,et al.Energy flux partitioning and evapotranspiration in a sub-alpine spruce forest ecosystem [J].Hydrological Processes,2014,28(19):5093-5104. [21] Zhang F W,Li H Q,Wang W Y,et al.Net radiation rather than moisture supply governs the seasonal variations of evapotranspiration over an alpine meadow on the northeastern Qinghai-Tibetan Plateau[J].Ecohydrology, 2018, 11(2):e1925. [22] Ma N,Zhang Y S,Guo Y H,et al.Environmental and biophysical controls on the evapotranspiration over the highest alpine steppe[J].Journal of Hydrology,2015,529:980- 992. [23] Gu S,Tang Y H,Cui X Y,et al.Characterizing evapotranspiration over a meadow ecosystem on the Qinghai-Tibetan Plateau[J].Journal of Geophysical Research-Atmospheres, 2008,113(D8). [24] Teuling A J,Seneviratne S I,Stockli R,et al.Contrasting response of European forest and grassland energy exchange to heatwaves[J].Nature Geosciences,2010,3(10):722-727. [25] Baldocchi D D.Assessing the eddy covariance technique for evaluating carbon dioxide exchange rates of ecosystems:past, present and future[J].Global Change Biology,2003,9(4): 479-492. [26] 原文文,张劲松,孟平,等.开路与闭路涡度相关系统对森林生态系统甲烷通量观测的比较[J].中国农业气象,2019, 40(11):669-677. Yuan W W,Zhang J S,Meng P,et al.Comparison of CH4 flux measurement by open- and close-path eddy covariance system[J].Chinese Journal of Agrometeorology,2019,40(11): 669-677.(in Chinese) [27] Wilson K,Goldstein A,Falge E,et al.Energy balance closure at FLUXNET sites[J].Agricultural and Forest Meteorology, 2002,113(1-4):223-243. [28] Jarvis P G,Mcnaughton K G.Stomatal control of transpiration:scaling up from leaf to region[J].Advances in Ecological Research,1986,15:1-49. [29] Baldocchi D D,Vogel C A,Hall B.Seasonal variation of energy and water vapor exchange rates above and below a boreal jack pine forest canopy[J].Journal of Geophysical Research-Atmospheres,1997,102(D24):28939-28951. [30] Elith J,Leathwick J R,Hastie T.A working guide to boosted regression trees[J].Journal of Animal Ecology,2008,77: 802-813. [31] R Development Core Team.R:a language and environment for statistical computing[DB/CD].Vienna:R Foundation for Statistical Computing,2006.