黄土丘陵沟壑区农林草地土壤热量状况及植被生长响应——以燕沟流域为例

利用CoupModel模型模拟了黄土丘陵沟壑区燕沟流域刺槐(Robinia pseudoacacia)林地、辽东栎(Quercus liaotungensis)林地、荒草地、农地等7种土地类型的土壤热量状况,分析了不同植被类型的潜热通量、感热通量、土壤热通量以及植被生长对土壤热量的响应.结果表明,农地潜热通量较小,林地和荒草地潜热通量较大,各地类潜热通量季节变化规律基本一致.潜热通量是黄土丘陵区土壤-植被-大气系统能量的主要支出项,占总净辐射的72.1%～81.4%以上;感热通量变化振幅相对较小,占总净辐射的16.4%～26.4%;土壤热通量仅占总净辐射的1.4%～2.4%,但直接影响土壤温度的变化速度和变化时间.试验地各地类地表温度随季节的变化趋势均呈单峰曲线型.2～7月份0～20cm平均土壤温度随累积土壤热通量的增大而升高,9月到翌年1月份0～20cm平均土壤温度随累积土壤热通量的减小而降低,但累积土壤热通量的变化滞后于土壤温度变化.同一植被类型条件下,阳坡土壤温度年变幅显著高于阴坡.在阴坡,0cm、10cm、20cm深土壤温度年变幅农地＞阴坡荒草地＞阴坡辽东栎林地＞阴坡刺槐林地;在阳坡,阳坡荒草地＞阳坡刺槐林地＞阳坡辽东栎林地.阴坡刺槐林地、阴坡荒草地和农地0～20cm土壤温度达到5℃以上的时间比阳坡刺槐林和阳坡荒草地推迟1周左右,根系开始生长活动的时间也推迟1周左右;而阴坡辽东栎林地则晚于阳坡辽东栎林地5d左右,根系开始生长活动的时间也较阳坡辽东栎林晚5d左右.出叶时间阳坡刺槐林和阳坡荒草地植物比阴坡刺槐林、阴坡荒草地和阳坡辽东栎林的早1周左右,比阴坡辽东栎林早12d左右.

Soil heat and response of vegetation growth in the loess hilly and gully region: a case study of Yangou Catchment

An energy balance was simulated under Robinia pseudoacacia woodlands, Quercus liaotungensis woodlands, grasslands and farmland with CoupModel in the Yangou Catchment of the hilly and gully region of the Loess Plateau. The impact of vegetation on latent heat flux, sensible heat flux and soil heat flux in sample-plots were studied. The results showed that latent heat fluxes in woodlands and grasslands were higher than in farmland, and the majority of energy released was by latent heat flux accounting for 72.1%-81.4% of total net radiation. The changes in latent heat flux in all experimental plots were similar, revealing peak values between July to August and minimum values between November and the following April. Energy released by sensible heat flux accounted for 16.4%-26.4% of net radiation, and sensible heat fluxes peaked between April and May and saw minimums between August and September. Soil heat flux accounted for only 1.4%-2.4% of net radiation, but had a direct effect on the timing and speed of soil temperature changes. The change of soil temperature showed a unimodel curve for all experimental plots. Soil temperature rose from February to July and decreased from August to January. Soil temperature went down gradually with soil depth from February to September and increased with soil depth from October to the following January. The average annual amplitude of soil temperature down to a 20cm depth in north-facing slopes decreased in the following order: farmland, grassland, Q. liaotungensis woodland, R. pseudoacacia woodland. On south-facing slopes, the amplitude in temperature decreased in the order of grassland, R. pseudoacacia woodland and Q. liaotungensis woodland. Vegetation growth was apparently affected by soil temperature. The date of leafing in grassland and R. pseudoacacia woodland on south-facing slopes occurred 1 week earlier than the same treatments in north-facing slopes as well as Q. liaotungensis woodland on the south-facing slope. Leafing in grassland and R. pseudoacacia woodland on south-facing slopes also preceded leaf out in Q. liaotungensis woodland on the north-facing slope by 12 days.