The Research Of The Characteristic And Mechanism Of Soil Temperature Change In China

Climate warming is an indisputable fact,the effect of climate change is a multi-scale,all-round,multi-level,both positive and negative effects.Recently,more and more people’s concern focus on climate change.Researches showed that global average of the daily mean air temperature has increased 0.76 °C during the nearly 150 years,Global warming influences a series of ecological processes and ecosystems’ stability.Although comprehensive studies have been done to investigate responses of various ecosystem processes to rising air temperatures,less is known about changes in soil temperatures and their impact on below-ground processes,particularly in deep layers.Using soil temperature meteorological data of China,this study firstly investigates the process of soil temperature change,based on Ecological Research Station for Grassland Farming,Changling,CAS,this paper focus on the effect of degraded grassland on soil warming in the temperate grassland region.We determined,apparently for the first time,that soil surface temperature increased by 0.38°C/10 a,31% more than air temperature,as potentially leading to more carbon release to the atmosphere than predicted.Annual mean surface temperature increased by 2.07–4.04°C and 0.66–2.21°C in northern and southern China,respectively,with the greatest in winter.Warming occurred as deep as 3.20 m.The soil temperature rise was predicted to have increased soil respiration by 8%,reinforcing climate warming and extending the potential growing season by 12 d across China.However,use of air temperature to estimate soil temperature changes would underestimate those impacts.In conclusion,these results highlighted the importance of soil warming and of using soil temperature to assess and predict soil processes.The authors found that the positive trends with time in the daily maximum surface soil temperature(maxST)and daily minimum surface soil temperature(minST)were detected at rates of 0.031°C/yr and 0.055°C/yr during the recent 50 years respectively.The diurnal temperature range of soil(SDTR)decreased at almost stations as the average rate of-0.025°C/yr because of the asymmetric increasing trends betweenmaxST andminST.The change ofmaxST andminST both had a clear spatial pattern,with more increases from south to north,and from east to west region.Solar duration(SD)and precipitation(p)has been proven to be the key cause of change in SDTR.To some extent,the different between soil and air temperature(DT),can reflect the change of sensible heat flux,also can provide the theoretical foundation for crop cultivation and management.At national level,the average value of 50 years DT was 2.05°C(soil temperature more than air temperature),the trends of DT change was declined by 0.006°C/yr over the whole period,mainly due to the change of winter.Past 30 years,the annual soil temperature in each layers fluctuated within 10.3-10.6°C in the temperate grassland region in China,with regular seasonal changes.The soil temperature in autumn and winter was increased with the soil layer deeper.On the contrary,the soil temperature spring and summer was decreased with soil layer deeper.And the range of change was maximum in summer and minimum in spring and autumn.In this paper,a couple of logarithmic function model is established in this paper to describe the vertical distribution characteristics of soil temperature in each month.The vertical distribution characteristics correspond to the curve of y=b+a(1-e-cx)in spring and summer,whereas y=b+a(1-e-c(d-x))in autumn and winter months.Then summer and winter show the better fitting.In the first half of the 30 years(1982-1996),the vertical distribution characteristics correspond to the curve of y=-14.7+15.54(1-e-0.1211x)in summer,whereas y=-14.7+15.54(1-e-0.1211(20-x))in winter.The two curves are symmetric about y=10,indicating that the annual soil temperature is 10°C during the first 15 years.In the last half of the 30 years(1997-2011),the vertical distribution characteristics correspond to the curve of y=-14.5+15.36(1-e-0.1121x)in summer,whereas y=-14.5+15.36(1-e-0.1121(22-x))in winter.The two curves are symmetric about y=11,indicating that the annual soil temperature is 11°C during the last 15 years.Grassland vegetation can intercept the solar radiation,the more serious the grassland degradation,the less interception.The time point of view,the percentages of illuminance intercepted by vegetation are ordered,17:00 pm>13:00 pm>9:00 am,at 13:00 pm for example,un-degraded grassland,slightly degraded grassland,heavily degraded grassland intercepted 88%,62%,29% illuminance respectively.Vegetation light interception is divided into physical barrier part and activities consumption part,the proportion of physical barrier part is largest in un-degraded grassland,at 9:00 am for example,the vegetation intercepted 80% illuminance from solar radiation,including 66% loss from physical barrier and 14% loss activities consumption,the remaining 20% illuminance were accepted by surface soil.The interception function of vegetation to light directly reduce the grassland soil temperature,the decrease were greater in un-degraded grassland,the surface soil temperature was lower about 10°C than bare soil at 13:00 pm,followed by that in slightly degraded grassland,and was least in heavily degraded grassland,but the surface soil temperature was still lower 2-4°C than bare soil.Grassland degradation could lead to the surface soil warming,this will break the balance of energy conduction to soil and heat exchange with air,change the air-plant-soil energy distribution in grassland.