江西官山亚热带森林近地表和土壤温度的海拔梯度变化及其季节动态

Altitudinal variations and seasonal dynamics of near⁃surface and soil temperatures in subtropical forests of Mt.Guanshan,Jiangxi Province,China

温度直减率作为反映温度沿海拔变化程度的参数,是研究山地生态系统众多生态过程的重要指标。目前大多数研究集中于流层或近地表温度,而土壤温度作为影响生物生长发育、生态系统物质循环等过程的重要因子,其垂直变化研究比较缺乏。本研究基于江西官山国家级自然保护区300~1300 m海拔范围内的12个亚热带森林样点2018年9月—2021年8月林下近地表(地上15 cm)和土壤温度(地下8 cm)数据,利用线性回归模型计算近地表和土壤的均温、最高温、最低温直减率和积温递减率,并分析其季节动态。结果表明:研究区近地表年均温、最高温、最低温的直减率分别为0.38、0.31、0.51℃·(100 m)^(-1),三者差异较大,而土壤的三者变化较小,分别为0.40、0.38、0.42℃·(100 m)^(-1);除最低温直减率,近地表和土壤的温度直减率均无显著季节差异。近地表最低温直减率在春、冬季节较大,而土壤最低温直减率在春、秋季节较大;近地表和土壤积温均与海拔呈显著负相关,≥5℃积温递减率分别为163和179℃·d·(100 m)^(-1),且相同海拔的土壤≥5℃积温持续天数均较近地表长15 d左右。近地表和土壤温度沿海拔的变化呈现出不同的规律,与近地表温度相比,土壤较强的缓冲能力使得土壤温度及其直减率的季节差异较小。

Temperature lapse rate(TLR),measured as the degree of temperature change along an altitudinal gra⁃dient,is a key indicator of multiple ecological processes of mountain systems.Although many studies have examined temperature changes of open air or near⁃surface along altitudes,we know little about altitudinal variations of soil temperature,which play an important role in regulating growth and reproduction of organisms,as well as ecosystem nutrient cycling.Based on temperature data of near⁃surface(15 cm above ground)and soil layers(8 cm below ground)from 12 sampling sites of subtropical forest along an altitudinal gradient(300-1300 m)in Jiangxi Guan⁃shan National Nature Reserve from September 2018 to August 2021,we calculated the lapse rates of mean,maxi⁃mum,and minimum temperatures,as well as accumulated temperatures by using simple linear regression for both near⁃surface and soil temperature.The seasonal dynamics of aforementioned variables were also evaluated.The results showed that there were large differences among mean,maximum,and minimum lapse rates for annual near⁃surface temperature,which were 0.38,0.31 and 0.51℃·(100 m)^(-1),respectively.But little variation was docu⁃mented for soil temperature which were 0.40,0.38 and 0.42℃·(100 m)^(-1),respectively.The seasonal variations of temperature lapse rates for near⁃surface and soil layers were minor except for minimum temperature.The lapse rates of minimum temperature were deeper in spring and winter for near⁃surface and in spring and autumn for soil layers.For growing degree days(GDD),the accumulated temperature under both layers were negatively correlated with altitude,and the lapse rates of≥5℃were 163℃·d·(100 m)^(-1) for near⁃surface and 179℃·d·(100 m)^(-1) for soil.The≥5℃GDD in soil were about 15 days longer than that in near⁃surface at the same alti⁃tude.The results showed inconsistent patterns of altitudinal variations between near⁃surface and soil temperature.Soil temperature and its lapse rates had minor seasonal variations compared with the near⁃surface counterparts,which was related to the strong buffering capacity of soil.