念青唐古拉山北麓草甸海拔分布上限土壤温湿度的季节变化

本研究基于西藏念青唐古拉山北麓高山嵩草草甸海拔分布上限(5125 m)地下10 cm和30 cm土壤温度和水分连续3年(2008-2010年)的监测数据,分析了草甸海拔分布上限土壤温度和未冻水含量的季节动态特征.结果表明:1)土壤在4月中下旬解冻,10月中下旬冻结;6-8月份土壤温度日振幅最大,10 cm和30 cm分别为3.8℃和1.4℃;2)土壤未冻水含量回升(下降)在解冻(冻结)开始后,5-10月份未冻水含量较高,其中10 cm和30 cm分别为2％～6％和15％～20％;3)基于10 cm土壤温度推算的本地区高山嵩草草甸海拔分布上限的生长季在6月初至8月末或9月初,持续时间为80-87天,生长季平均土壤温度和含水量分别为6.78±0.73℃和4.14±0.91％,生长季期间日最低温度集中在3～7℃之间(占90％以上天数);4)与较低海拔处(4980m)相比,高山嵩草草甸海拔分布上限处10 cm土壤温度和未冻水含量均明显偏低,生长季8月份出现日最低温＜5℃的天数也明显增加.

Seasonal Variations of Soil Temperature and Moisture at the Upper Limit of Alpine Meadow in North-facing Slope of the Nianqingtanggula Mountains

Based on the three-year observations in a plot at the upper limit of the alpine Kobresia meadow(5125 m a.s.l.) on the Nianqingtanggula Mountains in the southern part of Namco Basin in Tibet,we analyzed the seasonal variations of soil temperature and moisture at soil depths of 10 and 30 cm.The results were obtained as follows.1) The soil thawed in late April and froze in late October.The daily amplitude of soil temperature from June to August,which was 3.8 oC at 10 cm and 1.4 oC at 30 cm on average,reflected the highest values throughout the year.2) The unfrozen soil water content increased(declined) when the soil began to thaw(freeze).And the soil moisture was relatively high from May to October,which was 2%-6% at 10 cm and 15%-20% at 30 cm.3) Based on the soil temperature measurements at 10 cm depth,the growing season length for vegetation at the upper limit of the alpine Kobresia meadow was calculated to last 80-87 days,which began in early June and ended in late August or early September.And the average soil temperature and moisture were 6.78±0.73 oC and 4.14±0.91%,respectively.The lowest daily temperature during the growing season was mainly observed between 3 oC and 7 oC.4) Compared with the soil temperature and moisture at the lower altitude of 4980 m a.s.l.,those at 5125 m were significantly lower.Also,the number of days of daily minimum temperature < 5 oC in August at the higher altitude was far more than that at the lower.