海北高寒草甸的季节冻土及在植被生产力形成过程中的作用

海北高寒矮嵩草草甸区植被下的草毡寒冻雏形土属季节性冻土,因温度低,冻土在年内的每个月均可发生.一般在11月中旬可形成稳定的季节冻结层,至翌年3～4月冻土层厚度最大可达230cm.从3月下旬到4月中旬开始,土壤开始消融,至6月下旬到7月上旬冻土全部消失.分析发现,季节冻土在高寒草甸植被生产力形成过程中有着积极的影响作用,主要表现在:1)季节冻土的存在和维持将给高寒植物生长提供良好的土壤水分,对植物初期营养生长发育有利,可弥补春夏之交时降水不足所引起的干旱胁迫影响;2)季节冻土的长时间维持,有利于植物残体和土壤有机质留存于土壤,并随土壤冻结和融化过程发生迁移,可提高土壤肥力;3)较高的土壤水分有利于土壤胡敏酸的形成,可保证植物生长所需的其它有机元素的供给;4)冻土层所形成较高的土壤水分使土体热容量加大,从而调节因气候异常波动引起的土壤温度变化;5)季节冻土的变化对植物地上年生产量形成有一定的影响作用,表现出从10月或11月开始,土壤冻结速率快,对提高植物地上年生产量有利.这也证实,在未来气候变暖的趋势下,土壤有机质将加快分解速度,土壤水分因受温度升高、冻结期缩短,其贮存能力降低;受温度升高的影响,地表蒸发能力加大,若降水仍保持目前的水平,土壤水分将明显减少,将导致高寒草甸植被生产力有下降的可能.

Seasonal Frozen Soil and Its Effect on Vegetation Production in Haibei Alpine Meadow

Annual mean soil temperature at 0 to 160-cm depths is higher than 1~8℃ and annual mean air temperature is about -1.7℃ in Haibei alpine meadow. Mat-Cryic cambisols under vegetation belongs to seasonal frozen soil. Because of low air temperature, it is possible that frozen soil may form in all seasons. A stable layer of frozen soil can form from November. The frozen soil layer reaches the deepest, about 230 cm, in the period from March to April. Surface ground of the frozen soil thaws from March to April. The process of thawing also begins from the bottom of the frozen soil layer, with a lightly thawing rate. Process of thawing can last to the last ten days of June, or the first ten days of July. The seasonal frozen soil plays an active role on vegetation production in the alpine meadow. The role is: 1) The seasonal frozen soil supplies an ample water resource, which compensates the precipitation not enough in the period from end of the spring to initial of the summer, for plant growth, especially, for initial nutrient growth of herbage. 2) A long-term maintenance of the seasonal frozen soil is good for plant survivor and organism remaining in soil, which migrate with soil freezing and melting. So, the seasonal frozen soil plays an important role for increasing fertility of soil. 3) High water content in soil is also good for the formation of humscd, in turn; the humscd offers some other organism for plant growth. 4) High water content in frozen soil increases the thermal capacity of soil, able to regulate the sequent of climate unusually oscillating. 5) Changing rate of the seasonal frozen soil has an important effect on herbage biomass.