杉木人工林的养分归还动态

４２年生杉木人工林的年凋落量为３０８３．９ｋｇ／ｈｍ２，在一年中的５月和１１月出现两次高峰．凋落物中主要营养元素的年归还量为７２．１３８ｋｇ／ｈｍ２，其归还量大小顺序为Ｃａ＞Ｎ＞Ｍｇ＞Ｋ＞Ｐ．降水在杉木人工林中引起的养分淋溶也是养分归还的一个重要方面，五种营养元素的年总淋溶量为７１．２８９ｋｇ／ｈｍ２，在２月和５月亦出现两次高峰，淋溶量大小顺序为Ｋ＞Ｃａ＞Ｍｇ，而Ｎ和Ｐ出现负值，表明两者被林冠层直接吸收．

Dynamics of Nutrient Return in Chinese Fir Plantation

The annual litterfall in a 42-year-old Chinese fir plantation was 3083.9kg/hm2. The monthly patments in litterfall decreased in the order: calcium>nitrogen>magnesium>potassium>phosphorus, with a total content of 72. 138kg/ (hm2· a). The leaching of nutrients from standing trees was also an improtant · a) to the forest floor, exhibiting two peaks( in February and May) in monthly nutrient return. The relative extent to which precipitation leached nutrients decreased in the order:potassium>calcium>magnesium.However, the leached content of nitrogen and phosphorus were negative, which suggested that both of the nutrient elements were absorbed directly by tree crowns during precipitation.