北京西山地区油松林水文过程中营养元素迁移特征

对北京西山地区31a油松林降水化学进行定位监测与分析.结果表明：（1）大气降水流经油松林过程中,其营养元素（除Na^＋外）的浓度出现梯度变化：树干茎流高于穿透雨高于大气降水,并且有明显的月际变化,表明从林冠、树干淋洗大量的营养元素,林冠和树干中养分元素迁移是森林生态系统养分循环重要的组成部分.（2）营养元素变化中,浓度差异变化较大的元素是NO3^--N和K^＋,NO3^--N在穿透雨和树干茎流的浓度分别是大气降水的4.4倍、9.9倍,它们中的K^＋浓度分别为大气降水的4.1倍和8.1倍.（3）降水经过油松林,养分淋溶总量为54.12kg hm^-2,淋溶量较多的元素是Ca和K,淋溶强度最大的元素是K^＋.（4）北京西山地区大气降水输入林地的养分66.38kg hm^-2,较多的元素是Ca、N.降水经过油松林输入林地养分总量为120.50kg hm^-2,Ca元素最高,为61.22kg hm^-2,其次是N元素（NH4^＋-N＋N3^--N）,为31.34kg hm^-2,K元素为16.49kg hm^-2,Mg元素为8.11kg hm^-2,Na元素最少,为3.34kg hm^-2.

Transfer characteristics of nutrient elements through hydrological process of Pinus tabulaeformis stad in Beijing Xishan area

Forest precipitation chemistry is a key issue for forest hydrology and forest ecology.Chemical content in precipitation changed significantly when different kinds of external chemical materials were added,removed,translocated and transformed to or in the forest ecosystem along with precipitation.The chemistry of precipitation was monitored and analyzed at a 31a Pinus tabulaeformis forest in Beijing Xishan area.Movement patterns of nutrient elements in hydrological processes could be uncovered by studying the monitored data.Moreover,the information is useful in diagnosing the function of ecosystem and evaluating the impact of environment on the ecosystem.Samples of rainfall,throughfall and stemflow were collected on the site.In the lab,Ca~(2+) and Mg~(2+)were analyzed by flame atomic absorption and K~+and Na~+ by flame emission.NH~+_4-N was analyzed by indophenol blue colorimetry,and NO~-_3-N was analyzed by phenoldisulfonic acid colorimetry.The results showed:(1) The concentration gradient of nutrient elements clearly changed except for Na~+: The nutrients in stemflow were significantly higher than those of the throughfall and rainfall as the precipitation pass through the P.tabulaeformis forest.The monthly patterns were distinctly different.It is indicated that a large amount of nutrients were leached from canopy,which was a critical function of intraecosystem nutrient cycling to improve the efficiency of nutrient use.(2) the concentrations of NO~-_3-N and K~+were changed greater than that of other nutrient elements.The concentrations of NO~-_3-N in throughfall and stemflow were 4.4 times and 9.9 times higher than those in rainfall,respectively.The concentrations of K~+in throughfall and stemflow were 4.1 times and 8.1 times higher than those in rainfall,respectively.(3)The leaching of nutrient elements from stand was an important aspect of nutrient return in the P.tabulaeformis forest,which returned a total nutrient of 54.1 kg hm~(-2),with Ca~(2+) and K~+ being much greater than other elements.In addition,K~+ was the greatest in leaching intensity.(4)Nutrient input through precipitation was a main source in Beijing Xishan area and nutrient contents of 66.4 kg hm~(-2) were added,of which Ca~(2+) and N were much more than other nutrient elements.When precipitation passed through the P.tabulaeformis forest, there were 121 kg hm~(-2) nutrient added to the forest floor.Ca~(2+) recorded the greatest nutrient increase,with 61.2 kg hm~(-2),followed by N(NH~+_4-N & NO~-_3-N), K~+ and Mg~(2+),with 31.3,16.5,and 8.11 kg hm~(-2),respectively and the least was Na~+,3.34 kg hm~(-2).