杉木人工林生态系统水文学过程的养分特性

根据5a定位观测的数据，对湖南会同24～28a生的杉木人工林生态系统各水文学过程中的养分特性进行了研究。结果表明：林冠降水是杉木人工林生态系统养分输入的重要来源，其中Ca的养分含量最高，P的含量最低。林内穿透水各养分元素的含量明显高于林冠降水中养分的含量。除Ca外，树干茎流中其它养分元素的含量为林冠降水的6倍以上。可见，林内穿透水和树干茎流是杉木林生态系统内养分循环的重要组成部分，有利于提高系统的养分利用率。地表径流中除硝态氮外，各元素的含量与穿透水的含量接近，其中P、Na和K三种元素的含量较低，但未超过林冠降水中养分元素含量。地下径流中N和K的含量较低，而Ca的含量与林冠降水相比没有差异。因而地表径流和地下径流不可避免的造成生态系统的养分损失，但24～28a生杉木林生态系统的调控能力较强，地表径流和地下径流量较小，生态系统的养分损失也相对较小，养分为净积累。不同季节之间水文学过程中养分元素含量存在一定程度的差异。降水形态、雷电和地形等要素影响养分元素含量。硝态氮在冰雹中未检出，而在雨水中的含量是雪水的2倍。铵态氮、K和Mg等元素在雨水中的含量最高。P和Ca以雪水的含量最高，与雨水和冰雹相比不存在数量级差异。雷电明显增加降水中养分的含量，特别是林冠上层的低空放电使降水中N的含量增加3～5倍。由于山谷和山麓的立地条件较好，其穿透水中养分含量比山坡的高，山谷与山麓的大致相等。在采集水样进行养分分析时，应考虑降水时间、降水形态和地形等因子的影响。

Nutrient characteristics in hydrological processes of Chinese fir plantation ecosystem

Based on the data collected over 5 years from January of 1990 to December of 1994 at Huitong Located Research Station of Forest Ecology, the nutrient characteristics of hydrological processes in a Chinese fir plantation ecosystem of 24~28 years old were investigated. The results showed that precipitation was a main source of nutrient input in Chinese fir plantation. The concentration of Ca was the highest and that of P was the lowest in precipitation.The nutrients concentrations in throughfall were conspicuously higher than those in precipitation. Except for Ca, the concentrations of other nutrient elements in stemflow were 6 times higher than those in precipitation. The nutrient transfer in throughfall and stemfall was a critical function of the intrasystem nutrient cycling that could improve nutrient use efficiency. The nutrient concentrations in surface runoff were roughly the same as those in throughfall except for NO 3-N. Compared with other nutrient elements, the concentrations of P, Na and K were lower in surface runoff but did not exceed those in precipitation. In ground runoff, the concentrations of N and K were lower and no difference was found in Ca between ground runoff and precipitation. The differences of total nutrient concentration in hydrological processes over months and years were significant or even extremely significant. Although the surface runoff and ground runoff inevitably resulted in nutrient losses, a net nutrient accumulation in 24~28 year old China fir plantation indicated that the plantation at the stable stage could control nutrient loss. There were three factors, i.e. form of precipitation, lightning and location, that affected nutrient concentration and water quality variation. NO 3-N concentration in rainfall was almost 2 times as much as that in snow. The concentrations of NH 4-N, K and Mg were higher in rainfall than in snow and hailstone. Although the concentrations of P and Ca were higher in snow, no difference was found between the rainfall and hailstone. Lightning remarkably increased nutrient concentrations in precipitation. In particular, when lightning occurred in the lower atmosphere over the watershed, the concentration of N was increased by 3~5 times. Because of better site conditions in the valley and foot of the hill, nutrient concentrations in throughfall were higher than those in the slope, and the nutrient concentrations in the valley and foot of the hill were approximately the same. The factors such as rain time, precipitation form and topography should be considered when the samples are collected for chemical analysis.