作 者 ：卢晓强,丁访军,方升佐*,户田浩人,生原喜久雄,魏鲁明
期 刊 ：生态学报 2010年 30卷 20期 页码：5448~5455
Keywords:karst region, primary forestry, nutrient elements, precipitation,
摘 要 ：降水是森林生态系统的一个主要的养分输入源，观测并分析降水化学对于准确地估算森林生态系统养分循环的养分元素浓度与量显得极为重要。对贵州省茂兰国家自然保护区原始林森林群落2007年9月-2008年8月的降水进行定位观测与分析。结果表明：(1) 在林外雨、林内雨、树干流和溪流水中，除了Na+之外，pH值与大部分的养分元素的浓度表现出明显的季节变化，冬季与早春浓度较高，夏季浓度较低。这与各季节的降雨量不同而导致浓度稀释或者浓缩有关。(2) 大气降雨通过林冠的过程中，养分元素的浓度出现了较大的变化，林内雨与树干流中的浓度基本高于大气降雨；养分元素变化中，浓度差异较大的元素是K+、Mg2+和Ca2+，K＋在林内雨和树干流的浓度分别是大气降雨的14倍和21倍;Mg2+浓度分别为大气降雨的12倍和9倍;Ca2+浓度分别为大气降雨的4倍和3倍,这与大气降雨通过林冠,与树体的养分交换以及树体养分的溶脱有关。(3)通过林内雨，树干流输入样地较多的养分元素是K+和Ca2+，分别是35.8kg?hm-2?a-1和31.5kg?hm-2?a-1；通过溪流水输出的元素中，较多的是Ca2+和Mg2+，分别是-547.4 kg?hm-2?a-1和-144.5 kg?hm-2?a-1；其次是SO2-4，而Na＋＋K＋＋NH+4-N总量不足阳离子总量的1%, Cl－＋NO-3总量不足阴离子总量的1%。这可能与母岩风化是碳酸岩类岩石风化有关。(4)年养分的垂直移动量特征显示，土壤0cm到土壤5cm的养分元素量变化较明显，无机态N量的变化可能跟微生物的氮固定、无机化或者植被的吸收有关。(5)研究地的年间养分元素量收支分别为N 2.9 kg?hm-2?a-1; K 25.2kg?hm-2?a-1; Ca -547.4 kg?hm-2?a-1; Mg -144.5 kg?hm-2?a-1; Na -4.0 kg?hm-2?a-1；Cl 2.5kg?hm-2?a-1和SO2-4-S -5.9kg?hm-2?a-1。在年间养分的输入与输出中，无机态N跟K＋显示正收支，Ca2＋、Mg2＋为负收支，而Na＋、Cl－相对较稳定。
Abstract:Because of precipitation serves as one of major approaches of nutrient input into the forest ecosystem, the accurate measurement of its volume and ion concentration is of prime importance in an evaluation of nutrient biogeochemical cycle. Therefore, the chemistry of precipitation within a year was monitored and analyzed in a primary forest in the Maolan Natural Reserve, a Karst region in Libo, Guizhou Province. The movement patters of nutrient elements through hydrological processes could be understood by monitoring chemistry data of water. The investigation period was from September, 2007 to August, 2008. The results showed: (1) The pH and most concentrations of most nutrient elements in precipitation, throughfall, stemfall and streamflow varied seasonally except for Na+, with maxima in winter or early spring and minima in summer. This may be resulted from the concentration dilutions or inspissations due to the varieties of water discharge. (2) The nutrient elements in throughfall and stemflow were significantly higher than those in the precipitation when rainfall passed canopy. The concentrations of K+, Mg2+, and Ca2+ were altered more than the other nutrient elements. The concentration of K+ in throughfall and stemflow was 14 times and 21 times higher than those in precipitation, respectively. The concentration of Mg2+ in throughfall and stemflow was 12 times and 9 times higher than those in precipitation, respectively. The concentration of Ca2+ in throughfall and stemflow was 4 times and 3 times higher than those in precipitation, respectively. This probably resulted from the exchange of cations and the canopy leaching. (3) Through throughflow and stemflow, the most nutrient elements which was input the sites were K+ and Ca2+ i.e. 35.8 and 31.5 kg hm-2 a-1, respectively. The most nutrient elements output through streamflow were Ca2+ and Mg2+, i.e. 579.5 and 1529 kg hm-2 a-1, respectively, SO2-4-S coming next, Na++K++NH+4-N accounts for less than 1% of the total cations, and Cl-+NO-3-N accounts for less than 1% of the total anions. These general features indicated that the chemical composition of water was largely controlled by carbonate weathering. (4)The characteristics of annual vertical movements of elements indicated the concentrations of nutrient elements in soil water were varied from 0cm to 5cm. The concentration levels of NH+4-N and NO-3-N in the soil water suggested that the transformation might be caused by microbes through nitrogen fixation, nitrification and uptake by vegetation. (5) The nutrient budget (e.g. throughfall+stemflow-streamflow) within one year in the forest was 2.9 for N, 25.2 for K, -547.4 for Ca, -144.5 for Mg, -4.0 for Na, 2.5 for Cl, -5.9kg hm-2 a-1 for SO2-4-S, respectively. Our results showed that annual inputs exceeded outputs for dissolved inorganic N and K+, The watershed had net losses of Ca2+, Mg2+, and was close to steady state for Na+ and Cl- in the forest.
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