武夷山常绿阔叶林生态系统降水分配与离子输入特征

Reallocation and Chemical Characteristics of Atmospheric Precipitation in A Mid-subtropical Evergreen Broad-leaved Forest in Wuyi Mountains, Fujian Province, China

大气降水是森林生态系统重要的水源和养分的主要来源之一。于2014年11月-2015年11月对武夷山中亚热带常绿阔叶林生态系统林外雨、林内雨和树干流定位观测,分析了各类降水中的养分离子(NO3--N,SO42--S,Cl-和Ca2+、Mg2+、K+、Na+)浓度动态变化规律及养分离子输入量,以期为进一步研究常绿阔叶林生态系统的水量平衡及养分循环过程提供基础数据。结果表明:研究期间大气降水量(林外雨)为2 623.7 mm,树干流量仅占大气降水量的4.5%,9.8%的大气降水被冠层截留;林内雨、树干流与林外雨量的动态变化规律相似,林内雨、树干流量与林外雨量呈极显著正线性相关关系(P<0.001)。各类降水年加权平均pH值表现为林外雨>树干流和林内雨。各类降水在降水量较小的1-2月,各阴阳离子的浓度普遍较高,在降水量较大的3-8月,阴阳离子浓度普遍较低。整体上,树干流的离子浓度>林内雨>林外雨。研究表明武夷山常绿阔叶林生态系统降水分配过程中,林内雨是养分输入的主要形式,各养分离子年输入量占总输入量的比例均在90%以上。通过林内雨输入林地较多的养分离子是SO42--S和K+,分别为24.51、37.53kg·hm^-2·a-1;SO42--S和K+也是总养分输入量的主要离子,二者分别占离子输入总量的24%和36%,NO3--N的年输入量也达到了12.44kg·hm^-2·a-1,占到养分离子总输入量的11%以上。

Atmospheric precipitation is an important vehicle for water resource and nutrient input in forest ecosystems. In the present study, we investigated the amount of precipitation and nutrient ion concentrations of atmospheric precipitation, throughfall, and stemflow in a mid-subtropical evergreen broad-leaved forest during the period of November 2014 to November 2015, to provide basic data for further research on the water balance and nutrient cycle of evergreen broad-leaved forest ecosystems. The results showed that: the annual bulk precipitation from November 2014 to November 2015 was 2 623.7 mm. The temporal fluctuations in precipitation amounts in throughfall and stemflow were similar to those with bulk precipitation. Only 4.5% of the annual bulk precipitation was partitioned into stemflow. After subtracting throughfall and stemflow, approximately 9.8% of the annual precipitation was intercepted by the forest canopy. There was a significant positive linear correlation between bulk precipitation and throughfall or stemflow amount(P<0.001). The highest annual average p H value was in bulk precipitation, followed by stemflow and throughfall. The temporal fluctuations in different ion concentrations in bulk precipitation, throughfall, and stemflow were similar. The ion concentrations in different kinds of precipitation were higher during January to February, which had less bulk precipitation;whereas the ion concentrations were lower during March to Augest, which experienced greater bulk precipitation. The order of ion concentrations generally was stemflow>throughfall>bulk precipitation. The primary form of nutrient input was throughfall, the annual input of each nutrient ion accounted for over 90% of the total input nutrient ions;and the majority of the nutrient ions input into the forest ecosystem through throughfall were SO42--S and K+ with 24.51 and 37.53 kg·hm^-2·a-1, respectively. The main nutrient ions in annual nutrient input also were SO42--S and K+, which accounted for 24% and 36% of the total ion input, respectively;The annual input of NO3--N was 12.44 kg·hm^-2·a-1, which accounted for over 11% of the total input nutrient ions.