物候变化对落叶松人工林降雨分配过程中钾和钠离子迁移的影响

目的 森林冠层导致的穿透雨和树干茎流中离子通量的季节变化,能够影响森林生态系统生物地球化学循环,对物候变化明显的温带落叶林的影响更为突出。探究不同物候期(展叶期、盛叶期和落叶期)森林水化学过程,深入了解森林生态系统养分元素循环过程,为温带落叶林生物地球化学循环提供基础数据。方法 以东北林业大学城市林业示范基地内落叶松人工林为研究对象,在观测样地的中心位置十字交叉布设13个直径20 cm自制雨量筒,并选择5株落叶松安装树干茎流收集器,同时在林外布置1台翻斗式雨量计和3个自制雨量筒。在前期观察期(2015年5月1日—10月31日)每次降雨事件后,对林外降雨、穿透雨和树干茎流进行观测、取样,水样过滤酸化处理后用火焰原子吸收分光光度计测定Na⁺和K⁺质量浓度,探索冠层的物候变化对降雨分配过程中Na⁺和K⁺的质量浓度和净输入量的影响。结果 整个观测期间,林外降雨中Na⁺、K⁺的质量浓度分别为0.45 和1.89 mg/L,穿透雨中分别为0.44 和2.48 mg/L,树干茎流中分别为1.98和18.63 mg/L;大气降雨中Na⁺质量浓度在落叶期最高,盛叶期最低,K⁺质量浓度则在落叶期最高,展叶期最低;各时期穿透雨中Na⁺和K⁺质量浓度大小均为落叶期>盛叶期>展叶期;树干茎流中Na⁺和K⁺质量浓度大小均为展叶期>盛叶期>落叶期;生长季内林冠对降雨中Na⁺的截留量为0.252 kg/hm²,其中展叶期和落叶期的截留量分别为0.143和0.193 kg/hm²,截留率分别为30.63%和48.22%,盛叶期则表现为淋溶,淋溶量为0.083 kg/hm²;生长季内降雨对林冠中K⁺的淋溶量为0.903 kg/hm²,其中展叶期和盛叶期的淋溶量分别为0.999和0.157 kg/hm²,落叶期则为截留,截留量为0.254 kg/hm²,截留率为20.25%。结论 大气降雨经过森林冠层后离子质量浓度发生明显改变,且不同物候期、不同离子的变化强度不同。生长季内,兴安落叶松林对Na⁺总体表现为截留作用,对K⁺总体表现为淋溶作用。即落叶松叶片的物候变化能够影响大气降雨中Na⁺和K⁺的迁移。研究结果可为进一步探明我国温带森林生态系统伴随水文过程的养分循环过程及促进可持续经营管理提供借鉴。

Effects of phenoseason on transfer of potassium and sodium ions in the process of rainfall redistribution in larch (Larix gmelinii) plantations

【Objective】 The seasonal variations in ionic fluxes in throughfall and stemflow resulting from washoff and leaching by forest canopy indicate significant processes affecting the biogeochemical cycling of forested ecosystems, particularly in temperate deciduous forests with distinct phenological seasons. Previous studies on the water chemistry of forest ecosystems have been focused on the growing season as a time scale to discuss the changes in element fluxes, but ignored the influence of leaf phenology changes on water chemistry during the growing season. Therefore, our objective is to determine the impacts of phenological changes on the water chemistry of forest ecosystems and to better understand the nutrient element cycle process of temperate deciduous forest ecosystems.【Method】 In this study, we selected a Larix gmelinii plantation in the Northeast Forestry University Urban Forestry Demonstration Base as the research subject. Thirteen self-made rain gauges with a diameter of 20 cm were laid across the center of the observation plot, and five L. gmelinii trees were selected to install the stemflow collectors. Simultaneously, a tipping bucket rain gauge and three self-made rain gauges were arranged outside the forest. We measured and sampled in situ the solution of bulk precipitation, throughfall, and stemflow after each rainfall event from May 1 to October 30, 2015. After filtering and acidification of the water sample, the concentrations of Na ⁺ and K⁺ were measured with a flame atomic absorption spectrophotometer to explore the role of the canopy at different phenological stages (leaf expanding stage, full leaf stage, and senesced leaf stage) on the concentrations and net inputs of Na⁺ and K⁺ in the process of rainfall distribution.【Result】 Throughout the observation period, the concentrations of Na⁺ and K⁺ in rainfall were 0.45 and 1.89 mg/L, in throughfall were 0.44 and 2.48 mg/L, and in stemflow were 1.98 and 18.63 mg/L, respectively. The highest and lowest Na⁺ concentrations in the rainwater occurred at the senesced and full leaf stages, respectively. Meanwhile, higher K⁺ concentration in rainwater was also found at the senesced leaf stage, and the lowest concentration at the leaf expanding stage. In the throughfall, both Na⁺ and K⁺ concentrations were in the order of senesced leaf stage > full leaf stage > leaf expanding stage, and in the stemflow, the order was leaf expanding stage > full leaf stage > senesced leaf stage. During the whole growing season, the canopy intercepted Na ⁺ with the values of 0.252 kg/hm², and it intercepted both in the leaf expanding stage and senesced leaf stage, but showed leaching during the full leaf stage. The interceptions of Na⁺ were 0.143 and 0.193 kg/hm², with interception rates of 30.63% and 48.22% at the leaf expanding stage and senesced leaf stage, respectively, and the leaching flux of Na⁺ was 0.083 kg/hm². In contrast, the leaching flux of K⁺ was 0.903 kg/hm² from the canopy due to rainfall during the growing season, with fluxes of 0.999 and 0.157 kg/hm² at the leaf expanding stage and full leaf stage, respectively, and the interception was 0.254 kg/hm² at the senesced leaf stage, with an interception rate of 20.25%. In conclusion, the redistribution of Na⁺ and K⁺ in the rainfall affected by the larch plantation canopy varied considerably with phenological stages. 【Conclusion】 The ion concentration in bulk precipitation changed significantly after passing through the forest canopy, and the change intensity differed according to the phenological stages and the ions. Throughout the observation period, the L. gmelini forest exhibited an interception effect on Na ⁺, but showed a leaching effect on K⁺. In other words, the leaf phenology of L. gmelini affects the transfer of Na ⁺ and K⁺ in rainfall water. The results of this study can provide a reference for further understanding the nutrient cycling process associated with hydrological processes and its sustainable management in temperate forest ecosystems in China.