藏东南高山松天然林水文过程中养分元素变化特征

Variation Characteristics of Nutrient Elements through Hydrological Processes in Pinus densata Natural Forest of Southeast Tibet

对藏东南高山松天然林内的穿透雨、树干茎流以及林外大气降水进行了观测和取样,测定了水样中的N、P、K、Na、Ca、S、Mg、Si、Mn、Fe、Cu和Zn元素的含量,分析了其降水过程中养分元素浓度变化特征和输入规律。结果表明:大气降水、穿透雨和树干茎流中,养分元素浓度值的最大变异系数分别是1.485(Zn)、0.844(Na)和0.809(P),最小变异系数分别为0.255(S)、0.304(S)和0.318(Si)。3种形式水样中,微量元素之间以及微量元素与其他元素之间浓度值相关性不显著,其他元素俩俩之间浓度值相关性大部分达到显著水平。3种水样中,Cu元素年平均浓度值均最小,分别为0.023、0.047和0.066 mg/L,最大浓度分别为1.604 mg/L(N)、3.401 mg/L(Na)和4.371 mg/L(Na)。3种水样中各养分元素浓度值差异显著,并且均表现为:树干茎流>穿透雨>大气降水,各养分元素浓度月变化主要呈"∩"型、"N"型或"∪"型。所有元素的树干茎流和穿透雨淋溶系数均大于1,并且前者均大于相应的后者。研究期间,3种形式的养分输入量分别为64.172、79.949和15.623 kg/hm2。养分净淋溶量为34.057 kg/hm2(N除外),净淋溶量排序为:Na>Ca>K>Mg>Si>S>P>Mn>Fe>Zn>Cu,N元素净淋溶为-2.658 kg/hm2。

Pinus densata is a tree unique to China. P. densata natural forest is an important water conservation forest in the middle reaches of Yarlung Zangbo River in Tibetan Plateau. It plays an important role in maintaining water balance and soil and water conservation.Precipitation, throughfall and stemflow were monitored in natural forest of P. densata distributed in Gongbu Nature Reserve of Southeast Tibet from April to October of 2013.Meanwhile, nutrient elements（N, P, K, Na, Ca, S, Mg, Si, Mn, Fe, Cu, and Zn） contents in the water were determined. According to allotment of water amount, input of each element in the forest was calculated. The variation characteristics of nutrient elements through the hydrological processes of the forest were analyzed. The results showed that： Since the precipitation in Tibetan Plateau was divided into the obvious dry and wet season, temporal and spatial dynamics of nutrient elements contents from throughfall and stemflow changed remarkably when precipitation pass through canopy layer and after rainfall and surface of P.densata＇s interaction（needles, branches, and stem）. The biggest variation coefficient of concentration value in the precipitation was 1.485 for Zn, and the smallest was 0.255 for S. The biggest in the throughfall was 0.844 for Na, and the smallest was 0.304 for S, while those in the stemflow were 0.809 for P and 0.318 for Si, respectively. There were no significant relations among the trace elements（Mn, Fe, Cu, Zn）, and between the trace elements and the others,respectively. There were significant relations between the others. The average contents of Cu annually in the precipitation, throughfall and stemflow were the lowest, which were 0.023,0.047 and 0.066 mg/L, respectively. That of N was the highest in the precipitation, which was1.604 mg/L, and those of Na were highest in throughfall and stemflow, which were 3.401 and4.307 mg/L, respectively. The differences of each element contents in the samples collected from the precipitation, throughfall and stemflow were significant, and the order were：stemflowthroughfallprecipitation. The monthly patterns of nutrient concentration were＂∩＂,＂N＂or＂∪＂types. The leaching coefficients of the throughfall and stemflow were both more than one, and the stemflow leaching coefficients were greater than the corresponding throughfall leaching coefficient. The nutrients input of precipitation, throughfall and stemflow were 64.172, 79.949 and 15.623 kg/hm^2, respectively. The Na, K and Ca input of throughfall and stemflow accounted for more than 50%. The total input of throughfall was 5.12 times that of stemflow. The input of precipitation was main N element. The net leaching input was 34.057kg/hm^2（except for N）, and ranked in the order of Na〉Ca〉K〉Mg〉Si〉S〉P〉Mn〉Fe〉Zn〉Cu, and the input of N was- 2.658 kg/hm^2. The research results not only provided a theoretical basis for economic evaluation of P. densata forest ecosystem service function, but also enriched the assessment content of the national ecological security barrier in Tibet Plateau.