湘西喀斯特地区三种优良乡土树种人工林养分吸收、积累和分配特性

Nutrient absorption, accumulation, and distribution characteristics of three excellent native tree species plantations in karst area of western Hunan

为了解喀斯特地区不同人工林生态系统的养分利用特征,本文对湘西自治州森林生态站31年生的华榛(Corylus chinensis)、南酸枣(Choerospondias axillaris)、银鹊树(Tapiscia sinensis)人工林的N、P、K、Ca和Mg 5种营养元素含量、积累、分配、养分循环特征开展了研究。结果表明:(1)华榛、南酸枣和银鹊树3个树种林分的不同器官、地被物以及凋落物营养元素含量均以南酸枣最低;3个树种的不同器官、地被物以及凋落物的营养元素含量均以Ca元素含量最高,P元素含量最低,表现出典型的喀斯特地区植被养分特征;3个树种各器官的养分总含量大小均为树叶>树皮>树枝>树根>树干。(2)南酸枣乔木层和地被物富集P元素的能力最高;华榛和银鹊树均是乔木层富集P元素能力最高,地被物富集Ca的能力最高。(3)3种林分中营养元素积累量以华榛最低,银鹊树最高,后者约为前者的188%;5种营养元素中,3种林分均以Ca积累最多,P积累最少,与树种体内营养元素含量规律一致。(4)3个树种林分营养元素的吸收量、存留量和归还量大小顺序均为银鹊树>华榛>南酸枣;3个树种林分营养元素循环速率均以K元素最高、P元素最低;3个树种林分营养元素利用效率均为P元素的利用效率最高。(5)人工银鹊树林是高吸收、高现存、较慢循环、养分高度节约型林分;相比南酸枣和华榛而言,银鹊树更加喜喀斯特钙生环境,更适合喀斯特地区的生长。(6)3个树种林分均有P元素在各器官含量低、对土壤富集能力强、循环速率低、利用效率高的特点。可见,受试喀斯特地区土壤普遍存在低磷现象,需要及时改善,以保证林分正常生长。

The content, accumulation, distribution and cycling dynamics of five nutrient ele- ments （N, P, K, Ca, and Mg） in 31-year-old Corylus chinensis, Choerospondias axillaries and Tapiscia sinensis plantations in Xiangxi Autonomous Prefecture Forest Ecological Station were studied to clarify the nutrient use characteristics of different plantation ecosystems in karst area. The results showed that ： （ l ） The contents of nutrient elements in tree organs, forest floor and litter were the lowest in the Ch. Axillaries plantation among the three plantations. Maximum Ca and minimum P accumulations were found in tree organs, forest floor and litter in the three plan- tations, suggesting a typical characteristic of vegetation nutrient in karst region. The ranking order of nutrient element contents of different tree components in the three plantations was as follows： leaf 〉 bark 〉 branch 〉 root 〉 trunk. （2） Tree layer and forest floor layer had the biggest enrich- ment capacity of P in Ch. axiUaries plantation. Tree layer and forest floor layer had the biggestenrichment capacity of P and Ca respectively both in C. chinensis and T. sinensis plantations. （3） The lowest and highest nutrient accumulation occurred in C. chinensis plantation and T. sinensis plantation respectively, and the latter was 188% of the former. Among the five nutrient elements, maximum Ca and minimum P accumulated in the three plantations, showing a similar pattern to the nutrient contents in the organs of the three species. （4） The ranking order of nutrient uptake, remaining and return amount in the three plantations was as follows： T. sinensis 〉 Ch. Axillaries 〉 C. chinensis. The three plantations had a similar pattern of nutrient cycle rate, being the highest with K and the lowest with P ; they also had a similar pattern of nutrient use efficiency, being the highest with P. （5） T. sinensis plantation was the optimal choice among the three tree species in karst area for its advantages of high absorption capacity, high remaining, low cycling rate and highly economical nutrient use. （6） A similar pattern of low content in organs, high enrichment from soil, low cycling rate and high use efficiency of P occurred in the three plantations. There- fore, P deficiency generally existed in soil of our tested region, which should be improved to guarantee the normal growth of forest plantations.