Abstract: The content, accumulation, distribution and cycling dynamics of five nutrient elements (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: (1) 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 plantations, 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 enrichment capacity of P in Ch. axillaries plantation. Tree layer and forest floor layer had the biggest enrichment 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. Therefore, P deficiency generally existed in soil of our tested region, which should be improved to guarantee the normal growth of forest plantations.

Key words: apple, bag-controlled release fertilizer, ¹⁵N-urea, controlled-release nitrogen fertilizer