Objectives This study was to investigate the nutrient utilization characteristics in the material production of Chinese fir Cunninghamia lanceolata (Lamb. ) Hook plantations and to provide a scientific basis for the management of Chinese fir plantation.
Methods The study was conducted at the Ecosystem Research Station for Chinese Fir Plantation (National Outdoor Scientific Research Observation Station) in Huitong County, Hunan Province, China. Four localized observation sampling plots were established in a seven-year-old plantation. In the 7th, 11th, 16th, 20th and 25th year, the stand biomasses were measured, the total Ca, Mg, K, N and P contents in different plant parts were analyzed. The transferred nutrient amounts from the dead branch and leaves were calculated via multiplying their biomass by the nutrient concentration difference values before and after their death. According to the periodical nutrient concentration differences, the supplemented or removed quantities of nutrients from various organs born before this forest age stage were estimated. These nutrients were combined with nutrients absorbed from soil.
Results With the increasing of forest age, the percentage of nutrient provided by soil, which was in range of 79.3%–96.5%, became decreasing; that by transfer out of branches and leaves before death, which was accounted for 3.52%–17.55%, became rising. Only since the 12th year of stand, there occurred reuse of nutrients transferred out of the biomass born before and still alive in a certain forest age stage. These shifts accounted for 3.11%–3.40% and showed a small amplitude downward trend with the increase of forest age. Before the fast trunk growth stage, nutrient use efficiency declined with the increasing forest age. Since the fast trunk growth stage, nutrient use efficiency rose with the increasing forest age.
Conclusions The nutrients used for material production in stand come from three aspects: soil, pre-death transfer of branches and leaves and plant tissue transfer. As long as there are branches and leaves dying, nutrients will be transferred out for material reproduction before the dying of branches and leaves. Only after the closure of fir stand, the biomass produced by the previous stand in a certain forest age section, and some nutrients in the biomass still alive in the forest age section will be removed for reuse. The annual change of nutrient use in stands is restricted by the demand for nutrients in different growth stages, and the nutrient utilization processes are jointly controlled by the rules of nutrient redistribution and storage in Cunninghamia lanceolata, during the growth and development stages, along with the nutrient use efficiency in different growth stages.
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