Litterfall And Nutrient Seasonal Dynamics Of Dominant Tree Species In A Subtropical Evergreen Broad-leaved Forest In Xiaokeng, Southern Anhui

As the basic carrier of nutrients, litter acts as the ligament between the plant and soilin the nutrient cycling. Therefore, litter plays a very important role in maintaining soilfertility, facilitating the normal cycling and balance of nutrients in forest ecosystemsAdaptive strategy of plants are diverse, improving nutrient use efficiency of plant is one ofthe mechanisms to adapt to nutrient-poor habitats. Thus, nutrient use efficiency is a veryuseful concept in the ecosystem, which reflects the utilization of nutrients in plants. Clearlyhigh nutrient use efficiency of plants will make fuller use of limited nutrients to competewith other species in the same soil conditions, therefore, increasing the nutrient useefficiency which produces more biomass could be an important competitive strategy ofadaptation to the poor environment. In this study, nutrient use efficiency, nutrientdynamics, litter production, litter composition, litter rhythm, nitrogen and phosphorusstoichiometry of plant leaves and nutrient dynamics were studied for four dominant treespecies in a subtropical evergreen broad-leaved forest at Xiaokeng of southern Anhui. Theobjective of the study is to find some regulations of plants and to provide some usefulinformation for tree growth and cultivation.The result from the study are shown below.1. Litterfall productionAccording to a three-year observation, annual litterfall production ranged from 6.91～9.85 t·hm₂, annual average litterfall was 8.61t·hm^-2. Coefficient of variation was 17.69%.2. Litter componentsThe amount of leaf litter was the absolute dominance in the subtropical evergreenbroad-leaved forest in Xiaokeng. The percent of the average litter was 60% for leaf, 19%for branch bark, 16% for flowers and fruits, 5% for miscellaneous materials.3. Litter characteristicThe result showed evergreen broad-leaved forest had obvious litter rhythm andseasonal variation was bimodal. The peak of litterfall was different in different months, butgeneral rule was the same. The first peak was April and May, and the second peak wasJuly and August. In annual average litterfall,the first peak was April, and the second peakwas July. The least litterfall was January and February.4. Leaf litterfall of the dominant treesLeaf litterfall of the four dominant species account for 79.3% 83.2% of the total leaflitterfall. Within the annual leaf litter, Castanopsi seyrei contributed 41.7%, Lithocarpus glaber for 22.2%, Castanopsis sclerophlla for 10.1%, and Cylobalanopsis glauca for 7.3%.The pattern of leaf litterfall of Castanopsis eyrei was different from the other trees, represented irregular many peaks. However, Castanopsis sclerophlla showed single peak, Cyclobalanopsis glauca and Lithocarpus glaber were bimodal.5. The annual nutrient return by leaf litterThe total annual nutrient returns (five nutrient elements) of leaf litter from the four dominants, Castanopsis eyrei, Castanopsis sclerophlla, Cyclobalanopsis glauca, and Lithocarpus glaber were, respectively, 5.87 kg·hm^-2, 1.018 kg·hm₂, 1.547 kg·hm₂, 3.200 kg·hm₂. The total annual returns of leaf litter for the different elements showed the similar order for the dominants, Castanopsis eyrei, Castanopsis sclerophlla, Cyclobalanopsis glauca, Lithocarpus glaber with N > Ca > K > Mg > P.6. Seasonal dynamics of foliar nutrient concentrations of understory plantsIn different seasons, Camellia fraterna, Neolitsea aurata, Symplocos stellaris, Rhododendron simsii, Lindera aggregate had a strong seasonal dynamics with the different patterns.7. Seasonal dynamics of fresh and litter foliar nutrient concentrations in the dominantsThe four dominants had obvious seasonal dynamics. In average, the order of fresh foliar nutrient concentrations for Castanopsis eyreia and Castanopsis sclerophlla was N > K> Ca > Mg > P; for Cyclobalanopsis glauca and Lithocarpus glabe was N > Ca > K > Mg > P. The order of foliar litter nutrient concentration for the four dominants was similar with N > Ca > K > Mg > P. N, P, K, Mg showed clear retranslocation between fresh and litter leaf except for Ca.8. Seasonal dynamics of nutrient use efficiency in the dominantsDifferent trees have diversity in nutrient use efficiency. In annual average, the order of NUE_N and NUE_P was Castanopsis eyrei > Lithocarpus glabe r> Cyclobalanopsis glauca > Castanopsis sclerophlla; for NUE_k was Cyclobalanopsi glauca > Lithocarpus glabe r> Castanopsis sclerophlla > Castanopsis eyrei; for NUE_Ca was Castanopsis eyrei > Castanopsis sclerophlla > Cyclobalanopsis glauca > Lithocarpus glaber; for NUE_Mg was Lithocarpus glaber > Castanopsis sclerophlla > Cyclobalanopsis glauca > Castanopsis eyrei. In addition, only NUE_Ca and NUE_Mg was significantly correlated (p = 0.02).9. Characteristics of N:P stoichiometrical ratioThroughout the year in this region, N: P ratios were almost over 16 except for Castanopsis sclerophlla. It indicated that the growth of trees in XiaoKeng was limited by phosphorus.