Articles | Volume 14, issue 14
Biogeosciences, 14, 3461–3469, 2017
Biogeosciences, 14, 3461–3469, 2017

Research article 21 Jul 2017

Research article | 21 Jul 2017

Growth responses of trees and understory plants to nitrogen fertilization in a subtropical forest in China

Di Tian1, Peng Li1, Wenjing Fang1, Jun Xu2, Yongkai Luo3, Zhengbing Yan1, Biao Zhu1, Jingjing Wang2, Xiaoniu Xu2, and Jingyun Fang1 Di Tian et al.
  • 1Department of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing, 100871, China
  • 2Department of Forestry, Anhui Agricultural University, 230036, Hefei, Anhui, China
  • 3State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China

Abstract. Reactive nitrogen (N) increase in the biosphere has been a noteworthy aspect of global change, producing considerable ecological effects on the functioning and dynamics of the terrestrial ecosystems. A number of observational studies have explored responses of plants to experimentally simulated N enrichment in boreal and temperate forests. Here we investigate how the dominant trees and different understory plants respond to experimental N enrichment in a subtropical forest in China. We conducted a 3.4-year N fertilization experiment in an old-aged subtropical evergreen broad-leaved forest in eastern China with three treatment levels applied to nine 20 m  ×  20 m plots and replicated in three blocks. We divided the plants into trees, saplings, shrubs (including tree seedlings), and ground-cover plants (ferns) according to the growth forms, and then measured the absolute and relative basal area increments of trees and saplings and the aboveground biomass of understory shrubs and ferns. We further grouped individuals of the dominant tree species, Castanopsis eyrei, into three size classes to investigate their respective growth responses to the N fertilization. Our results showed that the plot-averaged absolute and relative growth rates of basal area and aboveground biomass of trees were not affected by N fertilization. Across the individuals of C. eyrei, the small trees with a DBH (diameter at breast height) of 5–10 cm declined by 66.4 and 59.5 %, respectively, in N50 (50 kg N ha−1 yr−1) and N100 fertilized plots (100 kg N ha−1 yr−1), while the growth of median and large trees with a DBH of  >  10 cm did not significantly change with the N fertilization. The growth rate of small trees, saplings, and the aboveground biomass of understory shrubs and ground-cover ferns decreased significantly in the N-fertilized plots. Our findings suggested that N might not be a limiting nutrient in this mature subtropical forest, and that the limitation of other nutrients in the forest ecosystem might be aggravated by the enhanced N availability, potentially resulting in an adverse effect on the development of natural subtropical forest.

Short summary
Previous studies have mainly focused on the effects of N deposition on tree growth in temperate and tropical forests, however, the responses of different trees and understory plants in subtropical forests to N deposition remain unknown. We conducted a 3.4-year experimentally simulated N enrichment and found that small trees were hindered while medium and large trees were not significantly affected by N fertilization. Additionally, the growth of understories was suppressed by N fertilization.
Final-revised paper