Growth responses of trees and understory plants to nitrogen fertilization in a subtropical forest in China
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...
Main Authors: | , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-07-01
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Series: | Biogeosciences |
Online Access: | https://www.biogeosciences.net/14/3461/2017/bg-14-3461-2017.pdf |
Summary: | 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, <i>Castanopsis eyrei</i>, 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 <i>C. eyrei</i>, 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<sup>−1</sup> yr<sup>−1</sup>)
and N100 fertilized plots (100 kg N ha<sup>−1</sup> yr<sup>−1</sup>), 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. |
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ISSN: | 1726-4170 1726-4189 |