Retention and partitioning of 15N-labeled deposited N in a tropical plantation forest

Autor: Jiangming Mo, Feifei Zhu, Yunting Fang, Geshere Abdisa Gurmesa, Qinggong Mao, Per Gundersen, Xiankai Lu
Rok vydání: 2021
Předmět:
Zdroj: Biogeochemistry. 152:237-251
ISSN: 1573-515X
0168-2563
DOI: 10.1007/s10533-020-00750-y
Popis: The effects of deposited nitrogen (N) on forest ecosystems largely depend on the amount of N retained in the ecosystems and its partitioning among ecosystem pools. However, our understanding of the capacity of tropical plantations to retain deposited N is limited. To evaluate the retention of deposited N in a human-disturbed pine plantation in southern China and compare the result with previous findings in an adjacent old-growth forest, we added 15N-tracer monthly to the forest floor for one year and determined its recovery in ecosystem compartments four months after the last addition. We monitored 15N recoveries in soil solution monthly to quantify leaching losses. The pine forest retained about 58 ± 5% of the 15N-labeled deposited N, which is lower than that reported in the adjacent old-growth forest (72 ± 6%). Both forests experience chronic N deposition (recently measured at 51 kg N ha−1 yr−1) and we attribute the difference in retention to effects of previous disturbance mainly understory and litter harvesting in the pine plantation. Only 3 kg N ha−1 yr−1 (5% of the 15N-labeled deposited N) out of the measured total leaching (54 kg N ha−1 yr−1) originated from deposited (and labeled) N from the measurement year, suggesting that N leaching is dominated by unlabeled N sources. Furthermore, results from our study and other similar 15N labeling experiments together show similar patterns of total ecosystem retention of deposited N in tropical and temperate forests, but here we demonstrate a decreasing retention of N with increased N deposition in these forests. Our findings indicate that plantation forests that experience human-disturbance and chronic N deposition have lower N retention compared to old-growth forests, and thus elevated N inputs in such ecosystems can cause risk of hydrological N losses, soil acidification, and freshwater pollution.
Databáze: OpenAIRE
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