Response of Photosynthetic Capacity to Nitrogen Addition in <i>Larix gmelinii</i> Trees in Different Crown Classes
We explored the response of photosynthetic capacity to nitrogen (N) deposition among <i>Larix gmelinii</i> trees in different crown classes (e.g., suppressed, intermediate, and dominant trees) in a 12-year field experiment in a forest in the Greater Khingan Mountains in Northeast China....
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-03-01
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| Series: | Plants |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2223-7747/14/7/1056 |
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| Summary: | We explored the response of photosynthetic capacity to nitrogen (N) deposition among <i>Larix gmelinii</i> trees in different crown classes (e.g., suppressed, intermediate, and dominant trees) in a 12-year field experiment in a forest in the Greater Khingan Mountains in Northeast China. Four N-addition treatments were established: control (CK), low N (LN), medium N (MN), and high N (HN) (0, 25, 50, and 75 kg N·ha<sup>−1</sup>·year<sup>−1</sup>, respectively). Photosynthesis and its influencing factors were measured in 2023. Nitrogen addition significantly increased the maximum net photosynthetic rate (<i>P</i><sub>max</sub>), maximum carboxylation rate (<i>V</i><sub>cmax</sub>), and maximum electron transport rate (<i>J</i><sub>max</sub>) of suppressed and intermediate trees. The suppressed trees showed maximum <i>P</i><sub>max</sub> and <i>V</i><sub>cmax</sub> in MN and HN, and maximum <i>J</i><sub>max</sub> in HN. The intermediate trees showed maximum <i>P</i><sub>max</sub>, <i>V</i><sub>cmax</sub>, and <i>J</i><sub>max</sub> in MN. For dominant trees, <i>P</i><sub>max</sub> was increased in LN and MN and decreased in HN, and <i>V</i><sub>cmax</sub> was increased by N addition and peaked in MN. Nitrogen addition significantly increased the leaf N content (N<sub>mass</sub>), chlorophyll content (Chl<sub>m</sub>), the ratio of N to phosphorous (N:P), and photosynthetic enzyme activities in all crown classes. N<sub>mass</sub> had significant nonlinear relationships with <i>P</i><sub>max</sub>, <i>V</i><sub>cmax</sub>, and <i>J</i><sub>max</sub>. Enzyme activity and Chl<sub>m</sub> positively affected the photosynthetic capacity of suppressed and intermediate trees, and N:P negatively affected the photosynthetic capacity of dominant trees. The promoting effect of N addition on photosynthetic capacity was stronger in suppressed and intermediate trees than in dominant trees. Therefore, the crown class should be considered when studying the effect of N deposition on the boreal forests. |
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| ISSN: | 2223-7747 |