Photochemical degradation of dissolved organic matter (DOM) has been the subject of numerous studies; however, its regulation along the inland water continuum is still unclear. We aimed to unravel the DOM photoreactivity and concurrent DOM compositional changes across 30 boreal aquatic ecosystems including peat waters, streams, rivers, and lakes distributed along a water residence time (WRT) gradient. Samples were subjected to a standardized exposure of simulated sunlight. We measured the apparent quantum yield (AQY), which corresponds to DOM photomineralization per photon absorbed, and the compositional change in DOM at bulk and individual compound levels in the original samples and after irradiation. AQY increased with the abundance of terrestrially derived DOM and decreased at higher WRT. Additionally, the photochemical changes in both DOM optical properties and molecular composition resembled changes along the natural boreal WRT gradient at low WRT (<3\uffc2\uffa0years). Accordingly, mass spectrometry revealed that the abundance of photolabile and photoproduced molecules decreased with WRT along the boreal aquatic continuum. Our study highlights the tight link between DOM composition and DOM photodegradation. We suggest that photodegradation is an important driver of DOM composition change in waters with low WRT, where DOM is highly photoreactive.We measured leaf photosynthetic traits in shade\uffe2\uff80\uff90grown seedlings of four tree species native to northern Japan, raised under an elevated CO2 condition, to investigate the effects of elevated CO2 on shade tolerance of deciduous broadleaf tree species with different successional traits. We considered Betula platyphylla var. japonica and Betula maximowicziana as pioneer species, Quercus mongolica var. crispula as a mid\uffe2\uff80\uff90successional species, and Acer mono as a climax species. The plants were grown under shade conditions (10% of full sunlight) in a CO2\uffe2\uff80\uff90regulated phytotron. Light compensation points (LCPs) decreased in all tree species when grown under elevated CO2 (720\uffc2\uffa0\uffce\uffbcmol\uffc2\uffb7mol\uffe2\uff88\uff921), which were accompanied by higher apparent quantum yields but no photosynthetic down\uffe2\uff80\uff90regulation. LCPs in Q.\uffc2\uffa0mongolica and A.\uffc2\uffa0mono grown under elevated CO2 were lower than those in the two pioneer birch species. The LCP in Q.\uffc2\uffa0mongolica seedlings was not different from that of A.\uffc2\uffa0mono in each CO2 treatment. However, lower dark respiration rates were observed in A.\uffc2\uffa0mono than in Q.\uffc2\uffa0mongolica, suggesting higher shade tolerance in A.\uffc2\uffa0mono as a climax species in relation to carbon loss at night. Thus, elevated CO2 may have enhanced shade tolerance by lowering LCPs in all species, but the ranking of shade tolerance related to successional traits did not change among species under elevated CO2, i.e. the highest shade tolerance was observed in the climax species (A.\uffc2\uffa0mono), followed by a gap\uffe2\uff80\uff90dependent species (Q.\uffc2\uffa0mongolica), while lower shade tolerance was observed in the pioneer species (B.\uffc2\uffa0platyphylla and B.\uffc2\uffa0maximowicziana).
", "keywords": ["0106 biological sciences", "CO2 enrichment", "photosynthesis", "Acclimatization", "Acer", "Carbon Dioxide", "15. Life on land", "650", "01 natural sciences", "Carbon", "Apparent quantum yield", "Trees", "shade tolerance", "Plant Leaves", "Quercus", "Phenotype", "Japan", "Seedlings", "Sunlight", "Photosynthesis", "dark respiration", "Betula"]}, "links": [{"href": "https://doi.org/10.1111/plb.12400"}, {"rel": "related", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/Plant%20Biology", "name": "related record", "description": "related record", "type": "application/json"}, {"rel": "self", "type": "application/geo+json", "title": "10.1111/plb.12400", "name": "item", "description": "10.1111/plb.12400", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10.1111/plb.12400"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2015-10-11T00:00:00Z"}}, {"id": "10261/383825", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-26T16:24:41Z", "type": "Dataset", "title": "[Dataset] Decreasing Photoreactivity and Concurrent Change in Dissolved Organic Matter Composition With Increasing Inland Water Residence Time", "description": "Open AccessPeer reviewed", "keywords": ["Ensure availability and sustainable management of water and sanitation for all", "Ensure sustainable consumption and production patterns", "Make cities and human settlements inclusive", " safe", " resilient and sustainable", "Dissolved organic matter quality", "Photodegradation", "Water retention time", "http://metadata.un.org/sdg/6", "Aquatic continuum", "http://metadata.un.org/sdg/3", "http://metadata.un.org/sdg/11", "Ensure healthy lives and promote well-being for all at all ages", "Apparent quantum yield"], "contacts": [{"organization": "Grasset, C., Einarsdottir, K., Catal\u00e1n, N., Tranvik, L. J., Groeneveld, M., Hawkes, J. A., Attermeyer, Katrin,", "roles": ["creator"]}]}, "links": [{"href": "https://doi.org/10261/383825"}, {"rel": "self", "type": "application/geo+json", "title": "10261/383825", "name": "item", "description": "10261/383825", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main/items/10261/383825"}, {"rel": "collection", "type": "application/json", "title": "Collection", "name": "collection", "description": "Collection", "href": "https://repository.soilwise-he.eu/cat/collections/metadata:main"}], "time": {"date": "2025-01-01T00:00:00Z"}}, {"id": "10261/350658", "type": "Feature", "geometry": null, "properties": {"updated": "2026-07-26T16:24:39Z", "type": "Journal Article", "created": "2024-03-07", "title": "Decreasing Photoreactivity and Concurrent Change in Dissolved Organic Matter Composition With Increasing Inland Water Residence Time", "description": "AbstractPhotochemical degradation of dissolved organic matter (DOM) has been the subject of numerous studies; however, its regulation along the inland water continuum is still unclear. We aimed to unravel the DOM photoreactivity and concurrent DOM compositional changes across 30 boreal aquatic ecosystems including peat waters, streams, rivers, and lakes distributed along a water residence time (WRT) gradient. Samples were subjected to a standardized exposure of simulated sunlight. We measured the apparent quantum yield (AQY), which corresponds to DOM photomineralization per photon absorbed, and the compositional change in DOM at bulk and individual compound levels in the original samples and after irradiation. AQY increased with the abundance of terrestrially derived DOM and decreased at higher WRT. Additionally, the photochemical changes in both DOM optical properties and molecular composition resembled changes along the natural boreal WRT gradient at low WRT (<3\uffc2\uffa0years). Accordingly, mass spectrometry revealed that the abundance of photolabile and photoproduced molecules decreased with WRT along the boreal aquatic continuum. Our study highlights the tight link between DOM composition and DOM photodegradation. We suggest that photodegradation is an important driver of DOM composition change in waters with low WRT, where DOM is highly photoreactive.