Contrasting effects of long term versus short-term nitrogen addition on photosynthesis and respiration in the Arctic

• Published in: Plant ecology Vol. 214; no. 10; pp. 1273 - 1286
• Main Authors: van de Weg, Martine J., Shaver, Gaius R., Salmon, Verity G.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 01.10.2013; Springer Netherlands; Springer Nature B.V
• Subjects: Agronomy. Soil science and plant productions; Animal and plant ecology; Animal, plant and microbial ecology; Applied Ecology; Arctic tundra; Betula nana; Biodiversity; Biogeochemistry; Biological and medical sciences; Biomedical and Life Sciences; Carbon dioxide; Chlorophyll; Chlorophylls; Community & Population Ecology; Ecology; Electron transport; Eriophorum vaginatum; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Leaves; Life Sciences; Marine ecosystems; Nitrogen; Nitrogen, phosphorus, potassium fertilizations; Nutrient availability; Photosynthesis; Phytochemistry; Plant Ecology; Plant nutrition; Plants; Respiration; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Terrestial Ecology; Tundras; Alaska; Arctic Region; United States; North America; America; Nitrogen use efficiency; Chlorophyll; Fertilisation; LTER; Canopy; Alaska; Leaf mass per area; Short term; Nitrogen fertilization; Nutrient recovery; Plant ecology; Plant leaf; Biomass; Nitrogen; Long term; Polar region; Photosynthesis; Respiration; Canopy(vegetation)
• ISSN: 1385-0237; 1573-5052
• DOI: 10.1007/s11258-013-0250-6

We examined the effects of short (<1–4 years) and long-term (22 years) nitrogen (N) and/or phosphorus (P) addition on the foliar CO2 exchange parameters of the Arctic species Betula nana and Eriophorum vaginatum in northern Alaska. Measured variables included: the carboxylation efficiency of Rubisco (Vcmax), electron transport capacity (Jmax), dark respiration (Rd), chlorophyll a and b content (Chl), and total foliar N (N). For both B. nana and E. vaginatum, foliar N increased by 20–50 % as a consequence of 1–22 years of fertilisation, respectively, and for B. nana foliar N increase was consistent throughout the whole canopy. However, despite this large increase in foliar N, no significant changes in Vcmax and Jmax were observed. In contrast, Rd was significantly higher (>25 %) in both species after 22 years of N addition, but not in the shorter-term treatments. Surprisingly, Chl only increased in both species the first year of fertilisation (i.e. the first season of nutrients applied), but not in the longer-term treatments. These results imply that: (1) under current (low) N availability, these Arctic species either already optimize their photosynthetic capacity per leaf area, or are limited by other nutrients; (2) observed increases in Arctic NEE and GPP with increased nutrient availability are caused by structural changes like increased leaf area index, rather than increased foliar photosynthetic capacity and (3) short-term effects (1–4 years) of nutrient addition cannot always be extrapolated to a larger time scale, which emphasizes the importance of long-term ecological experiments.