Inter-annual variability of precipitation constrains the production response of boreal Pinus sylvestris to nitrogen fertilization
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© 2015 Published by Elsevier B.V.Tree growth resources and the efficiency of resource-use for biomass production determine the productivity of forest ecosystems. In nutrient-limited forests, nitrogen (N)-fertilization increases foliage [N], which may increase photosynthetic rates, leaf area index (L), and thus light interception (I<inf>C</inf>). The product of such changes is a higher gross primary production and higher net primary production (NPP). However, fertilization may also alter carbohydrate partitioning from below- to aboveground, increasing aboveground NPP (ANPP). We analyzed effects of long-term N-fertilization on NPP, and that of long-term carbon storing organs (NPP<inf>S</inf>) in a Pinus sylvestris forest on sandy soil, a wide-ranging forest type in the boreal region. We based our analyses on a combination of destructive harvesting, consecutive mensuration, and optical measurements of canopy openness. After eight-year fertilization with a total of 70gNm-2, ANPP was 27±7% higher in the fertilized (F) relative to the reference (R) stand, but although L increased relative to its pre-fertilization values, I<inf>C</inf> was not greater than in R. On the seventh year after the treatment initiation, the increase of ANPP was matched by the decrease of belowground NPP (78 vs. 92gCm-2yr-1; ~17% of NPP) and, given the similarity of I<inf>C</inf>, suggests that the main effect of N-fertilization was changed carbon partitioning rather than increased canopy photosynthesis. Annual NPP<inf>S</inf> increased linearly with growing season temperature (T) in both treatments, with an upward shift of 70.2gCm-2yr-1 by fertilization, which also caused greater amount of unexplained variation (r2=0.53 in R, 0.21 in F). Residuals of the NPP<inf>S</inf>-T relationship of F were related to growing season precipitation (P, r2=0.48), indicating that T constrains productivity at this site regardless of fertility, while P is important in determining productivity where N-limitation is alleviated. We estimated that, in a growing season average T (11.5±1.0°C; 33-year-mean), NPP<inf>S</inf> response to N-fertilization will be nullified with P 31mm less than the mean (325±85mm), and would double with P 109mm greater than the mean. These results suggest that inter-annual variation in climate, particularly in P, may help explaining the reported large variability in growth responses to fertilization of pine stands on sandy soils. Furthermore, forest management of long-rotation systems, such as those of boreal and northern temperate forests, must consider the efficiency of fertilization in terms of wood production in the context of changes in climate predicted for the region.
Published Version (Please cite this version)10.1016/j.foreco.2015.03.029
Publication InfoLim, H; Oren, R; Palmroth, S; Tor-ngern, P; Mörling, T; Näsholm, T; ... Linder, S (2015). Inter-annual variability of precipitation constrains the production response of boreal Pinus sylvestris to nitrogen fertilization. Forest Ecology and Management, 348. pp. 31-45. 10.1016/j.foreco.2015.03.029. Retrieved from http://hdl.handle.net/10161/10638.
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Nicholas Professor of Earth Systems Science
With his graduate students, Dr. Oren quantifies the components of water flux in forest ecosystems and the influence of biotic and abiotic factors on water and, due to strong links between carbon and water, on carbon flux. Climate variability, including variations in air temperature, vapor pressure deficit, incoming radiation and soil moisture, and environmental change, including elevated atmospheric carbon dioxide, affect the intra- and inter-annual patterns and amounts of water used by forest e
Associate Research Professor in the Division of Environmental Science and Policy
Dr. Palmroth's research focuses on the effects of resource availability and climatic variability on carbon uptake and allocation of individual shoots, trees and forest ecosystems. She studies ecophysiological processes in trees from leaf to stand scales, with special emphasis on conifers. In particular, Dr. Palmroth is interested in the radiative transfer in forest canopies, how the radiation regime is affected by conifer shoot structure, and what the feedbacks are between availability of solar
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