| 1. |
- Franklin, Oskar, et al.
(författare)
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Organizing principles for vegetation dynamics
- 2020
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Ingår i: Nature plants. - : Springer Science and Business Media LLC. - 2055-026X .- 2055-0278. ; 6:5, s. 444-453
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Tidskriftsartikel (refereegranskat)abstract
- Plants and vegetation play a critical-but largely unpredictable-role in global environmental changes due to the multitude of contributing processes at widely different spatial and temporal scales. In this Perspective, we explore approaches to master this complexity and improve our ability to predict vegetation dynamics by explicitly taking account of principles that constrain plant and ecosystem behaviour: natural selection, self-organization and entropy maximization. These ideas are increasingly being used in vegetation models, but we argue that their full potential has yet to be realized. We demonstrate the power of natural selection-based optimality principles to predict photosynthetic and carbon allocation responses to multiple environmental drivers, as well as how individual plasticity leads to the predictable self-organization of forest canopies. We show how models of natural selection acting on a few key traits can generate realistic plant communities and how entropy maximization can identify the most probable outcomes of community dynamics in space- and time-varying environments. Finally, we present a roadmap indicating how these principles could be combined in a new generation of models with stronger theoretical foundations and an improved capacity to predict complex vegetation responses to environmental change. Integrating natural selection and other organizing principles into next-generation vegetation models could render them more theoretically sound and useful for earth system applications and modelling climate impacts.
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| 2. |
- Mäkelä, Annikki, et al.
(författare)
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Do mycorrhizal symbionts drive latitudinal trends in photosynthetic carbon use efficiency and carbon sequestration in boreal forests?
- 2022
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 520
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Tidskriftsartikel (refereegranskat)abstract
- There is evidence that carbon fluxes and stocks decrease with increasing latitude in boreal forests, suggesting a reduction in carbon use efficiency. While vegetation and soil carbon dynamics have been widely studied, the empirical finding that ectomycorrhizal fungi (ECM) become more abundant towards the north has not been quantitatively linked to carbon use efficiency. We formulated a conceptual model of combined fine-root and ECM carbon use efficiency (CUE) as NPP/GPP (net primary production/gross primary production). For this, we included the mycorrhiza as gains in plant NPP but considered the extramatrical hyphae as well as exudates as losses. We quantified the carbon processes across a latitudinal gradient using published eco-physiological and morphological measurements from boreal coniferous forests. In parallel, we developed two CUE models using large-scale empirical measurements amended with established models. All models predicted similar latitudinal trends in vegetation CUE and net ecosystem production (NEP). CUE in the ECM model declined on average by 0.1 from latitude 60 to 70 with overall mean 0.390 +/- 0.037. NEP declined by 200 g m(-2) yr(-1) with mean 171 +/- 79.4 g m(-2) yr(-)(1). ECM had no significant effect on predicted soil carbon. Our findings suggest that ECM can use a significant proportion of the carbon assimilated by vegetation and hence be an important driver of the decline in CUE at higher latitudes. Our model suggests the quantitative contribution of ECM to soil carbon to be less important but any possible implications through litter quality remain to be assessed. The approach provides a simple proxy of ECM processes for regional C budget models and estimates.
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| 3. |
- Pulliainen, Jouni, et al.
(författare)
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Early snowmelt significantly enhances boreal springtime carbon uptake
- 2017
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424. ; 114:42, s. 11081-11086
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Tidskriftsartikel (refereegranskat)abstract
- We determine the annual timing of spring recovery from spaceborne microwave radiometer observations across northern hemisphere boreal evergreen forests for 1979–2014. We find a trend of advanced spring recovery of carbon uptake for this period, with a total average shift of 8.1 d (2.3 d/decade). We use this trend to estimate the corresponding changes in gross primary production (GPP) by applying in situ carbon flux observations. Micrometeoro-logical CO2 measurements at four sites in northern Europe and North America indicate that such an advance in spring recovery would have increased the January–June GPP sum by 29 g·C·m−2 [8.4 g·C·m−2 (3.7%)/decade]. We find this sensitivity of the measured springtime GPP to the spring recovery to be in accordance with the corresponding sensitivity derived from simulations with a land ecosystem model coupled to a global circulation model. The model-predicted increase in springtime cumulative GPP was 0.035 Pg/decade [15.5 g·C·m−2 (6.8%)/decade] for Eurasian forests and 0.017 Pg/decade for forests in North America [9.8 g·C·m−2 (4.4%)/decade]. This change in the springtime sum of GPP related to the timing of spring snowmelt is quantified here for boreal evergreen forests.
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| 4. |
- Schiestl-Aalto, Pauliina, et al.
(författare)
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Linking canopy-scale mesophyll conductance and phloem sugar δ13C using empirical and modelling approaches
- 2021
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 229:6, s. 3141-3155
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Tidskriftsartikel (refereegranskat)abstract
- © 2020 The Authors. New Phytologist © 2020 New Phytologist Trust Interpreting phloem carbohydrate or xylem tissue carbon isotopic composition as measures of water-use efficiency or past tree productivity requires in-depth knowledge of the factors altering the isotopic composition within the pathway from ambient air to phloem contents and tree ring. One of least understood of these factors is mesophyll conductance (gm). We formulated a dynamic model describing the leaf photosynthetic pathway including seven alternative gm descriptions and a simple transport of sugars from foliage down the trunk. We parameterised the model for a boreal Scots pine stand and compared simulated gm responses with weather variations. We further compared the simulated δ13C of new photosynthates among the different gm descriptions and against measured phloem sugar δ13C. Simulated gm estimates of the seven descriptions varied according to weather conditions, resulting in varying estimates of phloem δ13C during cold/moist and warm/dry periods. The model succeeded in predicting a drought response and a postdrought release in phloem sugar δ13C indicating suitability of the model for inverse prediction of leaf processes from phloem isotopic composition. We suggest short-interval phloem sampling during and after extreme weather conditions to distinguish between mesophyll conductance drivers for future model development.
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| 5. |
- Wu, Sihong, 1981-
(författare)
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Impact of cold climate on boreal ecosystem processes : exploring data and model uncertainties
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The impact of cold climate on physical and biological processes, especially the role of air and soil temperature in recovering photosynthesis and transpiration in boreal forests, was investigated in a series of studies. A process-based ecosystem model (CoupModel) considering atmospheric, soil and plant components was evaluated and developed using Generalized Likelihood Uncertainty Estimation (GLUE) and detailed measurements from three different sites. The model accurately described the variability in measurements within days, within years and between years. The forcing environmental conditions were shown to govern both aboveground and belowground processes and regulating carbon, water and heat fluxes. However, the various feedback mechanisms between vegetation and environmental conditions are still unclear, since simulations with one model assumption could not be rejected when compared with another. The strong interactions between soil temperature and moisture processes were indicated by the few behavioural models obtained when constrained by combined temperature and moisture criteria. Model performance on sensible and latent heat fluxes and net ecosystem exchange (NEE) also indicated the coupled processes within the system. Diurnal and seasonal courses of eddy flux data in boreal conifer ecosystems were reproduced successfully within defined ranges of parameter values. Air temperature was the major limiting factor for photosynthesis in early spring, autumn and winter, but soil temperature was a rather important limiting factor in late spring. Soil moisture and nitrogen showed indications of being more important for regulating photosynthesis in the summer period. The need for systematic monitoring of the entire system, covering both soil and plant components, was identified as a subject for future studies. The results from this modelling work could be applied to suggest improvements in management of forest and agriculture ecosystems in order to reduce greenhouse gas emissions and to find adaptations to future climate conditions.
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