Publications

NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.

2021

Abstract

Forests have climate change mitigation potential since they sequester carbon. However, their carbon sink strength might depend on management. As a result of the balance between CO2 uptake and emission, forest net ecosystem exchange (NEE) reaches optimal values (maximum sink strength) at young stand ages, followed by a gradual NEE decline over many years. Traditionally, this peak of NEE is believed to be concurrent with the peak of primary production (e.g., gross primary production, GPP); however, in theory, this concurrence may potentially vary depending on tree species, site conditions and the patterns of ecosystem respiration (Reco). In this study, we used eddy-covariance (EC)-based CO2 flux measurements from 8 forest sites that are dominated by Norway spruce (Picea abies L.) and built machine learning models to find the optimal age of ecosystem productivity and that of CO2 sequestration. We found that the net CO2 uptake of Norway spruce forests peaked at ages of 30-40 yrs. Surprisingly, this NEE peak did not overlap with the peak of GPP, which appeared later at ages of 60-90 yrs. The mismatch between NEE and GPP was a result of the Reco increase that lagged behind the GPP increase associated with the tree growth at early age. Moreover, we also found that newly planted Norway spruce stands had a high probability (up to 90%) of being a C source in the first year, while, at an age as young as 5 yrs, they were likely to be a sink already. Further, using common climate change scenarios, our model results suggest that net CO2 uptake of Norway spruce forests will increase under the future climate with young stands in the high latitude areas being more beneficial. Overall, the results suggest that forest management practices should consider NEE and forest productivity separately and harvests should be performed only after the optimal ages of both the CO2 sequestration and productivity to gain full ecological and economic benefits. How to cite: Zhao, J., Lange, H., and Meissner, H.: Mismatch between the optimal ages for ecosystem productivity and net CO2 sequestration in Norway spruce forests, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4257, https://doi.org/10.5194/egusphere-egu21-4257, 2021.

Abstract

Biochar-based fertilizer products (BCF) are receiving increasing attention as potential win-win solutions for mitigating climate change and improving agricultural production. BCFs are reported to increase yields through increased N use efficiency, an effect which is often assumed to result from the slow-release of adsorbed N forms into the soil. Here, we review the magnitude of this effect, the potential for further improvement and the need to consider other mechanisms in product development. Current high-N commercial BCFs are mostly physical blends of biochar and mineral fertilizer, with little evidence of slow-release effects supported by sorption mechanisms. For such products, the main effect potentially results from root-growth promoting factors and from increases in soil pH and Eh and stimulation of beneficial micro-organisms in the rhizosphere, which all result in an increase in uptake of specific nutrients. Our reanalysis of literature data indicates that the median sorption capacity of untreated biochar for mineral N forms requires applying 200 times more biochar than N fertilizer. This ratio needs reducing by at least an order of magnitude for producing efficient sorption-based BCFs. Activation of biochar with acids and oxidizing agents, as reported in many studies, appears to only marginally increase sorption capacity in absolute values. Fixation of clay and organics within the porous structure of biochar appears a more promising technology, suggesting that macro- and mesoporosity is a key biochar property that deserves greater scrutiny and research towards making efficient sorption-based BCFs. Mechanisms of action and dose responses need to be more systematically studied in order to devise products that combine positive effects and can be used within realistic agronomic management practices. Long-term effects resulting from accumulated annual inputs of BCF also need to be better evaluated in terms of nutrient cycling and the progressive improvement of soil health.

Abstract

In a young Norway spruce stand (planted in 2012) at Hoxmark, Southeast Norway, Net Ecosystem Exchange (NEE) was measured using Eddy Covariance. The data were carefully processed with time-dependent stand parameters (i.e. canopy height), a detailed footprint analysis and calculated at 30 min temporal resolution. Photosynthetic Active Radiation (PAR) as the primary driver for carbon uptake was also available at the site. Despite its young age, the plantation already acted as a net carbon sink according to the annual NEE budget, e.g. by ca. 300 g C m-2 in 2019. However, the response of the system depended strongly on hydrometeorological conditions. We demonstrate this by investigating the relationship between NEE and PAR for this system in a temporally local fashion (30 days moving windows), using a Michaelis-Menten approach involving three parameters. Although the regression captured up to ca. 80% of the variance, the parameter estimates differed substantially throughout the season, and were contrasting between the very dry year 2018 and the close to normal year 2019. Comparison with other EC-equipped sites in a future study will clarify whether this variable sensitivity is due to the young age or is a pattern pertaining also to mature spruce stands. https://doi.org/10.5194/egusphere-egu21-5028