Carbon farming: Are soil carbon certificates a suitable tool for climate change mitigation?

Increasing soil organic carbon (SOC) stocks in agricultural soils removes carbon dioxide from the atmosphere and contributes towards achieving carbon neutrality. For farmers, higher SOC levels have multiple benefits, including increased soil fertility and resilience against drought-related yield losses. However, increasing SOC levels requires agricultural management changes that are associated with costs. Private soil carbon certificates could compensate for these costs. In these schemes, farmers register their fields with commercial certificate providers who certify SOC increases. Certificates are then sold as voluntary emission offsets on the carbon market. In this paper, we assess the suitability of these certificates as an instrument for climate change mitigation. From a soils' perspective, we address processes of SOC enrichment, their potentials and limits, and options for cost-effective measurement and monitoring. From a farmers' perspective, we assess management options likely to increase SOC, and discuss their synergies and trade-offs with economic, environmental and social targets. From a governance perspective, we address requirements to guarantee additionality and permanence while preventing leakage effects. Furthermore, we address questions of legitimacy and accountability. While increasing SOC is a cornerstone for more sustainable cropping systems, private carbon certificates fall short of expectations for climate change mitigation as permanence of SOC sequestration cannot be guaranteed. Governance challenges include lack of long-term monitoring, problems to ensure additionality, problems to safeguard against leakage effects, and lack of long-term accountability if stored SOC is re-emitted. We conclude that soil-based private carbon certificates are unlikely to deliver the emission offset attributed to them and that their benefit for climate change mitigation is uncertain. Additional research is needed to develop standards for SOC change metrics and monitoring, and to better understand the impact of short term, non-permanent carbon removals on peaks in atmospheric greenhouse gas concentrations and on the probability of exceeding climatic tipping points.

Evaluating ecosystem service changes in a frame of transportation development in Istanbul.

Rapid urbanization and growing transportation infrastructure in cities negatively affect ecosystems and their functions. Quantifying these effects is a prerequisite for integrating environmental considerations into all phases of transportation planning. However, in many developing or newly developed countries, research is lacking that helps to understand and manage the ecological impacts of transportation construction under local conditions. Presented research contributed to filling this gap by investigating the implications of growing transportation infrastructure on three ecosystem services: local climate regulation, erosion control, and photosynthesis potential. As a case study, we used spatial indicators to quantify changes in the supply of ecosystem services caused by the development of the 3rd Bosporus Bridge and its connecting highway in Istanbul, Turkiye. Our results indicate a substantial decrease in ecosystem services close to the transportation infrastructure, including a decrease in local climate regulation (- 5.4%), an increase in erosion (+ 9.4%), and a decline in photosynthesis potential or vegetation health (- 28%). Additionally, hotspots of ES supply change were detected. This study provides a blueprint for planning and impact mitigation studies.

Daily bursts of biogenic cyanogen bromide (BrCN) control biofilm formation around a marine benthic diatom.

The spatial organization of biofilms is strongly regulated by chemical cues released by settling organisms. However, the exact nature of these interactions and the repertoire of chemical cues and signals that micro-organisms produce and exude in response to the presence of competitors remain largely unexplored. Biofilms dominated by microalgae often show remarkable, yet unexplained fine-scale patchy variation in species composition. Because this occurs even in absence of abiotic heterogeneity, antagonistic interactions might play a key role. Here we show that a marine benthic diatom produces chemical cues that cause chloroplast bleaching, a reduced photosynthetic efficiency, growth inhibition and massive cell death in naturally co-occurring competing microalgae. Using headspace solid phase microextraction (HS-SPME)-GC-MS, we demonstrate that this diatom exudes a diverse mixture of volatile iodinated and brominated metabolites including the natural product cyanogen bromide (BrCN), which exhibits pronounced allelopathic activity. Toxin production is light-dependent with a short BrCN burst after sunrise. BrCN acts as a short-term signal, leading to daily "cleaning" events around the algae. We show that allelopathic effects are H(2)O(2) dependent and link BrCN production to haloperoxidase activity. This strategy is a highly effective means of biofilm control and may provide an explanation for the poorly understood role of volatile halocarbons from marine algae, which contribute significantly to the atmospheric halocarbon budget.

Diatom derived polyunsaturated aldehydes do not structure the planktonic microbial community in a mesocosm study.

Several marine and freshwater diatoms produce polyunsaturated aldehydes (PUA) in wound-activated processes. These metabolites are also released by intact diatom cells during algal blooms. Due to their activity in laboratory experiments, PUA are considered as potential mediators of diatom-bacteria interactions. Here, we tested the hypothesis that PUA mediate such processes in a close-to-field mesocosm experiment. Natural plankton communities enriched with Skeletonema marinoi strains that differ in their PUA production, a plankton control, and a plankton control supplemented with PUA at natural and elevated concentrations were observed. We monitored bacterial and viral abundance as well as bacterial community composition and did not observe any influence of PUA on these parameters even at elevated concentrations. We rather detected an alternation of the bacterial diversity over time and differences between the two S. marinoi strains, indicating unique dynamic bacterial communities in these algal blooms. These results suggest that factors other than PUA are of significance for interactions between diatoms and bacteria.

Potential of the economic valuation of soil-based ecosystem services to inform sustainable soil management and policy.

The concept of ecosystem services, especially in combination with economic valuation, can illuminate trade-offs involved in soil management, policy and governance, and thus support decision making. In this paper, we investigate and highlight the potential and limitations of the economic valuation of soil-based ecosystem services to inform sustainable soil management and policy. We formulate a definition of soil-based ecosystem services as basis for conducting a review of existing soil valuation studies with a focus on the inclusion of ecosystem services and the choice of valuation methods. We find that, so far, the economic valuation of soil-based ecosystem services has covered only a small number of such services and most studies have employed cost-based methods rather than state-of-the-art preference-based valuation methods, even though the latter would better acknowledge the public good character of soil related services. Therefore, the relevance of existing valuation studies for political processes is low. Broadening the spectrum of analyzed ecosystem services as well as using preference-based methods would likely increase the informational quality and policy relevance of valuation results. We point out options for improvement based on recent advances in economic valuation theory and practice. We conclude by investigating the specific roles economic valuation results can play in different phases of the policy-making process, and the specific requirements for its usefulness in this context.

Induction of protease release of the resistant diatom Chaetoceros didymus in response to lytic enzymes from an algicidal bacterium.

Marine lytic bacteria can have a substantial effect on phytoplankton and are even capable to terminate blooms of microalgae. The bacterium Kordia algicida was reported to lyse cells of the diatom Skeletonema costatum and several other diatoms by a quorum sensing controlled excretion of proteases. However the diatom Chaetoceros didymus is fully resistant against the bacterial enzymes. We show that the growth curve of this diatom is essentially unaffected by addition of bacterial filtrates that are active against other diatoms. By monitoring proteases from the medium using zymography and fluorescence based activity assays we demonstrate that C. didymus responds to the presence of the lytic bacteria with the induced production of algal proteases. These proteases exhibit a substantially increased activity compared to the bacterial counterparts. The induction is also triggered by signals in the supernatant of a K. algicida culture. Size fractionation shows that only the >30 kD fraction of the bacterial exudates acts as an inducing cue. Implications for a potential induced defense of the diatom C. didymus are discussed.

Interactions of the algicidal bacterium Kordia algicida with diatoms: regulated protease excretion for specific algal lysis.

Interactions of planktonic bacteria with primary producers such as diatoms have great impact on plankton population dynamics. Several studies described the detrimental effect of certain bacteria on diatoms but the biochemical nature and the regulation mechanism involved in the production of the active compounds remained often elusive. Here, we investigated the interactions of the algicidal bacterium Kordia algicida with the marine diatoms Skeletonema costatum, Thalassiosira weissflogii, Phaeodactylum tricornutum, and Chaetoceros didymus. Algicidal activity was only observed towards the first three of the tested diatom species while C. didymus proved to be not susceptible. The cell free filtrate and the >30 kDa fraction of stationary K. algicida cultures is fully active, suggesting a secreted algicidal principle. The active supernatant from bacterial cultures exhibited high protease activity and inhibition experiments proved that these enzymes are involved in the observed algicidal action of the bacteria. Protease mediated interactions are not controlled by the presence of the alga but dependent on the cell density of the K. algicida culture. We show that protease release is triggered by cell free bacterial filtrates suggesting a quorum sensing dependent excretion mechanism of the algicidal protein. The K. algicida / algae interactions in the plankton are thus host specific and under the control of previously unidentified factors.