The 4p1000 Initiative: opportunities, limitations and challenges for implementing soil organic carbon sequestration as a sustainable development strategy

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Invasions by exotic plant species can modify biogeochemical cycles and soil properties. We tested whether invasion by early goldenrod (Solidago gigantea, Asteraceae) modifies soil phosphorus pools at three sites in Belgium. Aboveground phytomass and soil samples (0-10 cm) were collected in early goldenrod patches and in adjacent, uninvaded, grassland vegetation. Soil P fractions varied between the three sites in line with corresponding differences in organic matter, carbonate and clay contents. In addition to site-specific impacts, plots invaded by goldenrods generally had higher concentrations of labile P (i.e. resinextractable inorganic P, bicarbonate-extractable inorganic and organic P). Soil CO 2 release, alkaline and acid phosphomonoesterase (PME) activities were also higher in invaded plots, 2 suggesting that the increase in labile Pi was due to enhanced mineralization. Phosphorus uptake by vegetation was 1.7-2.1 times higher in invaded plots, mostly due to the higher annual yield of Solidago gigantea. Altogether, the results indicate that S. gigantea enhances P turnover rates in invaded ecosystems.

Background and aims The introduction of Acacia mangium in Eucalyptus urophylla x grandis stands improves wood production on poor sandy soils of coastal plains of the Congo. We assessed the impact of A. mangium plantations in pure stands and in mixture with eucalypt trees on the physico-chemical properties of the soil after one rotation. Methods Bulk densities, N, C, available P and pH were determined on soil sampled in the pure acacia (100A), pure eucalypt (100E) and mixed-species (50A:50E) stands. N and P were determined in aboveground litters and in leaves, bark and wood of trees. Results N and C concentrations were higher in 50A:50E than in 100A and 100E in the top soil layer. The pH was lower in 100A and higher in 100E than in 50A:50E. The available P was lower in 50A:50E than in 100A and 100E. Leaf N was lower in 50A:50E than in 100A for acacia, and higher than in 100E for eucalypt. Leaf P was similar for acacia but higher for eucalypt in 50A:50E than in 100E. In contrast to P, the amount of N in aboveground litterfall increased with the proportion of acacia in the stand. Conclusions The introduction of acacia trees in eucalypt plantations increased C and N contents of the soil but decreased the available P content in the mixed-species stand. This may be related to a higher uptake of P needed to maintain the N:P stoichiometry in eucalypt leaves. (Résumé d'auteur

First, they need to know what the potential local impacts will be at the scales of counties to cities. Some of this information could be gleaned by combining fine-resolution climate impact assessments with artificial intelligence for 'big data' analyses of weather extremes, health, property damage and other variables. Second, policymakers need to understand uncertainties in the ranges of probable climate impacts and responses. Even regions that are proactive in setting adaptation policies, such as California, lack information about the ever-changing risks of extreme warming, fires and rising seas. Research must be integrated across fields and stakeholders-urban planners, publichealth management, agriculture and ecosystem services. Adaptation strategies should be adjustable if impacts unfold differently. More planning and costing is needed around the worst-case outcomes. Understand options for rapid response. Climate assessments must evaluate quick ways of lessening climate impacts, such as through reducing emissions of methane, soot (or black carbon) and HFCs. Per tonne, these three 'super pollutants' have 25 to thousands of times the impact of CO 2. Their atmospheric lifetimes are short-in the range of weeks (for soot) to about a decade (for methane and HFCs). Slashing these pollutants would potentially halve the warming trend over the next 25 years 10. There has been progress on this front. At Put more carbon in soils to meet Paris climate pledges Take these eight steps to make soils more resilient to drought, produce more food and store emissions, urge Cornelia Rumpel and colleagues.

Input of organic matter to soil may stimulate microbial activity and alter soil carbon storage by modifying the mineralization of native soil organic carbon (SOC). Assessing the age of SOC affected by the altered mineralization is a major challenge as the destabilisation of old SOC would be much more damageable for the overall carbon budget than the mobilization of recent SOC. Here, we investigated the microbial populations sequentially activated after the addition of a labile substrate. We questioned whether they have distinct metabolic potential and we characterised the age of the native SOC they primed. We used soils from Congolese Eucalyptus plantations that were previously under savannah and which old and recent SOC exhibited different ?13C. Soils were amended with glucose, in an amount sufficient to induce microbe growth, and incubated for one week. The ?13C of respired CO2 was continuously recorded using a tuneable diode laser spectrometer (TDLS). The combination of two glucose treatments with different ?13C signatures allowed partitioning the various sources of CO2 over time (recent SOC, old SOC and glucose). This was combined with phospholipids fatty acids (PLFA) analyses and potential metabolic activities measurements after 40 h and seven days of incubation. A peak of glucose mineralization occurred after 17 h of incubation. Before this peak (Stage 1), some specific communities with a strong feeding preference for recent SOC were activated. After the glucose peak (Stage 2), over-mineralization of native SOC occurred for some days. The recent C3 SOC was first preferentially used (Stage 3), while the old C4 SOC was destabilised in a later stage (Stage 4). Metabolic functions and composition of microbial communities also differed between Stages 3 and 4. Microbial populations collected at Stage 4 were slower compared to Stage 3, but more efficient in decomposing nutrient-containing substrates. Gram negative bacteria (16:1w7c and 18:1w7c) were stimulated at Stage 3 only, while Gram negative bacteria (cy17:0) were stimulated at both Stages 3 and 4. Our results demonstrated that the input of labile substrate alters the microbial community composition, potential metabolic activities, and the SOC pools utilisation. They pointed out the necessity to assess the age of destabilised SOC when investigating the impact of priming on carbon storage in soil. (Résumé d'auteur

Invasive exotic plants can modify soil organic matter (SOM) dynamics and other soil properties. We evaluated changes in particulate organic matter (POM) and carbon (C) mineralisation in adjacent plots invaded by Solidago gigantea, Prunus serotina, Heracleum mantegazzianum and Fallopia japonica, and non-invaded control plots on different soils in Belgium. Litter decomposition of S. gigantea and P. serotina was compared to that of the native species Epilobium hirsutum, Betula pendula and Fagus sylvatica. Disregarding the differences in site characteristics (soil texture, parental material and plant species), we argued that the invasion by S. gigantea and P. serotina enhance SOM dynamics by increasing C mineralisation in 2 out of 3 sites invaded by S. gigantea and in 1 out of 3 sites invaded by P. serotina; C in coarse POM (cPOM, 4,000-250 μm) and fine POM (fPOM, 250-50 μm) in 1 site invaded by S. gigantea and C content in total POM (tPOM, 4,000-50 μm) and the organo-mineral fraction (OMF, 0-50 μm) in 1 site invaded by P. serotina. H. mantegazzianum and F. japonica slowed down SOM dynamics by reducing C mineralisation in three out of four sites; C and nitrogen (N) of fPOM in the invaded compared with the non-invaded plots at one site invaded by H. mantegazzianum. However, N content of cPOM (4,000-250 μm) was higher in the invaded sites by F. japonica compared with the non-invaded plots. Our results indicated that the effects of invasion by exotic plant species were not species-specific but site-specific.

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