Grassland afforestation strongly influences the structure and function of soil microorganisms. Yet the mechanisms of how afforestation could simultaneously alter both the soil fungal and bacterial ...communities and its implications for ecosystem management are poorly understood, especially in nitrogen-limited ecosystems. Using high-throughput sequencing of 16S rRNA and ITS rRNA genes, the present study investigated the changes in soil properties and soil microorganisms after afforestation of natural grasslands with Chinese pine (Pinus tabuliformis) on the Loess Plateau in China. Results showed that soil bacterial diversity had no significant differences among the grassland (GL), forest–grassland transition zone (TZ), and forestland (FL), while soil fungal diversity in the GL was significantly higher than that in the FL and TZ (P < 0.05). The proportion of shared OTUs in the soil bacterial community was higher than that in the soil fungal community among the three land use types. The dominant bacterial phylum shifted from Proteobacteria to Actinobacteria, while the dominant fungal phylum shifted from Ascomycota to Basidiomycota after the GL conversion to the FL. The functional groups of ECM fungi increased significantly while biotrophic fungi decreased significantly after grassland afforestation. Both the soil bacterial and fungal communities in the TZ showed great similarity with those in the FL. In addition, among all examined soil properties, soil nitrogen (N) showed a more significant effect on the soil microbial communities. The reduction of soil N after grassland afforestation resulted in both the structure and function changes in soil microbial communities. Our results demonstrated simultaneously differential changes in the composition and diversity of both soil bacterial and fungal communities after afforestation from grasslands to planted forests.
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•Soil fungal diversity decreases significantly after afforestation.•ECM fungus abundance increases significantly due to pine plantation on grasslands.•Soil microbial diversity is similar between forest-grassland transitions & forestland.•Soil nitrogen plays critical roles in driving soil microbial community changes.
The conifer Taxodium hybrid ‘Zhongshanshan’ (T. hybrid ‘Zhongshanshan’) is characterized by rapid growth, strong stress resistance, and high ornamental value and has significant potential for use in ...afforestation, landscaping, and wood production. The main method of propagating T. hybrid ‘Zhongshanshan’ is tender branch cutting, but the cutting rooting abilities of different T. hybrid ‘Zhongshanshan’ clones differ significantly. To explore the causes of rooting ability differences at a molecular level, we analyzed the transcriptome data of cutting base and root tissues of T. hybrid ‘Zhongshanshan 149’ with a rooting rate of less than 5% and T. hybrid ‘Zhongshanshan 118’ with rooting rate greater than 60%, at the developmental time points in this study. The results indicated that differentially expressed genes between the two clones were mainly associated with copper ion binding, peroxidase, and oxidoreductase activity, response to oxidative stress, phenylpropanoid and flavonoid biosynthesis, and plant hormone signal transduction, among others. The expression pattern of ThAP2 was different throughout the development of the adventitive roots of the two clone cuttings. Therefore, this gene was selected for further study. It was shown that ThAP2 was a nuclear-localized transcription factor and demonstrated a positive feedback effect on rooting in transgenic Nicotiana benthamiana cuttings. Thus, the results of this study explain the molecular mechanism of cutting rooting and provide candidate gene resources for developing genetic breeding strategies for optimizing superior clones of T. hybrid ‘Zhongshanshan’.
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•C, N, P content in soil and microbial biomass increased by afforestation.•Higher C:P and N:P ratios following afforestation suggested P limitation.•Soil bacterial diversity and ...abundance increased by afforestation.•Soil N:P ratio influenced soil microbial biomass, diversity and composition.
Ecological stoichiometry (C:N:P ratios) in soil plays an important role in ecosystem dynamics and functioning; however, its relationship with below-ground microbial diversity following afforestation remains poorly understood. To illustrate the linkage of C, N, and P in soil and microbial biomass, and the effect on the soil bacterial community, soil samples were collected from farmland and from three afforested land, namely Robinia pseudoacacia L., Caragana korshinskii Kom, and abandoned land, which have been arable for the past 40years. Quantitative PCR and Illumina sequencing of the 16S rRNA genes were used to analyze soil bacterial abundance, diversity, and composition. Additionally, soil properties and C, N, and P levels in soil and microbial biomass were estimated. The results revealed that C, N, and P levels in soil and microbial biomass increased following afforestation, with a significant correlation observed, especially for the N:P ratio. Additionally, a rise in 〈alpha〉- and 〈beta〉-diversity of soil bacteria was observed in response to afforestation, and was linked to soil C:P and N:P ratios. Soil bacterial phyla with high relative abundance (relative abundance>1%) across all samples showed inconsistent directional trends in the composition response after afforestation. An increased abundance of Proteobacteria, Acidobacteria, and Nitrospirae were observed, while the abundance of Chloroflexi was opposite (P<0.05) following afforestation. Those were largely influenced by changes in the N:P ratio in soil and microbial biomass. Taken together, significantly increased N:P ratio in soil reflected the deficient P that would be limited for increased microbial biomass and diversity. Thus, P status should be an important factor for sustainable restoration of the forest during the process of afforestation.
Evaluates the effectiveness of attempts to remediate gully erosion over the last 20-year (1997–2017) period in the East Coast region, North Island, and reviews successes and failures since gully ...remediation began 60 years ago (1957–2017). Presents findings in the context of the scope and scale of future remediation efforts required to minimise the initiation of new gullies, the treatment of existing gullies, and the requirement for strategies better suited to preventing the re-activation of gullies located within existing areas of exotic production forests after forest removal. Source: National Library of New Zealand Te Puna Matauranga o Aotearoa, licensed by the Department of Internal Affairs for re-use under the Creative Commons Attribution 3.0 New Zealand Licence.
The recent IPCC reports state that continued anthropogenic greenhouse gas emissions are changing the climate, threatening severe, pervasive and irreversible impacts. Slow progress in emissions ...reduction to mitigate climate change is resulting in increased attention to what is called geoengineering, climate engineering, or climate intervention – deliberate interventions to counter climate change that seek to either modify the Earth's radiation budget or remove greenhouse gases such as CO2 from the atmosphere. When focused on CO2, the latter of these categories is called carbon dioxide removal (CDR). Future emission scenarios that stay well below 2 °C, and all emission scenarios that do not exceed 1.5 °C warming by the year 2100, require some form of CDR. At present, there is little consensus on the climate impacts and atmospheric CO2 reduction efficacy of the different types of proposed CDR. To address this need, the Carbon Dioxide Removal Model Intercomparison Project (or CDRMIP) was initiated. This project brings together models of the Earth system in a common framework to explore the potential, impacts, and challenges of CDR. Here, we describe the first set of CDRMIP experiments, which are formally part of the 6th Coupled Model Intercomparison Project (CMIP6). These experiments are designed to address questions concerning CDR-induced climate reversibility, the response of the Earth system to direct atmospheric CO2 removal (direct air capture and storage), and the CDR potential and impacts of afforestation and reforestation, as well as ocean alkalinization.>
Background and aims
Afforestation is considered one important means of mitigating climate change. However, it is still controversial whether mixed-species plantations (MP) were more conducive to the ...soil organic carbon (SOC) stocks than monoculture plantations (PP).
Methods
We conducted a meta-analysis based on 21 publications to assess the effects of different afforestation modes as well as controlling factors of SOC stocks on the Loess Plateau of China.
Results
Compared with monoculture plantations, mixed-species plantations could significantly increase the response size of SOC stocks by 28%. For different species combinations, tree-shrub mixtures were more conducive to increasing the SOC stocks. In climate-limited regions (MAT <8 °C, MAP <500 mm), the response size of SOC stocks of mixed-species plantations was 34% higher than that of monoculture plantations. Furthermore, significant differences were found in the response size of SOC stocks at young (< 10 yr) and mature stages (> 20 yr). Compared with abandoned land, afforestation on cropland, especially mixed-species plantations, could increase the SOC stocks by 10%. Additionally, compared with monoculture plantations, a stronger coupling relationship was observed between the soil total nitrogen (STN) and SOC stocks in mixed-species plantations.
Conclusion
Our results suggest that for the Loess Plateau of China, planting mixed-species plantations containing nitrogen-fixing plants is a more effective approach to enhancing the SOC stocks than monoculture plantations.
Tree planting is a prevalent strategy to mitigate urban heat. Tree cooling efficiency (TCE), defined as the temperature reduction for a 1% tree cover increase, plays an important role in urban ...climate as it regulates the capacity of trees to alter the surface energy and water budget. However, the spatial variation and more importantly, temporal heterogeneity of TCE in global cities are not fully explored. Here, we used Landsat‐based tree cover and land surface temperature (LST) to compare TCEs at a reference air temperature and tree cover level across 806 global cities and to explore their potential drivers with a boosted regression tree (BRT) machine learning model. From the results, we found that TCE is spatially regulated by not only leaf area index (LAI) but climate variables and anthropogenic factors especially city albedo, without a specific variable dominating the others. However, such spatial difference is attenuated by the decrease of TCE with tree cover, most pronounced in midlatitude cities. During the period 2000–2015, more than 90% of analyzed cities showed an increasing trend in TCE, which is likely explained by a combined result of the increase in LAI, intensified solar radiation due to decreased aerosol content, increase in urban vapor pressure deficit (VPD) and decrease of city albedo. Concurrently, significant urban afforestation occurred across many cities showing a global city‐scale mean tree cover increase of 5.3 ± 3.8% from 2000 to 2015. Over the growing season, such increases combined with an increasing TCE were estimated to on average yield a midday surface cooling of 1.5 ± 1.3°C in tree‐covered urban areas. These results are offering new insights into the use of urban afforestation as an adaptation to global warming and urban planners may leverage them to provide more cooling benefits if trees are primarily planted for this purpose.
We investigated how tree cooling efficiency (TCE) in global cities has recently changed in response to climate change and urbanization. Our satellite‐based evidence suggests a considerable increase of urban tree cooling benefits from both urban afforestation and widely increasing TCE that is likely explained by a combined result of the increase in leaf area index, intensified solar radiation, increase in urban vapor pressure deficit and decrease of city albedo.
Biodiversity experiments have shown that species loss reduces ecosystem functioning in grassland. To test whether this result can be extrapolated to forests, the main contributors to terrestrial ...primary productivity, requires large-scale experiments. We manipulated tree species richness by planting more than 150,000 trees in plots with 1 to 16 species. Simulating multiple extinction scenarios, we found that richness strongly increased stand-level productivity. After 8 years, 16-species mixtures had accumulated over twice the amount of carbon found in average monocultures and similar amounts as those of two commercial monocultures. Species richness effects were strongly associated with functional and phylogenetic diversity. A shrub addition treatment reduced tree productivity, but this reduction was smaller at high shrub species richness. Our results encourage multispecies afforestation strategies to restore biodiversity and mitigate climate change.
Land use changes such as savannah afforestation with eucalypts impact the soil carbon (C) balance, therefore affecting soil CO sub(2) efflux (F sub(s) ), a major flux in the global C cycle. We tested ...the hypothesis that F sub(s) increases with stand age after afforestation, due to an increasing input of fresh organic matter to the forest floor. In a Eucalyptus plantation established on coastal savannahs in Congo, bimonthly measurements of F sub(s) were carried out for 1 year on three adjacent stands aged 0.9, 4.4 and 13.7 years and presenting similar growth patterns. Litterfall and litter accumulation on the forest floor were quantified over a chronosequence. Equations were derived to estimate the contribution of litter decomposition to F sub(s) throughout the rotation. Litterfall increased with stand age after savannah afforestation. F sub(s), that was strongly correlated on a seasonal basis with soil water content (SWC) in all stands, decreased between ages 0.9 year and 4.4 years due to savannah residue depletion, and increased between ages 4.4 years and 13.7 years, mainly because of an increasing amount of decomposing eucalypt litter. The aboveground litter layer therefore appeared as a major source of CO sub(2), whose contribution to F sub(s) in old stands was estimated to be about four times higher than that of the eucalypt-derived soil organic C pool. The high litter contribution to F sub(s) in older stands might explain why 13.7 years-old stand F sub(s) was limited by moisture all year round whereas SWC did not limit F sub(s) for large parts of the year in the youngest stands.
Global atmospheric methane (CH4) concentrations are now approaching 1800 ppbv as a result of the growing imbalance between the net CH4 emissions from natural and anthropogenic sources of this potent ...greenhouse gas, and its consumption by physical and biological processes. The main focus of this review is on how land-use change and soil management can be used to correct this imbalance. Currently, the main terrestrial source for CH4 is from natural wetlands and irrigated rice cultivation, although improvements in water management during rice production have resulted in major reductions of CH4 emissions from this source. Afforestation and reforestation can also enhance soil CH4 oxidation by influencing the composition and activity of the soil methanotroph (aerobic proteobacteria) community. The effects of these and other land-use changes on soil CH4 oxidation are not generally well understood, but are known to influence this process through their effects on a range of soil properties such as soil moisture, nitrogen status, and pH that also affects methanotroph community structure and function.
Recent advances in molecular techniques have confirmed the central role of methanotroph communities in regulating soil CH4 consumption by revealing how they respond to land-use change. Community-level molecular analyses of methanotroph populations under different conditions now provide new insights into the distinct traits of the different subgroups and their ecology.
These advances in understanding the abiotic and biological processes regulating soil CH4 oxidation now offers the possibility of being able to predict which land-use and management practices, especially for afforestation and reforestation, will achieve high soil CH4 oxidation rates They also improve the prospects for integrated assessment of the atmospheric impacts on the global greenhouse gas budget from net soil emissions of CH4, N2O, and CO2 with land use and management change.
•Methanotroph communities respond rapidly to afforestation in undisturbed soil.•Soil CH4 oxidation is regulated mainly by methanotroph community activity.•Effective mitigation depends on particular functional traits of methanotrophs•Better understanding needed of functional traits of methanotroph sub-groups.
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