Effects of different intensities of long-term grazing on plant diversity, biomass and carbon stock in alpine shrubland on the Qinghai-Tibetan Plateau

Grazing is the main grassland management strategy applied in alpine shrubland ecosystems on the Qinghai-Tibetan Plateau. However, how different intensities of long-term grazing affect plant diversity, biomass accumulation and carbon (C) stock in these ecosystems is poorly understood. In this study, alpine shrubland with different long-term (more than 30 years) grazing intensities (excluded from grazing for 5 years (EX), light grazing (LG), moderate grazing (MG) and heavy grazing (HG)) on the Qinghai-Tibetan Plateau were selected to study changes in plant diversity, aboveground biomass and C accumulation, as well as distribution of C stock among biomass components and soil depths. A structural equation model was used to illustrate the impact of grazing on the soil carbon stock (SOC). The results showed that the Shannon–Wiener diversity index and richness index of herbaceous plants, shrubs, and communities first significantly increased and then decreased with increasing grazing intensity, reaching maxima at the LG site. The aboveground and belowground and litter biomass of understory herbaceous plants, shrubs and communities decreased with increasing grazing intensity, reaching maxima at the EX site. The aboveground and belowground biomass C storage decreased with increasing grazing intensity, reaching maxima at the EX site. The SOC stock and total ecosystem C stock decreased with increasing grazing intensity, reaching maxima at the EX and LG sites. A structural equation model showed that grazing-induced changes in the belowground biomass of understory herbaceous plants greatly contributed to the SOC stock decrease. Thus, considering the utilization and renewal of grassland resources, as well as local economic benefits and ecological effects, LG may be a more rational grazing intensity for species diversity conservation and ecosystem C sequestration in alpine shrubland. Our results provide new insights for incorporating grazing intensity into shrub ecosystem C stock and optimizing grazing management and grassland ecosystem C management.

Climate Benefit of Different Tree Species on Former Agricultural Land in Northern Europe

The new European Union Forest Strategy for 2030 aims to plant an additional 3 billion trees on non-forest land to mitigate climate change. However, the choice of tree species for afforestation to achieve the maximum climate benefit is unclear. We compared the climate benefit of six different species in terms of carbon (C) sequestration in biomass and the harvested wood substitution in products to avoid carbon dioxide (CO2) emissions from fossil-based materials over the 100-year period by afforesting about ¼ of the available area in northern Europe. The highest climate benefit was observed for larch, both at a stand scale (1626 Mg CO2 eqv. ha−1) and at the landscape level for the studied scenario (579 million Mg CO2 eqv.). Larch was followed by Norway spruce, poplar, hybrid aspen and birch, showing a climate benefit about 40–50% lower than that for larch. The climate benefit of willow was about 70% lower than larch. Willow showed 6–14-fold lower C stocks at the landscape level after 100 years than other tree species. The major climate benefit over the 100-year period comes from wood substitution and avoided emissions, but C stock buildup at the landscape level also removes significant amounts of CO2 already present in the atmosphere. The choice of tree species is important to maximize climate change mitigation.

Growth, Quality, and Nitrogen Assimilation in Response to High Ammonium or Nitrate Supply in Cabbage (Brassica campestris L.) and Lettuce (Lactuca sativa L.)

Plants grow better when they are supplied with a combination of ammonium (NH4+) and nitrate (NO3−) than when either one is supplied as the sole N (nitrogen) source. However, the effects of N forms on N metabolism and major N assimilation enzymes in different plants, especially vegetables, are largely neglected. This study was conducted on two plants with distinct NH4+ tolerances to compare the responses of two popular leafy vegetables, Korean cabbage (Brassica campestris L.) ‘Ssamchu’ and lettuce (Lactuca sativa L.) ‘Caesar green’, to the N source. To this end, plant growth and quality, photosynthesis, carbohydrate, N contents (in the forms of NO3−, NO2−, NH4+, total protein), and key N assimilation-related enzyme (NR, NIR, GS, GDH) activities were investigated. When plants were subjected to one of three NH4+:NO3− regimes, 0:100, 50:50, or 100:0, lettuce was relatively more tolerant while cabbage was extremely sensitive to high NH4+. Both plants benefited more from being grown with 50:50 NH4+:NO3−, as evidenced by the best growth performance, ameliorated photosynthesis, and enriched carbohydrate (C) stock content. In addition, as compared to cabbage, the GS and GDH activities were reinforced in lettuce in response to an increasing external NH4+ level, resulting in low NH4+ accumulation. Our findings suggested that boosting or maintaining high GS and GDH activities is an important strategy for the ammonium tolerance in vegetables.

Massive C loss from subalpine grassland soil with seasonal warming larger than 1.5 °C in an altitudinal transplantation experiment

Climate change is associated with a change in soil organic carbon (SOC) stocks, implying a feedback mechanism on global warming. Grassland soils represent 28 % of the global soil C sink and are therefore important for the atmospheric greenhouse gas concentration. In a field experiment in the Swiss Alps we recorded changes in the ecosystem organic carbon stock under climate change conditions, while quantifying the ecosystem C fluxes at the same time (ecosystem respiration, gross primary productivity, C export in plant material and leachate water). We exposed 216 grassland monoliths to six different climate scenarios (CS) in an altitudinal transplantation experiment. In addition, we applied an irrigation treatment (+12–21 % annual precipitation) and an N deposition treatment (+3 and +15 kg N ha−1 a−1) in a factorial design, simulating summer-drought mitigation and atmospheric N pollution. In five years the ecosystem C stock, consisting of plant C and SOC, dropped dramatically by about −14 % (−1034 ± 610 g C m−2) with the CS treatment representing a +3.0 °C seasonal (Apr.–Oct.) warming. N deposition and the irrigation treatment caused no significant effects. Measurements of C fluxes revealed that ecosystem respiration increased by 10 % at the +1.5 °C warmer CS site and by 38 % at the +3 °C warmer CS site (P ≤ 0.001 each), compared to the CS reference site with no warming. However, gross primary productivity was unaffected by warming, as were the amounts of exported C in harvested plant material and leachate water (dissolved organic C). As a result, the five year C flux balance resulted in a climate scenario effect of −936 ± 138 g C m−2 at the +3.0 °C CS, similar to the C stock climate scenario effect. It is likely that this dramatic C loss of the grassland is a transient effect before a new, climate adjusted steady state is reached.

Distribution of carbon stocks in drainage areas on peatlands of Sungai Tohor Village, Meranti Islands District, Indonesia

Silviana SH, Saharjo BH, Sutikno S. 2021. Distribution of carbon stocks in drainage areas on peatlands of Sungai Tohor Village, Meranti Islands District, Indonesia. Biodiversitas 22: 5106-5114. Peatland ecosystems provide a variety of environmental services and biodiversity with their ability to store and absorb carbon. The increase of land clearing followed by the construction of drainage or canal has resulted in the degradation of peatlands and is prone to fire incidences. Canal construction, whether we realize it or not, has a negative ecological impact on the in situ (local) environment, namely land degradation and subsidence, as well as a wider (global) impact in the form of loss of carbon stocks, increased GHG emissions that can trigger global warming. This study aims to identify the distribution of carbon in the area where drainage is made where the distribution of carbon stock in starting at a distance of 10 m, 50 m, 100 m, 250 m, and 350 m from the canal. The study was conducted on the community plantations including unburned areas (rubber plantations and secondary forests) and burned areas. The influence of land use and drainage development on carbon stock distribution is rarely known. The results showed a decrease in C-Stock with a decrease in drainage distance. The quantity of carbon stock in secondary forests ranged from 13.275 ton ha-1 - 24.839 ton ha-1, Burnt Area-1 ranged from 6.995 ton ha-1 - 11.59 ton ha-1, and Burnt Area 2 ranged from 4.677 ton ha-1 - 12.580 ton ha-1. In contrast, rubber plantations had higher C-stock in the initial observation distance, around 9.064 ton ha-1 - 11.805 ton ha-1, which may be due to intensive land use near the canal.

Stability of Woodchips Biochar and Impact on Soil Carbon Stocks: Results from a Two-Year Field Experiment

Biochar has been shown to improve soil quality and crop yields. Furthermore, thanks to its high carbon content (C) and stable chemical structure, biochar can sequester C in the soil for a long time, mitigating climate change. However, the variability in published biochar stability in the soil makes verifying this trait under different environmental and agricultural conditions necessary. Moreover, most of the published literature refers to short-term incubation experiments, which are considered to not adequately represent long-term dynamics under field conditions. This article reports the results of a field experiment carried out in a vineyard near Merano, northern Italy, where the stability of woodchips biochar in soil, its impact on the total soil C stocks as well as on the original soil organic C (priming effect) were studied over two years. Vineyard soil (Dystric Eutrochrept) was amended with biochar (25 and 50 t ha−1) alone or together with compost (45 t ha−1) and compared with unamended control soil. Two methods assessed the stability of biochar in soil: the isotopic mass balance approach and the quantification of Benzene PolyCarboxylic Acids (BPCAs), molecular markers of biochar. The amount of C in the soil organic matter (SOM-C) was determined in the amended plots by subtracting the amount of biochar-C from the total soil organic C stock, and the occurrence of priming effect was verified by comparing SOM-C values at the beginning and at the end of the experiment. Results did not show any significant biochar degradation for both application rates, but results were characterized by a high variation. The application of 50 t ha−1 of biochar significantly increased soil C stock while no effect of biochar on the degradation of SOM-C was observed. Results were confirmed in the case of biochar application together with compost. It can be concluded that the use of woodchips biochar as a soil amendment can increase soil C content in the medium term. However, further analyses are recommended to evaluate the impact of biochar on climate change mitigation in the long term.

Variability in Carbon Stocks Across a Chronosequence of Masson Pine Plantations and the Trade-Off Between Plant and Soil Systems

Plantations sequester atmospheric carbon dioxide and positively respond to climate change, but the carbon (C) sequestration capacity and the trade-off between plant and soil systems in plantations may vary significantly across a chronosequence. Masson pine (Pinus massoniana Lamb.) plantations were selected to investigate the variability of C stocks in 7-, 14-, and 30-year-old stands. The total ecosystem C stock increased with stand age from 14.82 to 19.21 Mg C. Carbon stocks increased with stand age in the plant system but decreased in the soil system, with the ratio of plant-to-soil C stocks increasing from 0.06 in the 7-year-old plantation to 0.70 in the 30-year-old plantation. Carbon stocks in the first 20 cm of the soil accounted for 44.60%, 43.01%, and 30.18% of the total ecosystem carbon stock in 7-, 14-, and 30-year-old plantations, respectively. The variation trends for the proportions of C stock in soil decreased with soil depth as a result of tree and root growth regardless of stand age. Most C was stored in the stems, which contributed 1.36%, 6.85%, and 29.57% of total ecosystem C stock across the chronosequence. Results of structural equation model indicated that the effect of plant system C stock on ecosystem C stock was far larger than soil system C stock, and saturated hydraulic conductivity (ks) and fractal dimension (D) could be the primary parameters affecting ecosystem C stocks according to redundancy analysis (Variance explained by the variables selected). In summary, the plant system increased biomass C stocks by regulating soil properties to meet their growth requirements, the growth of plants in turn changed the soil organic carbon (SOC) stock, then both regulated ecosystem carbon sequestration in Masson pine plantations.

The Role of Small Woody Landscape Features and Agroforestry Systems for National Carbon Budgeting in Germany

The intensification of food production systems has resulted in landscape simplification, with trees and hedges disappearing from agricultural land, principally in industrialized countries. However, more recently, the potential of agroforestry systems and small woody landscape features (SWFs), e.g., hedgerows, woodlots, and scattered groups of trees, to sequester carbon was highlighted as one of the strategies to combat global climate change. Our study was aimed to assess the extent of SWFs embedded within agricultural landscapes in Germany, estimate their carbon stocks, and investigate the potential for increasing agroforestry cover to offset agricultural greenhouse gas (GHG) emissions. We analyzed open-source geospatial datasets and identified over 900,000 hectares of SWFs on agricultural land, equivalent to 4.6% of the total farmland. The carbon storage of SWFs was estimated at 111 ± 52 SD teragrams of carbon (Tg C), which was previously unaccounted for in GHG inventories and could play a role in mitigating the emissions. Furthermore, we found cropland to have the lowest SWF density and thus the highest potential to benefit from the implementation of agroforestry, which could sequester between 0.2 and 2 Tg of carbon per year. Our study highlights that country-specific data are urgently needed to refine C stock estimates, improve GHG inventories and inform the large-scale implementation of agroforestry in Germany.

Global Landscape of Organic Carbon and Total Nitrogen in the Soils of Oasis Ecosystems in Southern Tunisia

The oasis soils of Tunisia face several climatic and soil constraints. Trying to have cultures that are profitable and beneficial in terms of soil C and N sequestration in such environments is already a challenge. To conduct this, we tested under identical conditions four types of occupation in sub-plots adjacent to the crops; barley alone, alfalfa alone, intercropping barley/alfalfa, and a control fallow in a saline gypseous desert soil poor in organic matter. Field experimentation was carried out in the oasis of Degache, which is very representative of other Tunisian oases. The stocks of C and N of the plot were calculated from the start in September 2019 before the installation of the different crops. After 21 months, the control plot shows a decrease of −41% in its stock of C and −25% in its stock N. However, the best result is that of the barley/alfalfa intercropping with an increase of +126.46% in the C stock and +178.67% in the N stock. After almost two years of experience, the beneficial effect of the intercropping system in the oasis is clear. These results are very motivating and seem to be a solution to the rapid decline in soil organic stocks.