Search Results (54)

Plantation forests (PFs) play a crucial role in China’s climate change mitigation strategy due to their significant capacity to sequestrate carbon (C). Understanding the long-term trend in PFs’ C uptake capacity and the key drivers influencing it is crucial for optimizing PF management and planning for climate mitigation. In this study, we quantified the long-term (1981–2019) C sequestration of PFs in Jiangsu Province, where PFs have expanded considerably in recent decades, particularly since 2015. Seasonal and interannual variations in gross primary productivity (GPP), net primary productivity (NPP), and net ecosystem productivity (NEP) were assessed using the boreal ecosystem productivity simulator (BEPS), a process-based terrestrial biogeochemical model. The model integrates multiple sources of remote-sensing datasets, such as leaf area index and land cover data, to simulate the critical biogeochemical processes governing land surface dynamics, enabling the quantification of vegetation and soil C stocks and nutrient cycling patterns. The results indicated a significant increasing trend in GPP, NPP, and NEP over the past four decades, suggesting enhanced C sequestration by PFs across the study region. The interannual variability in these indicators was associated with that of nitrogen (N) deposition in recent years, implying that nutrient availability could be a limiting factor for plantation productivity. Seasonal GPP and NPP exhibited peak values in spring (April to May) or late summer (August to September), with increases in growing season productivity in recent years. In contrast, NEP peaked in spring (April to May) but declined to negative values in early summer (July to August), indicating a seasonal C source–sink transition. All three indicators showed a general negative correlation with late-growing-season temperature (August to September), suggesting that summer droughts probably highly constrained the C sequestration of the existing PFs. These findings provide insights for the strategic implementation and management of PFs, particularly in regions with a warm temperate climate undergoing afforestation expansion. Full article

Microplastics have a large surface area and hydrophobic characteristics, which helps them to easily adsorb organic matter and trace metals in soil. This interaction has the potential to alter soil physicochemical properties, affect the bioavailability of metals, and finally influence the toxicity of organisms. In the present study, we exposed Cd or As (Cd/As) to the earthworm Eisenia fetida (Savigny, 1826) in uncontaminated paddy soil, both in the presence and absence of polystyrene (PS) MPs (100~300 μm). The results show that MPs exhibit a significant influence on the physicochemical properties of As-contaminated soil, notably reducing the pH while increasing the electrical conductivity (EC), redox potential (Eh), and dissolved organic carbon (DOC), relative to single As treatment. At a Cd concentration of 40 mg·kg⁻¹, the addition of MPs substantially altered the soil properties, decreasing the pH while increasing the EC and DOC. The effect of MPs on the bioavailable Cd content in soil was associated with Cd concentration. Specifically, MPs significantly increased the content of DGT (diffusion gradient technology)-Cd at a Cd concentration of 60 mg·kg⁻¹. Regarding the bioavailable As content in the soil, MPs led to an increase at a high As concentration (40 mg·kg⁻¹). Moreover, the addition of MPs amplified the uptake rate constants (k_u) of DGT-Cd/As at various exposure concentrations, expediting the uptake of Cd/As by earthworms. In addition, compared to Cd treatment, the growth inhibition of earthworms in the As-treatment group was more significant due to microplastics. The results show that MPs in terrestrial environments magnify the negative effects of (semi-)metals, a phenomenon intricately tied to the degree of contamination by (semi-)metals. The interaction between MPs and metals may induce higher ecological risks for organisms. Full article

The diffusive availability of CO₂ for photosynthesis is orders of magnitude lower in water than in air. This, and the low affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) for CO₂, implies that most marine photoautotrophs (cyanobacteria, microalgae, macroalgae and marine angiosperms or seagrasses) would be severely restricted were they to rely only on dissolved CO₂ for their photosynthetic performance. On the other hand, the ~120 times higher concentration of bicarbonate (HCO₃⁻) makes this inorganic carbon (Ci) form more available for utilisation by marine photosynthesisers. The most common way in marine macrophytes to utilise HCO₃⁻ is to convert it to CO₂ within acidic micro-zones of diffusion boundary layers (DBLs), including the cell walls, as catalysed by an outwardly acting carbonic anhydrase (CA). This would then generate an intra-chloroplastic (or for cyanobacteria intra-carboxysomal) CO₂-concentrating mechanism (CCM). Some algae (e.g., the common macroalgae Ulva spp.) and most cyanobacteria and microalgae feature direct HCO₃⁻ uptake as the most efficient CCM, while others (e.g., some red algae growing under low-light conditions) may rely on CO₂ diffusion only. We will in this contribution summarise our current understanding of photosynthetic carbon assimilation of submerged marine photoautotrophs, and in particular how their ‘biophysical’ CCMs differ from the ‘biochemical’ CCMs of terrestrial C₄ and Crassulacean Acid Metabolism (CAM) plants (for which there is very limited evidence in cyanobacteria, algae and seagrasses). Full article

The unequivocal understanding of the planetary-global climate change has rendered the apportionment of sources and sinks of greenhouse gases in the terrestrial domain, an urgent priority. In the present study, the micrometeorological method of “dynamic gradient fluxes” coupled with the Monin–Obukhov similarity theory, was utilised for the determination of net ecosystem exchange of carbon dioxide (CO₂) from a kiwi plantation. This annual net exchange, in conjunction with the energy and fertiliser equivalent CO₂ used, established the CO₂ footprint of the produce. For the year 2023, the CO₂ Net Ecosystem Exchange (NEE) is −16.20 tonnes per hectare per year (CO₂ uptake by the plantation). The cultivation processes used throughout the year consumed +2.96 tonnes per hectare per year, and after deduction of this value from the NEE, the result is in a net CO₂ sink for the kiwi plantation of −13.24 tonnes per hectare per year. It is hence obvious that, under these conditions, the kiwi plantations in Greece can be net CO₂ sinks. This result is of increasing importance since the country is the fourth largest producer of kiwi globally, with production increasing in later years. Full article

The gross primary productivity (GPP) of vegetation stores atmospheric carbon dioxide as organic compounds through photosynthesis. Its spatial heterogeneity is primarily influenced by the carbon uptake period (CUP) and maximum photosynthetic productivity (GPP_max). Grassland, cropland, and forest are crucial components of China’s terrestrial ecosystems and are strongly influenced by the seasonal climate. However, it remains unclear whether the evolutionary characteristics of GPP are attributable to physiology or phenology. In this study, terrestrial ecosystem models and remote sensing observations of multi-source GPP data were utilized to quantitatively analyze the spatio-temporal dynamics from 1982 to 2018. We found that GPP exhibited a significant upward trend in most areas of China’s terrestrial ecosystems over the past four decades. Over 60% of Chinese grassland and over 50% of its cropland and forest exhibited a positive growth trend. The average annual GPP growth rates were 0.23 to 3.16 g C m⁻² year⁻¹ for grassland, 0.40 to 7.32 g C m⁻² year⁻¹ for cropland, and 0.67 to 7.81 g C m⁻² year⁻¹ for forest. GPP_max also indicated that the overall growth rate was above 1 g C m⁻² year⁻¹ in most regions of China. The spatial trend pattern of GPP_max closely mirrored that of GPP, although local vegetation dynamics remain uncertain. The partial correlation analysis results indicated that GPP_max controlled the interannual GPP changes in most of the terrestrial ecosystems in China. This is particularly evident in grassland, where more than 99% of the interannual variation in GPP is controlled by GPP_max. In the context of rapid global change, our study provides an accurate assessment of the long-term dynamics of GPP and the factors that regulate interannual variability across China’s terrestrial ecosystems. This is helpful for estimating and predicting the carbon budget of China’s terrestrial ecosystems. Full article

The peak of growing season (POG) represents the timing of the maximum capacity of vegetation photosynthesis and acts as a crucial phenological indicator for the carbon cycle in terrestrial ecosystems. However, little is known about how POG responds to extreme climate events such as drought across different biomes. Based on two drought indices, we analyzed the temporal–spatial pattern of drought and POG in China and then investigated how drought influenced the POG in different periods of the early season through correlation analysis. In general, a trend towards increased aridity and earlier POG was found in most areas. The impact of drought on POG differed among periods. On the one hand, an earlier POG enabled plants to reduce evapotranspiration and mitigate the risk of severe summer drought. On the other hand, the drought that occurred in spring impeded plant growth and caused a delay in spring phenology, thereby postponing POG. Summer drought led to an earlier POG in relatively dry biomes but inversely led to a later peak in photosynthetic activity in wetter biomes. We also observed a 1-month/2-month lagged effect of drought on POG in almost half of the areas and a 2-month/ 3-month cumulative effect of drought in the north of 50° N. These findings enhance our understanding of carbon uptake in terrestrial ecosystems by clarifying the mechanisms by which climate change impacts vegetation growth and photosynthetic activity. Full article

Understanding the oceanic carbon cycle, particularly in the Arctic regions, is crucial for addressing climate change. However, significant research gaps persist, especially regarding climate effects on the oceanic carbon cycle in these regions. This review systematically explores Arctic-related research, focusing on mechanisms, regulatory frameworks, and modelling approaches in the oceanic carbon cycle, carbon sink, climate change impact, and maritime shipping. The findings highlight the Arctic’s limited observer presence and high operational costs, hindering the data availability and studies on carbon-cycle changes. This underscores the need to integrate real-time Arctic Ocean monitoring data. Carbon sink research urgently requires direct methods to measure anthropogenic carbon uptake and address uncertainties in air–ocean carbon fluxes due to sea ice melting. Unlike terrestrial carbon cycling research, carbon-cycle studies in the oceans, which are essential for absorbing anthropogenic emissions, receive insufficient attention, especially in the Arctic regions. Numerous policies often fall short in achieving effective mitigation, frequently depending on voluntary or market-based approaches. Analyzing carbon-cycle and sink models has uncovered limitations, primarily due to their global perspective, hampering in-depth assessments of climate change effects on the Arctic regions. To pave the way for future research, enhancing Arctic Ocean climate data availability is recommended, as well as fostering international cooperation in carbon-cycle research, enforcing carbon policies, and improving regional modelling in the Arctic Ocean. Full article

Irrigation with water containing a variety of microcystins (MCs) may pose a potential threat to the normal growth of agricultural plants. To investigate the phytotoxicity of MC-LR at environmental concentrations on rice (Oryza sativa L.), the characteristics of uptake and accumulation in plant tissues, as well as a series of key physio-biochemical process changes in leaves of rice seedlings, were measured at concentrations of 0.10, 1.0, 10.0, and 50.0 μg·L⁻¹ in hydroponic nutrient solutions for 7, 15, 20, and 34 days. Results showed that MC-LR could be detected in rice leaves and roots in exposure groups; however, a significant accumulation trend of MC-LR in plants (BCF > 1) was only found in the 0.10 μg·L⁻¹ group. The time-course study revealed a biphasic response of O₂^•− levels in rice leaves to the exposure of MC-LR, which could be attributed to the combined effects of the antioxidant system and detoxification reaction in rice. Exposure to 1.0–50.0 μg·L⁻¹ MC-LR resulted in significant depletion of GSH and MDA contents in rice leaves at later exposure times (15–34 days). Low MC-LR concentrations promoted nitric oxide synthase (NOS) activity, whereas high concentrations inhibited NOS activity during the later exposure times. The reduced sucrose synthase (SS) activities in rice exposed to MC-LR for 34 days indicated a decrease in the carbon accumulation ability of plants, and therefore may be directly related to the inhibition of plant growth under MC exposure. These findings indicate that the normal physiological status would be disrupted in terrestrial plants, even under exposure to low concentrations of MC-LR. Full article

Diesel contamination of farming soils is of great concern because hydrocarbons are toxic to all forms of life and can potentially enter the food web through crops or plants used for remediation. Data on plant ability to uptake, translocate and accumulate diesel-derived compounds are controversial not only due to the probable diverse attitude of plant species but also because of the lack of a reliable method with which to distinguish petrogenic from biogenic compounds in plant tissues. The purpose of this study was to set up a GC-MS-based protocol enabling the determination of diesel-derived hydrocarbons in plants grown in contaminated soil for assessing human and ecological risks, predicting phytoremediation effectiveness and biomass disposal. To this end, two plant species, Vicia sativa L. and Secale cereale L., belonging to two diverse vascular plant families, were used as plant models. They were grown in soil spiked with increasing concentrations of diesel fuel, and the produced biomass was used to set up the hydrocarbon extraction and GC-MSD analysis. The developed protocol was also applied to the analysis of Typha latifolia L. plants, belonging to a different botanical family and grown in a long-time and highly contaminated natural soil. Results showed the possibility of distinguishing diesel-derived compounds from biogenic hydrocarbons in most terrestrial vascular plants, just considering the total diesel compounds in the n-alkanes carbon range C10–C26, where the interference of biogenic compounds is negligible. Diesel hydrocarbons quantification in plant tissues was strongly correlated (0.92 < r² < 0.99) to the concentration of diesel in spiked soils, suggesting a general ability of the considered plant species to adsorb and translocate relatively low amounts of diesel hydrocarbons and the reliability of the developed protocol. Full article

Terrestrial carbon fluxes are crucial to the global carbon cycle. Quantification of terrestrial carbon fluxes over the Tibetan Plateau (TP) has considerable uncertainties due to the unique ecosystem and climate and scarce flux observations. This study evaluated our recent improvement of terrestrial flux parameterization in the weather research and forecasting model coupled with the vegetation photosynthesis and respiration model (WRF-VPRM) in terms of reproducing observed net ecosystem exchange (NEE), gross ecosystem exchange (GEE), and ecosystem respiration (ER) over the TP. The improvement of VPRM relative to the officially released version considers the impact of water stress on terrestrial fluxes, making it superior to the officially released model due to its reductions in bias, root mean square error (RMSE), and ratio of standard deviation (RSD) of NEE to 0.850 μmol·m⁻²·s⁻¹, 0.315 μmol·m⁻²·s⁻¹, and 0.001, respectively. The improved VPRM also affects GEE simulation, increasing its RSD to 0.467 and decreasing its bias and RMSE by 1.175 and 0.324 μmol·m⁻²·s⁻¹, respectively. Furthermore, bias and RMSE for ER were lowered to −0.417 and 0.954 μmol·m⁻²·s⁻¹, with a corresponding increase in RSD by 0.6. The improved WRF-VPRM simulation indicates that eastward winds drive the transfer of lower CO₂ concentrations from the eastern to the central and western TP and the influx of low-concentration CO₂ inhibits biospheric CO₂ uptake. The use of an improved WRF-VPRM in this study helps to reduce errors, improve our understanding of the role of carbon flux cycle over the TP, and ultimately reduce uncertainty in the carbon flux budget. Full article

The Mediterranean basin is an area particularly exposed to fire risk due to its climate and fire-prone vegetation. In recent decades, the frequency and intensity of wildfires increased, leading to negative effects on forests, such as a decrease in tree growth or an increase in tree mortality, producing a relevant loss of carbon sequestration ecosystem service. This study of the impacts of fires on forests is fundamental for planning adequate forest management strategies aimed at recovering and restoring the affected areas. In this framework, our research delves into the effects of a forest fire that, in 2017, affected a forest of black pine (Pinus nigra Arnold) in Central Italy. Combining satellite and terrestrial analyses, this study evaluated the impact of the fire on tree growth, water use efficiency and carbon sequestration capacity. Our findings highlight the importance of using remote sensing for the accurate identification of fire-affected areas and precise planning of ground-based activities. However, the integration of satellite data with forest surveys and sampling has proven crucial for a detailed understanding of fire’s effects on trees. Dendrochronology and stable isotopes have revealed the post-fire growth decline and altered water usage of defoliated trees. Furthermore, the quantification of CO₂ sequestration highlighted a significant reduction in carbon uptake by damaged trees, with severe implications for this ecosystem service. Full article

Fine roots are essential for terrestrial biogeochemical cycles. Mycorrhizal fungi’s functions in regulating the uptake of carbon (C), nitrogen (N), and phosphorus (P) in plants are increasingly being recognized. However, the influence of mycorrhizae on Chinese plants’ fine-root stoichiometry has not been considered. Herein, 772 plants with identified mycorrhizal types were divided into arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) types to investigate the differences in their fine-root stoichiometry and their driving factors. The results showed that the AM and ECM fine-root stoichiometries were significantly different (p < 0.001; p < 0.05). The AM plants’ fine-root stoichiometry was mainly affected by the soil environment (8.76–90.12%), while ECM plants were more sensitive to climatic factors (23.51–52.41%). Further analysis showed that the mean annual temperature (MAT) was significantly correlated with AM plants’ fine-root C and P and ECM plants’ fine-root N and P. Mean annual precipitation (MAP) was significantly correlated with all AM plants’ fine-root elements (p < 0.01) but was only negatively correlated with ECM fine-root P. It was concluded that the mycorrhizal type affects the response of the fine-root stoichiometry to climate and soil variations. Therefore, the mycorrhizal effect deserves attention when studying the relationship between plant nutrient uptake and environmental changes. Full article

The carbon (C) cycle in inland waters, including carbon concentrations in and carbon dioxide (CO₂) emissions from water surfaces, are at the forefront of biogeochemical studies, especially in regions strongly impacted by ongoing climate change. Towards a better understanding of C storage, transport and emission in Central Asian mountain regions, an area of knowledge that has been extremely poorly studied until now, here, we carried out systematic measurements of dissolved C and CO₂ emissions in rivers and lakes located along a macrotransect of various natural landscapes in the Sayan–Altai mountain region, from the high mountains of the Western Sayan in the northwest of Tyva to the arid (dry) steppes and semideserts in the intermountain basins in the southeast of Tyva on the border with Mongolia. New data on major hydrochemical parameters and CO₂ fluxes (fCO₂) gathered by floating chambers and dissolved organic and inorganic carbon (DOC and DIC, respectively) concentrations collected over the four main hydrological seasons allowed us to assess the current C biogeochemical status of these water bodies in order to judge possible future changes under climate warming. We further tested the impact of permafrost, river watershed size, lake area and climate parameters as well as ‘internal’ biogeochemical drivers (pH, mineralization, organic matter quality and bacterial population) on CO₂ concentration and emissions in lakes and rivers of this region and compared them with available data from other subarctic and mountain settings. We found strong environmental control of the CO₂ pattern in the studied water bodies, with thermokarst lakes being drastically different from other lakes. In freshwater lakes, pCO₂ negatively correlated with O₂, whereas the water temperature exerted a positive impact on pCO₂ in large rivers. Overall, the large complexity of counteracting external and internal drivers of CO₂ exchange between the water surfaces and the atmosphere (CO₂-rich underground DIC influx and lateral soil and subsurface water; CO₂ production in the water column due to dissolved and particulate OC biodegradation; CO₂ uptake by aquatic biota) precluded establishing simple causalities between a single environmental parameter and the fCO₂ of rivers and lakes. The season-averaged CO₂ emission flux from the rivers of Tyva measured in this study was comparable, with some uncertainty, to the C uptake fluxes from terrestrial ecosystems of the region, which were assessed in other works. Full article

Grassland ecosystems are an important component of global terrestrial ecosystems and play a crucial role in the global carbon cycle. Therefore, it is important to study the carbon dioxide (CO₂) process in the Middle Tien Shan grassland ecosystem, which can be regarded as a typical representative of the mountain grasslands in Xinjiang. Eddy covariance (EC) and the global carbon fluxes dataset (GCFD) were utilized to continuously monitor the Middle Tien Shan grassland ecosystem in Xinjiang throughout the 2018 growing season. The findings revealed notable daily and monthly fluctuations in net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco). On a daily basis, there was net absorption of CO₂ during the day and net emission during the night. The grassland acted as a carbon sink from 6:00 to 18:00 and as a carbon source for the remaining hours of the day. On a monthly scale, June and July served as carbon sinks, whereas the other months acted as carbon sources. The accumulated NEE, GPP, and Reco during the growing season were −329.49 g C m⁻², 779.04 g C m⁻², and 449.55 g C m⁻², respectively. On the half-hourly and daily scales, soil temperature (Ts) was the main contributor to CO₂ fluxes and had the greatest influence on the variations in CO₂ fluxes. Additionally, air temperature (Ta) showed a strong correlation with CO₂ fluxes. The grassland ecosystems exhibited the strongest CO₂ uptake, reaching its peak at soil temperatures of 25 °C. Moreover, as the air temperatures rose above 15 °C, there was a gradual decrease in NEE, while CO₂ uptake increased. The applicability of GCFD data is good in the grassland ecosystem of the Middle Tien Shan Mountains, with correlations of 0.59, 0.81, and 0.73 for NEE, GPP, and Reco, respectively, compared to field observations. In terms of remote sensing spatial distribution, the Middle Tien Shan grassland ecosystem exhibits a carbon sink phenomenon. Full article

Despite the acknowledged importance of terrestrial ecosystems in achieving carbon neutrality, current carbon accounting predominantly focuses on CO₂ uptake, neglecting indirect contributions from ecosystem services, such as temperature regulation and air purification. We established a carbon benefit (C benefit) accounting framework that integrated these services and analyzed the drivers influencing the spatial and temporal changes in the C benefit. It was found that the average annual growth rate of C benefits in Chengdu over the past 20 years was 0.91 Tg/a, and the CO₂ emissions reduction due to ecosystem services was 22.47 times that of carbon sinks. Therefore, the contribution of ecosystem regulating services to carbon neutrality cannot be ignored. In addition, the elevation, gross domestic product (GDP), and normalized differential vegetation index (NDVI) are key factors affecting C benefits. It is worth noting that the intensive management of constructed ecosystems can result in significant reductions in ecosystem C benefits. Finally, our findings underline the need for low-carbon policies to not only promote carbon sink projects but also enhance the overall capacity of ecosystem services, which could substantially mitigate global climate change. Full article