Sources and export fluxes of inorganic and organic carbon and nutrient species from the seasonally ice-covered Yukon River

Climate and environmental changes are having profound impacts on Arctic river basins, but the biogeochemical response remains poorly understood. To examine the effect of ice formation on temporal variations in composition and fluxes of carbon and nutrient species, monthly water and particulate samples collected from the lower Yukon River between July 2004 and September 2005 were measured for concentrations of organic and inorganic C, N, and P, dissolved silicate (Si(OH)₄), and stable isotope composition (δD and δ¹⁸O). All organic carbon and nutrient species had the highest concentration during spring freshet and the lowest during the winter season under the ice, indicating dominant sources from snowmelt and flushing of soils in the drainage basin. In contrast, inorganic species such as dissolved inorganic carbon (DIC) and Si(OH)₄ had the highest concentrations in winter and the lowest during spring freshet, suggesting dilution during snowmelt and sources from groundwater and leaching/weathering of mineral layer. The contrasting relation with discharge between organic, such as dissolved organic carbon (DOC), and inorganic, such as DIC and Si(OH)₄, indicates hydrological control of solute concentration but different sources and transport mechanisms for organic and inorganic carbon and nutrient species. Concentration of DOC also shows an inter-annual variability with higher DOC in 2005 (higher stream flow) than 2004 (lower stream flow). Average inorganic N/P molar ratio was 110?±?124, with up to 442 under the ice and 38–70 during the ice-open season. While dissolved organic matter had a higher C/N ratio under the ice (45–62), the particulate C/N ratio was lower during winter (21–26) and spring freshet (19). Apparent fractionation factors of C, N, P, Si and δD and δ¹⁸O between ice and river water varied considerably, with high values for inorganic species such as DIC and Si(OH)₄ (45 and 9550, respectively) but lower values for DOC (4.7). River ice formation may result in fractionation of inorganic and organic solutes and the repartitioning of seasonal flux of carbon and nutrient species. Annual export flux from the Yukon River basin was 1.6?×?10¹² g-DOC, 4.4?×?10¹² g-DIC, and 0.89?×?10¹² g-POC during 2004–2005. Flux estimation without spring freshet sampling results in considerable underestimation for organic species but significant overestimation for inorganic species regardless of the flux estimation methods used. Without time-series sampling that includes frozen season, an over- or under-estimation in carbon and nutrient fluxes will occur depending on chemical species. Large differences in carbon export fluxes between studies and sampling years indicate that intensive sampling together with long-term observations are needed to determine the response of the Yukon River to a changing climate.     

Geochemical composition,phosphorus speciation and mass transport of fine-grained sediment in two Lake Erie tributaries

The concentration of major elements (Si, Al, Ca, Mg, Na, K, Fe, Ti, Mn and P), particulate phosphorus forms (NH₄Cl-RP, BD-RP, NaOH-RP, HCl-RP and NaOH₍₈₅₎-RP) and carbon content were determined in six size fractions (<8, 8–12, 12–19, 19–31, 31–42 and 42–<60 µm) of sediment collected at gauging stations located in two Lake Erie tributaries (Big Creek and Big Otter Creek). Concentrations of major elements and phosphorus forms were remarkably similar in sediment size fractions from both rivers. Nonapatite inorganic P (NAIP) and organic P (OP) concentrations increased with decreasing grain size while apatite inorganic P (AIP) content decreased with decreasing grain size. Results of phosphorus fractionation studies were combined with historical (particle size) and hydrometric data to simulate the export of particle P on tributary sediment < 63 µm. AIP represents 67 and 70% of the calculated particulate P mass while NAIP accounts for 26 and 23% of sediment-bound P transported in Big Otter Creek and Big Creek, respectively. The < 8 µm size fraction of tributary sediment is the most significant for the potential release of bioavailable P into the water column.     

Soil solution chemistry in lodgepole pine (Pinus contorta ssp. latifolia) ecosystems,southeastern Wyoming,USA

Concentrations of the principal inorganic and organic solutes in the soil root-zone were measured in six contrasting lodgepole pine (Pinus contorta ssp.latifolia) forest ecosystems for five years (1979–1983). Consistent temporal changes in the principal inorganic solutes (Ca, Mg, K, Na, SO₄, Cl) were observed in all the forest stands and years of study: high concentrations at the initiation of snowmelt in the spring were followed by rapid declines to rather constant values in the mid to late stages of snowmelt. Except for K, concentrations of these solutes differed significantly between sites and between years. Sulfate was the principal mobile anion in the root-zone soil solutions, but contributions of bicarbonate and organic anions also were important.The pH of root-zone solutions was relatively high (6.0), did not change significantly as snowmelt proceeded, and was significantly lower in high-clay soils. No consistent trends in bicarbonate alkalinity were observed and soil atmosphere CO₂ concentrations were only about 10 to 20 times above atmospheric levels, peaking at the end of the snowmelt interval. Concurrent changes in the concentrations of dissolved organic carbon, non-volatile acid-neutralizing capacity, and total Al and Fe indicated that these soil-forming metals were transported vertically in the soil as organic complexes. Precipitation of these complexes was more rapid and more complete in the soils with high clay content than in the coarser soils. Moreover, organic anions comprised up to 30% of the total anionic charge in the coarse-textured soils but less than 10% in the fine soils.Little seasonal or spatial variation of inorganic N and P concentrations was observed in root-zone solutions, probably as a result of high biotic demand for these limiting nutrients. Flux of N and P in these ecosystems was predominately via organic forms so that losses of these nutrients was strongly linked to the mobility of dissolved organic carbon. However, a two-fold increase in the organic N:P and C:P ratios was observed during passage of melt water from the forest floor to mineral soil, evidence of more rapid mineralization of organic P.     

Microalgal bacterial floc properties are improved by a balanced inorganic/organic carbon ratio

Microalgal bacterial floc (MaB‐floc) reactors have been suggested as a more sustainable secondary wastewater treatment. We investigated whether MaB‐flocs could be used as tertiary treatment. Tertiary influent has a high inorganic/organic carbon ratio, depending on the efficiency of the secondary treatment. In this study, the effect of this inorganic/organic carbon ratio on the MaB‐flocs performance was determined, using three sequencing batch photobioreactors. The MaB‐flocs were fed with synthetic wastewater containing 84, 42, and 0 mg L⁻¹ C‐KHCO₃ supplemented with 0, 42, 84 mg L⁻¹ C‐sucrose, respectively, representing inorganic versus organic carbon. Bicarbonate significantly decreased the autotrophic index of the MaB‐flocs and resulted in poorly settling flocs. Moreover, sole bicarbonate addition led to a high pH of 9.5 and significant lower nitrogen removal efficiencies. Sucrose without bicarbonate resulted in good settling MaB‐flocs, high nitrogen removal efficiencies and neutral pH levels. Despite the lower chlorophyll a content of the biomass and the lower in situ oxygen concentration, 92–96% of the soluble COD‐sucrose was removed. This study shows that the inorganic/organic carbon ratio of the wastewater is of major importance and that organic carbon is requisite to guarantee a good performance of the MaB‐flocs for wastewater treatment. Biotechnol. Bioeng. 2011; 108:549–558. © 2010 Wiley Periodicals, Inc.     

Strong seasonal patterns of DOC release by a temperate seaweed community: Implications for the coastal ocean carbon cycle

Release of dissolved organic carbon (DOC) by seaweed underpins the microbial food web and is crucial for the coastal ocean carbon cycle. However, we know relatively little of seasonal DOC release patterns in temperate regions of the southern hemisphere. Strong seasonal changes in inorganic nitrogen availability, irradiance, and temperature regulate the growth of seaweeds on temperate reefs and influence DOC release. We seasonally surveyed and sampled seaweed at Coal Point, Tasmania, over 1 year. Dominant species with or without carbon dioxide (CO₂) concentrating mechanisms (CCMs) were collected for laboratory experiments to determine seasonal rates of DOC release. During spring and summer, substantial DOC release (10.06–33.54 μmol C · g DW⁻¹ · h⁻¹) was observed for all species, between 3 and 27 times greater than during autumn and winter. Our results suggest that inorganic carbon (C_i) uptake strategy does not regulate DOC release. Seasonal patterns of DOC release were likely a result of photosynthetic overflow during periods of high gross photosynthesis indicated by variations in tissue C:N ratios. For each season, we calculated a reef-scale net DOC release for seaweed at Coal Point of 7.84–12.9 g C · m⁻² · d⁻¹ in spring and summer, which was ~16 times greater than in autumn and winter (0.2–1.0 g C · m⁻² · d⁻¹). Phyllospora comosa, which dominated the biomass, contributed the most DOC to the coastal ocean, up to ~14 times more than Ecklonia radiata and the understory assemblage combined. Reef-scale DOC release was driven by seasonal changes in seaweed physiology rather than seaweed biomass.     

Seasonal distribution and changes in the nutritive quality of living,dead and detrital fractions of Zostera marina L.

Samples of eelgrass, Zostera marina L., were collected monthly from December 1974 through December 1975 in a shallow embayment near Beaufort, N.C., and separated into green leaves, dead leaves, and leaf detrital material. Each component was analysed for dry weight, organic matter, inorganic and organic carbon, nitrogen and amino compounds.The standing crop of green and dead blades reached a maximum in April through June, while detrital matter had peaks in December, April and July–September. Inorganic carbon in the three grass fractions showed seasonal variations similar to those observed for epiphytic biomass in previous years, and represented 14, 24, and 30% of the total carbon associated with the green and dead leaves and detrital fragments, respectively. Organic carbon represented a decreasing proportion of the dry weight of these three fractions on a dry weight basis while there was a significant increase in organic carbon on an ash-free dry weight basis in the detrital fragments relative to the head dead blades. During senescence there was a loss of nitrogen from the leaves and an increase in the nitrogen content of the organic matter of the detritus relative to the dead leaves. The latter suggests that there was microbial growth on the detritus and subsequent nitrogen immobilization from the surrounding medium. There were significant decreases of lysine, histidine, arginine, glycine, tyrosine, and glucosamine in the dead leaves relative to the detritus. The glucosamine, derived from N-acetyl-glucosamine, a product of murein which is a component of microbial cell walls, had a seasonal distribution similar to that of the epiphytic community and available inorganic nitrogen in the surrounding water. The relative proportions of N-acetyl-glucosamine, nitrogen and organic carbon were all higher in the fall and winter.     

Nutrient availability affects the response of the calcifying chlorophyte Halimeda opuntia (L.) J.V. Lamouroux to low pH

Atmospheric carbon dioxide emissions cause a decrease in the pH and aragonite saturation state of surface ocean water. As a result, calcifying organisms are expected to suffer under future ocean conditions, but their physiological responses may depend on their nutrient status. Because many coral reefs experience high inorganic nutrient loads or seasonal changes in nutrient availability, reef organisms in localized areas will have to cope with elevated carbon dioxide and changes in inorganic nutrients. Halimeda opuntia is a dominant calcifying primary producer on coral reefs that contributes to coral reef accretion. Therefore, we investigated the carbon and nutrient balance of H. opuntia exposed to elevated carbon dioxide and inorganic nutrients. We measured tissue nitrogen, phosphorus and carbon content as well as the activity of enzymes involved in inorganic carbon uptake and nitrogen assimilation (external carbonic anhydrase and nitrate reductase, respectively). Inorganic carbon content was lower in algae exposed to high CO₂, but calcification rates were not significantly affected by CO₂ or inorganic nutrients. Organic carbon was positively correlated to external carbonic anhydrase activity, while inorganic carbon showed the opposite correlation. Carbon dioxide had a significant effect on tissue nitrogen and organic carbon content, while inorganic nutrients affected tissue phosphorus and N:P ratios. Nitrate reductase activity was highest in algae grown under elevated CO₂ and inorganic nutrient conditions and lowest when phosphate was limiting. In general, we found that enzymatic responses were strongly influenced by nutrient availability, indicating its important role in dictating the local responses of the calcifying primary producer H. opuntia to ocean acidification.     

Soil Respiration in Different Agricultural and Natural Ecosystems in an Arid Region

The variation of different ecosystems on the terrestrial carbon balance is predicted to be large. We investigated a typical arid region with widespread saline/alkaline soils, and evaluated soil respiration of different agricultural and natural ecosystems. Soil respiration for five ecosystems together with soil temperature, soil moisture, soil pH, soil electric conductivity and soil organic carbon content were investigated in the field. Comparing with the natural ecosystems, the mean seasonal soil respiration rates of the agricultural ecosystems were 96%–386% higher and agricultural ecosystems exhibited lower CO₂ absorption by the saline/alkaline soil. Soil temperature and moisture together explained 48%, 86%, 84%, 54% and 54% of the seasonal variations of soil respiration in the five ecosystems, respectively. There was a significant negative relationship between soil respiration and soil electrical conductivity, but a weak correlation between soil respiration and soil pH or soil organic carbon content. Our results showed that soil CO₂ emissions were significantly different among different agricultural and natural ecosystems, although we caution that this was an observational, not manipulative, study. Temperature at the soil surface and electric conductivity were the main driving factors of soil respiration across the five ecosystems. Care should be taken when converting native vegetation into cropland from the point of view of greenhouse gas emissions.     

The winter and summer partitioning of dissolved nitrogen and phosphorus. Observations across the Irish Sea during 1997 and 1998

Winter and summer water column profiles from a transect co-inciding with the 54° N parallel across the Irish Sea were examined for relationships between the fractions of total dissolved nitrogen and phosphorus. Inorganic nitrogen and phosphorus gave the expected seasonal variation. As inorganic nitrogen concentrations decreased during the summer, dissolved organic nitrogen concentrations increased. Dissolved organic phosphorus showed little seasonal variation and formed a smaller fraction of the total dissolved pool compared to nitrogen. Winter inorganic nitrogen and phosphorus salinity relationships were conservative: winter organic nitrogen and phosphorus salinity relationships were not conservative. In the winter, dissolved organic nitrogen and phosphorus formed a significant fraction of the total dissolved pool.     

Temporal variation in organic carbon spiraling in Midwestern agricultural streams

Inland freshwaters transform and retain up to half of the carbon that enters from the terrestrial environment and have recently been recognized as important components of regional and global carbon budgets. However, the importance of small streams to these carbon budgets is not well understood due to the lack of globally-distributed data, especially from streams draining agricultural landscapes. We quantified organic carbon pools and heterotrophic metabolism seasonally in 6 low-order streams draining row-crop fields in northwestern Indiana, USA, and used these data to examine patterns in organic carbon spiraling lengths (S_OC; km), downstream velocities (V_OC; m/d), and turnover rates (K_OC; day^?1). There were seasonal differences in S_OC, with the longest spiraling lengths in winter (range: 7.7–54.4?km) and the shortest in early and late summer (range: 0.2–9.0?km). This seasonal pattern in S_OC was primarily driven by differences in discharge, suggesting that hydrology tightly controls the fate of organic carbon in these streams. K_OC did not differ seasonally, and variability (range: 0.0007–0.0193?day^?1) was controlled by differences in stream water soluble reactive phosphorus concentrations. Compared to previous studies conducted primarily in forested streams, agricultural streams tended to be less retentive of organic carbon. These systems function predominantly as conduits transporting organic carbon to downstream ecosystems, except during low, stable-flow periods (i.e., late summer) when agricultural streams can be as retentive of organic carbon as forested headwaters. High organic carbon retention in the late summer has implications for coupled carbon and nitrogen cycling (i.e., denitrification), which may play an important role in removing nitrate from stream water during periods of low flow.     

Specific ultra-violet absorbance as an indicator of mercury sources in an Adirondack River basin

The Adirondack region of New York has been identified as a hot spot where high methylmercury concentrations are found in surface waters and biota, yet mercury (Hg) concentrations vary widely in this region. We collected stream and groundwater samples for Hg and organic carbon analyses across the upper Hudson River, a 493 km² basin in the central Adirondacks to evaluate and model the sources of variation in filtered total Hg (FTHg) concentrations. Variability in FTHg concentrations during the growing seasons (May–Oct) of 2007–2009 in Fishing Brook, a 66-km² sub-basin, was better explained by specific ultra-violet absorbance at 254 nm (SUVA₂₅₄), a measure of organic carbon aromaticity, than by dissolved organic carbon (DOC) concentrations, a commonly used Hg indicator. SUVA₂₅₄ was a stronger predictor of FTHg concentrations during the growing season than during the dormant season. Multiple linear regression models that included SUVA₂₅₄ values and DOC concentrations could explain 75 % of the variation in FTHg concentrations on an annual basis and 84 % during the growing season. A multiple linear regression landscape modeling approach applied to 27 synoptic sites across the upper Hudson basin found that higher SUVA₂₅₄ values are associated with gentler slopes, and greater riparian area, and lower SUVA₂₅₄ values are associated with an increasing influence of open water. We hypothesize that the strong Hg–SUVA₂₅₄ relation in this basin reflects distinct patterns of FTHg and SUVA₂₅₄ that are characteristic of source areas that control the mobilization of Hg to surface waters, and that the seasonal influence of these source areas varies in this heterogeneous basin landscape.     

Significance of ocean carbonate budgets for the global carbon cycle

Changes in the trace gas composition of the atmosphere over glacial–interglacial cycles are linked to changes in the oceanic carbon cycle. This paper examines the role of biologically driven fluxes of organic and inorganic carbon in modifying the carbon dioxide chemistry of the oceans, and the corresponding implications for the partitioning of CO₂ between the atmosphere and ocean. Relevant details of the marine carbon system are presented together with an assessment of the significance of remineralization and dissolution processes. Recent estimates of the marine carbonate fluxes show significant uncertainties and inconsistencies which must be resolved in order to assess fully the role of the oceans' biota in the marine carbon system. Various types of ocean carbon cycle models have been developed in order to interpret the changes in past atmospheric carbon dioxide. Some take account of the role of the oceans' biota, focussing in the main on the cycling of organic matter. Relatively few have considered the role of the carbonate pump and the subtle interactions between organic and inorganic carbon cycling. The significance of carbonate formation and dissolution, and of the effects of global change on the marine carbonate system, for air–sea fluxes of CO₂ are discussed. Finally some recommendations for future research are made in order to improve our understanding of how spatial and temporal variation in marine carbonate fluxes, in conjunction with processes determining the oxidation and burial of organic matter in the oceans, affect levels of CO₂ in the atmosphere.     

Net annual global warming potential and greenhouse gas intensity in Chinese double rice‐cropping systems: a 3‐year field measurement in long‐term fertilizer experiments

The impact of agricultural management on global warming potential (GWP) and greenhouse gas intensity (GHGI) is not well documented. A long‐term fertilizer experiment in Chinese double rice‐cropping systems initiated in 1990 was used in this study to gain an insight into a complete greenhouse gas accounting of GWP and GHGI. The six fertilizer treatments included inorganic fertilizer [nitrogen and phosphorus fertilizer (NP), nitrogen and potassium fertilizer (NK), and balanced inorganic fertilizer (NPK)], combined inorganic/organic fertilizers at full and reduced rate (FOM and ROM), and no fertilizer application as a control. Methane (CH₄) and nitrous oxide (N₂O) fluxes were measured using static chamber method from November 2006 through October 2009, and the net ecosystem carbon balance was estimated by the changes in topsoil (0–20 cm) organic carbon (SOC) density over the 10‐year period 1999–2009. Long‐term fertilizer application significantly increased grain yields, except for no difference between the NK and control plots. Annual topsoil SOC sequestration rate was estimated to be 0.96 t C ha^?1 yr^?1 for the control and 1.01–1.43 t C ha^?1 yr^?1 for the fertilizer plots. Long‐term inorganic fertilizer application tended to increase CH₄ emissions during the flooded rice season and significantly increased N₂O emissions from drained soils during the nonrice season. Annual mean CH₄ emissions ranged from 621 kg CH₄ ha^?1 for the control to 1175 kg CH₄ ha^?1 for the FOM plots, 63–83% of which derived from the late‐rice season. Annual N₂O emission averaged 1.15–4.11 kg N₂O–N ha^?1 in the double rice‐cropping systems. Compared with the control, inorganic fertilizer application slightly increased the net annual GWPs, while they were remarkably increased by combined inorganic/organic fertilizer application. The GHGI was lowest for the NP and NPK plots and highest for the FOM and ROM plots. The results of this study suggest that agricultural economic viability and GHGs mitigation can be simultaneously achieved by balanced fertilizer application.     

Budgets of organic and inorganic carbon in a Mediterranean coastal lagoon dominated by submerged vegetation

In this article, we studied the fluxes of organic and inorganic (DIC) carbon in a coastal lagoon dominated by highly productive macrophyte meadows (Albufera des Grau, Balearic Islands). Seasonal and annual carbon budgets were performed from estimates of whole-system fluxes, and the fate of organic matter production was evaluated through a stable isotope exploration of the food web. The results showed an extremely intense cycling of DIC, with a turnover between 65 and 13 times faster than water turnover. The metabolic fluxes were the main contributors to the seasonal and annual DIC budgets, which were secondarily affected by calcite precipitation, atmospheric exchange and hydrological fluxes. The inorganic carbon dynamics was strongly determined by the seasonal cycle of the meadows. Accordingly the air?Cwater CO₂ flux shifted seasonally, and the lagoon was a sink of atmospheric CO₂ during the vegetated period and a source during the period without macrophytes. The high macrophytic production played a minor role in the lagoon food web, which apparently relied on phytoplanktonic or allochthonous organic matter. A fast decomposition of macrophytic biomass appeared to be the main destiny of the annual macrophytic production, which was only secondarily buried in the sediments.     

Temporal variations in microbenthic metabolism and inorganic nitrogen fluxes in sandy and muddy sediments of a tidally dominated bay in the northern Wadden Sea

Factors controlling seasonal variations in benthic metabolism (O₂ flux) and dissolved inorganic nitrogen (DIN) fluxes were examined during a 12–14 month period at three intertidal Wadden Sea stations. Since the flux measurements were made as small-scale laboratory core incubations, the results are primarily related to the microbenthic community (microalgae, bacteria, micro-, meio- and small macrofauna) and cannot be considered representative of the total benthic community in the Wadden Sea. Furthermore, it has to be emphasized that light intensity during day-time simulations were constant and saturating at all times. Benthic primary production and oxygen uptake appeared to be temperature dependent with a ‘seasonal Q₁₀’ of 1.7–1.8 and 2.7–4.3, respectively. Inundation had no effect on oxygen fluxes as evidenced by similar sediment respiration with and without water cover. A stronger temperature dependence of primary production in muddy than in sandy sediment indicated that the overall control in the latter may be complex due to factors like macrofaunal grazing and nutrient availability. Benthic respiration may not be controlled by temperature alone, as sedimentary organic matter content correlated significantly with both temperature and benthic respiration. Annual gross primary production in high intertidal sandy sediment was 10 and 50% higher than in low intertidal sandy and muddy sediments, respectively. Since annual benthic community respiration was 2 times higher in muddy than sandy sediments, the annual net primary production was about 0 in the former and 17–19 mol C m^?2 yr^?1 in the latter. However, heterotrophic contribution by larger faunal components as well as removal of organic carbon by waves and tidal currents, which are not included here, may balance the budget at the sandy stations. There was no or only weak relationships between (light and dark) DIN exchange and factors like temperature, sedimentary organic content, and oxygen fluxes. Factors related to nutrient fluxes, such as denitrification and nutrient concentration in the overlying water, may have hampered any such relationships. In fact, DIN fluxes at all three stations appeared to be strongly controlled by DIN concentrations in the overlying water. On an annual basis, the sediment appeared to be a net sink for DIN.     

Soil biological activity and their seasonal variations in response to long-term application of organic and inorganic fertilizers

The objectives of this study were to explore the effects of long-term and continued application of fertilizers and manures on microbial biomass, soil biological activity and their seasonal variations in surface and subsurface soils in relation to soil fertility. For this, soils were sampled in spring, summer and autumn from Shenyang Long-term Experimental Station, northeastern China. The results showed that soil total nitrogen (N), organic carbon (C), basal respiration, microbial biomass and enzymatic activity increased in manure-amended surface soils, but decreased with soil depth. Long-term application of inorganic fertilizers significantly decreased soil pH value, sucrase activity and microbial biomass C, but increased soil metabolic quotient (qCO₂). However, no significant effect of inorganic fertilizers on soil total N, urease activity and microbial biomass N was observed in comparison with CK0 (neither tillage nor fertilization) and CK (no fertilizers). There was no significant difference between CK0 and CK in soil total N, organic C and microbial activity in surface soil layer (0–20 cm), but these parameters in subsurface soil layer (20–40 cm) were higher in CK than in CK0. Moreover, seasonal changes were observed in terms of soil nutrient contents, enzymatic activity, microbial biomass and soil respiration. There were significant correlations between soil microbial biomass C and N, between organic C and sucrase activity and between total N and urease activity, respectively. It is recommended that combined use of organic manure with inorganic fertilizers should be considered to maintain higher microbial biomass, soil biological activity and soil fertility. Considering considerably high nutrients reserve and microbial activity in subsurface layers of soil and wind-erosion-caused nutrient loss in spring in north China, we also propose that low tillage should be considered to make use of nutrients in soils.     

MACl‐Assisted Ge Doping of Pb‐Hybrid Perovskite: A Universal Route to Stabilize High Performance Perovskite Solar Cells

Interfacial engineering, grain boundary, and surface passivation in organic–inorganic hybrid perovskite solar cells (HyPSCs) are effective in achieving high performance and enhanced durability. Organic additives and inorganic doping are generally used to chemically modify the surface contacting charge transport layers, and/or grain boundaries so as to reduce the defect density. Here, a simple but tricky one‐step method to dope organic–inorganic hybrid perovskite with Ge for the first time is reported. Unlike Ge doping to all‐inorganic perovskites, application of GeI₂ in organic–inorganic perovskite precursors is challenging due to the extremely poor solubility of GeI₂ in hybrid perovskite ink, leading to failure in the formation of uniform films. However, it is found that addition of methylammonium chloride (MACl) into the precursor remarkably increases the solubility of GeI₂. This MACl‐assisted Ge doping of hybrid perovskites produces high‐quality crystalline film with its surface passivated with nonvolatile GeI₂ (GeO₂) and the volatile MACl additive also improves the uniformity of GeO₂ distribution in the perovskite films. The resulting Ge‐doped mixed cation and mixed halide perovskite films with composition FA_0.83MA_0.17Ge_0.03Pb_0.97(I_0.9Br_0.1)₃ show superior photoluminescence lifetime, power conversion efficiency above 22%, and greater stability toward illumination and humidity, outperforming photovoltaic properties of HyPSCs prepared without the Ge doping.     

冻融季帽儿山森林改变有机碳输入方式对土壤活性氮含量的影响

根系与凋落物有机碳输入变化对土壤碳氮循环的影响已成为当前学界关注的热点,但冻融季不同有机碳输入方式将对土壤活性氮含量产生何种影响尚不明确。为此在春季具有明显冻融作用的温带森林设立凋落物去除、根系去除处理以代表仅根系有机碳输入方式、仅凋落物有机碳输入方式,并设置自然条件有机碳输入方式即保留根系及凋落物作为对照,多角度探究土壤微生物量氮、矿质氮动态变化。结果表明：(1)有机碳输入方式对土壤活性氮含量有重要影响：与自然条件下有机碳输入方式相比,仅根系输入处理使土壤微生物氮、总矿质氮含量升高10.5%、12.3%。(2)输入时长改变了有机碳输入方式对土壤活性氮含量的作用效果：长期单一有机碳输入使土壤微生物量氮含量下降,反应率值为0.451、0.422。(3)季节差异是影响有机碳输入方式对土壤活性氮含量作用效果的关键因素：仅根系有机碳输入在冻融季使总矿质氮含量上升,反应率值为0.404,生长季相反,呈下降趋势,其值为0.121。以上结果表明,有机碳输入方式对土壤活性氮含量有重要调控作用,且作用效果会受季节、输入时长等因素影响。     

Seasonal variability in the individual carbon content of the calanoid copepod Acartia bifilosa from the northern Baltic Sea

The seasonal variation in the carbon content of the calanoid copepod Acartia bifilosa was studied in the northern Baltic Sea. Monthly length-weight relationships were followed from November 1990 to October 1991 by analysing the organic carbon content of individuals, using a high temperature combustion method. The monthly length (L) on carbon (C) regressions of copepodites were best described by power functions (C = aL^b), where 75% to 88% of the variation could be explained by length. Nauplii length explained less of their carbon content (63–71 %). The carbon content per length was highest in summer when the nutritional situation was good and temperature at its highest. However, the carbon-length regressions differed significantly between months, except in winter, when two subsequent months had similar regressions. The results pointed out the importance of seasonal variation as well as the risk of making errors if biomass estimates based on length on carbon regressions are used. Carbon analysis should, if possible, be done on every sample or should at least be tested as to whether the regressions are consistent with the study material before estimations are calculated.     

马尾松人工林土壤各粒径团聚体湿筛后的有机碳分配

选取25a、45a和65a马尾松人工林为研究对象,采用湿筛法对各粒径土壤团聚体分别湿筛。探究了马尾松人工林各粒径团聚体湿筛后的团聚体有机碳分配,以探讨各粒径团聚体湿筛后分配到同一粒级团聚体有机碳含量及其对团聚体水稳性的贡献差异。结果表明：种植年限增加显著降低土壤团聚体水稳性（P<0.05）;各粒径团聚体湿筛后分配的有机碳随粒级减小含量呈先降后增趋势,以保持原粒级团聚体有机碳（12.96-32.01 g/kg）含量最高,其次是<0.25 mm粒级（8.08-23.53 g/kg）。各粒径团聚体湿筛分配到同一粒级的有机碳以保持原粒级的含量最高（P<0.05）;土壤团聚体水稳性与各粒径团聚体湿筛后保持原粒径的有机碳呈显著或极显著正相关（P<0.05或0.01）,分配到越小的粒级正相关性越不显著。此外,团聚体水稳性与各粒径团聚体湿筛分配到同一粒级的有机碳呈正相关,以保持原粒级相关性最高（P<0.01或0.05）;回归方程及相关性系数表明,有机碳与保持原粒径团聚体呈显著呈或极显著正相关（P<0.05或0.01）,与消散到其他粒级的团聚体呈负相关或极显著负相关（P>0.05或<0.01）。本研究得出有机碳含量增加促进更大粒径团聚体形成。反之,促使大粒径团聚体向较小粒径团聚体转化。同一粒级团聚体间,保持原粒级团聚体比易转化形成更大粒级团聚体有更高的有机碳含量和更强的水稳性,这对团聚体的固碳提供了新的认识。