Soil carbon sequestration and land‐use change: processes and potential

When agricultural land is no longer used for cultivation and allowed to revert to natural vegetation or replanted to perennial vegetation, soil organic carbon can accumulate. This accumulation process essentially reverses some of the effects responsible for soil organic carbon losses from when the land was converted from perennial vegetation. We discuss the essential elements of what is known about soil organic matter dynamics that may result in enhanced soil carbon sequestration with changes in land‐use and soil management. We review literature that reports changes in soil organic carbon after changes in land‐use that favour carbon accumulation. This data summary provides a guide to approximate rates of SOC sequestration that are possible with management, and indicates the relative importance of some factors that influence the rates of organic carbon sequestration in soil. There is a large variation in the length of time for and the rate at which carbon may accumulate in soil, related to the productivity of the recovering vegetation, physical and biological conditions in the soil, and the past history of soil organic carbon inputs and physical disturbance. Maximum rates of C accumulation during the early aggrading stage of perennial vegetation growth, while substantial, are usually much less than 100 g C m^?2 y^?1. Average rates of accumulation are similar for forest or grassland establishment: 33.8 g C m^?2 y^?1 and 33.2 g C m^?2 y^?1, respectively. These observed rates of soil organic C accumulation, when combined with the small amount of land area involved, are insufficient to account for a significant fraction of the missing C in the global carbon cycle as accumulating in the soils of formerly agricultural land.     

Are Sulfurous Soil Amendments (S0, Fe(II)SO4, Fe(III)SO4) an Effective Tool in the Restoration of Heathland and Acidic Grassland after Four Decades of Rock Phosphate Fertilization?

This paper deals with the complex issue of reversing long‐term improvements of fertility in soils derived from heathlands and acidic grasslands using sulfur‐based amendments. The experiment was conducted on a former heathland and acid grassland in the U.K. that was heavily fertilized and limed with rock phosphate, chalk, and marl. The experimental work had three aims. First, to determine whether sulfurous soil amendments are able to lower pH to a level suitable for heathland and acidic grassland re‐creation (approximately 3 pH units). Second, to determine what effect the soil amendments have on the available pool of some basic cations and some potentially toxic acidic cations that may affect the plant community. Third, to determine whether the addition of Fe to the soil system would sequester PO₄^? ions that might be liberated from rock phosphate by the experimental treatments. The application of S⁰ and Fe^(II)SO₄^? to the soil was able to reduce pH. However, only the highest S⁰ treatment (2,000 kg/ha S) lowered pH sufficiently for heathland restoration purposes but effectively so. Where pH was lowered, basic cations were lost from the exchangeable pool and replaced by acidic cations. Where Fe was added to the soil, there was no evidence of PO₄^? sequestration from soil test data (Olsen P), but sequestration was apparent because of lower foliar P in the grass sward. The ability of the forb Rumex acetosella to apparently detoxify Al³⁺, prevalent in acidified soils, appeared to give it a competitive advantage over other less tolerant species. We would anticipate further changes in plant community structure through time, driven by Al³⁺ toxicity, leading to the competitive exclusion of less tolerant species. This, we suggest, is a key abiotic driver in the restoration of biotic (acidic plant) communities.     

The relationship between respiration and temperature in leaves of the arctic plant Saxifraga cernua

Abstract Saxifraga cernua, a perennial herb distributed throughout the arctic and subarctic regions, shows high levels of dark respiration. The amount of respiration exhibited by leaves and whole plants at any temperature is influenced by the pretreatment temperature. Plants grown at 10°C typically show higher dark respiration rates than plants grown at 20°C. The levels of alternative-pathway respiration (or cyanide-insensitive respiration) in leaves of S. cernua grown at high and low temperatures were assessed by treating leaf discs with 0.25 mol m^?3 salicylhydroxamic acid during measurements of oxygen consumption. Alternative pathway respiration accounted for up to 75% of the total respiration. Tissues from 20°C-grown plants yielded a Q₁₀ of 3.37 for normal respiration, and of 0.97 for alternative-pathway respiration. Tissues from 10°C-grown plants yielded a Q₁₀ of 2.55 for normal respiration, and of 0.79 for alternative-pathway respiration. The alternative pathway does not appear to be as temperature sensitive as the normal cytochrome pathway. A simple energy model was used to predict the temperature gain expected from these high rates of alternative-pathway respiration. The model shows that less than 0.02°C can be gained by leaves experiencing these high respiration rates.     

Differences between Indica and Japonica rice varieties in CO2 exchange rates in response to leaf nitrogen and temperature

Four Indica and five Japonica varieties of rice (Oryza sativa L.) were examined to elucidate their differences in photosynthetic activity and dark respiratory rate as influenced by leaf nitrogen levels and temperatures. The photosynthetic rates of single leaf showed correlations with total nitrogen and soluble protein contents in the leaves. Respiratory rate was also positively correlated with the leaf nitrogen content. When compared at the same level of leaf nitrogen or soluble protein content, the four Indica varieties and one of Japonica varieties, Tainung 67, which have some Indica genes derived from one of its parents, showed higher photosynthetic rates than the remaining four Japonica varieties. At the same photosynthetic rate, the Indica varieties showed lower respiratory rate than Japonica varieties. When the leaf temperature rose from 20°C to 30°C, the photosynthetic rate increased by 18 to 41%, whereas the respiratory rate increased by 100 to 150%. These increasing rates in response to temperature were higher in the Japonica than in the Indica varieties. In this respect, Tainung 67 showed the same behavior as of the other four Japonica varieties.Abbreviations 30/20 ratios the ratios of photosynthetic and respiratory rates at 30°C to those at 20°C     

In vivo P-31 NMR measurements of phosphate metabolism in Platymonas subcordiformis as related to external pH

The phosphate metabolism of Platymonas subcordiformis was investigated by 31P-NMR spectroscopy with special attention on the effect of external pH. Glycolyzing cells and cells energized by respiration or photosynthesis gave spectra dependent upon their metabolic state. The transition from deenergized to energized states is accompanied by a shift of cytoplasmic pH from 7.1–7.4, an increase of ATP level and-in well energized cells-the appearance of a new signal tentatively assigned to phosphoarginine.The spectra remain stable over a wide range of external pH. Cytoplasmic pH is well regulated in respiring cells for external pH in the range 5.3–12.3. The typical 0.4 units difference of internal pH in energized as compared to deenergized cells is not affected by external pH in the range 6–12. The intensity of a signal attributed to PEP is markedly increased at high external pH. pH regulation is less efficient below external pH of 6 in deenergized cells. Below pH 3.8 oxidative phosphorylation ceases. Upon raising cytoplasmic pH to 7.4 in deenergized cells polyphosphate chains start to disintegrate.Abbreviations PEP Phosphoenolpyruyate - P _i inorganic phosphate - PP _i inorganic pyrophosphate - poly P polyphosphates - PP-1, PP-2, PP-3 terminal, second, and third phosphate residue of polyphosphates - PP-4 core phosphate residues of polyphosphates - pH _i , pH _o internal (cytoplasmic) and external pH - NTP/NDP nucleotide triphosphate/-diphosphate - S/N signal to noise ratio     

The population dynamics of Cheilosia fasciata (Diptera,Syrphidae): significance of environmental factors and behavioural adaptations in a phytophagous insect

Summary A population of Cheilosia fasciata Schin. & Egg., 1853 was studied in a beech forest (Melico-Fagetum allietosum) near Göttingen (FRG). This syrphid species is closely associated with ramson (Allium ursinum L.), as the larvae mine the plant's leaves. Adult abundance was determined using emergence traps (1981–1986); egg and larval abundance was determined by examining ramson leaves: puparia were extracted from soil samples (1984 and 1986). Cheilosia fasciata is a univoltine species; the imagines emerge in late April/early May. Larval development took five (1986) to six (1984) weeks. In late June/early July the larvae enter the soil for pupariation. A linear relationship was found between the area of the mines and larval biomass (dry wt.). It was concluded that one larva had to mine 51.90 cm² of leaf area in order to gain the mean maximum dry weight (11.15 mg). Furthermore, it was shown that ovipositing females, laying just one egg per leaf, tended to select large leaves providing this minimum amount of food. It is hypothesized that females probably follow straight-lined routes on their oviposition flights, rather than ovipositing on leaves chosen at random. By applying such a strategy, females can almost completely avoid competition for food among their own offspring. Furthermore, competition among the progeny of the whole population is also reduced, particularly in years when adult abundance is very low. The significance of certain factors influencing the population dynamics of Cheilosia fasciata was evaluated by applying a rank correlation analysis. It was shown that high precipitation rates in April reduced the time available for mating and oviposition resulting in low emergence abundance in the next spring. Larval survivorship was enhanced by high precipitation rates in May and June, indicating that drought may be unfavourable to larvae and reduce food availability. Predation by a parasitoid Phygadeuon ursini Horstmann, 1986 (Hymenoptera, Ichneumonidae), appears to be just an imperfect (Milne 1984) density-dependent control mechanism; in fact, it was shown that food limitation is the only significant mechanism of density-dependent population control.     

Ethylene and wound-induced cyanide-resistant respiration climaxes in potato: The synergistic role of CO2 and the selective role of lycorine

When treated with ethylene in O₂, conditioned potato (Solanum tuberosum L. cv. Russet Burbank) tubers – that is, tubers kept at room temperature for 10 days or more – yield slices that are CN^? resistant. Ten % CO₂ in the gas mixture not only synergizes the effect of ethylene, but replaces the need for conditioning as well. The response to CO₂ is more pronounced with increasing time from harvest. By contrast fresh slices from untreated tubers are CN^? sensitive, as are slices from tubers incubated in O₂ or O₂ plus CO₂. The suggestion is made that CN^? resistance is constitutive, and that treatment with ethylene/CO₂ in O₂ confers on potato tuber tissue a resistance to the extensive degradation of membrane phospholipids that normally attends slicing and leads to the loss of CN^? resistance. In this connection respiration inhibition by imidazole, an inhibitor of fatty acid α-oxidation, is extensive in slices of untreated tubers, and sharply diminished in slices of ethylene-treated tubers in proportion to their CN^? resistance. The coextensive rise of respiration rate and CN^? resistance in aged potato slices has led to the presumption that the CN^?-resistant path mediates the respiration climax. Accordingly the alkaloid, lycorine, has been considered to inhibit the development of CN^? resistance in aging potato slices because it curtails the wound-induced respiration. A comparison was carried out on the effect of lycorine on CN^?-sensitive and CN^?-resistant fresh slices – the latter obtained from ethylene/CO₂-treated tubers. Lycorine suppressed the development of the wound-induced respiration without restricting the development of CN^? resistance.