• Authors:
    • Mitchell, C. D.
    • Sochacki, S. J.
    • George, S. J.
    • Dean, C.
    • Tibbett, M.
    • Stilwell, A. T.
    • Okom, A. E. A.
    • Harper, R. J.
    • Mann, S. S.
    • Dods, K.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 163
  • Year: 2012
  • Summary: In the Western Australian wheatbelt, the restoration of native eucalypt forests for managing degraded agricultural landscapes is a critical part of managing dryland salinity and rebuilding biodiversity. Such reforestation will also sequester carbon. Whereas most investigative emphasis has been on carbon stored in biomass, the effects of reforestation on soil organic carbon (SOC) stores and fertility are not known. Two 26 year old reforestation experiments with four Eucalyptus species ( E. cladocalyx var nana, E. occidentalis, E. sargentii and E. wandoo) were compared with agricultural sites (Field). SOC stores (to 0.3 m depth) ranged between 33 and 55 Mg ha -1, with no statistically significant differences between tree species and adjacent farmland. Farming comprised crop and pasture rotations. In contrast, the reforested plots contained additional carbon in the tree biomass (23-60 Mg ha -1) and litter (19-34 Mg ha -1), with the greatest litter accumulation associated with E. sargentii. Litter represented between 29 and 56% of the biomass carbon and the protection or utilization of this litter in fire-prone, semi-arid farmland will be an important component of carbon management. Exch-Na and Exch-Mg accumulated under E. sargentii and E. occidentalis at one site. The results raise questions about the conclusions of SOC sequestration studies following reforestation based on limited sampling and reiterate the importance of considering litter in reforestation carbon accounts.
  • Authors:
    • Verfaillie, J.
    • Deverel, S. J.
    • Sonnentag, O.
    • Detto, M.
    • Hatala, J. A.
    • Baldocchi, D. D.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 150
  • Year: 2012
  • Summary: The Sacramento-San Joaquin Δ in California was drained and converted to agriculture more than a century ago, and since then has experienced extreme rates of soil subsidence from peat oxidation. To reverse subsidence and capture carbon there is increasing interest in converting drained agricultural land-use types to flooded conditions. Rice agriculture is proposed as a flooded land-use type with CO 2 sequestration potential for this region. We conducted two years of simultaneous eddy covariance measurements at a conventional drained and grazed degraded peatland and a newly converted rice paddy to evaluate the impact of drained to flooded land-use change on CO 2, CH 4, and evaporation fluxes. We found that the grazed degraded peatland emitted 175-299 g-C m -2 yr -1 as CO 2 and 3.3 g-C m -2 yr -1 as CH 4, while the rice paddy sequestered 84-283 g-C m -2 yr -1 of CO 2 from the atmosphere and released 2.5-6.6 g-C m -2 yr -1 as CH 4. The rice paddy evaporated 45-95% more water than the grazed degraded peatland. Annual photosynthesis was similar between sites, but flooding at the rice paddy inhibited ecosystem respiration, making it a net CO 2 sink. The rice paddy had reduced rates of soil subsidence due to oxidation compared with the drained peatland, but did not completely reverse subsidence.
  • Authors:
    • Stewart, J. S.
    • Menge, B. A.
    • Gouhier, T. C.
    • Iles, A. C.
    • Haupt, A. J.
    • Lynch, M. C.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 2
  • Year: 2012
  • Summary: Eastern boundary current systems are among the most productive and lucrative ecosystems on Earth because they benefit from upwelling currents. Upwelling currents subsidize the base of the coastal food web by bringing deep, cold and nutrient-rich water to the surface. As upwelling is driven by large-scale atmospheric patterns, global climate change has the potential to affect a wide range of significant ecological processes through changes in water chemistry, water temperature, and the transport processes that influence species dispersal and recruitment. We examined long-term trends in the frequency, duration, and strength of continuous upwelling events for the Oregon and California regions of the California Current System in the eastern Pacific Ocean. We then associated event-scale upwelling with up to 21 years of barnacle and mussel recruitment, and water temperature data measured at rocky intertidal field sites along the Oregon coast. Our analyses suggest that upwelling events are changing in ways that are consistent with climate change predictions: upwelling events are becoming less frequent, stronger, and longer in duration. In addition, upwelling events have a quasi-instantaneous and cumulative effect on rocky intertidal water temperatures, with longer events leading to colder temperatures. Longer, more persistent upwelling events were negatively associated with barnacle recruitment but positively associated with mussel recruitment. However, since barnacles facilitate mussel recruitment by providing attachment sites, increased upwelling persistence could have indirect negative impacts on mussel populations. Overall, our results indicate that changes in coastal upwelling that are consistent with climate change predictions are altering the tempo and the mode of environmental forcing in near-shore ecosystems, with potentially severe and discontinuous ramifications for ecosystem structure and functioning.
  • Authors:
    • Krumhardt, K. M.
    • Kaplan, J. O.
    • Zimmermann, N. E.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 3
  • Year: 2012
  • Summary: The long residence time of carbon in forests and soils means that both the current state and future behavior of the terrestrial biosphere are influenced by past variability in climate and anthropogenic land use. Over the last half-millennium, European terrestrial ecosystems were affected by the cool temperatures of the Little Ice Age, rising CO 2 concentrations, and human induced deforestation and land abandonment. To quantify the importance of these processes, we performed a series of simulations with the LPJ dynamic vegetation model driven by reconstructed climate, land use, and CO 2 concentrations. Although land use change was the major control on the carbon inventory of Europe over the last 500 years, the current state of the terrestrial biosphere is largely controlled by land use change during the past century. Between 1500 and 2000, climate variability led to temporary sequestration events of up to 3 Pg, whereas increasing atmospheric CO 2 concentrations during the 20th century led to an increase in carbon storage of up to 15 Pg. Anthropogenic land use caused between 25 Pg of carbon emissions and 5 Pg of uptake over the same time period, depending on the historical and spatial pattern of past land use and the timing of the reversal from deforestation to afforestation during the last two centuries. None of the currently existing anthropogenic land use change datasets adequately capture the timing of the forest transition in most European countries as recorded in historical observations. Despite considerable uncertainty, our scenarios indicate that with limited management, extant European forests have the potential to absorb between 5 and 12 Pg of carbon at the present day.
  • Authors:
    • Karamanos, A. J.
    • Travlos, I. S.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 1
  • Year: 2012
  • Summary: The water relations of the tropical tuber-producing legume marama bean [ Tylosema esculentum (Burch) A. Schreib] which produces both tubers and beans for human consumption in the dry regions of southern Africa, were studied in field and greenhouse experiments in Athens, Greece. Two water treatments were imposed by means of different irrigation frequencies on plants grown from seed and tuber in the field experiment, whereas four water treatments were set up in the greenhouse on plants grown from seed for two cultivation periods by applying different amounts of water. Leaf water potential (Psi l) and relative water content (RWC), the solute potential at zero turgor (psi so), leaf stomatal conductance (g s), the angle between the two leaflets, and soil water content were recorded throughout the experiments, both on seasonal and diurnal basis. The values of Psi l were systematically lower in the drier treatments but never fell below -1.15 MPa. The plants grown from tubers exhibited consistently higher values of Psi l and RWC in comparison to those grown from seeds, indicating higher levels of hydration in the former. Progressive osmotic adjustment, more intense in plants grown from tubers, was detected as plants grew older. An exponential relation between g s and leaflet angle was also detected. Our results are discussed in conjunction with field observations taken in Botswana and indicate that marama is endowed with several drought avoidance mechanisms, which, in parallel with osmotic adjustment, enable it to survive under very harsh conditions.
  • Authors:
    • Kunkel, K.
    • Reddy, K. R.
    • Gao, W.
    • Xu, M.
    • Liang, X. Z.
    • Schmoldt, D. L.
    • Samel, A. N.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Climate variability and changes affect crop yields by causing climatic stresses during various stages of the plant life cycle. A crop growth model must be able to capture the observed relationships between crop yields and climate stresses before its credible use as a prediction tool. This study evaluated the ability of the geographically distributed cotton growth model redeveloped from GOSSYM in simulating U.S. cotton ( Gossypium hirsutum L.) yields and their responses to climate stresses during 1979 to 2005. Driven by realistic climate conditions, the model reproduced long-term mean cotton yields within 10% of observations at the 30-km model resolution across virtually the entire U.S. Cotton Belt and correctly captured the critical dependence of their geographic distributions on regional climate characteristics. Significant correlations between simulated and observed interannual variations were found across 87% of the total harvest grids. The model also faithfully represented the predictive role of July to August air temperature and August to September soil temperature anomalies on interannual cotton yield changes on unirrigated lands, with a similar but weaker predictive signal for irrigated lands as observed. The modeled cotton yields exhibited large, positive correlations with July to August leaf area index. These results indicate the model's ability to depict the regional impact of climate stresses on cotton yields and suggest the potential predictive value of satellite retrievals. They also provide a baseline reference for further model improvements and applications in the future study of climate-cotton interactions.
  • Authors:
    • Chefetz, B.
    • Oren, A.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 2
  • Year: 2012
  • Summary: Interactions of dissolved organic matter (DOM) with soil minerals, such as metal oxides and clays, involve various sorption mechanisms and may lead to sorptive fractionation of certain organic moieties. While sorption of DOM to soil minerals typically involves a degree of irreversibility, it is unclear which structural components of DOM correspond to the irreversibly bound fraction and which factors may be considered determinants. To assist in elucidating that, the current study aimed at investigating fractionation of DOM during sorption and desorption processes in soil. Batch DOM sorption and desorption experiments were conducted with organic matter poor, alkaline soils. Fourier-transform infrared (FTIR) and UV-Vis spectroscopy were used to analyze bulk DOM, sorbed DOM, and desorbed DOM fractions. Sorptive fractionation resulted mainly from the preferential uptake of aromatic, carboxylic, and phenolic moieties of DOM. Soil metal-oxide content positively affected DOM sorption and binding of some specific carboxylate and phenolate functional groups. Desorptive fractionation of DOM was expressed by the irreversible-binding nature of some carboxylic moieties, whereas other bound carboxylic moieties were readily desorbed. Inner-sphere, as opposed to outer-sphere, ligand-exchange complexation mechanisms may be responsible for these irreversible, as opposed to reversible, interactions, respectively. The interaction of aliphatic DOM constituents with soil, presumably through weak van der Waals forces, was minor and increased with increasing proportion of clay minerals in the soil. Revealing the nature of DOM-fractionation processes is of great importance to understanding carbon stabilization mechanisms in soils, as well as the overall fate of contaminants that might be associated with DOM.
  • Authors:
    • Rousk, J.
    • Gertler, C.
    • Marsden, K. A.
    • Quilliam, R. S.
    • DeLuca, . H.
    • Jones, D. L.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 158
  • Year: 2012
  • Summary: Evidence suggests that in addition to sequestering carbon (C), biochar amendment can increase crop yields, improve soil quality and nutrient cycling, reduce the leaching of nutrients from soil and stimulate soil microbial activity. However, biochar application primarily benefits soils of intrinsic poor quality, thus the advantages of adding biochar to temperate agricultural soils remains controversial. In addition, there is limited information about the longer term effects of biochar application, or of increasing the rate of biochar loading to soil. Therefore, the aim of this study was to determine the effect of biochar residency time and application rate on soil quality, crop performance, weed emergence, microbial growth and community composition in a temperate agricultural soil. We used replicated field plots with three wood biochar application rates (0, 25 and 50 t ha -1). Three years after biochar amendment, the plots were further split and fresh biochar added at two different rates (25 and 50 t ha -1) resulting in double-loaded reapplications of 25+25 and 50+50 t ha -1. After a soil residency time of three years, there were no significant differences in soil nutrients, microbial growth, mycorrhizal colonisation or weed emergence between biochar amended and unamended soil. In contrast, the reapplication of biochar had a significant effect on soil quality, (e.g. increased PO 43-, K + and Ca 2+, DOC, soil moisture, organic matter and EC), microbial growth, (e.g. decreased saprophytic fungal growth), increased mycorrhizal root colonisation and inhibition of weed emergence. Whilst biochar application is unquestionably a strategy for the sequestration of C, in this case, other benefits, e.g. improved soil nutrient levels or crop performance, seemed to be short lived. Reapplication of biochar exemplifies the transient nature of biochar-mediated benefits rather than any lasting differences in soil nutrient dynamics or microbial communities. These results emphasise the need for more long-term field studies to provide data that can meaningfully inform agronomic management decisions and climate change mitigation strategies.
  • Authors:
    • Craine, J. M.
    • Ramirez, K. S.
    • Fierer, N.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 6
  • Year: 2012
  • Summary: Ecosystems worldwide are receiving increasing amounts of reactive nitrogen (N) via anthropogenic activities with the added N having potentially important impacts on microbially mediated belowground carbon dynamics. However, a comprehensive understanding of how elevated N availability affects soil microbial processes and community dynamics remains incomplete. The mechanisms responsible for the observed responses are poorly resolved and we do not know if soil microbial communities respond in a similar manner across ecosystems. We collected 28 soils from a broad range of ecosystems in North America, amended soils with inorganic N, and incubated the soils under controlled conditions for 1 year. Consistent across nearly all soils, N addition decreased microbial respiration rates, with an average decrease of 11% over the year-long incubation, and decreased microbial biomass by 35%. High-throughput pyrosequencing showed that N addition consistently altered bacterial community composition, increasing the relative abundance of Actinobacteria and Firmicutes, and decreasing the relative abundance of Acidobacteria and Verrucomicrobia. Further, N-amended soils consistently had lower activities in a broad suite of extracellular enzymes and had decreased temperature sensitivity, suggesting a shift to the preferential decomposition of more labile C pools. The observed trends held across strong gradients in climate and soil characteristics, indicating that the soil microbial responses to N addition are likely controlled by similar wide-spread mechanisms. Our results support the hypothesis that N addition depresses soil microbial activity by shifting the metabolic capabilities of soil bacterial communities, yielding communities that are less capable of decomposing more recalcitrant soil carbon pools and leading to a potential increase in soil carbon sequestration rates.
  • Authors:
    • Saia, S.
    • Frenda, A. S.
    • Miceli, G. di
    • Giambalvo, D.
    • Ruisi, P.
    • Amato, G.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 5
  • Year: 2012
  • Summary: The no-tillage (NT) technique represents a valuable alternative to conventional tillage (CT) for many crops, but little research has evaluated the effects of its use on the performance of grain legumes, particularly in Mediterranean regions. The present study assessed the effects of NT compared with CT on the grain yield and N 2 fixation of chickpea ( Cicer arietinum L.), faba bean ( Vicia faba L. variety minor), pea ( Pisum sativum L.), and lentil ( Lens culinaris Medik.). The experiment was performed under rainfed conditions during four growing seasons. Nitrogen fixation was estimated using the 15N isotope dilution technique. The response of the four species to the tillage system varied significantly by year. The grain yield was significantly higher under NT than under CT only for pea and chickpea, but the differences between the two tillage techniques were consistent only when rainfall was very scarce. The percentage of N fixed differed by species in the order faba bean > chickpea > pea > lentil. The effects of tillage on the N 2 fixation process varied significantly by species and year. Nitrogen balance was positive for faba bean and lentil and negative for chickpea and pea, with no differences by tillage. The results indicate that in cereal-dominated Mediterranean agro-ecosystems NT can be a valuable option for producing grain legumes, as it can improve productivity, particularly under conditions of deficient soil moisture.