Stand level estimation of root respiration for two subtropical plantations based on in situ measurement of specific root respiration

In this study, the stand level root respiration was estimated for two monoculture plantations: Acacia crassicarpa and Eucalyptus urophylla, based on in situ measurement of specific root respiration using simplified root chamber method. The respiration rates of fine roots (<5 mm) were significantly higher than those of coarse roots (>5 mm) for both A. crassicarpa and E. urophylla species. The root respiration of A. crassicarpa showed a clear seasonal pattern with a higher value in the wet season. For E. urophylla, the seasonal pattern was observed for fine roots but not for coarse roots. After determining the biomass of fine roots and coarse roots and their specific rates of respiration at different time points, root respiration at the stand level (R_a) was estimated using a direct up-scaling model. We found that the R_a accounted for 14% and 19% of total soil respiration (R_s) for A. crassicarpa and E. urophylla, respectively. The fine (R_Tf) and coarse (R_Tc) root respiration at the stand level accounted for about 47% and 53% of the R_a for A. crassicarpa, and accounted for 58% and 42% for E. urophylla. This suggests that coarse root respiration cannot be ignored when estimating the root respiration at the stand level. Our results showed that the Q₁₀ values were more accurate in representing the temperature dependence when the confounding effect of soil moisture was considered. This study introduces an alternative approach to estimate stand level root respiration, but its reliability is largely dependent on the accuracy of root biomass quantification.     

Pasteurization Conditions and Evaluation of Quality Parameters of Frozen Packaged Crab Meat

ABSTRACT

Ovalipes trimaculatus is a crab recognized as a new resource with fishing value to obtain frozen products. Pasteurization conditions of meat crab at temperatures below 85ºC (60, 72, and 82ºC) were established to achieve better quality attributes in the frozen product. The lethality curves of Staphylococcus aureus and Listeria monocytogenes were measured, and the decimal reduction times (D) and Z values were determined. Heat transfer during the pasteurization process of pouches containing crab meat was simulated using a computational code in finite elements, and the mathematical model was experimentally validated. Thermal histories were coupled to the microbial lethality kinetics of the most heat resistant pathogen microorganism in order to establish pasteurization times necessary for the process system design. The predicted pasteurization conditions were microbiologically validated. The pouches were frozen under industrial conditions and stored at ?22ºC for 1 year. The influence of the type of packaging (vacuum and nonvacuum plastic pouches) on physicochemical and sensory quality parameters of frozen crab meat (color, exudate, lipid oxidation, water holding capacity, and overall acceptability) were analyzed observing better performance under vacuum conditions.     

Seasonally dependent impacts of grazing on soil nitrogen mineralization and linkages to ecosystem functioning in Inner Mongolia grassland

Previous studies have suggested grazing may alter nitrogen (N) cycling of grasslands by accelerating or decelerating soil net N mineralization. The important mechanisms controlling these fluxes remain controversial, and more importantly, the consequences on carbon storage and site productivity remain uncertain. Here we present results on the seasonal patterns of soil inorganic N pools and net N mineralization and their linkages to ecosystem functioning from a grazing experiment in the Inner Mongolia grassland, which has been maintained for five years with 7 levels of grazing intensity (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep ha⁻¹). Net N mineralization and nitrification rates were determined using an in situ soil core incubation method. Our findings demonstrated that, in the non-growing season, the net N mineralization rate was reduced by 181% in the lightly and moderately grazed plots (1.5-4.5 sheep ha⁻¹) and by 147% in the heavily grazed plots (6.0-9.0 sheep ha⁻¹), and the net N immobilization was observed in all grazed treatments. In the early growing season, however, it was increased by 107% in the lightly and moderately grazed plots and by 128% in the heavily grazed plots. In the peak growing season, grazing diminished the net mineralization rate by 71% in the lightly and moderately grazed plots and 108% in the heavily grazed plots. The seasonally dependent effects of grazing on soil inorganic N pools and net N mineralization were strongly mediated by grazing-induced changes in soil temperature and moisture, with soil moisture being predominant in the peak growing season. Grazing alterations of soil inorganic N and net N mineralization were closely linked to the changes in aboveground primary productivity, biomass N allocation, N use efficiency, and soil total nitrogen. Based upon the five year study, we conclude that grazing at moderate to high intensities is unsustainable in terms of productivity and soil N cycling and storage in these systems.     

Understory plants can make substantial contributions to soil respiration: Evidence from two subtropical plantations

Although the importance of understory plants for ecosystem function and processes has been increasingly recognized, the contribution of understory root respiration to soil respiration in forest ecosystems has seldom been studied. In this experiment, we quantified understory root respiration in two subtropical Eucalyptus plantations (2-year-old and 24-year-old). When Eucalyptus was not girdled, understory root respiration accounted for 16% and 36% of total soil respiration in the young and old plantation, respectively. However, the percentages of understory root respiration to total soil respiration were 30% and 11% in the young and old plantation when Eucalyptus was girdled, respectively. We propose that understory root respiration can be substantial in subtropical forests and should be considered in ecosystem carbon budget.     

Subtropical plantations are large carbon sinks: Evidence from two monoculture plantations in South China

Quantifying the net carbon (C) storage of forest plantations is required to assess their potential to offset fossil fuel emissions. In this study, a biometric approach was used to estimate net ecosystem productivity (NEP) for two monoculture plantations in South China: Acacia crassicarpa and Eucalyptus urophylla. This approach was based on stand-level net primary productivity (NPP, based on direct biometric inventory) and heterotrophic respiration (R_h). In comparisons of R_h determination based on trenching vs. tree girdling, both trenching and tree girdling changed soil temperature and soil moisture relative to undisturbed control plots, and we assess the effects of corrections for disturbances of soil moisture and soil moisture on the estimation of soil CO₂ efflux partitioning. Soil microbial biomass and dissolved organic carbon were significantly lower in trenched plots than in tree girdled plots for both plantations. Annual soil CO₂ flux in trenched plots (R_h-t) was significantly lower than in tree-girdled plots (R_h-g) in both plantations. The estimates of R_h-t and R_h-g, expressed as a percentage of total soil respiration, were 58 ± 4% and 74 ± 6%, respectively, for A. crassicarpa, and 64 ± 3% and 78 ± 5%, respectively, for E. urophylla. By the end of experiment, the difference in soil CO₂ efflux between the trenched plots and tree-girdled plots had become small for both plantations. Annual R_h (mean of the annual R_h-t and R_h-g) and net primary production (NPP) were 470 ± 25 and 800 ± 118 g C m⁻² yr⁻¹, respectively, for A. crassicarpa, and 420 ± 35 and 2380 ± 187 g C m⁻² yr⁻², respectively, for E. urophylla. The two plantations in the developmental stage were large carbon sinks: NEP was 330 ± 76 C m⁻² yr⁻¹ for A. crassicarpa and 1960 ± 178 g C m⁻² yr⁻¹ for E. urophylla.     

Rapid 20th-century increase in coastal upwelling off northwest Africa

Near-shore waters along the northwest African margin are characterized by coastal upwelling and represent one of the world's major upwelling regions. Sea surface temperature (SST) records from Moroccan sediment cores, extending back 2500 years, reveal anomalous and unprecedented cooling during the 20th century, which is consistent with increased upwelling. Upwelling-driven SSTs also vary out of phase with millennial-scale changes in Northern Hemisphere temperature anomalies (NHTAs) and show relatively warm conditions during the Little Ice Age and relatively cool conditions during the Medieval Warm Period. Together, these results suggest that coastal upwelling varies with NHTAs and that upwelling off northwest Africa may continue to intensify as global warming and atmospheric CO2 levels increase.