Rates and intensity of freeze–thaw cycles affect nitrous oxide and carbon dioxide emissions from agricultural soils

In cool temperate regions, large emissions of nitrous oxide (N2O), an important greenhouse and ozone-depleting gas, have been observed during freeze–thaw (FT) cycles. However, it is unclear how freezing and thawing rates, freezing intensity, and freezing duration influence N2O emissions. We used a laboratory incubation to measure N2O emissions from two soils (sandy loam, silty clay) undergoing a single FT cycle of various freezing and thawing rates [rapid (0.5 °C h−1) vs. slow (0.017 °C h−1)], freezing intensity (−1 vs. −3 °C), and freezing duration (24 vs. 48 freezing degree-days). In general, soil carbon dioxide fluxes during freezing were highest when soils were frozen slowly at −1 °C, whereas fluxes after thawing were highest from the soils frozen and thawed rapidly at −3 °C. Soil N2O emissions during both the freezing and thawing periods were greatest in the soils exposed to rapid freezing to −3 °C, intermediate under rapid freezing to −1 °C and slow freezing to −3 °C, and smallest under slow freezing to −1 °C and the control treatment (constant +1 °C). The similar N2O emissions between the unfrozen control and the slowly frozen −1 °C treatment was unexpected as previous field studies with similar freezing rates and temperatures still experienced high N2O emissions during thaw. This suggests that the physical disruptions caused by freezing and thawing of the surface soil are not the primary driver of FT-induced N2O emissions under field conditions.

Effect of freezing and thawing rates on sperm motility in Bocachico Prochilodus magdalenae (Pisces, Characiformes)

ABSTRACTObjective. To determine the freezing and thawing rates necessary to maintain sperm viability during cryopreservation of Bocachico semen. Materials and methods. Four interactional treatments were implemented between two freezing (rapid and slow) and two thawing (rapid and slow) curves, in a 2x2 factorial as follows: rapid freezing-rapid thawing, rapid freezing-slow thawing, slow freezing-rapid thawing, and slow freezing-slow thawing. After thawing by Sperm Class Analyzer (SCA) curvilinear velocity (VCL) and straight-line (VSL) (μm sec-1) were analyzed; total, rapid, medium, and slow motility, were compared among treatments. Results. The rapid freezing-slow thawing treatment was lethal for all variables of velocity and motility, causing a significant (p<0.01) post-thaw inmotility of 100%. The slow freezing-rapid thawing interaction had a significantly higher effect than the other treatments (p<0.05), particularly on variables such as rapid motility (10.1 ± 1.1%), medium motility (30.16 ± 4.1%), and curvilinear velocity (51.5 ± 4.75 μm sec.-1) also decreased the percentage of sperm with slow motility (41.7 ± 4.45%). Independently of the applied thawing rate, the freezing rate generated the main significant effect on total motility. Conclusions. It is possible to conclude that the interaction effect between freezing and thawing rates is nil (except for slow motility) during cryopreservation process. However, the independent effects of these factors (main effects) on remaining motility variables are positively significant and decisive to the maintenance of these features, especially the freeze factor (when it is slow). This becomes the first successful report of sperm cryopreservation from Bocachico Prochilodus magdalenae in the world and may be used in conservation programs for this endangered species.