Soil type and wetting intensity control the enhancement extent of N_(2)O efflux in soil with drought and rewetting cycles

Climate change alters the intensity and frequency of drought and rewetting(D/W)events;however,the influence patterns of D/W on soil N_(2)O efflux in the water-limited area were not fully understood.Therefore,the impacts of D/W cycles varying in different extent of rewetting and frequency to N_(2)O efflux in two kinds of soil on the Loess Plateau were investigated.The incubation conditions consisted of 1)D/W treatments with four 7-day cycles from 10%water holding capacity(WHC)to 60%WHC or 90%WHC,2)constant moisture of 60%WHC and 90%WHC.The pulse of N_(2)O efflux rate under 10-60%WHC treatment was higher than that under 10-90%WHC treatment in calcic cambisols,while opposite trend was observed in earth-cumuli-orthic anthrosols.Meanwhile,the pulse of N_(2)O efflux rate decreased as cycle number increased for different wetting intensities and soil types.The direct N_(2)O efflux under 10-60%WHC and 10-90%WHC treatments were 5.49 and 1.89μg N_(2)O-N g^(-1)soil in calcic cambisols,with those being 1.92 and 10.85μg N_(2)O-N g^(-1)soil in earth-cumuli-orthic anthrosols,respectively.The N loss in earth-cumuli-orthic anthrosols was approximately 5.74 times greater than that in calcic cambisols under 10-90%WHC treatment,whereas the N loss under 10-60%WHC treatment was about 2.86 times greater in calcic cambisols than that in earth-cumuli-orthic anthrosols.This study suggested that extreme rainfall events can enhance the N_(2)O efflux and N loss in agricultural soils on the Loess Plateau in terms of soil type and wetting intensity,which should not be ignored in the N fertilizer management.

Energy Transfer from Phycobilisomes to Photosystems of Nostoc flagelliforme Born. et Flah. During the Rewetting Course and Its Physiological Significance

During the non-frost season, the condensation of dew makes Nostoc flagelliforme Born. et Flah., a highly drought-tolerant terrestrial cyanobacterium, frequently undergo rehydration-dehydration. Rehydration begins in the dark at night. After rewetting in the dark, photochemical activity and the structure of photosystem (PS) II were not recovered at all; the structure of PSI, energy transfer in phycobilisomes, and energy transfer from phycobilisomes to PSI were recovered within 5 min, as in the light. The recovery of energy transfer from phycobilisomes to PSII was light dependent and energy transfer from phycobilisomes to PSII was only partially recovered in the dark. These results suggest that the two-trigger control (water and light) of photo synthetic recovery may make N. flagelliforme avoid unnecessary energy consumption and, at the same time, the partial recovery of energy transfer from phycobilisomes to PSII in the dark could help N. flagelliforme accumulate more photosynthetic products during the transient period of rehydration-dehydration.

Copper pollution decreases the resistance of soil microbial community to subsequent dry–rewetting disturbance

Dry–rewetting（DW） disturbance frequently occurs in soils due to rainfall and irrigation, and the frequency of DW cycles might exert significant influences on soil microbial communities and their mediated functions. However, how microorganisms respond to DW alternations in soils with a history of heavy metal pollution remains largely unknown.Here, soil laboratory microcosms were constructed to explore the impacts of ten DW cycles on the soil microbial communities in two contrasting soils（fluvo-aquic soil and red soil）under three copper concentrations（zero, medium and high）. Results showed that the fluctuations of substrate induced respiration（SIR） decreased with repeated cycles of DW alternation. Furthermore, the resistance values of substrate induced respiration（RS-SIR）were highest in non-copper-stressed（zero） soils. Structural equation model（SEM） analysis ascertained that the shifts of bacterial communities determined the changes of RS-SIR in both soils. The rate of bacterial community variance was significantly lower in noncopper-stressed soil compared to the other two copper-stressed（medium and high） soils,which might lead to the higher RS-SIR in the fluvo-aquic soil. As for the red soil, the substantial increase of the dominant group WPS-2 after DW disturbance might result in the low RS-SIR in the high copper-stressed soil. Moreover, in both soils, the bacterial diversity was highest in non-copper-stressed soils. Our results revealed that initial copper stress could decrease the resistance of soil microbial community structure and function to subsequent DW disturbance.

Rewetting and Flow Film Boiling Along Hot Surface

The recent investigations on the rewettmg and film boiling of liquid flowing along a hot/heated surface are briefly reviewed and discussed.Some advanced theoretical analyses are conducted and new conclusions achieved.These investigations describe the fundamental characteristics of liquid flow boiling and further the complicated rewetting phenomena,and have resulted in considerable insight intothe mechanism.

Wet Pressing Models to Reduce Energy Consumption in Papermaking

Improved wet pressing reduces the need for drying and consequently energy needed in papermaking. Accordingly, it is desirable to optimize wet pressing, but the process is very complex with many interacting variables. It is therefore desirable to employ a mathematical model that accounts for the major variables to estimate the effects of changes in equipment and operating variables. This paper descibes such a model called the Decreasing Permeability Model (DPM). Mill and pilot plant applications over a wide range of basis weights for paper and paper board are described.

Heat transfer characteristics for double-jet in different flow regions on a thick plate

During multi-jet cooling,the complex hydrodynamic characteristics caused by the interaction between jets will affect the heat transfer of the plate.To further clarify the heat transfer characteristics in different flow regions,the double-jet cooling experiments were completed on a 50-mm-thick plate with the initial cooling temperature and jet angle in the range of 300–900°C and 0°–60°,respectively.The inverse heat conduction was used to calculate the surface temperature and heat flux.Furthermore,the rewetting phenomenon,maximum heat flux and maximum cooling speed were studied.The results show that increasing the angle between jet and wall normal would increase the wetting front’s width downstream of the jet point.When the jet angle was 60°,the maximum value increased by 37.29 mm compared with that when the angle was 0.The correlation between the width of the wetting front and the radial temperature gradient was further confirmed.In addition,it was found that the maximum heat flux would be affected by the duration of transition boiling,but not affected by complete wetting time.The results clarified the heat transfer mechanisms under various initial cooling temperature and inclination angle conditions on plate cooling in different flow regions,and provided valuable data for controlling heat transfer efficiency and improving cooling uniformity.