The transpiration and respiration as mechanisms of water loss in cold storage of figs

Transpiration and respiration are two mechanisms of water loss in fresh agricultural products, resulting in visual and texture degradation. Neglecting respiration as a mechanism of water loss may lead to erroneous results at saturation where water vapour pressure deficit is zero and thus water loss is expected to be zero, however, the existence of a finite water loss is noted. In this context, an analysis of the associated with transpiration and respiration water loss in figs (Ficus carica L.) was carried out at 0oC, 10oC and 20oC and 45.64%, 80.22% and 98.65% relative humidity as well as the air conditions of walk-in cold storage rooms. The estimated transpiration rate ranged between 0.11-1.416 mg cm-2 h -1 for a water vapour pressure deficit of 0.0-0.98 kPa. The water vapour pressure deficit estimation was based on the difference between cold air temperature and figs’ surface temperature. The respiration rate was calculated at 0oC, 10oC and 20oC as 0.47±0.08, 0.94±0.11 and 2.69±0.17 mLCO2100g-1 h -1 . Quantification of the water loss showed that at 20oC and saturation, the water loss due to respiration accounts for 3.9% of the respective water loss due to water vapour pressure deficit while on average, the water loss due to respiration accounts for 1.5%, 2.1% and 2.6% of the water loss due to water vapour pressure deficit at 0oC, 10oC and 20oC.

Can birds do it too? Evidence for convergence in evaporative water loss regulation for birds and mammals

Birds have many physiological characteristics that are convergent with mammals. In the light of recent evidence that mammals can maintain a constant insensible evaporative water loss (EWL) over a range of perturbing environmental conditions, we hypothesized that birds might also regulate insensible EWL, reflecting this convergence. We found that budgerigars ( Melopsittacus undulatus ) maintain EWL constant over a range of relative humidities at three ambient temperatures. EWL, expressed as a function of water vapour pressure deficit, differed from a physical model where the water vapour pressure deficit between the animal and the ambient air is the driver of evaporation, indicating physiological control of EWL. Regulating EWL avoids thermoregulatory impacts of varied evaporative heat loss; changes in relative humidity had no effect on body temperature, metabolic rate or thermal conductance. Our findings that a small bird can regulate EWL are evidence that this is a common feature of convergently endothermic birds and mammals, and may therefore be a fundamental characteristic of endothermy.

Time vs. light: a potentially useable light sum hybrid model to represent the juvenile growth of Douglas-fir subject to varying levels of competition

Substitution of potential useable light sum for time in a commonly used mensurational equation resulted in a better fit to data from a complex vegetation management experiment. The experiment involved Douglas-fir ( Pseudotsuga menzeisii (Mirb.) Franco) as a crop species and a variety of competing species. Site occupancy by competing vegetation varied with time because control operations were intermittently either included or excluded from treatments over a period of 4 years. There were four randomized complete blocks of eight competition control treatments. Potentially useable light sum was estimated using measurements of radiation from a meteorological station that were modified by coefficients representing the ability of the crop plants to use light with varying soil water, vapour pressure deficit, and temperature. Light sums were further reduced by estimated competition for light from competing vegetation. Fits of the model to individual plots within the experiment yielded coefficients that did not differ significantly between competition control treatments, suggesting that the model accounted for significant variations in growth resource availability between treatments. Potentially useable light sum equations provide an integrated link between traditional mensurational modeling and ecophysiological modeling.

Processes controlling understorey evapotranspiration

The understorey often accounts for a significant proportion of forest evapo- transpiration. In this paper we discuss the role of the understorey radiation regime, and the aerodynamic and stomatal conductance characteristics of the understorey in understorey evapotranspiration. Values of the McNaughton—Jarvis parameter Ω for the understorey in two mid-rotation Douglas-fir stands indicate considerable coupling between the understorey and the atmosphere above the overstorey. However, the stronger coupling between the overstorey and the atmosphere accounts for the observation that the fraction of stand evapotranspiration originating at the understorey increases as the water vapour pressure deficit increases and the soil dries. We also discuss the approaches to describing the process of evaporation from the forest floor and the results of understorey removal experiments. These show small decreases in stand evapotranspiration and root-zone soil water content, but significant increases in the transpiration and growth of the trees.