Cross-validation of the high-capacity tensiometer and thermocouple psychrometer for continuous monitoring of xylem water potential in saplings.

The pressure chamber, the most popular method used to measure xylem water potential, is a discontinuous and destructive technique and is therefore not suitable for automated monitoring. Continuous non-destructive monitoring could until very recently be achieved only by use of the thermocouple psychrometer (TP). Here we present the high-capacity tensiometer (HCT) as an alternative method for continuous non-destructive monitoring. This provided us with a unique chance to cross-validate the two instruments by installing them simultaneously on the same sapling stem. The HCT and the TP showed excellent agreement for xylem water potential less than -0.5 MPa. Response to day/night cycles and watering was remarkably in phase, indicating excellent response time of both instruments despite substantially different working principles. For xylem water potential greater than -0.5 MPa, the discrepancies sometimes observed between the HCT and TP were mainly attributed to the kaolin paste used to establish contact between the xylem and the HCT, which becomes hydraulically poorly conductive in this range of water potential once dried beyond its air-entry value and subsequently re-wetted. Notwithstanding this limitation, which can be overcome by selecting a clay paste with higher air-entry value, the HCT has been shown to represent a valid alternative to the TP.

Effect of lactose on gut microbiota and metabolome of infants with cow's milk allergy.

Allergic infants have an unusual gastrointestinal microbiota with low numbers of Bifidobacterium/Lactobacilli and high levels of Clostridium, staphylococci and Escherichia coli. Hydrolyzed formula used to treat these infants is deprived of lactose that instead may influence the gut microbial composition. The aim of the present study is to investigate the influence of lactose on the composition of the gut microbiota and metabolome of infants with cow's milk allergy. Infants prospectively enrolled received an extensively hydrolyzed formula with no lactose for 2 months followed by an identical lactose-containing formula for an additional 2 months. Healthy, age-gender-matched infants were used as controls. The following determinations were performed before and after the introduction of lactose in the diet: enumeration of cells present in the feces using FISH, counts of viable bacterial cells and gas-chromatography mass spectrometry/solid-phase microextraction analysis. The addition of lactose to the diet significantly increases the counts of Bifidobacteria and lactic acid bacteria (p < 0.01), decreases that of Bacteroides/clostridia (p < 0.05) reaching counts found in healthy controls; lactose significantly increases the concentration of total short-chain fatty acids (p < 0.05). The addition of lactose to an extensively hydrolyzed formula is able to positively modulate the composition of gut microbiota by increasing the total fecal counts of Lactobacillus/Bifidobacteria and decreasing that of Bacteroides/Clostridia. The positive effect is completed by the increase of median concentration of short chain fatty acids, especially for acetic and butyric acids demonstrated by the metabolomic analysis.