Stem diameter variations of cotton under different water conditions

Stem diameter variations of cotton cultivated in pots were monitored continuously by using stem growth measurement transducer(DD-type). The diurnal variations of stem diameter under different weather conditions and the stem diameter responses to water deficits at different growth stages were investigated, while the influences of environmental variables on stem diameter variations were evaluated. The results showed that parameters derived from stem diameter measurements were reliable plant water status indicators. Since stem diameter variations reflect the combined effects of environmental variables and plant vegetate characteristic, the influence of phenology on stem growth must be taken into account when selecting suitable plant water status indicators. During stem growth stages, the trend of maximum stem diameter (MXSD) had greater response to water stress but there were no obvious differences in maximum daily shrinkage (MDS) under different water conditions. Conversely, MDS can be a reliable indicator of plant water status at the stem mature stages with its high sensitivity to water deficits. Then, stem diameter variations were correlated to environmental factors. Soil water content, radiation and vapor pressure deficit (VPD) were found to be the predominant factors affecting MDS, followed by the relative humidity, while air temperature and wind velocity had the least effect. The established relationship between MDS and environmental variables (radiation, vapor pressure deficit, relative humidity, and soil water content) can be used to detect crop water deficits.