Abstract
The abiotic and biotic stresses including drought, cold, and disease stress are linked by the fact that they all decrease the availability of water to plant cells. In previous studies, some physiological factors related with plant water status, such as stem sap flow, leaf transpiration rate, and water potential, were used to assess the effects of these stresses on plants. But there are few studies about the effects of these stresses on stem water content (StWC) which can be measured by a novel SWR sensor. In this study, crape myrtle was selected as an experimental subject and its StWC was observed in four experiments including no stress, drought, cold, and disease stress. Before conducting stress experiments, the StWC and environmental and physiological parameters were synchronously monitored under unstressed conditions on a typical day in summer. In the experiment of drought stress, the StWC was monitored under different gradients of soil moisture. In the experiment of cold stress, the StWC was monitored in warm and cold weather, respectively. In the experiment of disease stress, the StWC was monitored under different frequencies of disease treatment. The results showed that the correlation coefficients between StWC and PAR and VPD were larger than 0.5 and the correlation coefficients between StWC and Pn, Tr, Gs, and Ci were larger than 0.8 under no stress. The diurnal mean of StWC decreased firstly, then remained stable for a period of time, and eventually continued to fall under drought stress. On the whole, there was a negative correlation between the diurnal mean of StWC and the degree of drought stress. The StWC showed opposite diurnal variation rules in warm and cold weather. There was a positive correlation between the diurnal range of StWC and the degree of cold stress. The diurnal minimum, maximum, and mean of StWC showed a positive correlation with the health level of plants and the diurnal range of StWC showed a negative correlation with the health level of plants. In conclusion, the StWC can be used as a qualitative evaluation index of the degree of the three types of stress.
Highlights
Plants often suffer from continuous exposure to various abiotic and biotic stresses in natural and agricultural settings
Correlation analysis suggests that air temperature (AT), photosynthetically active radiation (PAR), and vapor pressure deficit (VPD) were significantly negatively correlated with stem water content (StWC) and AH was significantly positively correlated with StWC
As PAR or VPD reached a certain threshold at midday, there was a dynamic balance between water loss and water absorption due to the midday depression, resulting in small fluctuations of StWC
Summary
Plants often suffer from continuous exposure to various abiotic and biotic stresses in natural and agricultural settings. As the drought stress becomes severe, the plant is no longer able to keep a balance between water loss and uptake. Under this condition, some additional mechanisms, such as solutes accumulation [4, 5] and cell wall hardening [6] play an important role in keeping plants from dehydration. As the drought stress becomes more severe, it is increasingly difficult for the plant to avoid dehydration In this case, some additional mechanisms, including protective proteins [7], metabolic changes [8], and reactive oxygen
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