Maize (Zea mays L.) physiological responses to drought and rewatering, and the associations with water stress degree

A thorough understanding of the plant drought response mechanism and the relationships between plant functional traits and drought will help to improve the key biophysical process parameterization scheme in ecological and crop growth models. In this study, a drought level evaluation indicator, named water stress degree (D-ws), was established by synthetically considering soil water content (WC), evapotranspiration, and drought duration to obtain a quantitative description of drought level. The maize physiological and functional traits responses to drought and subsequent rewatering were also investigated. Drought-rewatering field experiments with no water addition for 40 days during the vegetative period (VP) and reproductive period (RP) were respectively conducted at Jinzhou Agrometerological Experimental Station, northeast China in 2014 and 2016. The D-ws values indicated that there were significant differences between growth stages and between years because the environmental conditions in 2014 and 2016 were different during the maize growth periods. Furthermore, D-ws was larger in 2016 than in 2014 during the VP and RP. Leaf photosynthesis had a certain adaptability to drought, and the transpiration rate (E) drought response (DR) was quicker than the photosynthetic rate (Pn) response, and P-n recovery was greater than E recovery when the plants were rewatered during the VP. However, leaf photosynthesis is more sensitive to drought and less available to recover as normal in subsequent rewatering during the RP than the VP, which was intensified as D-ws rose between 2014 and 2016. In addition, the leaf WC drought response was faster than the photosynthetic DR during the VP and RP, and leaf and stalk WCs responded more rapidly to drought during the VP than the RP. The decrease in ear WC during the earlier grouting period was larger in the VP than in the RP treatment. However, the drought-induced decrease in daily sap flow rate (DSF) during the RP was larger than during the VP, while the differences in DSF drought response and DSF recovery during rewatering were attributed to the inter-annual variation in Dws. Furthermore, the drought-caused reductions in leaf, stalk, and plant total dry matters and in leaf and stalk WCs had positively exponential or linear relationships with D-ws. The results can help to understand the disaster-causing mechanism of drought-stricken maize.