Differential responses of stomatal morphology to partial root-zone drying and deficit irrigation in potato leaves under varied nitrogen rates

The effects of partial root-zone drying (PRO) as compared with deficit irrigation (DI) on stomatal morphology of potato (Solanum tuberosum L) under varied nitrogen (N) rates were investigated. The plants were grown in split-root pots under three N rates, viz., 70 (N1), 125 (N2), and 200 (N3) mg N kg(-1) soil, respectively. For each N rate, PRO and DI plants received the same amount of water, which allowed refilling one half of the PRO pot to 100% water holding capacity. Across the three N rates, guard cell size was larger in DI than in PRD, whereas stomatal pore aperture area (SA) was similar between the two irrigation treatments. Stomatal density (SD) was affected by both N rate and irrigation treatment and was lower in PRO than in DI under N2 and N3, whereas the reverse was the case under N1. Plant leaf area increased with increasing N rate, but was unaffected by the irrigation treatment. SD positively correlated with leaf N concentration and xylem sap ABA concentration for the DI plants, but not for the PRO plants. Nonetheless, negative linear relationships of SD to the mean soil water content in the pots and the carbon isotope discrimination in the leaves were found across all treatments. Regression analyses showed that it was SA rather than SD positively correlated with the stomatal conductance and the transpiration rate per unit leaf area in the DI; however such relationships were not evident in the PRO. In conclusion, compared to DI, PRO led to a more conservative control in plant water use via modulating stomatal morphology; the smaller stomata combined with a lower SD in the plants had efficiently reduced plant water use under high N rate, which maintained a better soil water moisture condition in the PRO pots. (C) 2012 Elsevier B.V. All rights reserved.