Photosynthetic, chlorophyll fluorescence and growth changes in hot pepper under deficit irrigation and partial root zone drying

Abstract

There is increasing evidence that the spatial distribution of water within the root zone, as well as total soil water 
status, determines plant physiological and agronomic responses. To examine the response of photosynthesis, 
chlorophyll fluorescence and growth of hot pepper (Capsicum annuum L.) to deficit irrigation (DI50, 50% of the 
control) and partial root-zone drying (PRD, with half of the root system exposed to soil drying and the other half 
watered with 50% irrigation water of the control), two water deficit treatments were imposed on greenhouse grown hot 
pepper during the growing period in 2006. Control plants received irrigation to both halves of the root system when 
soil water content was < 80% of field capacity. Both PRD and DI50 treatments decreased total dry mass by 33 to 44%, 
shoot biomass by 31 to 44% compared to the control. These treatments increased root-shoot ratio by 35 to 44% in 
relation to the control, with significant differences between PRD, DI50 and the control. Deficit irrigation led to a relative 
leaf water content of about 77.91 to 92.71%. Two water deficit treatments reduced photosynthetic rate (Pn) slightly and 
transpiration rate (Tr) significantly, thus improving leaf water use efficiency (WUEL, defined as the ratio of Pn to Tr) by 
24 to 26%. During water stress, a down-regulation of PSII activity was observed along with some impairment of 
photochemical activity, as revealed by decreases in the maximum quantum yield of PSII (Fv/Fm). Although Fv/Fm did 
not significantly differ between the deficit treatments and the control, Fv/Fm of PRD plants was higher than that of 
DI50 plants. The mean values of Fv, Fm, qP at four stages decreased and Fo and qN increased in the soil drought 
environment. Development of non-radiative energy dissipation mechanisms was evidenced during stress by increases 
in non-photochemical quenching and decreases in efficiency of excitation capture by open centers.