Abstract

Shao Guang-cheng*, Guo Rui-qi, Liu Na , Yu Shuang-en and Xing Weng-gang

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.