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Pak. J. Bot., 44(4): 1405-1412, 2012.

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EFFECTS OF NITROGEN FORMS AND DROUGHT STRESS ON GROWTH, PHOTOSYNTHESIS, AND SOME PHYSICO-CHEMICAL PROPERTIES  OF STEM JUICE OF TWO MAIZE (ZEA MAYS L.) CULTIVARS AT ELONGATION STAGE

LIXIN ZHANG^1,2*, YOUYA ZHAI¹ , YUNFEI LI³, YONGGUI ZHAO¹, LIXIA LV³, MEI GAO¹, JIANCHAO LIU¹ AND JINJIANG HU¹

Abstract: Drought stress (DS) usually causes a serious yield reduction in maize production. Nitrogen (N) has been reported to be able to alleviate DS damage in previous studies; however, which N form is beneficial for plant growth in drought-stress maize and its mechanism is still poorly understood. The objective of this study is to examine the effects of different nitrogen forms on growth, photosynthesis and stem juice characteristics of maize (Zea mays L.) under drought, and find out better and convenient measurers for drought resistance ability of the C₄ crop. Pot experiments were carried out using two maize cultivars (Zhengdan 958 and Jundan 20) under integrated root-zone drought stress (IR-DS) by irrigating 10% PEG-6000 solution and non-DS conditions grown for 33 days, and their tested indexes were determined at elongation stage. Dry matter (DM), net photosynthetic rate (Pn), stomatal conductance (gs) and oxidation-reduction potential (ORP) in stem juice were decreased while pH, electric conductivity (EC), soluble protein concentration (SPC) and ABA concentration (ABAC) in stem juice increased of both cultivars in all N forms treatments under IR-DS above non-DS. However, the responses of two examined cultivars to DS were different: significantly higher DM production, Pn and drought index (DI) were observed for ZD958 than JD20, therefore the former could be treated as a drought tolerance cultivar comparatively. Better correlations were obtained amongst the above parameters, especially for DM, Pn and pH, EC, ORP, ABAC in stem juice under IR-DS than non-DS. By comparison with sole ammonium (NH₄⁺), sole nitrate (NO₃^-) and the mixed supply of NH₄⁺ and NO₃^- both obviously improved DM and Pn as well as pH, EC, SPC and ABAC whereas decreased Gs and ORP in both drought-stressed cultivars. The effects of NO₃^--supplied were more evident than NH₄⁺+NO₃^--supplied in the above responses. These impacts were superior in ZD958 than JD20. Further analysis of variation indicated that the impact of N form treatment on almost all parameters measured were, in general, less than those of water regime. It is, therefore, concluded that pH, EC and ORP in stem juice could be regarded better and convenient indicators for evaluating drought resistance ability of the C₄ crop. The NO₃^- supplied could be more beneficial for enhancing photosynthesis and plant growth by improving stem juice characteristics than NH₄⁺ supplied, especially for a drought tolerant cultivar.

¹College of Life Sciences, Northwest A & F University, 712100, Yangling, Shaanxi, P.R. China

²State Key Laboratory of Soil Erosion and Dryland Farming, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Northwest A & F University, 712100, Yangling, Shaanxi, P.R. China,

³College of Forestry, Northwest A & F University, 712100, Yangling, Shaanxi, P.R. China

*Corresponding author E-mail: zhanglixinyangling88@yahoo.com.cn