Dynamics of leaf transpiration in two contrasting maize (Zea mays L Dynamics of leaf transpiration in two contrasting maize (Zea mays L.) hybrids under water stress and biochar amendment Leila Romdhane1 , Teofilo Vamerali2, Marianna Bandiera2, Giuseppe Barion2, Giuliano Mosca2 and Leila Radhouane1 1 University of Carthage-Faculty of Sciences of Bizerte / National Institute of Agronomic Research of Tunisia (INRAT) - Tunisia 2 University of Padova, Department of Agronomy, Food, Natural Resources, Animals and the Environment, (DAFNAE) – Legnaro, Padova - Italy Introduction Soil water retention is determined by the distribution and connectivity of pores in the soil matrix, which is largely affected by soil texture, aggregation and soil organic matter content (Brady and Weill, 2004). Biochar, a C-rich material produced by pyrolysis (temperature 300-700 °C, anoxic conditions) of organic biomass, including agricultural wastes, has a higher surface area and greater porosity relative to other types of soil organic materials and therefore can improve soil texture and aggregation, and consequently soil water retention (Kongthod et al., 2015). A pot trial was conducted during summer 2014 at the experiment farm of the University of Padova at Legnaro (NE Italy) in order to follow the dynamics of leaf transpiration in two contrasting maize hybrids with and without biochar addition to the soil in conditions of progressively decreased water availability. Materials and Methods 2 maize hybrids (Pionneer Hi-Bred-Dupont; FAO class 700): Drought tolerant (T): D24 Drought sensitive (S): P1921 2 treatments , 5 replicates ( Fig. 1): Biochar (1% w/w) (BC1%): soil pH 7.88, EC 0.58 mS cm-1 ; 5 kg of soil + 50 g biochar +2.5 g NPK fertilizer (15-15-15) per pot. Untreated controls (C): soil pH=7.55, EC 0.50 mS cm-1 (Fig.1) Growing period: August 11th – October 10th. The effects of water stress were evaluated by calculating the “linear plateau regression” obtained by relating daily relative transpiration (RT) over the fraction of transpirable soil water (FTSW) (Vamerali et al., 2003), as follows: y = a + b * (x - c) * (x <= c) Fig. 1 . Pot trial BC (1% w/w) C Fig. 2. Relationships between relative transpiration (RT) and fraction of transpirable soil water (FTSW) of maize hybrids D24 and P1921 (Plateaux Linear Regression), under progressive water deficit regime under biochar-amended soil (1% w/w) and unamended controls. Coefficients of regression curves are: a = 97,13, b = 0,80, R2 = 85,6% (Untreated D24); a = 97,88, b = 1,69, R2 = 94,33% (Untreated P1921); a = 95,63, b = 1,65, R2 = 92,92% (BC1% D24); a = 93,95, b = 3,87, R2 = 95,49% (BC P1921). Threshold at which RT begins to decline was estimated by the plateau linear regression model as coefficient “c”. Results Results showed that in both hybrids biochar was able to maintain a high rate of transpiration down to low FTSW values. The linear plateau regression model of un-amended controls of D24 start to decline earlier (82 % FTSW value) than in P1921 (45% FTSW value), confirming the water-saving strategy of D24. Instead, soil amended with biochar allowed plants of both hybrids to transpire at their maximum down to lower FTSW, i.e., 45% and 22% in D24 and P1921, respectively (Fig. 2). Conclusions It is concluded that biochar can delay the inhibition of transpiration in condition of limited water availability in agreement with the commonly observed capacity of biochar to improve the water holding capacity, a fact that is attributed to the high surface area of biochar which helps it to increase water retention. Bibliography Vamerali T., Saccomani M., Bona S., Mosca G., Guarise M., Ganis A. (2003). A comparison of root characteristics in relation to nutrient and water stress in two maize hybrids. Plant and soil 255: 157-167. Brady NC, Weil PR. 2004. The nature and properties of soils.??????? KONGTHOD T., THANACHIT S., ANUSONTPORNPERM S., WIRIYAKITNATEEKUL W. (2015). Effects of biochars and other oganic soil amendments on plant nutrient availability in an Ustoxic Quartz ipsamment. Pedosphere 25(5):790 – 798, 2015.