Responses of hydroponically-grown chickpea to low phosphorus: pH changes, nutrient uptake rates, and root morphological changes

Plants grown in highly weathered or high alkaline soils often experience P stress, but never a P free environment. Thus, applications of mineral P fertilizers are often required to achieve maximum yield. Responses of different plant species or cultivars were the subject of numerous investigations in which P was withheld from the growth media. In this study, chickpea plants (Cicer arietinum L.) grown hydroponically in complete nutrient solution for 17 days (1 mM P) were then maintained at low-P supply for 14 days (0.01 mM). Measurements included dry matter (DM)(1), production of shoots and roots, PEP carboxylase, organic acid anion (Org A(-)), and root morphological responses. Dry matter of shoots and roots were reduced equally in plants subjected to Low-P supply. The uptake rates of all mineral nutrients were reduced soon after low-P was imposed within 1-2 days for Ca2+, Mg2+, and SO42- and within 3-4 days in case of K+ and NO3-. High and low P plants continued to alkalize the nutrient solution, but the rate of OH- released from the roots was considerably reduced in low-P plants. Cumulative values of OH- released from the roots after low P treatment was imposed linearly correlated with the difference of anion-cation uptakes in high-P (R-2 = 0.9989) and in low-P plants (R-2 = 0.9947). Physiological responses to low-P include an enhanced activity of PEPcase in shoots and to a greater extent in roots, which could explain the higher concentrations of Org A(-) in shoots and roots of low-P plants. Root image analyses showed an enhanced branching density in low-P plants resulting in shorter but slender roots than those in high-P plants. These responses could probably explain the greater inflow rates and SAcR rates of micronturient cations (Zn, Cu, Mn, and Fe) into the shoots of P-limited plants.