Season and genotype effect on whole plant water use efficiency of coconut (Cocos nucifera L.) seedlings grown in a hydroponic system

Abstract

• Significantly high water use in summer than monsoon, biomass change non-significant. • WUE of dwarfs was low during summer compared to talls. • Stomata was insensitive to high VPDL in dwarfs while sensitive in talls. • High PAR during summer might be limiting biomass gain in dwarfs. A study was conducted to understand the influence of climatic factors on nutrient use, and whole plant water use efficiency (WUE) of hydroponically grown coconut seedlings. Two dwarf (Chowghat green dwarf, CGD and Malayan yellow dwarf, MYD) and two tall (Kalpa Pratibha, KP and Kalpatharu, KT) coconut genotypes were grown in triplicates and their water use, and biomass production were measured and WUE was analyzed across summer, monsoon and winter seasons, characterized with distinct climatic variability. In comparison to monsoon, during summer the morning temperature was (6 ℃) high, and relative humidity (RH) was low during summer resulting in two folds increase in vapour pressure deficit on leaf surface (VPDL). Increasing VPDL had direct influence on water consumption of the plant per day which was significantly high during summer (3.14 L) compared to monsoon (1.83 L), but the difference in biomass gain was not significant. This had led to a weakly negative [R 2 (144) =0.12, p < .0001] relation between water use and WUE, the WUE was only 3.35 g L −1 during summer as against 6.6 g L −1 of monsoon. The response of genotypes to increasing VPDL was also significantly different. The sensitive stomata of talls could conserve water and maintain significantly high WUE while insensitive stomata of dwarfs allowed greater water loss without a concomitant increase in biomass resulted in low WUE. The early photosynthetic light saturation at 1400 μ mole photon m −2 s −1 might have also contributed to low biomass production in dwarfs. This study divulges that, at high temperature and low humidity in general, coconut WUE is low and especially dwarfs are not suitable for those regions with dry weather or regions expected to become dry under future climate scenario.