Aims Pot experiments were conducted to investigate effects of water deficit and duration of the deficit (0, 15, 36 and 14 days recovery) on four hybrid Populus: 15-29 (P. trichocarpa × P. deltoids), DN-2 (P. deltoids × P. nigra), DN-14274 (P. deltoids × P. nigra) and R-270 (P. deltoids × P. nigra). Our objective was to examine the responses of Populus plants to soil water deficit by analyzing eco-physiological, morphological, and growth characteristics, as well as several parameters of plant performance.
Methods Seedlings were exposed to four treatments: 100%, 70%, 50% and 30% of soil field water capacity (treatments T1-T4, respectively).
Important findings The four hybrids were sensitive to water deficit. All developed physiological adaptive mechanisms as well as configurational strategies to cope with water shortages to different degrees by closing stomata and reducing leaf number and leaf area to regulate water loss, by depressing net photosynthetic rate (Pn), transpiration rate (Tr) and leaf water potential (ψ) to enhance water use efficiency (WUE), or by changing allocation of biomass productivity (Bp). Under water stress, R-270 only decreased its leaf dry weight but the other three hybrids decreased their dry weight of leaf, stem and root. With declining soil moisture, root/shoot of 15-29 and R-270 increased, implying the roots obtained more carbohydrates, which favors water absorption. Carbon isotope composition (δ13) of DN-2 was significantly positively correlated to WUE, but δ13 of R-270 was significantly negatively correlated to WUE. Pn, stomatal conductance (Gs), Tr,ψ, biomass and canopy areas of the seedlings in T1 and T2 are higher than those in T3 and T4, suggesting that the four hybrids can obtain high production in arid areas under sufficient-moderate irrigation. Lower Pn, Gs, Tr,ψ, biomass, canopy areas and higher WUE of the seedling in T3 and T4 indicate that the four hybrids can develop survival strategies under water stress, but biomass production was negatively affected. Clone 15-29 and R-270 showed a stronger adaptive response than DN-2 and DN-14274 under water stress, implying they have greater drought-resistance ability.