Abstract:

Jatropha curcas L. is a kind of tree that can be used as raw material for production of bio-energy, and hence called bio-diesel tree. As it is also quite high in tolerance to environmental stresses, it can be used as pioneer plant in restoring vegetation in ecologically fragile environment and in phyto-remedying polluted soils as well, therefore, planting this kind of trees may achieve the win-win goal in both energy and environment. An indoor pot experiment was carried out to explore effects of concentration of heavy metal nickel (Ni) (0,500 and 1 000 mg kg^-1) on photosynthetic properties, morphological characteristics and water utilization of Jatropha curcas L. and mechanisms of the plant regulating its growth and utilizing efficiently soil water, while adapting to Ni-polluted soils. Results show that plant height growth rate, and breast-height diameter growth rate, diurnal variation of net photosynthetic rate (P_n), diurnal variation of transpiration rate (R_t), robust seedling index, Huber value, and irrigation water utilization efficiency (W_i,u,e) were all decreased significantly (P < 0.05), while leaf water utilization efficiency (E_w,u) and soil moisture content in root-zone of the plant increased with increasing nickel concentration. Compared with CK(Ni0),Treatment Ni1 did not have much effect on stomatal conductance (Gs) of plants(P>0.05), but Treatment Ni2 did (P<0.05). As nickel contamination significantly reduced Rt of Jatropha curcas L., and affected the plant’s water transport capacity from roots to shoots and its capacity of water supply to leaves per cross-sectional area of sapwood, it significantly reduced E_i,w,u, of the plant and eventually total dry mass of the plant. However, it is worth noting that by increasing its E_i,_w,u of leaves to significantly mitigate the water stress caused by reduced transpiration rate, the tree is able to grow in Ni-polluted soils. In this experiment, the highest concentration of nickel in the soil still conducive to growth of Jatropha curcas L. was up to 500 mg kg^-1.

Key words: Jatropha curcas L., heavy metal, nickel, soil, photosynthetic properties, morphological characteristics, water utilization efficiency