Silicon Drenches Improve Drought Stress Tolerance in Poplar, Poster Board #210

Aridity due to depletion of water resources and climate change poses a problem for agriculture worldwide. Increasing evidence demonstrates that silicon (Si), the second most abundant element in the soil, can improve plant response to various abiotic stresses. In this work, we examined whether drought tolerance of poplar (Populus tremuludes x P. Alba) could be improved following Si application. Poplar, which has substantial water needs, is an important tree source for the paper industry and for potential bio-fuel production. Poplar plants were transplanted into 1.75 L containers with a peat-based potting mix and grown in a greenhouse at 25 °C and with 50 µmol·m^-2·s^-1 supplemental light for 16 hours daily. Plants were regularly irrigated with a commercial complete fertilizer.  Silicon treated plants received twice weekly drenches (500 mL per plant) with 4mM potassium silicate; control counterpart received corresponding drenches with potassium chloride to equal the potassium of the Si treatment. After 6 weeks, irrigation was withheld to impose drought stress and plants were transferred to growth chambers (16 hours of light at 100 µmol·m^-2·s^-1 supplemental and 22 °C). Observations were conducted immediately upon transferring of plants to chambers and for three subsequent days (2, 3, and 4 days post water withholding). Leaf angle measurements from 8 leaves per plant were taken with a digital protractor to quantify the degree to which leaves had wilted; and the daily leaf angle change was calculated. A visual wilt index of whole plants on the scale of 1 (no wilted leaves) to 9 (whole plant wilted) was also determined. Leaf angle change was significantly lower in Si-treated poplar plants as compared to their control counterparts at days 2, 3, and 4 into drought stress.  At day 2 leaf angle was 23 ± 3 for Si plants and 32 ±3 degrees for control plants. The greatest difference in leaf angle was found 3 days after drought stress (44 ± 4 degrees for Si treatment versus 61 ± 4 degrees for control).  Visual wilt index results corresponded to leaf angle measurements; at day 2 and 3, wilt index was significantly lower for silicon treated plants. On day 4 post water withholding, wilt index did not significantly differ among treatments, indicating that the Si effect was exhausted at this point. Overall, we have demonstrated the applicability of Si drenches for delaying drought stress response in poplar plants.