Relationships between mineral nutrition, drought resistance and clone in Populus

• Main Author: Harvey, Helen Penelope Penny
• Other Authors: van den Driessche, R.
• Format: Others
• Language: English; en
• Published: 2018
• Subjects: Poplar; Growth; Drought resistance; Mineral nutrition
• Online Access: https://dspace.library.uvic.ca//handle/1828/9760

Effects of mineral nutrition on drought and cavitation resistance of poplars were examined in two sets of greenhouse-grown trees. First, two drought-sensitive and two drought-resistant hybrid clones of black cottonwood (Populus trichocarpa Torr. & Gray) and eastern cottonwood (P. deltoides Bartr.) were grown at three concentrations of nitrogen (N) applied factorially with two concentrations of phosphorus (P) in a sub-irrigation sand-culture system. The trees were subjected to 0, 4, 6, and 8 days of gradual drought stress before measurements of cavitation, anatomical features affecting cavitation, and nutrient mobilization during drought. High foliar concentrations of N increased cavitation compared to barely adequate concentrations, whereas high concentrations o f P decreased cavitation as measured by both hydraulic flow apparatus and dye perfusion techniques. For one test, cavitation was 48% at high N and low P, but only 28% at high N and high P. Vessel pit membrane mean pore diameters were 0.132 μm at low P and 0.074 μm at high P: smaller pores would decrease air-seeding cavitation. No other significant effects of mineral nutrition on vessel dimensions were observed. Scanning election microscopy showed less damage to pit membranes, suggesting greater membrane strength in drought-resistant clones than in drought-sensitive clones. In the second experiment, three drought-resistant and three drought-sensitive poplar clones (including P. trichocarpa) were grown at two levels of N and three levels of potassium (K) and either well-watered, cyclically droughted, or droughted once. Cavitation, osmotic potential, gas exchange, and nutrient mobilization were measured at each stage of drought and re watering, and fall nutrient retranslocation was monitored. Cavitation was greater with adequate foliar N than at deficiency levels. Moderate supplies of K increased cavitation, but luxury levels sometimes reduced cavitation by decreasing foliar water loss and thus xylem tension. Preconditioning did not reduce vulnerability to cavitation, but there was some evidence of cavitation reversal in a drought resistant clone at high N supply. Vessel diameters were 36.6 μm at low N but 45.2 μm at high N, so within Populus, larger diameter vessels correlated with susceptibility to cavitation. High N supply increased water stress during the first drought, but also increased instantaneous water use efficiency (WUE) before drought occurred, and osmotic adjustment and hardening after drought. Increased K also increased WUE before drought and decreased water stress (decreasing transpiration and wilting) at luxury levels, but did not influence osmotic adjustment or hardening. Mobilization of nutrients differed with speed and intensity of drought. Gradual drought led to resorption of N and P. In the second experiment, drought was too rapid for retranslocation. Nutrients became more concentrated; some (e.g., N) facilitated hardening and osmotic adjustment, and some (e.g., K) moved out of the leaves on re watering. In fall, N, P, Cu and K were resorbed, the latter more proficiently with greater N supply at low levels of K. Clones which were more productive on dry sites resisted severe, but not moderate cavitation. Cavitation-resistant clones maintained high transpiration rates (and less negative water potentials) in drought, especially after hardening, had more, but smaller, stomata and decreased leaf loss in drought, but did not have increased WUE or osmotic adjustment. Nitrogen fertilization increased cavitation, greater P supply reduced this effect, and K fertilization may make vessels more vulnerable to cavitation but decrease the tension on the xylem that causes cavitation. Nitrogen fertilization levels should be tailored to site water supplies, and appropriate P, and possibly K additions may increase drought resistance. === Graduate