COS 40-3
Drought shifts internal carbon partitioning and use of recent photosynthates in black spruce trees: From bud to mature shoot

Tuesday, August 12, 2014: 2:10 PM
Regency Blrm A, Hyatt Regency Hotel
Anna M. Jensen, Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN
Jeffrey M. Warren, Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN
Background/Question/Methods

Springtime bud-break and shoot development induces substantial carbon (C) costs in trees, temporally altering the internal canopy source-sink relationships. Drought stress impedes C translocation delaying shoot development and potentially increasing the total C costs associated with foliar development. We studied effects of drought and re-hydration on shoot development and C use, in 10-year old Picea mariana [black spruce] trees to identify and quantify key morphological/ physiological processes. Trees were subjected to one of two treatments in a growth chamber; well-watered control (C) or drought and re-hydration (D). We monitored changes in morphological, biochemical (osmolality, [chlorophyll], [nitrogen], [C] and [non-structural carbohydrates (NSC)]) and physiological (rates of respiration (Rd) and light-saturated photosynthesis (Asat)) processes during shoot development. Further, to study functional compartmentalization and use of new assimilates; we 13C-pulse labeled shoots at multiple development stages (at individual branch level), and measured isotopic signatures of leaf respiration, NSC pool and structural biomass.

Results/Conclusions

Overall shoot development was delayed by drought. Water deficit during shoot expansion resulted in longer, yet more compact shoots with on average greater (63%) needle osmolality compared to the shoots on the control-trees. The positive non-linear relationship through time between xylem water pressure potential and needle osmolality suggests osmoregulation occurs independent of developmental stage. Development of the photosynthetic apparatus was delayed, as shoots on C-trees broke-even (Asat > 0) 14 days prior to D-shoots. Average values of Rd decreased with shoot maturation, generally smaller in D-trees, ranging from 224.8 to 12.8 and from 96.8 to 12.5 nmol g-1 s-1, in treatment C and D, respectively. 12C:13C isotopic patters, indicated that the internal C partitioning and use was dependent on foliar developmental stage and treatment. Shoots on D-tress respired a greater proportion of recently fixed C; this was especially true during early stages of shoot development. Mean residence time of C was dependent on rates of respiration more so than Asat. In conclusion, temporary periods of water deficit inhibits C translocation from older organs delaying new shoot development (increasing C input) in black spruce, entailing shift in the internal C partitioning and use of recent carbon ensuring/prioritizing substrate availability for growth and mainten