High Soil Salinity Threatens Key Tree Cactus in the Florida Keys
Joyce Maschinski and Devon Powell U.S. Endangered Key Tree Cactus (Pilosocereus robinii) Populations
Key Tree Cactus Survey Results
2500
2000
1500 Lower Keys Middle Keys Upper Keys
1000 Number Number of Stems
500
0 1994 2007 2011 In 2007, In Lower Keys Soil Salinity was Greater Around Dead Plants
700
600
500
400
300
200 Mean Mean Soil Salinity (ppm)
100
0 DEAD ALIVE Thanks to funding from USFWS and FDACS
Steps for species conservation:
1. Make collections for long-term storage ex situ at FTBG and DBG. 2. Rescue populations if necessary. 3. Testing Salinity Tolerance. 4. Genetics studies planned. 5. Identify potential reintroduction sites. 6. Spread the risk by reintroducing plants to the wild (increasing total numbers of plants and populations). Testing Salinity Tolerance of Key Tree Cactus
Seedlings germinated in 2008 from 2 maternal lines
Maternal 1 – cultivated source Maternal 2 - BPK What do Salinity Measures Mean?
40 mM Na = Soils 100 mM Na = level at considered saline; which salt sensitive Plants experience species cannot osmotic stress complete life cycle
0 2 15 40 80mM 469 mM Sea water
0 94 390 670 1800ppm 11,000 ppm X = 11g Na in 1000 ml water
Live Dead in 2007 Five Salinity Levels
1. 0 mM NaCl =control plants received only RO water with no detectable Na
2. 2 mM NaCl = low soil Na concentrations detected at one proposed reintroduction site
3. 15 mM NaCl = Na soil concentration detected at BPKE, where P. robinii had low mortality between 1994 and 2007
4. 40 mM NaCl = the threshold for osmotic stress in salt-sensitive plants and comparable to Na concentrations measured at BPKW
5. 80 mM NaCl = 2X threshold stress Na concentrations Setting Up the Experiment
Initial and 7 week Growth Measurements
Stem Weight and Length
Dry Root Weight Stem Growth
1.8
1.6
1.4
1.2
1 Maternal 1 Maternal 2 0.8
Stem Growth Stem (cm) Growth 0.6
0.4
0.2
0 0 2 15 40 80 mM NaCl Root:Shoot Ratio
0.2
0.15
0.1
0.05
0 Maternal 1 0 2 15 40 80 mM NaCl Maternal 2
-0.05 Log Root:Shoot Log Root:Shoot -0.1
-0.15
-0.2
-0.25 Transpiration Rate
0.1
0.08
0.06
Maternal 1 0.04 Maternal 2
0.02
0 Change in Water Content (kg water loss) water (kg Content in Change Water 0 2 15 40 80 mM NaCl
-0.02 Levels of Sodum in Plant Tissue
450
400
350
300
250 Maternal 1
200 Maternal 2
Na in Na (ppm) tissue 150
100
50
0 0 2 15 40 80 mM NaCl Sodium Concentration in Florida Keys Soils Collected Winter 2011
300.00
250.00
200.00
150.00
Mean Na (ppm) Mean Na 100.00
50.00
0.00 NKDR W NKDR E LKLT LVK KTCP KL CLWR Conclusions
• There was variation in salt tolerance across maternal lines of Key tree cactus. BPK collection was very salt sensitive.
• At least one reintroduction site (CLWR) had salinity levels well within the tolerance of both maternal lines that were tested.
• BPKW salinity levels were significantly greater than other sites even 4 yrs post storm-surge event.
• Reintroductions with some salt-tolerant genotypes would be beneficial.
• A second source of mortality may have been inundation. Trials are underway. Thanks to the South Florida Conservation Team and to funding agencies U.S. Fish and Wildlife Service and Florida Dept of Agriculture and Consumer Services