Total Root and Shoot Biomass Inhibited by Paclobutrazol Application on Common Landscape Trees

Chad M. Rigsby; E. Thomas Smiley; Sean Henry; Liza Holmes; Andrew L. Loyd

doi:10.48044/jauf.2024.017

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Figure 1.
Root, stem, and leaf dray mass (g) associated with different application rates of paclobutrazol (Cambistat^®) across 5 species. P-values below 0.05 are in bold font and considered significant; different letters indicate significant differences between dose rates. Columns are species and rows are the response variable. Treatment rate based on the species-specific category on the Cambistat^® label is indicated as “Full”; the category below full rate is indicated as “1CL”; 2 categories below full rate is indicated as “2CL”; and non-treated were controls. The species-specific category on the Cambistat^® label is listed beside the species name as well as beside the “Full” treatment. The dose category is also listed beside 1CL and 2CL.
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Figure 2.
Root:shoot ratios (g), length of longest root (cm), and estimated total root length (cm) associated with different application rates of paclobutrazol (Cambistat^®) across 5 species. P-values below 0.05 are in bold font and considered significant and different letters indicate significant differences between dose rates. Columns are species and rows are the response variable. Treatment rate based on the species-specific category on the Cambistat^® label is indicated as “Full”; the category below full rate is indicated as “1CL”; 2 categories below full rate is indicated as “2CL”; and non-treated were controls. The species-specific category on the Cambistat^® label is listed beside the species name as well as beside the “Full” treatment. The dose category is also listed beside 1CL and 2CL. The total root length for silver maple was not statistically analyzed due to low replication.

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Table 1.

Summary of experimental set up.

Tree species (label category)	Treatment^¹ (label category)	Replicates after mortality^²	Replicates used to quantify average total root length	Cambistat^® dose^³ (mL/cm)	Paclobutrazol dose^⁴ (g/cm)
Silver maple (D)	Full rate (D)	3	2	4.6	1.1
	1CL(C)	3	3	4.2	1.0
	2CL (B)	3	2	2.3	0.6
	Non-treated	8	8	0.0	0.0
White oak (D)	Full rate (D)	10	4	4.6	1.1
	1CL(C)	10	4	4.2	1.0
	2CL (B)	10	4	2.3	0.6
	Non-treated	10	4	0.0	0.0
Pecan (E)	Full rate (E)	5	4	5.0	1.2
	1CL (D)	5	4	4.6	1.1
	2CL(C)	5	3	4.2	1.0
	Non-treated	9	6	0.0	0.0
Laurel oak (F)	Full rate (F)	9	4	6.7	1.6
	1CL (E)	8	3	5.0	1.2
	2CL (D)	9	4	4.6	1.1
	Non-treated	10	4	0.0	0.0
Stone pine (F)	Full rate (F)	10	3	6.7	1.6
	1CL (E)	10	3	5.0	1.2
	2CL (D)	9	4	4.6	1.1
	Non-treated	9	3	0.0	0.0

↵¹ Treatment rate based on the species-specific category on the Cambistat^® label is indicated as “full rate”; the category below full rate is indicated as “1CL”; 2 categories below full rate is indicated as “2CL”; and non-treated were controls.
↵² Replicates that survived the duration of the experiment were used to quantify all response variables except for average total root length.
↵³ Rates were based on stem caliper of plant. The amount of water applied per application was 11 mL of water/mL of Cambistat^® for all treatments.
↵⁴ Dosage based on the amount of grams of paclobutrazol administered based on stem caliper of plant.

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Table 2.

Growth effects associated with different application rates of paclobutrazol (Cambistat^®) with all 5 species included in analysis. Biomass parameters were log transformed to normalize variance prior to running a restricted maximum likelihood mixed model, where treatment was a fixed effect and species was considered a random effect. P-values in bold are significant, and means separation letters not connected by the same letter are significantly different according to the Tukey’s honestly significant difference (HSD) post-hoc calculation.

Treatment^¹	Root dry mass (g)(± SE)	Stem dry mass (g)(± SE)	Leaf dry mass (g)(± SE)	Root:shoot (g)(± SE)
Full rate	10.3 (0.8)^b	7.3 (0.7)^c	4.5 (1.1)^c	1.3 (0.1)
1 CL	11.5 (0.9)^b	7.2 (0.6)^bc	4.7 (1.0)^bc	1.3 (0.1)
2 CL	12.4 (0.9)^b	8.4 (0.8)^b	5.5 (1.2)^b	1.2(0.1)
Non-treated	23.6 (1.8)^a	10.4 (0.8)^a	10.5 (1.2)^a	1.4 (0.1)
F-statistic_df	44.0 _3,148	17.8 _{3, 148}	89.8 _{3, 148}	0.08 _{3, 148}
P-value	*< 0.0001*	*< 0.0001*	*< 0.0001*	0.7502

↵¹ Treatment rate based on the species-specific category on the Cambistat^® label is indicated as “full rate”; the category below full rate is indicated as “1CL”; 2 categories below full rate is indicated as “2CL”; and non-treated were controls.