Failure of Foliar-Applied Biostimulants to Enhance Drought and Salt Tolerance in Urban Trees

Article Figures & Data

Table 1.

Selected biostimulants evaluated to enhance drought and salt tolerance.

Product	Active ingredient	Supplier
Maxicrop Original	Seaweed extract	Maxicrop (UK) Ltd, P.O. Box 6027, Corby, UK
Resistim	Betaine	Mandops UK Ltd, Eastleigh, Hampshire, UK
Bioplex	Seaweed + humic acid extract	United Agri Products Ltd, Alconbury Weston, UK
Fulcrum CRV	Molasses	Banks Cargill Agriculture Ltd, St Hughs, Lincoln, UK
Redicrop	Seaweed (cytokinin activity)	United Agri Products Ltd, Alconbury Weston, UK
Crop Set	Lactobacillus fermentation product and B5 vitamins	United Agri Products Ltd, Alconbury Weston, UK
Superthrive	Vitimin B and Auxin (NAA)	Bartlett Tree Research Laboratory, Charlotte, NC, USA

Table 2.

The influence of 48 hours dehydration on chlorophyll fluorescence (Fv/Fm) of detached leaves of woody plants.

Treatment	Concentration per L	Quercus ilex	Sorbus aucuparia	Fagus sylvatica
Water (control)	-	0.777a	0.588a	0.349a
Maxicrop Original	10 ml	0.769a	0.566a	0.339a
Maxicrop Original	20 ml	0.801a	0.572a	0.361a
Resistim	10 ml	0.779a	0.583a	0.352a
Resistim	20 ml	0.761a	0.551a	0.347a
Bioplex	10 ml	0.780a	0.557a	0.344a
Bioplex	20 ml	0.788a	0.583a	0.327a
Fulcrum CRV	10 ml	0.770a	0.592a	0.350a
Fulcrum CRV	20 ml	0.766a	0.553a	0.341a
Redicrop	10 ml	0.758a	0.549a	0.340a
Redicrop	20 ml	0.761a	0.571a	0.333a
Crop Set	10 ml	0.772a	0.600a	0.360a
Crop Set	20 ml	0.762a	0.607a	0.362a
Superthrive	0.25 ml	0.790a	0.592a	0.353a
Superthrive	0.50 ml	0.789a	0.560a	0.349a
SD		0.0126	0.0189	0.0101
CV		0.0161	0.0330	0.0286

Note: All values mean of 10 trees; five leaves per tree. Different letters represent significant differences between treatments at the 95% confidence level. SD = Standard Deviation, CV = Coefficient of Variation.

Table 3.

Lethal salt concentration (SC₅₀) required to reduce leaf photochemical efficiency by 50% based on chlorophyll fluorescence (Fv/Fm) values.

Treatment	Concentration per L	Quercus ilex SC₅₀	Ilex aquifolium SC₅₀
Water (control)	-	7.7%a	6.7%a
Maxicrop Original	10 ml	7.6%a	6.5%a
Maxicrop Original	20 ml	7.4%a	6.8%a
Resistim	10 ml	7.9%a	6.5%a
Resistim	20 ml	8.0%a	6.6%a
Bioplex	10 ml	7.7%a	6.9%a
Bioplex	20 ml	7.3%a	6.6%a
Fulcrum CRV	10 ml	7.9%a	6.5%a
Fulcrum CRV	20 ml	8.0%a	6.3%a
Redicrop	10 ml	7.4%a	6.6%a
Redicrop	20 ml	7.4%a	6.8%a
Crop Set	10 ml	7.6%a	6.9%a
Crop Set	20 ml	7.2%a	6.9%a
Superthrive	0.25 ml	7.8%a	6.6%a
Superthrive	0.50 ml	7.8%a	6.4%a
SD		0.2499	0.1803
CV		0.0342	0.0267

Note: Results are expressed as the percentage concentration of salt spray required to reach the SC₅₀. All values mean of 10 trees; five leaves per tree. Different letters represent significant differences between treatments at the 95% confidence level. SD = Standard Deviation, CV = Coefficient of Variation.