Heavy Metal-Induced Variability in Leaf Nutrient

Overview

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Key numbers

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reached 0.92 and 3.54 mg/kg DW, respectively, with BAF values >1 in multiple sites. PLSR
25% of modeled cases. PCA and HCA distinguished five orchard clusters based on combined soil–leaf
approximately 14–17% of the world’s croplands, representing over 240 million hectares are
accounting for roughly 15% of the total land surface (Sanad et al., 2024c). The agricultural economy of
conducted using ICP-MS after digestion using a solution of 2.25% Nitric acid and 0.5% Hydrochloric
Table 1. macronutrient, micronutrient, and heavy metal concentrations in avocado leaves across
Table 2. Macronutrient, micronutrient, and heavy metal concentrations in avocado leaves across
The optimal N concentration for mature avocado leaves ranges from 1.8% to 2.4% (Newett et al.,
from 0.20% to 0.38%, averaging 0.27% and generally fell within or slightly above the optimal range
avocado fruit quality, exhibited considerable variability, ranging from 1.10% to 2.94% with a mean
of 2.01%, surpassing the recommended range (0.75% DW to 2.0% DW) for mature avocado leaves
rich in K. Ca concentrations ranged between 1.58% and 3.50%, with a mean of 2.45%, falling within
optimal limits (1.0% to 3.0%) reported for avocado leaves (UCANR, 2020; Bender and Faber, 2004).
and structure. Mg presented distinct variability, ranging from 0.32% to 0.98% across sites, with a mean
value of 0.68%. These values generally align with the recommended range of 0.25% to 0.80% for
82.1 to 245.0 mg/kg (mean: 157.3 mg/kg), generally aligning with the adequate range of 50 to 200 mg/kg
with enhanced micronutrient bioavailability under such conditions (Table 1 and Table 2). In contrast,
23.4 to 65.5 mg/kg (mean: 42.7 mg/kg), with most sites meeting the recommended range of 30 to 150
mg/kg (UCANR, 2020; Bender and Faber, 2004). Sites exhibiting optimal Zn levels, particularly S7 and
ranging from 5.3 to 19.2 mg/kg (mean: 11.6 mg/kg), generally within the recommended range of 5 to
11.2 and 68.3 mg/kg (mean: 39.7 mg/kg). Sites with moderate to high Mn content, such as S7, S20, and
cell wall structure and sugar transport, varied from 31.2 to 69.8 mg/kg (mean: 51.4 mg/kg). All sites
remained within the typical range of 20 to 100 mg/kg recommended for avocado (UCANR, 2020;
maximum permissible limit for Cd in edible leafy tissues is typically around 0.2 to 0.3 mg/kg (Magesa
excessive use of phosphate fertilizers and manures (Table 1 and Table 2). In contrast, orchards with
ranging from 0.31 to 1.78 mg/kg (mean: 0.94 mg/kg). While the FAO/WHO recommends a general
upper limit of 2 mg/kg for Pb in leafy vegetables, lower thresholds are often applied for sensitive crops
from 0.92 to 4.89 mg/kg across sites, with a mean of 2.78 mg/kg. Sites with higher Ni accumulation
adjustments in photosynthetic apparatus. In this study, SPAD index values across sites ranged from 20.1
(2.74%), Mg (0.87%), and Fe (242.9 mg/kg) concentrations, alongside low Cd (0.094 mg/kg) and Pb
(0.312 mg/kg) levels. These trees displayed “Healthy green” leaf coloration, reflecting optimal
29.6 with low Mg (0.37%), low Fe (81.2 mg/kg), and high Cd (0.352 mg/kg) and Pb (1.307 mg/kg),
a/b ratio, which ranged from 1.31 to 2.85 (mean: 2.17), clearly distinguished photosynthetic efficiency
(Table 3 and Table 4). In contrast, ratios below 1.8 (notably in S17, S18, and S3) were linked to stressed
from 0.51 to 11.75 and a mean value of 3.52. Elevated BAF values (above 1) were widespread,
variability between trees was evident, for example in Site S3 BAFs ranged from 4.1 to 9.5, likely
of these essential micronutrients. Fe BAF ranged from 15.23 to 60.88 (mean: 36.26), while Mn ranged
from 6.67 to 51.02 (mean: 11.71). Sites with moderate organic matter and slightly acidic soils such
differences were observed, for instance in Site S4 Fe BAF ranged from 30.2 to 55.7, reflecting local
Ni ranged from 0.06 to 0.12 (mean: 0.09). The generally low bioavailability of these metals can be
Pb showed the lowest BAF values among all elements studied, with a narrow range from 0.006 to
such as S17 and S18. Zn exhibited moderate BAF values, ranging from 0.41 to 0.62 (mean: 0.51). While

Methods (brief)

Methods: Twenty representative sites were sampled, each comprising soil and mature avocado leaf
leaf samples were assessed for macronutrients (NPK, Ca, Mg), micronutrients (Fe, Mn, Zn, Cu, B),
planted in soils previously sampled for physicochemical and metal analyses were randomly selected
(Fig 1). All sampled trees were in the harvest maturity stage to ensure comparability in physiological
Fully expanded, healthy leaves were collected from the mid-canopy of each tree, avoiding older or
damaged tissues. A minimum of 20 leaves per tree were harvested to ensure a representative sample,
tree was recorded to minimize variability. Samples were carefully placed in polyethylene bags, labeled,
Leaf Sample Preparation and Analytical Procedures
Upon arrival at the laboratory, the collected avocado leaf samples were carefully rinsed with
deionized water to eliminate surface dust and contaminants. The samples were then oven-dried at 65°C
Fig 1. Map showing the location of soil samples and avocado orchards.
conducted using ICP-MS after digestion using a solution of 2.25% Nitric acid and 0.5% Hydrochloric
The supernatant was collected to quantify the content of chlorophyll a and chlorophyll b using the Eq.
samples but also exhibited strong correlations with soil metal content and BAFs. To capture the

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised