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Peer-reviewedCC BY 4.0Frontiers in Microbiology

Microbial quotient responses to altitudinal and edaphic variability in Himalayan apple orchard soil

  • Stanzin Khenrab1
  • Sarabdeep Kour1
  • Vikas Sharma1
  • Tsering Lanzes2
  • Tsewang Dolma3
  • Disket Dolkar4
  • Mohd Rafee5
  • Sourav Singh6
  • Manjot Singh Sidhu6
  • Jigmet Namgial6
6 affiliations
  1. 1Division of Soil Science and Agricultural Chemistry, FoA, SKUAST-Jammu
  2. 2Division of Fruit Science, FoH&F, SKUAST-Jammu
  3. 3Division of Agricultural Extension Education, FoA, SKUAST-Jammu
  4. 4Krishi Vigyan Kendra-Leh
  5. 5Department of Commerce, University of Ladakh
  6. 6Division of Silviculture and Agroforestry, FoH&F, SKUAST-Jammu
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Abstract

Introduction: Soil biological health is a critical determinant of sustainable fruit production in mountain ecosystems, yet microbial dynamics in high-altitude orchards remain poorly understood. Whereas total organic carbon (TOC) changes only slowly, the microbial quotient (MQ)—the ratio of microbial biomass carbon (MBC) to TOC—responds early and sensitively to shifts in organic matter turnover and soil biological quality.

Methods: This study quantified MQ across four altitude classes (<1,550, 1,550–1,650, 1,650–1,850 and >1,850 m a.s.l.), three orchard age classes (<8, 8–14, and >14 years) and three soil depths (0–25, 25–50, and 50–75 cm) in apple orchards of the Jammu Himalaya, using 144 stratified samples. MBC and TOC were measured and MQ computed as (MBC/TOC) × 100; dehydrogenase (DHA) and alkaline phosphatase activities were determined as supporting indicators. Data were analysed by three-way ANOVA, Tukey HSD, Pearson correlation, principal component analysis (PCA) and regression.

Results: MQ averaged 3.57 ± 0.08% (range 2.06–8.28%) and declined significantly with altitude, from 4.13% at <1,550 m to 3.11% at >1,850 m ( p < 0.005), the inverse of the MBC and TOC trends. MQ was lowest in surface soil (2.82%) and highest in the 25–50 cm layer (4.14%; p < 0.005) and decreased modestly with orchard age ( p = 0.010); significant altitude × depth and altitude × age interactions were detected. MQ correlated strongly and negatively with TOC ( r = −0.745; R ² = 0.556) but was decoupled from MBC ( r = −0.082, ns), indicating that MQ carries information about the substrate-normalised size of the biomass pool that absolute MBC does not. PCA separated a biomass-substrate axis (PC1, 48.3%) from an MQ-dominated axis.

Discussion: Because microbial carbon-use efficiency, community composition and necromass were not measured directly, the efficiency interpretation of these gradients is advanced as a hypothesis consistent with the data rather than as a demonstrated mechanism. The study nevertheless establishes MQ as a sensitive, substrate-normalised descriptor of biological soil quality and provides the first MQ baseline for mountain apple orchards of the north-western Himalaya.

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Cite

BibTeXRIS
BibTeX
@article{khenrab2026microbial,
  title = {{Microbial quotient responses to altitudinal and edaphic variability in Himalayan apple orchard soil}},
  author = {Stanzin Khenrab and Sarabdeep Kour and Vikas Sharma and Tsering Lanzes and Tsewang Dolma and Disket Dolkar and Mohd Rafee and Sourav Singh and Manjot Singh Sidhu and Jigmet Namgial},
  journal = {Frontiers in Microbiology},
  year = {2026},
  month = oct,
  doi = {10.3389/fmicb.2026.1957054},
  url = {https://www.frontiersin.org/articles/10.3389/fmicb.2026.1957054/full},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Microbial quotient responses to altitudinal and edaphic variability in Himalayan apple orchard soil
AU  - Stanzin Khenrab
AU  - Sarabdeep Kour
AU  - Vikas Sharma
AU  - Tsering Lanzes
AU  - Tsewang Dolma
AU  - Disket Dolkar
AU  - Mohd Rafee
AU  - Sourav Singh
AU  - Manjot Singh Sidhu
AU  - Jigmet Namgial
PY  - 2026
DA  - 2026/10/08
JO  - Frontiers in Microbiology
DO  - 10.3389/fmicb.2026.1957054
UR  - https://www.frontiersin.org/articles/10.3389/fmicb.2026.1957054/full
AB  - Introduction: Soil biological health is a critical determinant of sustainable fruit production in mountain ecosystems, yet microbial dynamics in high-altitude orchards remain poorly understood. Whereas total organic carbon (TOC) changes only slowly, the microbial quotient (MQ)—the ratio of microbial biomass carbon (MBC) to TOC—responds early and sensitively to shifts in organic matter turnover and soil biological quality.  Methods: This study quantified MQ across four altitude classes (<1,550, 1,550–1,650, 1,650–1,850 and >1,850 m a.s.l.), three orchard age classes (<8, 8–14, and >14 years) and three soil depths (0–25, 25–50, and 50–75 cm) in apple orchards of the Jammu Himalaya, using 144 stratified samples. MBC and TOC were measured and MQ computed as (MBC/TOC) × 100; dehydrogenase (DHA) and alkaline phosphatase activities were determined as supporting indicators. Data were analysed by three-way ANOVA, Tukey HSD, Pearson correlation, principal component analysis (PCA) and regression.  Results: MQ averaged 3.57 ± 0.08% (range 2.06–8.28%) and declined significantly with altitude, from 4.13% at <1,550 m to 3.11% at >1,850 m ( p < 0.005), the inverse of the MBC and TOC trends. MQ was lowest in surface soil (2.82%) and highest in the 25–50 cm layer (4.14%; p < 0.005) and decreased modestly with orchard age ( p = 0.010); significant altitude × depth and altitude × age interactions were detected. MQ correlated strongly and negatively with TOC ( r = −0.745; R ² = 0.556) but was decoupled from MBC ( r = −0.082, ns), indicating that MQ carries information about the substrate-normalised size of the biomass pool that absolute MBC does not. PCA separated a biomass-substrate axis (PC1, 48.3%) from an MQ-dominated axis.  Discussion: Because microbial carbon-use efficiency, community composition and necromass were not measured directly, the efficiency interpretation of these gradients is advanced as a hypothesis consistent with the data rather than as a demonstrated mechanism. The study nevertheless establishes MQ as a sensitive, substrate-normalised descriptor of biological soil quality and provides the first MQ baseline for mountain apple orchards of the north-western Himalaya.
SN  - 1664-302X
ER  -