Thermal Evaluation Of Microbial Consortia For Drought Tolerance In Lettuce

Summary

This study demonstrates that microbial inoculants, particularly a 67-strain consortium, mitigate water stress in Lactuca sativa by acting as physiological buffers. Using infrared thermography and the Crop Water Stress Index (CWSI), we quantified how microbial-mediated Induced Systemic Tolerance (IST) maintains transpirational cooling and prevents homeostatic collapse under severe water deficit.

Abstract

Increased water scarcity represents a significant threat to global lettuce production, reducing crop quality and yield. While producers often resort to overfertilization to mitigate water stress, biological alternatives such as microbial inoculants offer a more sustainable approach. This study evaluated the effectiveness of a 67-strain microbial consortium and a Trichoderma harzianum isolate in enhancing water stress tolerance in Romaine lettuce (Lactuca sativa var. Paspartu) under controlled conditions. Nine treatments were established, combining microbial inoculation with three irrigation levels (50%, 75%, and 100% of evapotranspiration). Crop water status was monitored using infrared thermography to calculate the Crop Water Stress Index (CWSI) from fluctuations in canopy temperature (Tc). The statistical analysis (ANOVA) of the CWSI showed no globally significant differences between treatments (F = 0.67, p = 0.778); however, distinct numerical trends were observed during peak thermal stress events. Under severe water deficit (50% irrigation), plants inoculated with the microbial consortium maintained lower CWSI values (averaging 0.38) compared to non-inoculated controls, which reached maximum stress thresholds (CWSI = 1.0). Furthermore, microbial treatments demonstrated a faster thermal recovery following acute stress periods. These results suggest that while global variance is high, microbial consortia function as physiological buffers that enhance transpiration efficiency. Infrared thermography proved to be a precise, non-destructive tool for early detection of water stress. This study highlights the potential of beneficial microorganisms to improve crop resilience and provides a standardized protocol for thermal evaluation in horticultural research.

Introduction

Lettuce (Lactuca sativa L.) is a high-value horticultural crop characterized by a shallow root system and high-water content, making it exceptionally sensitive to hydric deficit¹. Under water stress, plants activate immediate physiological responses, primarily stomatal closure, to minimize water loss through transpiration². While this mechanism preserves internal water status, it leads to a significant increase in canopy temperature (Tc) due to reduced evaporative cooling³. In greenhouse production and controlled environments, managing these thermal and hydric fluctuations is fundamental ....

Protocol

The experimental workflow for evaluating the efficacy of microbial inoculants in enhancing water-stress tolerance in Romaine lettuce (Lactuca sativa L. var. Paspartu) is summarized in Figure 1. The protocol integrated continuous monitoring of precise irrigation regimes with periodic acquisition of physiological and thermal data. Two distinct microbial products were utilized: (I) microbial consortium, a complex consortium of 67 strains comprising PGPR, actinomycetes, and beneficial fungi, designed to act as a physiological buffer through root colonization and exopolysaccharide (EPS) secretion; and (II) Trichoderma harzianum

Results

Stress resistance of treatments with respect to hydration at three levels

The physiological and morphological response of lettuce (Lactuca sativa L. var. Paspartu) to water stress was evaluated across three irrigation levels (50%, 75%, and 100%). A one-way factorial ANOVA was conducted to determine the main effects of microbial treatments (Treatments (T): TI: Microbial consortium, TII: Trichoderma harzianum, and TC: Control), days after sowing (DAS), and thei.......

Discussion

The empirical evidence derived from this study corroborates that the strategic application of multi-strain microbial consortia functions as a robust biotechnological buffer against the deleterious effects of hydric deficit in Lactuca sativa. Although the global inferential analysis (ANOVA) did not yield statistically significant differences (F = 0.67, p = 0.778), a high-resolution examination of the temporal thermal dynamics reveals a critical numerical mitigation trend. Under the most restrictive irrig.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Arabidopsis Chamber	Percival Scientific Inc	AR-95L3	Controlled environment chamber for uniform growth conditions (temperature, humidity, light).
Arduino Uno R3	Arduino	A000066	Microcontroller board based on the ATmega328P for sensor data processing.
Calcium Nitrate	Nouryon Chemicals SA de CV	https://adob.com.pl/en/product/adob-calcium-nitrate/	Soluble inorganic fertilizer. Composition: 15.2% Nitrogen and 27.5% Calcium.
Infrared Thermal Camera	HIKMICRO	https://webassets.hikmicrotech.com /global/asset/d802895de0b44f46 8a49913953e590ff.pdf	High-resolution thermal imaging camera (256 x 192 pixels) for canopy temperature measurement.
Lettuce seeds	Enza Zaden	Paspartu	Certified seed of Romaine lettuce (Lactuca sativa L. var. longifolia).
Microbial consortium (BPG plus)	Alibio Science SAPI DE CV	https://alibio.ag/productos/bgp-plus	Consortium of 67 strains (fungi, bacteria, actinomycetes). 4x10^8 CFU/g.
Monopotassium Phosphate	SQM	https://www.sqmnutrition.com/ec/marca/ultrasol/ultrasol-mkp-4-2	Soluble inorganic Monopotassium Phosphate fertilizer. Composition: 52%Pphosphorus and 34% Potassium(w/w).
Peat Moss Substrate	Sun Gro Horticulture	https://www.sungro.com/professional-product/sun-gro-perlite-free-mix-x-coarse-resilience/	Canadian Sphagnum Peat Moss, professional grade without vermiculite.
Perlite	INVERFARMS MEXICO	https://inverfarms.com/product/ perlita-hortiperl-saco-125-l/?srsltid =AfmBOorwncGHkTcSpgDb9OS bN2-7Mi3ZwQR-uObQte8QQotaD Li-JgLy	High-quality inert substrate used to optimize soil aeration and improve the retention of water and nutrients.
Plant growth regulator (RADIX 3000)	Intercontinental SA DE CV	https://www.interie.net/productos	Induces root formation. Active ingredient: Indole-3-Butyric Acid at 0.3% (v/v).
Potassium Nitrate	SQM	https://sqm.com/producto/ultrasol-k-plus/	Soluble inorganic fertilizer. Composition: 13.7% Nitrogen and 46.3% Potassium.
R Studio	Free version	https://www.r-project.org/	R is a free and open-source programming language and software environment used for statistical computing, data analysis, and visualization, widely adopted in science and data science for its powerful modeling tools, rich package ecosystem, and support for reproducible research.
Soil Moisture Sensor	Various (Generic)	FC-28 / HW-080	Resistive soil moisture sensor with LM393 comparator for analog/digital output.
Thermography Software	HIKMICRO	Analyzer	Specialized software for thermal image analysis and temperature extraction.D6
Trichoderma harzianum (PROTRI)	Aguilares SPR de RL	N/A Internal reference	Native strain isolated from agricultural soils in Salamanca, Gto. Cultured and standardized for experimental use at Aguilares SPR de RL
Vermiculite	INVERFARMS MEXICO	https://inverfarms.com/product/vermiculita-verlite-saco-114-litros/?srsltid=AfmBOoo61hIX-Eg4N-LXUWTY9NLlc5QC5I-iVe85UZRFrNHWQNQ3FwCZ	Expanded vermiculite for tray covering. Density: 60-120 kg/m3.