Estimating leaf water content at the leaf scale in soybean inoculated with arbuscular mycorrhizal fungi from in situ spectral measurements

Weiping Kong,Xianfeng Zhou,Hugh Mortimer,Lingling Ma,Lingli Tang,Wenjiang Huang,Chuanrong Li

doi:10.25165/j.ijabe.20191206.4950

Abstract

Leaf water content (LWC) of crops is a suitable parameter for evaluation of plant water status and arbuscular mycorrhizal effect on the host plant under drought stress. Remote sensing technology provides an effective avenue to estimate LWC in crops. However, few LWC retrieval models have been developed specifically for the arbuscular mycorrhizal inoculated crops. In this study, soybean with inoculation and non-inoculation treatments were planted under the severe drought, moderate drought and normal irrigation levels. The LWC changes under different treatments at the 30th, 45th and 64th day after the inoculation were investigated, and the spectral response characteristics of inoculated and non-inoculated soybean leaves under the three drought stresses were analyzed. Five types of spectral variables/indices including: raw spectral reflectance (R), continuum-removed spectral reflectance (RC), difference vegetation index (DVI), normalized difference vegetation index (NDVI) and ratio vegetation index (RVI) were applied to determine the best estimator of LWC. The results indicate that LWC decreased as the aggravating of drought stress levels. However, LWC in inoculated leaves was higher than that in the counterparts under the same drought stress level, and the values of raw reflectance measured at inoculated leaves were lower than the non-inoculated leaves, especially around 1900 nm and 1410 nm. These water spectral features were more evident in the corresponding continuum-removed spectral reflectance. The newly proposed DVIC(2280, 1900) index, derived from the continuum-removed spectral reflectance at 2280 nm and the raw spectral reflectance at 1900 nm in DVI type of index, was the most robust for soybean LWC assessment, with R2 value of 0.72 (p < 0.01) and root mean square error (RMSE) and mean absolute error (MAE) of 2.12% and 1.75%, respectively. This study provides a means to monitor the mycorrhizal effect on drought-induced crops indirectly and non-destructively. Keywords: leaf water content, remote sensing, arbuscular mycorrhizal fungi, drought, crops DOI: 10.25165/j.ijabe.20191206.4950 Citation: Kong W P, Huang W J, Zhou X F, Mortimer H, Ma L L, Tang L L, et al. Estimating leaf water content at the leaf scale in soybean inoculated with arbuscular mycorrhizal fungi from in situ spectral measurements. Int J Agric & Biol Eng, 2019; 12(6): 149–155.

Highlights

Drought stress is one of the main factors threating the agricultural development on the earth, as it limits crops growth and yield, especially in arid and semi-arid regions[1]
We explored the three types of vegetation indices (VIs) to combine the information on the raw spectral reflectance (R( )) with the November, 2019 Kong W P, et al Estimating leaf water content at the leaf scale in soybean inoculated with arbuscular mycorrhizal fungi Vol 12 No.6 151 continuum-removed spectral reflectance (RC( )) of soybean leaves, and the new VIs were formulated by Equation (3)-(5), referred to as the DVIC(λ1, λ2), NDVIC(λ1, λ2) and RVIC(λ1, λ2)
Under the other two drought stress levels, there was the opposite of the occurrence, because this period was the end of soybean growth stage, the +M plants had relatively larger leaf area compared to the CK plants, which increased the transpiration and led to the low leaf water content (LWC)

Summary

Introduction

Drought stress is one of the main factors threating the agricultural development on the earth, as it limits crops growth and yield, especially in arid and semi-arid regions[1]. About 45% land in China belongs to arid and semi-arid regions, and is expected to increase with climate change[2], which exposes soybean to drought stress. Some studies have demonstrated that arbuscular mycorrhizal fungi associates with the plant roots in such relationship enhances the plant ability of water and nutrition uptakes[1,4,5], in particular when plants suffer from drought stress[6], increasing drought resistance in plants and improve the water-use efficiency. Drought resistance in plants can occur via the maintenance of high internal water potential[7]. Leaf water content (LWC) is a suitable parameter for evaluation of plant water status and mycorrhizal effect under drought stress

Objectives

Methods

Results

Conclusion