Resilience Assessment of Tomato Crop Chlorophyll Fluorescence Against Water Stress Under Elevated CO2 and Protective Cultivation

Abstract

Water scarcity is a crucial issue that reduces plant growth and yield worldwide. Chlorophyll fluorescence parameters, which are associated with plant growth and yield under water stress, are the most sensitive plant parameters. The mitigation of water stress by elevated CO₂ (e[CO₂]) by chlorophyll fluorescence for tomato growth is rare. Tomato plants were grown in a controlled environment chambers (CECs) under eight treatments under controlled environmental conditions for two growing seasons: autumn–winter (AW) 2021 and spring–summer (SS) 2022. The four irrigation regimes included 40%–50% soil water holding capacity (WHC) (I₁), 60%–70% WHC (I₂), 80%–90% WHC (I₃) and 100% WHC (I₄). Eight treatments of four irrigation regimes coupled with e[CO₂] (700 μmol·mol⁻¹) and ambient CO₂ (a[CO₂], 500 μmol·mol⁻¹) were designed, respectively: I₁e[CO₂], I₂e[CO₂], I₃e[CO₂], I₄e[CO₂], I₁a[CO₂], I₂a[CO₂], I₃a[CO₂] and I₄a[CO₂], where I₄a[CO₂] was considered the control treatment (CK). The chlorophyll fluorescence parameters maximum photochemical efficiency of PSII (F_v/F_m), photochemical efficiency of PSII (Ф_PSII), electron transport rate (ETR) and photochemical quenching (qP) significantly decreased, whereas nonphotochemical quenching (NPQ) significantly increased under drought stress. Compared with that under CK, the maximum reduction in F_v/F_m under I₁a[CO₂] was 14% in AW 2021, whereas it was 19% in SS 2022. The Ф_PSII was reduced by 13%–3% and 13%–6% under I₁a[CO₂] in AW 2021 and SS 2022, respectively (under the fixed photosynthetically active radiation range of 125–625 μmol·m⁻²·s⁻¹) compared with that in the CK. The ETR and qP decreased under I₁a[CO₂] at their maximum level in AW 2021 and SS 2022 with respect to those in the CK. The results showed that e[CO₂] mitigated water stress as the F_v/F_m, Ф_PSII, ETR and qP were increased under water stress coupled with e[CO₂]. I₁e[CO₂] was the most influential treatment for chlorophyll fluorescence parameters assessed via principal component analysis (PCA) in AW 2021 and SS 2022. This study explained the approach to develop crop resilience against water stress by inducing e[CO₂], which will play a vital role in sustainable agriculture under drought stress.