Use of soil respiration as a trial of drought susceptibility in Eucalyptus genotypes

Soil respiration (Rs) is important in the carbon cycle; it is regarded as an indicator of plant metabolism due to its close relationship with biological activity in the soil. However, this component lacks rigorous experimental studies considering its use as a drought indicator. This study evaluated the Rs and increment diameter breast height (iDBH) of Eucalyptus globulus and E. nitens x globulus (high and low yield), E. nitens, E. badjensis, E. smithii, and E. camaldulensis x globulus in drought conditions (~25% over the permanent wilting point). Measurements were carried out from 2020 to 2023 (7 to 9-year-old plants); Rs was measured monthly with a chamber LICOR-8200s; iDBH was evaluated seasonally. The results showed an annual Rs of 0.75 to 1.42 gC/m² and iDBH of 0.4 to 14.4 mm, with maximum values in the summer (December to February) and minimum in the winter (June to August). Also, a strong correlation between Rs and DBH increment (r-value=0.88) is explained with the equation iDBH=1.29*Rs (R²=0.85, p-value=0.002). This resulted in three groups: i.) E. globulus and E. nitens x globulus (low productivity) hads high drought susceptibility with minimum Rs and iDBH values (average 0.83 gC/m²/yr and 0.85 mm/yr, respectively); ii.) E. nitens, E. badjensis, E. smithii, and E. camaldulensis x globulus with moderated drought susceptibility with average Fs of 1.08 gC/m²/yr and iDBH of 9.60 mm/yr.; and iii.) E. globulus and E. nitens x globulus (high productivity) were classified as low drought susceptible maximum Rs and iDBH (average 1.38 gC/m²/yr and 13.8 mm/yr, respectively). Our results suggest that Rs is an ideal trait to differentiate Eucalyptus genotype susceptibility to drought and its effect on growth.