Effect of soil aeration on root morphology and photosynthetic characteristics of potted tomato plants (Solanum lycopersicum) at different NaCl salinity levels

Abstract

Background: Salt stress is one of the environmental factors that greatly limits crop production worldwide because high salt concentrations in the soil affect morphological responses and physiological and metabolic processes, including root morphology and photosynthetic characteristics. Soil aeration has been reported to accelerate the growth of plants and increase crop yield. The objective of this study was to examine the effects of 3 NaCl salinity levels (28, 74 and 120 mM) and 3 aeration volume levels (2.3, 4.6 and 7.0 L/pot) versus non-aeration and salinity treatments on the root morphology, photosynthetic characteristics and chlorophyll content of potted tomato plants.

Results: The results showed that both aeration volume and salinity level affected the root parameters, photosynthetic characteristics and chlorophyll content of potted tomato plants. The total length, surface area and volume of roots increased with the increase in aeration volume under each NaCl stress level. The effect was more marked in the fine roots (especially in ≤1 mm diameter roots). Under each NaCl stress level, the photosynthetic rate and chlorophyll content of tomato significantly increased in response to the aeration treatments. The net photosynthetic rate and chlorophyll a and t content increased by 39.6, 26.9, and 17.9%, respectively, at 7.0 L/pot aeration volume compared with no aeration in the 28 mM NaCl treatment. We also found that aeration could reduce the death rate of potted tomato plants under high salinity stress conditions (120 mM NaCl).

Conclusions: The results suggest that the negative effect of NaCl stress can be offset by soil aeration. Soil aeration can promote root growth and increase the photosynthetic rate and chlorophyll content, thus promoting plant growth and reducing the plant death rate under NaCl stress conditions.

Keywords: NaCl salinity; Photosynthetic characteristics; Root morphology; Soil aeration; Tomato.

Fig. 1

Effects of NaCl stress and soil aeration on root length (cm/plant) distribution by root diameter for potted tomato. Columns with the same letter represent values that are not significantly different at the 5% level of probability according to the Duncan’s new multiple-range test. Under the S3A0 treatment plants all died, So the S3A0 column is empty. Multiple comparison can’t be performed for S3A1 treatment because only 1 plant survived

Fig. 2

Effects of NaCl stress and soil aeration on root surface area (cm2/plant) distribution by root diameter for potted tomato. Columns with the same letter represent values that are not significantly different at the 5% level of probability according to the Duncan’s new multiple-range test. Under the S3A0 treatment plants all died, So the S3A0 column is empty. Multiple comparison can’t be performed for S3A1 treatment because only 1 plant survived

Fig. 3

Effects of NaCl stress and soil aeration on root volume (cm3/plant) distribution by root diameter for potted tomato. Columns with the same letter represent values that are not significantly different at the 5% level of probability according to the Duncan’s new multiple-range test. Under the S3A0 treatment plants all died, So the S3A0 column is empty. Multiple comparison can’t be performed for S3A1 treatment because only 1 plant survived

Fig. 4

Effects of NaCl stress and soil aeration on (a) net photosynthetic rate (Pn), (b) stomatal conductance (Gs), (c) transpiration rate (Tr) and (d) instantaneous water use efficiency at different growth stages for potted tomato. Columns with the same letter represent values that are not significantly different at the 5% level of probability according to the Duncan’s new multiple-range test for different treatments at same growth stage, and same capital letter represent values that are not significantly different at the 5% level of probability according to the Duncan’s new multiple-range test at different growth stage for the same treatments. At the fruit ripening stage, under the S3A0 treatment plants all died, so the column is empty

Fig. 5

Sketch map of potted tomato plants at different NaCl stress and soil aeration levels. Notes: A0, A1, A2, and A3 represent aeration volume are non-aeration, 2.3, 4.6 and 7.0 L/pot, respectively. S1, S2 and S3 represent light, moderate and heavy NaCl stress, respectively. No NaCl stress with non-aeration served as control and was identified by the designation CK