Fig 1.
A main pot with a dimension of 70 x 30 cm (h x d) was filled with different layers of soil, sand and gravel. A finger millet compartment (FC) was made with nylon mesh (21 μm pore size) to restrict the growth of plant roots but allow mycorrhizal hyphae to pass through and connect PP and FM roots. The FC contained two FM plants per pot. The pigeon pea compartment (PC) contained two PP plants per pot. The main pot was placed into a wider pot of 31 x 45 cm (h x d) to water the main pot from the bottom during the drought treatment (see also Fig 2).
Fig 2.
A two-pot set up was used to grow the plants, where the outer pot was used as reservoir to water the main pot from the bottom layer during the drought treatment. The picture was taken towards the end of drought period.
Fig 3.
Experiment design with different treatments.
The study included eight different treatments: FM monoculture without and with CMN, PP monoculture without and with CMN, non-split-root (NSR) treatment without and with CMN, and split-root (SR) treatment without and with CMN. In the split-root (SR) treatment, lateral roots of PP plant were inserted into the FM compartment. Monoculture treatments had two PP plants in the PP control and two FM plants in the FM control. Intercropping treatments had two PP plants and two FM plants. Thus, the intercropping system we tested followed an “addition design”.
Fig 4.
Colonization of FM and PP roots by AM fungi.
Bars represent the average of five replicates with one standard error of the mean. Tukey`s test was used for multiple comparison (PP and FM separately) and values with same letters are not significantly different at p>0.05. Treatments with AMF and PGPR additions are represented with CMN (+), and without AMF and PGPR additions as CMN (-). Control represents the monoculture treatments, while NSR and SR represent non-split root and split root treatments of the intercropping treatments, respectively.
Fig 5.
Soil moisture of the topsoil layer of all treatments (Fig 5A), stomatal conductance (gs, Fig 5B) and plant height of FM during drought (Fig 5C). Treatments with AMF and PGPR additions are represented as CMN (+), and without AMF and PGPR additions as CMN (-). Control represents monoculture, while NSR and SR represent non-split root and split root treatments of intercropping, respectively. Values shown in the graph are the average of five replicates and bars represent Tukey`s HSD0.05 value above data with significant differences among treatments. The drought period started at day 168 of the experiment. Star (↔) symbols in Fig 5B represent data points for control treatments where some replicate plants did not survive. Only living plants were used to measure stomatal conductance (see Table 3).
Fig 6.
Percent foliar damage of FM at day 245 of the experiment.
Treatments without or with AMF and PGPR application are shown as CMN (-) and CMN (+), respectively. Control represents monoculture, while NSR and SR represent non-split root and split root treatments of intercropping, respectively. Bars show average values of five replicates with one standard error of mean. Tukey`s test was used for multiple comparison. Values with the same letters indicate no significantly different values at p>0.05. For a general analysis of treatment effects see Tables 1 and 2.
Table 1.
Two-way ANOVA showing the effects of monocropping vs. intercropping and presence of a CMN on foliar damage in all treatments.
Table 2.
Two-way ANOVA showing the effect of root treatments (split roots (SR) vs. non-split roots (NSR)) and presence of a CMN on foliar damage in intercropping treatments.
Table 3.
Number of surviving FM plants between days of experiment (DOE) 224 and 245 when all treatments experienced similar levels of drought.
FM in all five replicates of intercropping treatments were alive throughout the experiment, while in FM control treatments started to die from DOE 231 to 245.
Fig 7.
Shoot and root dry biomass of FM and PP in different treatments.
Treatments without or with AMF and PGPR application are shown as CMN (-) and CMN (+), respectively. Control represents monoculture, while NSR and SR represent non-split root and split root treatments of intercropping, respectively. Bars represent average dry weight (dw) of five replicates with one standard error of the mean. Tukey`s test was used for multiple comparison (PP and FM separately) and values with same letters are not significantly different at p>0.05. For a general analysis of treatment effects see Tables 4 and 6.
Table 4.
Two-way ANOVA showing the effects of monocropping vs. intercropping with and without CMN on FM total biomass (shoot and root) in all treatments.
Table 5.
Two-way ANOVA showing the effects of root treatments (split roots (SR) vs. non-split roots (NSR)) with and without CMN on FM total biomass (shoot and root) in intercropping treatments only.
Table 6.
Two-way ANOVA table showing the effects of monocropping vs. intercropping with and without CMN on PP total biomass (shoot and root) in all treatments.
Table 7.
Two-way ANOVA showing the effects of root treatments (split roots (SR) vs. non-split roots (NSR)) with and without CMN on PP total biomass (shoot and root) produced in intercropping treatments only.
Table 8.
Total biomass (shoot + root) of FM and PP were used to calculate and compare the LER of each treatment. Only the treatments NSR and SR (without CMN) showed significantly (p<0.05) higher LER values than sole crops (i.e. control of PP and FM).
Table 9.
Two-way ANOVA showing the effects of root treatments (split roots (SR) vs. non-split roots (NSR)) and the presence or absence of a CMN on LER (total biomass), on partial LER of FM, PP, and total LER.