Yield and yield attributes
Number of flowers dropped per plant ranged from 32.5 to 40.3 (Table 1). The lowest flower drop per plant (32.5) was recorded in black gram plants grown under ambient condition (T
1), which was statistically on par with stress imposed from 7 to 14 DAS (T
2) (33.9). This differed statistically from stress imposed during 50 to 56 DAS (T
8) (40.3) which was on par with stress imposed from 43 to 49 DAS (T
7) (40). This present study corroborates with
Prasad et al., (2008) and
Bahuguna et al., (2017), they reported that the peak flowering stage of the rice was most sensitive to high night temperature and reduced the overall number of flowers per plant.
The data analysis shows that the HMT and en CO
2 had significant (p = 0.05) influence on the pod setting per cent of black gram (Table 1). The highest pod setting per cent of black gram was recorded under ambient condition (T
1) (57.1%) which was lower under stress imposed from 50 to 56 DAS (T
8) (47.7%). This current study was in conformity with findings of
Shi et al., (2017), which reported that the 8% reduction was measured at grain filling percent in rice crop under high minimum temperature.
From the Table 1, the grain yield per plant was highest under stress imposed from 7 to 14 DAS (T
2) (13.8 g/plant) followed by ambient condition (T
1) and stress imposed from 15 to 21 DAS (T
3) (13.4 g/plant). There was a significant reduction in the grain yield with stress imposed from 43 to 49 DAS (T
7) and stress imposed from 57 to 63 DAS (T
9) (10 g/plant) which on par with stress imposed from 50 to 56 DAS (T
8) (10.2 g/plant). The current findings are consistent with the results of
Hein et al., (2019), who reported that field-based heat tents experiment shows stress imposed from 50 percent flowering to maturity on wheat will reduce grain yield by 7 to 14%.
When compared to stress imposed from 7 to 14 DAS (17.6 g/plant), HMT and
enCO
2 significantly reduced the total biomass (14.4 g/plant) when stress imposed from 43 to 49 DAS (T
7) followed by stress imposed from 50 to 56 DAS (T
8) (14.7 g/plant) and stress imposed from 36 to 42 DAS (T
6) (14.8 g/plant) (Table 1). This result correlated with the findings of
Impa et al., (2020), who reported that increasing the high night temperature during anthesis and maturity stage would reduce the above ground biomass by 2 to 46% in wheat.
Nutritional and anti-nutritional compositions
The black gram plants that were grown in the ambient condition (T
1) recorded high seed protein content (21.6%) on par with stress imposed from 7 to 14 DAS (T2) (21.2%) and was significantly (p=0.05) different from stress imposed from 50 to 56 DAS (T
8) (17.4%). This was statistically on par with stress imposed from 43 to 49 DAS (T
7) (17.7%) and stress imposed from 57 to 63 DAS (T
8) (18.1%) (Table 2). Also, according to
Impa et al., (2019), the seed protein of wheat crop was sensitive to high night temperature and illustrated 21% reduction of protein content in wheat.
Total sugar content (492.3 mg/g) was higher in black gram seed grown under stress imposed from 7 to 14 DAS (T
2), which was statistically on par with ambient condition (T
1) (491.3 mg/g). A significant difference was observed stress during 50 to 56 DAS (T
8) (375 mg/g), which was on par with stress imposed from 36 to 42 DAS (T
6) (377.8 mg/g) and stress imposed from 43 to 49 DAS (T
7) (378.2 mg/g) (Table 2). According to
Gogoi et al., (2018) total sugar content of groundnut seed was reduced by 24.5% under heat stress.
The total polyphenols content (7.4 mg/g) was significantly higher in black gram seeds grown under ambient condition (T
1) which was statistically on par with stress imposed from 15 to 21 DAS (T
3) (7.3 mg/g) and stress imposed from 7 to 14 DAS (T
2) (7.2 mg/g) and lower polyphenol was recorded in stress imposed from 50 to 56 DAS (T
8) (6.2 mg/g) (Table 2). Total polyphenols help to overcome various stresses like heat and cold stress
(Kaushal et al., 2016). Singh et al., 2015, reported that the flowering to pod development stage of legume crops would be affected by the high temperature stress.
The level of seed moisture as influenced by the HMT and
enCO
2 are given in Table 2. The range varies from 8 to 11.9% among the treatments. The stress imposed from 64 to 70 DAS (T
10) had the lowest moisture content (8%), followed by stress imposed from 57 to 63 DAS (T
9) and stress imposed from 50 to 56 DAS (T
8) (8.4%) whereas the highest seed moisture content (11.9%) was recorded under stress imposed from 7 to 14 DAS (T
2). Based on the research findings of
Sehgal et al., 2018, the heat stress on pulse crops reduced the seed moisture content under the maturity stage than the other stages. In the present study, lower seed moisture content was observed during the maturity stage of the crop.
Significantly (p = 0.05) lower proline content (39.9 mg/g) was recorded under ambient condition (T
1) which was statistically on par with stress imposed from 15 to 21 DAS (T
3) (40.5 mg/g). The highest proline content (61.4 mg/g) was found in stress imposed from 50 to 56 DAS (T
8) followed by stress imposed from 43 to 49 DAS (T
7) (59 mg/g) (Table 3). Similar to present studies
Liu et al., 2019 found that increased proline content by 40% in bean seeds.
The phytic acid content was found significantly lower (8.3 mg/g) under stress imposed from 15 to 21 DAS (T
3) followed by stress imposed from 7 to 14 DAS (T
2) (8.6 mg/g) and ambient condition (T
1) (8.8 mg/g). Higher phytic content was recorded in stress imposed from 50 to 56 DAS (T
8) (14 mg/g) which was on par with stress imposed from 43 to 49 DAS (T
7) (12.8 mg/g) (Table 3). Temperature stress on pulse crops during reproductive stages increases phytic acid, which leads to malnutrition, according to
Gillman et al., 2021. The essential minerals like calcium, iron and zinc were known to be absorbed by phytic acid. As a result, increasing the high minimum temperature in the black gram seeds will increase the phytic acid content.
Choukri et al., 2022 findings reveal that 14% phytic acid content had increased during the reproductive stage in lentils.
Significantly (p = 0.05) higher calcium content (239 mg/100 g) was recorded under stress imposed from 7 to 14 DAS (T
2) which was on par with ambient condition (T
1) (238 mg/100 g). Comparatively, lower calcium content (168 mg/100g) was found when stress imposed from 50 to 56 DAS (T
8) followed by stress imposed from 43 to 49 DAS (T
7) (175 mg/100 g) (Table 3). The present study corroborates the results of
Farooq et al., 2018, also found that decreased calcium content in legume crops under the high night temperature on the pod filling stage.
Higher iron content of black gram (34.3 mg/100 g) was recorded in stress imposed from 7 to 14 DAS (T
2) which was on par with stress imposed from 15 to 21 DAS (T
3) (34 mg/100 g) and ambient condition (T
1) (33.1 mg/100 g) and statistically differed with stress imposed from 50 to 56 DAS (T
8) (23.1 mg/100g) followed by stress imposed from 43 to 49 DAS (T
7) (24.1 mg/100 g) due to HMT and
enCO
2 (Table 3). The current investigation supports the findings of
Sarkar et al., (2021), who assessed decreased iron content in legume crops under temperature and CO
2 stress during the pod filling stage.