Field application of silicon alleviates drought stress and improves water use efficiency in wheat

Abstract

Detrimental impacts of drought on crop yield have tripled in the last 50 years with climate models predicting that the frequency of such droughts will intensify in the future. Silicon (Si) accumulation, especially in Poaceae crops such as wheat (Triticum aestivum L.), may alleviate the adverse impacts of drought. We have very limited information, however, about whether Si supplementation could alleviate the impacts of drought under field conditions and no studies have specifically manipulated rainfall. Using field-based rain exclusion shelters, we determined whether Si supplementation (equivalent to 39, 78 and 117 kg ha^-1) affected T. aestivum growth, elemental chemistry [Si, carbon (C) and nitrogen (N)], physiology (rates of photosynthesis, transpiration, stomatal conductance, and water use efficiency) and yield (grain production) under ambient and drought (50% of ambient) rainfall scenarios. Averaged across Si treatments, drought reduced shoot mass by 21% and grain production by 18%. Si supplementation increased shoot mass by up to 43% and 73% in ambient and drought water treatments, respectively, and restored grain production in droughted plants to levels comparable with plants supplied with ambient rainfall. Si supplementation increased leaf-level water use efficiency by 32-74%, depending on Si supplementation rates. Water supply and Si supplementation did not alter concentrations of C and N, but Si supplementation increased shoot C content by 39% and 83% under ambient and drought conditions, respectively. This equates to an increase from 6.4 to 8.9 tonnes C ha^-1 and from 4.03 to 7.35 tonnes C ha^-1 under ambient and drought conditions, respectively. We conclude that Si supplementation ameliorated the negative impacts of drought on T. aestivum growth and grain yield, potentially through its beneficial impacts on water use efficiency. Moreover, the beneficial impacts of Si on plant growth and C storage may render Si supplementation a useful tool for both drought mitigation and C sequestration.

Keywords: Triticum aestivum L.; carbon capture; cereals; climate change; drought stress; silica; water deficits.

Figure 1

Soil volumetric water content (%) of the ambient well-watered plots and drought (50% rainfall reduction) treatment plots in the rain exclusion shelters, including key events of drought treatment application and the two harvests during the field experiment. Days since seedling emergence given in parentheses.

Figure 2

Shoot mass of plants grown with Si supplementation (low, medium and high; 39, 78 and 117 kg ha^-1) compared to plants without Si supplementation (none) under ambient and drought conditions. Dashed lines represent mean values; solid lines depict the inclusive median (N = 6). The interquartile range is shown. Statistically significant differences between Si supplemented plants and non-supplemented plants indicated *P < 0.05 and **P < 0.01.

Figure 3

Shoot (A) Si and (B) N content of plants grown with Si supplementation (low, medium and high; 39, 78 and 117 kg ha^-1) compared to plants without Si supplementation (none) under ambient and drought conditions (details as in Figure 2 ; N = 6). Statistically significant differences between Si supplemented plants and non-supplemented plants are indicated as *P < 0.05 and **P < 0.01. Marginal non-significance (P < 0.10) at the 95% confidence interval indicated #.

Figure 4

Shoot C content of plants grown with Si supplementation (low, medium and high; 39, 78 and 117 kg ha^-1) compared to plants without Si supplementation (none) under ambient and drought conditions (details as in Figure 2 ; N = 6). Statistically significant differences between Si supplemented plants and non-supplemented plants indicated **P < 0.01. Marginal non-significance (P < 0.10) at the 95% confidence interval indicated #. The estimated total C content of plants per hectare is shown for comparison (mean ± standard error plotted).

Figure 5

Grain mass of plants grown with Si supplementation (low, medium and high; 39, 78 and 117 kg ha^-1) compared to plants without Si supplementation (none) under ambient and drought conditions (details as in Figure 2 ; N = 6). Statistically significant differences between Si supplemented plants and non-supplemented plants indicated as *P < 0.05. Marginal non-significance (P < 0.10) at the 95% confidence interval indicated #. The estimated grain yield per hectare is shown for comparison (mean ± standard error plotted).

Figure 6

Instantaneous water use efficiency (WUE _i ) of plants grown with Si supplementation (low, medium and high; 39, 78 and 117 kg ha^-1) compared to plants without Si supplementation (none) under ambient and drought conditions (details as in Figure 2 ; N = 6). Statistically significant differences between Si supplemented plants and non-supplemented plants indicated *P < 0.05 and **P < 0.01. Marginal non-significance (P < 0.10) at the 95% confidence interval indicated #.