Effects of concentration-dependent graphene on maize seedling development and soil nutrients

Abstract

The long-term use of chemical fertilizers to maintain agricultural production has had various harmful effects on farmland and has greatly impacted agriculture's sustainable expansion. Graphene, a unique and effective nanomaterial, is used in plant-soil applications to improve plant nutrient uptake, reduce chemical fertilizer pollution by relieving inadequate soil nutrient conditions and enhance soil absorption of nutrient components. We investigated the effects of graphene amendment on nutrient content, maize growth, and soil physicochemical parameters. In each treatment, 5 graphene concentration gradients (0, 25, 50, 100, and 150 g kg−1) were applied in 2 different types (single-layer and few-layers, SL and FL). Soil aggregates, soil accessible nutrients, soil enzyme activity, plant nutrients, plant height, stem diameter, dry weight, and fresh weight were all measured throughout the maize growth to the V3 stage. Compared to the control (0 g kg−1), we found that graphene increased the percentage of large agglomerates (0.25–10 mm) in the soil and significantly increased the geometric mean diameter (GMD) and mean weight diameter (MWD) values of > 0.25 mm water-stable agglomerates as the increase of concentration. Soil available nutrient content (AN, AP, and AK) increased, peaking at 150 g kg−1. Graphene boosted nutrient absorption by maize plants, and aboveground total nitrogen (TN), total phosphorus (TP), and total potassium (TK) contents rose with the increasing application, which raised aboveground fresh weight, dry weight, plant height, and stalk thickness. The findings above confirmed our prediction that adding graphene to the soil may improve maize plant biomass by enhancing soil fertility and improving the soil environment. Given the higher manufacturing cost of single-layer graphene and the greater effect of few-layer graphene on soil and maize plants at the same concentration, single-layer graphene and few-layer graphene at a concentration of 50 g kg−1 were the optimal application rates.

Regulatory effect of graphene on growth and carbon/nitrogen metabolism of maize (Zea mays L.)

“…We speculate that a small graphene concentration stimulates plant growth due to its large specific surface area, extremely high absorption capacity, and ability to act as an ion transport channel. The extra graphene covered the root surface and prevented nutrient transfer, 32 contrary to our earlier findings, 20 when the graphene addition exceeded the specific threshold (100 g kg −1 ). This resulted in a downward trend in plant height, stem diameter, and biomass.…”

“…This supports our previous findings that graphene reduces fertilizer volatilization and leaching, promotes nitrogen metabolism enzyme activity, and increases nitrogen accumulation in maize seedlings. 20 Nitrate reductase is a crucial enzyme in NO 3 − assimilation, that regulates nitrogen metabolism by participating in nitrate reduction, reflects to some extent the intensity of protein metabolism, and is related closely to photosynthetic carbon metabolism. 27 In this study, NR activity increased significantly at a graphene concentration of 50 g kg −1 (T2), which may be because CNTs promoted the conversion and absorption of NO 3 − in maize leaves, increasing chlorophyll content, and accelerated protein synthesis.…”

“…The available nitrogen (AN), available phosphorus (AP), and available potassium (AK) concentrations of the soil were 88.75, 48.69, and 94.01 g kg −1 , respectively (Wang et al .) 20 …”

“…The available nitrogen (AN), available phosphorus (AP), and available potassium (AK) concentrations of the soil were 88.75, 48.69, and 94.01 g kg −1 , respectively (Wang et al). 20 Graphene was purchased as a black, fluffy powder from Shuncheng Chemical Products Co., Ltd, Zhengzhou, China. The graphene flakes were 10 to 20 nm in diameter and the average thicknesses was 1 to 3 nm.…”

Prospects of 2D graphene nanomaterials in plant-based agriculture and their fate in terrestrial soil: a critical review

“…For instance, low concentrations (100 mg L −1 ) of GO promoted growth whereas high concentrations (1000 mg L −1 ) resulted in inhibition of seedling root growth. 101 GNMs have also been reported to improve plant yield, 12,88,131 possibly through improvement in photosynthesis, root growth, soil structure, available nutrient content or enzyme activities. Another study 111 reported injecting GO into plant stems which resulted in increased watermelon perimeter, sugar content and ripeness.…”