A recent paper by Wang et al. (2025) “Nanotechnology-driven coordination of shoot–root systems enhances rice nitrogen use efficiency” published in PNAS claims that foliar application of Se engineered nanomaterials (Se ENMs) is able to enhance the rice net photosynthesis rate by 40.3% and subsequently boosts biomass productivity and nitrogen use efficiency in rice. At the same time, rice quality improves, Se accumulation in the grain increases, and negative environmental impacts relative to conventional practice reduce.
However, a critical examination of the experiments behind this exceptional finding does not provide evidence that this is the case. Wang et al. (2025) reduced N fertilization by 30% (189 kg N/ha) relative to the control (270 kg N/ha) which led to a reduction in grain yield by 27.9%. But applying Se nanoparticles (NP) as foliar sprays prevented the yield decrease, which is indeed remarkable. This leads the authors to conclude that using a nano-enabled approach makes it possible to lower N fertilization by 30% without a yield penalty provided that plants are sprayed just once with a tiny amount of Se ENMs. However, a close inspection of the study identifies major problems with the experimental design as well as the data interpretation:
- There is no evidence that the leaves took up the Se nanoparticles. The description provided by the authors, “Se ENMs (1 g in 20 L H2O) were sprayed at a 0.05 mg/L during tillering/panicle stages via UAV.”, leaves it unclear how many times the Se ENMs were applied, and what the actual application rate was in L ha-1. Irrespective of that, we note that at these early growth stages of rice the canopy is not closed yet. Hence, a large amount of the drone-applied Se ENMs must have ended up in the floodwater or soil surface layer, not on plant leaves. There are no bioimages (TEM-EDS, single particle ICP-MS, labelled NPs with fluorescent or elemental tags, XANES etc.) showing the presence of intact particles inside leaves. Selenium could have dissolved on the surface and be taken up as ions or have leached from the leaves and be taken up via the root system in the rice ponds. This is a serious shortcoming that basically invalidates the title. Moreover, we note that the Se NPs were large 139 nm structures and that no adjuvant was added to ensure wetting and adhesion to the leaf surface. Thus, the Se enrichment in the grain could very well originate from dissolving Se NPs and subsequently selenate/selenite ions taken up via the root system in the rice fields.
- There were no appropriate controls for this work. It is not possible to isolate the NP effect when there is no control treatment in which the same concentration of Se is added in ionic form, ideally also foliar applied at the same time, concentration and amount. The same results could very well be obtained by adding Se as a conventional Se fertilizer. Furthermore, Se NP’s should also have been added to the control. Without this treatment, it is not possible to conclude that the Se NP treatment would indeed be able to compensate for a reduction in N application.
- Odd agronomic observations and interpretations are widespread. The Control treatment had an excessively high N rate of 270 kg/ha, which does not represent best management. Reducing the N rate from 270 kg/ha to 189 kg/ha was reported to reduce rice photosynthesis by a huge 77.7%, which is hard to believe because the reduced N rate is still high (about average N rate of rice in China) and unlikely to lead to a strongly N-limiting growth situation. Besides, the soils at both locations were quite rich in organic matter and nitrogen (Tables S2 and S3). Most surprisingly, reducing the N rate decreased N use efficiency (NUE) from 38.7% to 27.4%, whereas the opposite would have generally been expected. When looking at the raw data supplied with the suppl. data, we also note that some of the pct. calculations are wrong, which is critical in itself.
- No explanation is given for the unusual and remarkable impact on NUE. Ionic Se and Se nanoparticles have previously been shown to activate the antioxidative capacity of plants (like many other essential and beneficial micronutrients, both in ionic form and as NPs) by g. increasing superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione peroxidase (GPx). It is possible that we simply are looking at yet another example of this effect in the paper by Wang et al. (2025), although N limitation cannot have been severe and it remains a mystery to us that a minute Se addition can fully compensate for a nearly 30% reduction in N fertilization and crop yield. Furthermore, increased root exudates and dissolved organic matter, as reported for the RF+Se ENMs treatment, would be expected to increase methane emissions, whereas the opposite was reported.
- No mechanistic evidence to support the exceptional findings. The paper provides no convincing experimental evidence to support why Se NP is able to increase net photosynthesis rate as the authors claim. The discussion of this appears highly speculative and several references to existing literature on the subject is based on misinterpretation – see further below. Given the fact that Se is not an essential element for plant growth and development, it is hard to imagine that applying a small amount of Se NP has such a great effect on rice grain yield, as claimed by the authors.
Other methodological flaws in the paper include:
- No information is provided about soil texture and soil Se level at the two experimental sites
- The authors provide no details about the plant density and row spacing
- There is no clear description of how the actual rice yield was measured. To avoid sampling bias, normally this is done by harvesting and weighing all plants in a pre-marked 5-6 m2 harvest area
- Greenhouse gas emissions were measured only a few times (on days 2, 4 and 6 after each of the two N fertilizer applications), which does not allow obtaining a reliable whole-season estimate
- There is no detailed description of how NUE was calculated, including assumptions made about N inputs from other sources (atmospheric deposition, biological N fixation, irrigation, etc.).
Apart from the flaws mentioned above, we also notice that the paper is rich in plant science-based misunderstandings:
- Page 2, section 3: Here we find the following sentence: “Selenium (Se), an essential micronutrient with proven immunomodulatory functions (17). Compared to traditional Se fertilizer, Se engineered nanomaterials (Se ENMs) demonstrate superior efficacy in regulating crop absorption of key nutrients (N, P, Mg, and Fe) (18 – 20).”
Selenium is not an essential plant nutrient and it makes no sense to talk about immunomodulatory functions in plants. The reference (1) is from the journal The Lancet and deals with the functionality in humans. The references 18-20 are all from Environmental Science journals and papers 18 and 19 do not provide experimental evidence to postulate that Se NPs are superior in terms of ionic Se (conventional Se); this is not at all the topic of these papers. In reference 20, selenate was added as a comparison with Se NPs, but data does not provide evidence that NPs are superior relative to conventional Se in terms of key allocation of nutrients. - On page 3, the first section states: “Se and sulfur (S) belong to the same group in the periodic table and share many similar physiological properties and chemical behaviors (23, 24). Previous studies have demonstrated that Se can significantly enhance kinase-modulating activity through the allelic substitution of S with Se, which was previously attributed to the increased synthesis of ferredoxin and Fe/S proteins in plants (19)”.
From a plant science perspective, it makes no sense to talk about allelic substitution of Se with S. The referred study does not provide experimental evidence that this is indeed taking place; it is being discussed based on chemical modelling – but so far this is not known to happen in plants. Furthermore, plants require S in a large amount as an essential macronutrient. So, a small amount of Se applied only plays a minor role in allelic substitution – even if it happens. - The authors claim that Se NP foliar application resulted in increased root exudates through enhancement of the synthesis and translocation of carbohydrates, but no data are presented on what kind of compounds (citrate?, malate?) are secreted into the rhizosphere.
- Expression analysis showed that some N-related genes were up-regulated by Se NPs application (Fig. 4). However, on the other hand, the authors claim that Se NP application increased soil N availability (Fig. 4). In paddy fields, ammonium is the major form of N under submerged condition. The expression levels of ammonium transporter genes including AMT’s were reported to be upregulated by low N. Therefore, it seems contradictory that the Se NP treatment increased ammonium transporter gene expression in the study with the paper being completely void of a proper discussion of this important aspect.
We conclude that the theoretical framework provided in Fig. 2 of Wang et al. (2025) for how Se ENMs might achieve the benefits claimed is highly speculative and is not backed up by their experimental evidence. Despite numerous flaws, the authors go on extrapolating their findings to all 29.3 million ha of rice planted in China. This not only results in exaggerated claims of economic and environmental benefits in general, but it also ignores the huge diversity of rice cropping environments and systems.
For example, the average N application rate for rice in China is around 180 kg N/ha, which is far less than the 270 kg N/ha applied by Wang et al. (2025), but it also varies geographically. Experimental results from just two locations in Jiangsu Province – even if they were true – are hardly representative for millions of hectares of riceland in other areas.
Besides, the rice system in the two field experiments was a single-crop Japonica rice system. Yet, China has huge areas of rice-rice and rice-wheat cropping under Indica hybrid rice varieties, on a wide range of soils and under different climates.
In summary, we are surprised by the numerous errors and unexplainable results presented in Wang et al. (2025), the unrealistic scaling of it, and the fact that the paper got published in its present form.
