PlantView Supports Willow Adaptation Research: Where there is nitrogen, there is growth: Willows' fast uptake and transportabilities facilitate their thriving in extremely low-nitrogen environments

New progress has been made in the study of nitrogen-use efficiency in willow under low-nitrogen conditions.

Professor Jun Tao from the College of Horticulture and Landscape Architecture, Yangzhou University, in collaboration with Professor Guohua Xu from the College of Resources and Environmental Sciences, Nanjing Agricultural University, have made new progress in elucidating the physiological and molecular mechanisms underlying the adaptation of willow to ammonium-limited soils. Their findings were published in “Industrial Crops and Products” (IF = 5.6, a top journal in Q1).

This study provides new insights into the highly efficient nitrogen utilization of willow under extremely low-nitrogen conditions, revealing the physiological basis of its adaptation to low-nitrogen environments and supporting the development of low-input biomass production systems.

Nitrogen (N) is an essential element for plant growth and development, participating in key physiological processes such as photosynthesis and protein synthesis, and its uptake rate far exceeds that of other mineral nutrients. According to data from the Food and Agriculture Organization of the United Nations (FAO), global nitrogen fertilizer consumption increased from 81 million tons in 2000 to 108 million tons in 2022. Although nitrogen fertilizers have contributed to increased crop yields, their excessive use has caused serious environmental problems, including water pollution, greenhouse gas emissions, and health risks. Improving plant nitrogen-use efficiency (NUE) has therefore become an urgent priority for sustainable agriculture, with optimization of nitrogen transport from root uptake (source) to utilization organs (sink) being a key step. However, research on nitrogen transport mechanisms in woody plants, particularly willow, lags far behind that in herbaceous model plants, limiting the optimization of low-nitrogen agricultural systems.

Willows (Salix spp.) are considered short-rotation coppice (SRC) bioenergy crops because of their rapid growth, high biomass production, and ease of propagation. Their nutrient cycling pattern is distinctive: nitrogen is allocated to leaves during the early growing season to establish the canopy, then recovered and stored in perennial tissues during autumn senescence, before being remobilized to newly developing tissues the following spring. This cycling pattern has led willow to be regarded as a “low-nitrogen-demand species” for many years, but existing evidence remains contradictory. Some studies indicate that mature willow stands require only 30 kg N ha⁻¹ year⁻¹ by relying on highly efficient nitrogen cycling, whereas agricultural guidelines in Ireland and the United States recommend much higher fertilizer inputs of 120–150 kg N ha⁻¹ year⁻¹ because substantial amounts of nitrogen are removed during harvesting. This discrepancy highlights a fundamental question: does willow truly possess high nitrogen-use efficiency, and what are the underlying mechanisms governing nitrogen uptake and transport? Resolving this issue is critical for optimizing willow cultivation.

Nitrogen metabolism in woody plants remains poorly understood. Soil nitrogen is primarily present in inorganic forms such as NO₃⁻ and NH₄⁺, and willow tends to preferentially absorb ammonium (NH₄⁺). However, the regulatory mechanisms of related transporters, such as AMT ammonium transporters, and assimilation enzymes, such as glutamine synthetase (GS), remain unclear in willow. By contrast, nitrogen transport genes such as LHT amino acid transporters have been identified as key targets for improving NUE in herbaceous plants. Based on this background, the study proposed three core hypotheses: (1) willow can maintain healthy growth under extremely low-nitrogen conditions; (2) willow possesses an efficient nitrogen uptake, transport, and recycling system; and (3) nitrogen-related genes respond rapidly to nitrogen stress. To test these hypotheses, the authors used the fast-growing Chinese willow species Salix suchowensis, whose genome has been sequenced, as a model. Through a series of multiscale experiments, including analysis of spatial heterogeneity in soil nitrogen in natural habitats, ^15N isotope tracing to investigate nitrogen transport dynamics, and quantification of nitrogen metabolism gene expression, the study aimed to elucidate the molecular and physiological mechanisms underlying willow adaptation to low-nitrogen environments and provide a theoretical basis for sustainable biomass production.

Experiments using PlantView

Three-week-preconditioned Salix suchowensis ecotype NANJING seedlings were transferred to half-strength Hoagland nutrient solution containing nine ammonium-nitrogen concentrations (0, 0.01, 0.05, 0.1, 0.3, 0.6, 1, 5, and 10 mM) and hydroponically cultured for 10 weeks, with 2 mg·L⁻¹ dicyandiamide added to inhibit nitrification. At the end of the experiment, even at the extremely low nitrogen concentration of 0.01 mM, willow showed significantly greater plant height and fresh weight than the nitrogen-free control, with increases of 18% and 26%, respectively. Growth peaked at 0.3 mM, with plant height reaching 37.2 cm, a 35% increase, and fresh weight reaching 9.8 g, a 42% increase. At the same time, chlorophyll fluorescence imaging of the maximum quantum yield of photosystem II (Fᵥ/Fₘ), performed using the PlantView 230F plant imaging system from Guangzhou Biolight Biotechnology reached a saturated level of 0.82. However, ammonium toxicity became evident at concentrations ≥5 mM, with fresh weight decreasing by 23% compared with the optimal concentration group and leaf margins becoming yellow. Analysis of tissue nitrogen accumulation showed that root nitrogen content remained stable at 16.1 ± 0.8 mg·g⁻¹ dry weight under low-to-moderate nitrogen concentrations of 0.1–1 mM. Under high nitrogen concentrations ≥5 mM, roots, stems, and leaves exhibited luxury nitrogen uptake, reaching 25.4, 23.1, and 28.9 mg·g⁻¹ dry weight, respectively, but this nitrogen accumulation did not translate into increased biomass. These findings demonstrate that Salix suchowensis can achieve efficient growth under extremely low nitrogen concentrations of 0.01–0.3 mM, approximately one-tenth of the nitrogen requirement of conventional crops, while remaining sensitive to high nitrogen levels, providing key physiological evidence for its potential as a low-input bioenergy crop.

DOI: org/10.1016/j.indcrop.2025.121088