Nitrogen Limits Plant Growth Research Articles

A mechanistic model for nitrogen-limited plant growth.

Nitrogen is often regarded as a limiting factor to plant growth in various ecosystems. Understanding how nitrogen drives plant growth has numerous theoretical and practical applications in agriculture and ecology. In 2004, Göran I. Ågren proposed a mechanistic model of plant growth from a biochemical perspective. However, neglecting respiration and assuming stable and balanced growth made the model unrealistic for plants growing in natural conditions. The aim of the present paper is to extend Ågren's model to overcome these limitations. We improved Ågren's model by incorporating the respiratory process and replacing the stable and balanced growth assumption with a three-parameter power function to describe the relationship between nitrogen concentration (Nc) and biomass. The new model was evaluated based on published data from three studies on corn (Zea mays) growth. Remarkably, the mechanistic growth model derived in this study is mathematically equivalent to the classical Richards model, which is the most widely used empirical growth model. The model agrees well with empirical plant growth data. Our model provides a mechanistic interpretation of how nitrogen drives plant growth. It is very robust in predicting growth curves and the relationship between Nc and relative growth rate.

Efeitos da omissão de nutrientes em plantas de Caesalpinia echinata

O objetivo deste trabalho foi avaliar o crescimento, as alterações morfológicas e a composição mineral de plantas de pau-brasil (Caesalpinia echinata) decorrentes da omissão de nutrientes pela técnica do elemento faltante em experimento em casa de vegetação. O delineamento experimental foi inteiramente casualizado, com 12 tratamentos: testemunha (solo natural), completo (N, P, K, Ca, Mg, S, B, Cu, Mn e Zn), e adubação com omissão de cada um dos nutrientes do tratamento completo e cinco repetições. Cada parcela foi constituída por uma planta em vaso contendo 7 dm³ de Neossolo Quartzarênico. Foram avaliados sintomas visuais de deficiência nutricional, altura, diâmetro do caule, matéria seca da parte aérea das plantas, incluindo caule, ramos e folhas e teor dos nutrientes nas folhas. A omissão de nitrogênio em Neossolo Quartzarênico limitou o crescimento em altura e a produção de biomassa da parte aérea das plantas de pau-brasil. Os primeiros sintomas de deficiência nutricional foram decorrentes da omissão de N, em seguida apareceram os sintomas de P, Ca, Mg, S, Cu e Mn e, mais tardiamente, os sintomas da deficiência de K e B. Para cada nutriente, houve diferença entre as médias de teores nas folhas em função dos tratamentos.

Grasses have larger response than shrubs to increased nitrogen availability: A fertilization experiment in the Patagonian steppe

Nitrogen limits plant growth in almost all terrestrial ecosystems, even in low-precipitation ecosystems. Vegetation in arid ecosystems is usually composed of two dominant plant-functional types, grasses and shrubs, which have different rooting and water acquisition patterns. These plant-functional types may respond differently to N availability because they have different strategies to absorb and retranslocate N. We hypothesized that grasses are more N limited than shrubs, and consequently will show higher responses to N addition. To test this hypothesis, we added 50 kg N ha−1 year−1 as NH4NO3 during two years in the Patagonian steppe, Argentina, and we evaluated the responses of aboveground net primary production and N concentration of green leaves of the dominant grass and shrub species. Grass biomass significantly (P = 0.007) increased with increased N availability whereas shrub biomass did not change after two years of N addition. Shrubs have higher nitrogen concentration in green leaves than grasses, particularly the leguminous Adesmia volkmanni, and showed no response to N addition whereas foliar N concentration of grasses significantly increased with N fertilization (P < 0.05). Grasses may have a larger response to increase N availability than shrubs because they have a more open N economy absorbing up to 30% of their annual requirement from the soil. In contrast, shrubs have a closer N cycle, absorbing between 7 and 16% of their annual N requirement from the soil. Consequently shrubs depend less on soil N availability and are less responsive to increases in soil N.

Species-driven changes in nitrogen cycling can provide a mechanism for plant invasions.

Traits that permit successful invasions have often seemed idiosyncratic, and the key biological traits identified vary widely among species. This fundamentally limits our ability to determine the invasion potential of a species. However, ultimately, successful invaders must have positive growth rates that longer term result in higher biomass accumulation than competing established species. In many terrestrial ecosystems nitrogen limits plant growth, and is a key factor determining productivity and the outcome of competition among species. Plant nitrogen use may provide a powerful framework to evaluate the invasive potential of a species in nitrogen-limiting ecosystems. Six mechanisms influence plant nitrogen use or acquisition: photosynthetic tissue allocation, photosynthetic nitrogen use efficiency, nitrogen fixation, nitrogen-leaching losses, gross nitrogen mineralization, and plant nitrogen residence time. Here we show that among these alternatives, the key mechanism allowing invasion for Pinus strobus into nitrogen limited grasslands was its higher nitrogen residence time. This higher nitrogen residence time created a positive feedback that redistributed nitrogen from the soil into the plant. This positive feedback allowed P. strobus to accumulate twice as much nitrogen in its tissues and four times as much nitrogen to photosynthetic tissues, as compared with other plant species. In turn, this larger leaf nitrogen pool increased total plant carbon gain of P. strobus two- to sevenfold as compared with other plant species. Thus our data illustrate that plant species can change internal ecosystem nitrogen cycling feedbacks and this mechanism can allow them to gain a competitive advantage over other plant species.

A simple model for nitrogen-limited plant growth and nitrogen allocation.

and Aims In many studies of nitrogen-limited plant growth a linear relationship has been found between relative growth rate and plant nitrogen concentration, showing a negative intercept at a plant nitrogen concentration of zero. This relationship forms the basis of the nitrogen productivity theory. On the basis of empirical findings, several authors have suggested that there is also a distinctive relationship between allocation and plant nitrogen concentration. The primary aim of this paper is to develop a simple plant growth model that quantifies this relationship in mathematical terms. The model was focused on nitrogen allocation to avoid the complexity of differences in nitrogen concentrations in the different plant compartments. The secondary aim is to use the model for examining the processes that underlie the empirically based nitrogen productivity theory. In the construction of the model we focused on the formation and degradation of biologically active nitrogen in enzymes involved in the photosynthetic process (photosynthetic nitrogen). It was assumed that, in nitrogen-limiting conditions, the formation of photosynthetic nitrogen is proportional to nitrogen uptake. Furthermore it was assumed that the degradation of photosynthetic nitrogen is governed by first-order kinetics. Model predictions of nitrogen allocation were compared with data from literature describing four studies of growth. Model predictions of whole plant growth were compared with the above-mentioned nitrogen productivity theory. Allocation predictions agreed well with the investigated empirical data. The ratio of leaf nitrogen and plant nitrogen declines linearly with the inverse of plant nitrogen concentration. Nitrogen productivity is proportional to this ratio. Predictions for whole-plant growth were in accordance with the nitrogen productivity theory. The agreement between model predictions and empirical findings suggests that the derived equation for nitrogen allocation and its relationship to plant nitrogen concentration might be generally applicable. The negative intercept in the linear relationship between relative growth rate and plant nitrogen concentration is interpreted as being equal to the degradation constant of photosynthetic nitrogen.

Relative importance of macrophyte leaves for nitrogen uptake from flood water in tidal salt marshes

Nitrogen limits plant growth in most salt marshes. As foliar N-uptake makes a significant contribution to the overall N-requirements of submerged plant species such as (e.g.) seagrasses, we tested if foliar N-uptake was also significant in Spartina anglica Hubbard, a species that dominates the lowest, regularly flooded areas of salt marshes in the SW Netherlands. Foliar N-uptake was compared for plants from 2 estuaries with contrasting N-loads in their water column. N-uptake was quantified by (1) flooding detached leaves in test tubes, (2) spraying leaves still attached to the plants, and (3) flooding whole plants, with solutions containing either 15NO3- or 15NH4+. We found that detaching the leaves from the plant underestimated NH4+ uptake by between 30 and 50%. Higher salinity also reduced foliar N-uptake. Uptake rates were higher for NH4+ than for NO3-, as has been found for many submerged and terrestrial angiosperms and marine algae. Methodology also had a major effect on the uptake rate, with flooding of intact plants yielding higher uptake rates than spraying attached leaves. However, in general, foliar N-uptake rates were low at the NO3- and NH4+ concentrations that are actually present in the tidal waters during the growth season, and may at most contribute to around 10% of the growth requirement. This percentage is much less than for seagrasses, but in line with data for some terrestrial systems. We conclude that in contrast to seagrasses, foliar N-uptake does not form a significant contribution to the overall N-requirements of S. anglica. This low N-uptake capacity of the S. anglica leaves appears to be a consequence of adaptations to survive tidal flooding. [KEYWORDS: Foliar uptake · Nitrate · Ammonium · Tidal marsh · 15N labelling]

Modelling Nitrogen Uptake in Ingestad Units Using Michaelis-Menten Kinetics

The concept of nutrient flux density was developed to grow plants at a controlled and stable relative growth rate whilst maintaining a constant internal concentration of a limiting nutrient. The method requires frequent and exponentially increasing additions of nutrients to replenish uptake. In developing this approach there has been little reference to Michaelis-Menten-like nutrient uptake kinetics for characterising uptake by roots. This paper applies a simple model of nitrogen-limited plant growth using Michaelis-Menten uptake kinetics to data from previously published experiments based on the nutrient flux density approach. It is shown that the model can indeed reproduce key features of experiments: (1) plant relative growth rate equals nitrogen relative addition rate up to a limit; (2) when nitrogen uptake kinetic parameters are within the range reported in the literature, this limiting growth rate agrees with that observed; and (3) solution nitrogen concentrations are consistent with those published. We suggest that the understanding of nutrient uptake and utilisation by plants could be advanced by jointly considering these two approaches.