Nitrate and ammonium differ in their impact on δ¹³C of plant metabolites and respired CO₂from tobacco leaves

Abstract

The carbon isotopic composition (δ 13 C) of foliage is often used as proxy for plant performance. However, the effect of NO3vs. NH4 + supply on δ 13 C of leaf metabolites and respired CO2 is largely unknown. We supplied tobacco plants with a gradient of NO3to NH4 + concentration ratios and determined gas exchange variables, concentrations and δ 13 C of TCA cycle intermediates, δ 13 C of dark respired CO2, and activities of key enzymes nitrate reductase, malic enzyme and phosphoenolpyruvate carboxylase.Net assimilation rate, dry biomass and concentrations of organic acids and starch decreased along the gradient. In contrast, respiration rates, concentrations of intercellular CO2, soluble sugars and amino acids increased. As NO3decreased, activities of all measured enzymes decreased. δ 13 C of CO2 and organic acids closely co-varied and were more positive under NO3supply, suggesting organic acids as potential substrates for respiration. Together with estimates of intra-molecular 13 C enrichment in malate, we conclude that a change in the anaplerotic reaction of TCA cycle possibly contributes to 13 C enrichment in organic acids and respired CO2 under NO3supply. Thus, the effect of NO3vs. NH4 + on δ 13 C is highly relevant, particularly if δ 13 C of leaf metabolites or respiration is used as proxy for plant performance.Key words: ammonium (NH4 + ), nitrate (NO3 -), nitrate reductase (NR), phosphoenolpyruvate carboxylase (PEPC), compound specific carbon isotope analysis (CSIA), stable carbon isotopes.

Biochemical and biophysical drivers of the hydrogen isotopic composition of carbohydrates and acetogenic lipids

“…Our results of the N treatment experiment also provide evidence that the change in the relative abundance of plant compounds and its consequences for hydrogen isotope patterns in plants is strongly interlinked with various biophysical traits (Fig. 4), which function as indicators of plant performance and were deduced from a previous study performing the same experiment but focusing on carbon isotope fractionation (48). We found that tobacco plants having higher relative starch than sugar concentrations under high NO 3 − treatments performed well, as indicated by biomass production and A net being at the highest (Fig.…”

“…Both experiments are described to cause substantial changes in leaf gas exchange (e.g., assimilate rates and stomatal conductance) and assimilate pools (e.g., sugar and starch concentrations). In the first experiment (48), tobacco plants were treated with 6 mM N fertilization solutions differing in their nitrate to ammonium ratio (NO 3…”

“…Both experiments are described to cause substantial changes in leaf gas exchange (e.g., assimilate rates and stomatal conductance) and assimilate pools (e.g., sugar and starch concentrations). In the first experiment ( 48 ), tobacco plants were treated with 6 mM N fertilization solutions differing in their nitrate to ammonium ratio (NO 3 − /NH 4 + ) with plants under NO 3 − - performing better than under NH 4 + -dominated conditions (e.g., higher assimilation rates, starch concentrations, and biomass) (figs. S1 and S2).…”

Effects of different botanical oil meal mixed with cow manure organic fertilizers on soil microbial community and function and tobacco yield and quality

“…NO 3 – -N is easily dissolved and has high activity in the soil, which can quickly provide nitrogen nutrition for crops; however, it is also easy to lose. This characteristic meets the growth demand for tobacco; tobacco grows rapidly and can turn senescence and mature at an appropriate time ( Ghiasi et al, 2021 ).…”

Arctic Plant Responses to Summer Climates and Flooding Events: A Study of Carbon and Nitrogen‐Related Larch Growth and Ecosystem Parameters in Northeastern Siberia

“…Elevated air temperatures, which result in higher surface soil temperatures, can accelerate soil microbial activity, promoting SOM decomposition and N mineralization, thus increasing needle N content. N is vital for photosynthesis, particularly for enzymes like Rubisco (Evans, 1989; Ghiasi et al., 2020). In the circum‐Arctic ecosystem, located above 67°N latitude, tree‐ring data suggest that tree growth responds positively to rising summer temperatures (Tei & Sugimoto, 2018).…”