Abstract. Ecologists need a common language of plant traits in order to make comparisons across regions and scales, pool data, and maximize the utility of the data. To develop such a set of traits we began with the primary challenges faced by plants: dispersal, establishment, and persistence in order to identify fundamental traits. Most of these traits are hard to measure, but advances in comparative ecology have suggested a number of easy to measure analogs. Unfortunately, some of the fundamental traits have no simple analog. The common core list includes: seed mass, seed shape, dispersal mode, clonality, specific leaf area, leaf water content, height, above‐ground biomass, life history, onset of flowering, stem density, and resprouting ability. Most of the traits can be measured quantitatively, but several traits on the list must still be measured qualitatively due to logistical problems or lack of an easy analog. Key problem areas include: dispersal ability, capacity for vegetative spread, germination, palatability, plasticity, and all the various below‐ground traits. Comparative studies need to address these problem areas. The common core list is suggested as a common starting point for studies of functional ecology. The idiosyncrasies of regional floras and specific research agendas will dictate which traits can be ignored and those that need to be added.

Summary The results of a single publication stating that terrestrial plants emit methane has sparked a discussion in several scientific journals, but an independent test has not yet been performed. Here it is shown, with the use of the stable isotope 13C and a laser‐based measuring technique, that there is no evidence for substantial aerobic methane emission by terrestrial plants, maximally 0.3% (0.4 ng g−1 h−1) of the previously published values. Data presented here indicate that the contribution of terrestrial plants to global methane emission is very small at best. Therefore, a revision of carbon sequestration accounting practices based on the earlier reported contribution of methane from terrestrial vegetation is redundant.

The rates of growth, net rate of nitrate uptake and root respiration of 24 wild species were compared under conditions of optimum nutrient supply. The relative growth rate (RGR)of the roots of these species varied between 110 and 370 mg g‐1 day‐1 and the net rate of nitrate uptake between 1 and 7 mmol (g root dry weight)‐1 day‐1. The rate of root respiration was positively correlated with the RGR of the roots. Root respiration was also calculated from the measured rate of growth and nitrate uptake, using previously determined values for the costs of maintenance, growth and ion uptake of two slow‐growing species. The calculated rate of respiration was slightly lower than the measured one for slow‐growing species, but twice as high as measured rates for rapid‐growing species. This discrepancy was not due to a relatively smaller electron flow through the alternative pathway and, consequently, a more efficient ATP production in the fast‐growing species. Neither could variation in specific costs for root growth or maintenance explain these differences. Therefore, we conclude that fast‐growing species have lower specific respiratory costs for ion uptake than slow‐growing ones. Due partly to these lower specific costs of nutrient uptake, the fraction of respiration that rapid‐growing species spend on anion uptake is lower than that of slow‐growing species, in spite of the much higher rate of ion uptake of the fast‐growing ones.

Respiratory energy costs for the maintenance of biomass, for growth and for ion uptake in roots of Carex diandra and Carex acutiformis. -Physiol. Plant. 72: 483491.The respiratory characteristics of the roots of Carex diandra Schrank and Carex acutiformis Ehrh. were investigated. The aims were, firstly to determine the respiratory energy costs for the maintenance of root biomass, for root growth and for ion uptake, and secondly to explain the higher rate of root respiration and ATP production in C. diandra. The three respiratory energy components were derived from a multiple regression analysis, using the relative growth rate and the net rate of nitrate uptake as independent variables and the rate of ATP production as a dependent variable. Although the rate of root respiration and ATP production was significantly higher in C. diandra than in C. acutiformis, the two species showed no significant difference in their rate of ATP production for the maintenance of biomass, in the respiratory energy coefficient for growth (the amount of ATP production per unit of biomass produced) and the respiratory energy coefficient for ion uptake (amount of ATP production per unit of ions absorbed). It is concluded that the higher rate of root respiration of C. diandra is caused by a higher rate of nitrate uptake. At relatively high rates of growth and nitrate uptake, the contribution of the rate of ATP production for ion uptake to the total rate of ATP production amounted to 38 and 25% for C. diandra and C. acutiformis, respectively. At this growth rate, the respiratory energy production for growth contributed 37 and 50%, respectively, to the total rate of ATP production. The relative contribution of the rate of ATP production for the maintenance of biomass increased from 25 to 70% with increasing plant age for both species. The results suggest that ion uptake is one of the major sinks for respiratory energy in roots. These experimentally derived values for the rate of ATP production for the maintenance of biomass, the respiratory energy coefficient for growth and the respiratory energy coefficient for ion uptake are discussed in relation to other experimentally and theoretically derived values. A. van der werf (corresponding author) et al.,

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Why do inherently fast-growing species from productive habitats generally have a higher rate of biomass production in short-term low-nitrogen experiments than slow-growing species from unproductive habitats, whereas the opposite is found in long-term experiments? Is this mainly due to inherent differences in biomass allocation, leaf characteristics or the plants' physiology? To analyse these questions we grew five monocotyledonous species from productive and unproductive habitats in a climate chamber at both high and low nitrogen supply. Nitrate was supplied exponentially, enabling us to compare inherent differences in morphological and physiological traits between the species, without any interference due to differences in the species' ability to take up nutrients. At high nitrogen supply, we found major inherent differences in specific leaf area and nitrogen productivity, i.e. daily biomass increment per unit plant nitrogen, where-as there were only small differences in net assimilation rate, i.e. daily biomass increment per unit leaf area, and biomass partitioning. We propose that the higher specific leaf area and nitrogen productivity of inherently fast-growing species are the key factors explaining their high abundance in productive habitats compared with inherently slow-growing ones. At low nitrogen supply, the net assimilation rate was decreased to a similar extent for all species, compared with that at high nitrogen supply. The nitrogen productivity of the inherentlyfast-growing species decreased with decreasing nitrogen supply, whereas that of the inherently slow-growing species remained constant. There were no inherent differences in nitrogen productivity in this treatment. At this low nitrogen supply, the inherently fast-growing species invested relatively more biomass in their roots that the slow-growing ones did. The inherently fast-growing species still had a higher specific leaf area at low nitrogen supply, but the difference between species was less than that at high nitrogen supply. Based on the present results and our optimization model for carbon and nitrogen allocation (Van der Werf et al. 1993a), we propose that the relatively large investment in root biomass of fast-growing species is the key factor explaining their higher biomass production in short-term experiments. We also propose that in the long run the competitive ability of the slow-growing species will increase due to a lower turnover rate of biomass. It is concluded that the plant's physiology (net assimilation rate and nitrogen productivity), only plays a minor role in the species' competitive ability in low-nitrogen environments.

BACKGROUNDSince available arable land is limited and nitrogen fertilizers pollute the environment, cropping systems ought to be developed that do not rely on them. Here we investigate the rapidly growing, N2‐fixing Azolla/Nostoc symbiosis for its potential productivity and chemical composition to determine its potential as protein feed.RESULTSIn a small production system, cultures of Azolla pinnata and Azolla filiculoides were continuously harvested for over 100 days, yielding an average productivity of 90.0–97.2 kg dry weight (DW) ha−1 d−1. Under ambient CO2 levels, N2 fixation by the fern's cyanobacterial symbionts accounted for all nitrogen in the biomass. Proteins made up 176–208 g kg−1 DW (4.9 × total nitrogen), depending on species and CO2 treatment, and contained more essential amino acids than protein from soybean. Elevated atmospheric CO2 concentrations (800 ppm) significantly boosted biomass production by 36–47%, without decreasing protein content. Choice of species and CO2 concentrations further affected the biomass content of lipids (79–100 g kg−1 DW) and (poly)phenols (21–69 g kg−1 DW).CONCLUSIONSBy continuous harvesting, high protein yields can be obtained from Azolla cultures, without the need for nitrogen fertilization. High levels of (poly)phenols likely contribute to limitations in the inclusion rate of Azolla in animal diets and need further investigation. © 2018 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Sustainable agriculture demands reduced input of man-made nitrogen (N) fertilizer, yet N2 fixation limits the productivity of crops with heterotrophic diazotrophic bacterial symbionts. We investigated floating ferns from the genus Azolla that host phototrophic diazotrophic Nostoc azollae in leaf pockets and belong to the fastest growing plants. Experimental production reported here demonstrated N-fertilizer independent production of nitrogen-rich biomass with an annual yield potential per ha of 1200 kg−1 N fixed and 35 t dry biomass. 15N2 fixation peaked at noon, reaching 0.4 mg N g−1 dry weight h−1. Azolla ferns therefore merit consideration as protein crops in spite of the fact that little is known about the fern’s physiology to enable domestication. To gain an understanding of their nitrogen physiology, analyses of fern diel transcript profiles under differing nitrogen fertilizer regimes were combined with microscopic observations. Results established that the ferns adapted to the phototrophic N2-fixing symbionts N. azollae by (1) adjusting metabolically to nightly absence of N supply using responses ancestral to ferns and seed plants; (2) developing a specialized xylem-rich vasculature surrounding the leaf-pocket organ; (3) responding to N-supply by controlling transcripts of genes mediating nutrient transport, allocation and vasculature development. Unlike other non-seed plants, the Azolla fern clock is shown to contain both the morning and evening loops; the evening loop is known to control rhythmic gene expression in the vasculature of seed plants and therefore may have evolved along with the vasculature in the ancestor of ferns and seed plants.