Uptake and utilization of atmospheric ammonia in three native Poaceae species: leaf conductances, composition of apoplastic solution and interactions with root nitrogen supply

Abstract

The physiological potential for acquisition of atmospheric ammonia (NH $ ) was investigated in three European meadow grasses (Arrhenatherum elatius, Bromus erectus and Brachypodium pinnatum) competing in chalk grasslands. Experiments were carried out with plants cultivated for about three months on a soil-sand mixture at high root nitrogen supply or in nutrient solutions at low root nitrogen supply. Two different root nitrogen regimes were applied to the solution-grown plants : 130 µmol NO $ plant −" wk −" (approx. 50 kg nitrogen ha −" in three months) ; or 130 µmol NO $ − plus 130 µmol NH % + plant −" wk −" . Each regime was combined with two levels of NH $ fumigation (0 and 70 nmol mol −" air for 24 d). Uptake of gaseous NH $ in the shoots was investigated under controlled environmental conditions including NH $ concentrations ranging from 0 to 30 nmol mol −" air. Concurrently, photosynthesis, glutamine synthetase activity, nitrogen allocation, biomass allocation and apoplastic cation composition were measured. For A. elatius, the influence of photorespiration on NH $ acquisition was also assessed.Independently of plant nitrogen status, ammonia compensation points in A. elatius and B. erectus plants were 0.5 nmol mol −" . The total leaf conductance to NH $ absorption remained constant at increasing NH $ concentrations, showing that the capacity for assimilation was unaltered. Whereas internal factors in the leaves did not cause differences in the potential for NH $ acquisition between the species, other factors of NH $ acquisition were quite different : B. erectus had higher stomatal conductance and, thus, higher NH $ uptake rates per unit leaf area compared to A. elatius and B. pinnatum ; higher stomatal conductances of B. erectus were to a large extent offset by a lower leaf area per plant, resulting from a lower growth rate and thicker leaves than in the two other species. The rate of photorespiration in Arrhenatherum constituted at least 15% of the net photosynthetic rate. Surprisingly, suppression of photorespiration indicated that NH $ uptake was supported by photorespiration. Bromus responded to fumigation with 70 nmol NH $ mol −" air for 24 d by lowering the root : shoot ratio and increasing the nitrogen concentration in the stem dry matter. The total leaf conductance to NH $ uptake decreased in all three species upon exposure to NH $ , while the stomatal conductance was unaffected. The NH $ exposure caused lower apoplastic concentrations of H + , Mg# + and Ca# + in A. elatius and B. erectus.

Fate of ammonia in the atmosphere?a review for applicability to hazardous releases

“…Subsequent studies confirmed the existence of this compensation point and found its value was in the range of 0.5-4 |xg m~3 (0.66-5.28 ppbv) with a median value between 1.5 and 2|j,gm _3 (2-2.64 ppbv) [50][51][52][53][54][55][56]. Distinction can be made [57] between stomatal and canopy compensation points.…”

“…(53)- (55). Using these equilibrium constants and Henry's law constants, they outlined an iterative method to calculate the composition of the aqueous solution and vapor pressure above it for a wide range of ammonia concentrations, ratio of mole-fractions of total C0 2 and total ammonia (R = (C0 2 + C0 3 H -+ CO 2 , -+ NH 2 COO~)/(NH 3 +NHj-|-NH2COO _ )), and temperature.…”

Ecological ramifications of the direct foliar uptake of nitrogen

“…1 Primary biochemical processes describing the foliar uptake and assimilation of atmospheric ammonia (NH 3 ), nitric oxide (NO), and nitrogen dioxide (NO 2 ). Adapted from Stulen et al (1998 gaseous NH 3 is strongly controlled by the stomatal aperture (Duyzer et al 1994;Hanstein et al 1999;Gessler et al 2000Gessler et al , 2002. However, as described in ''Uptake mechanisms'', the concentration of NH 4 ?…”

“…A common observation of plants under fumigation by reactive N is an increase in at least some aspects of leaf N (Rowland 1986;Rowland et al 1987;Segschneider et al 1995;Hanstein et al 1999;Takahashi et al 2005) and there is some level of correspondence between natural variation in foliar uptake and leaf N contents (Calanni et al 1999;Tomaszewski and Sievering 2007;Sievering et al 2007). Therefore, foliar uptake has the potential to alter the stoichiometry of C and N in plant tissues in opposition to that driven by elevated CO 2 .…”

“…Currently, laboratory and field measurements have generated leaf-area specific flux rates for NO (e.g., Hereid and Monson 2001;Teklemariam and Sparks 2006), NO 2 (e.g., Thoene et al 1996;Weber and Rennenberg 1996;Gessler et al 2000Gessler et al , 2002Sparks et al 2001;Eller and Sparks 2006), NH 3 (e.g., Fangmeier et al 1994;Hanstein et al 1999;Ashraf et al 2003;Castro et al 2006), PAN (e.g., Sparks et al 2003;Teklemariam and Sparks 2004), and HONO (e.g., Schimang et al 2006). Direct estimates of leaf uptake of HNO 3 and ionic and particulate forms of NO 3 -and NH 4 ?…”