Effects of enhanced atmospheric ammonia on photosynthetic characteristics of two maize (Zea mays L.) cultivars with various nitrogen supply across long-term growth period and their diurnal change patterns

Abstract

We investigated the effect of enhanced atmospheric ammonia (NH(3)) in combination with low and high nitrogen (LN and HN, respectively) growth medium on photosynthetic characteristics of two maize (Zea mays L.) cultivars (NE5 with high- and SD19 with low N-use efficiency) across long-term growth period and their diurnal change patterns exposed to 10 nl l(-1) and 1,000 nl l(-1) NH(3) fumigation in open-top chambers (OTCs). Regardless of the level of N in medium, increased NH(3) concentration promoted maximum net photosynthetic rate (P (max)) and apparent quantum yield (AQY) of both cultivars at earlier growth stages, but inhibited P (max) of NE5 from silking to maturity stage and that of SD19 at maturity stage only above the ambient concentration. Greater positive/less negative responses were predominant in the LN than in the HN treatment, especially for SD19. Dark respiration rate (R (D)) remained more enhanced in the LN than in the HN treatment for SD19 as well as increased in the LN while decreased in the HN treatment for NE5 at their silking stage, following exposure to elevated NH(3) concentration. Additionally, enhanced atmospheric NH(3) increased net photosynthetic rate (P (N)) and stomatal conductance (g (s)) but reduced intercellular CO(2) concentration (C (i)) of both cultivars with either the LN or HN treatment during the diurnal period at tasseling stage. The diurnal change patterns of P (N) and g (s) showed bimodal curve type and those of C (i) presented single W-curve type for NE5, when NH(3) concentration was enhanced. As for SD19, single-peak curve type was showed for both P (N) and g (s) while single V-curve type for C (i). All results supported the hypothesis that appropriately enhanced atmospheric NH(3) can increase assimilation of CO(2) by improving photosynthesis of maize plant, especially at earlier growth stages and after photosynthetic noon-break point. These impacts of elevated NH(3) concentration were more beneficial for SD19 as compared to those for NE5, especially in the LN supply environment.