Nitrogen uptake kinetics and saltmarsh plant responses to global change

Abstract

Coastal wetlands are important carbon sinks globally, but their ability to store carbon hinges on their nitrogen (N) supply and N uptake dynamics of dominant plant species. In terrestrial ecosystems, uptake of nitrate (NO3−) and ammonium (NH4+) through roots can strongly influence N acquisition rates and their responses to environmental factors such as rising atmospheric CO2 and eutrophication. We examined the 15N uptake kinetics of three dominant plant species in North American coastal wetlands (Spartina patens, C4 grass; Phragmites australis, C3 grass; Schoenoplectus americanus, C3 sedge) under ambient and elevated CO2 conditions. We further related our results to the productivity response of these species in two long-term field experiments. S. patens had the greatest uptake rates for NO3− and NH4+ under ambient conditions, suggesting that N uptake kinetics may underlie its strong productivity response to N in the field. Elevated CO2 increased NH4+ and NO3− uptake rates for S. patens, but had negative effects on NO3− uptake rates in P. australis and no effects on S. americanus. We suggest that N uptake kinetics may explain differences in plant community composition in coastal wetlands and that CO2-induced shifts, in combination with N proliferation, could alter ecosystem-scale productivity patterns of saltmarshes globally.

Asynchronous nitrogen supply and demand produce nonlinear plant allocation responses to warming and elevated CO2

“…We propose that the same biogeochemical mechanisms operate in both plant communities, but they are less dominant in the C 4 community due to plant physiological traits that are specific to the C 4 species in this system. In particular, the dominant C 4 species (S. patens) has a lower affinity for N uptake than the dominant C 3 species (S. americanus) (47) and may therefore be relatively insensitive to changes in N availability at in situ rates of mineralization.…”

Theoretical and Experimental Analyses of Nutrient Control in Electrical Conductivity-Based Nutrient Recycling Soilless Culture System

“…(1) A plant's nutrient uptake phenomenon can be approximated by the Michaelis-Menten equation (Clarkson, 1985;Le Bot et al, 1998;Cott et al, 2018), and a system that follows this mechanism can have a steady-state solution according to the conditions of input variables and parameters (Golicnik, 2011). (2) Transpiration produces fluctuations in all nutrients' uptake concentrations in the nutrient solution (van Noordwijk, 1990;Le Bot et al, 1998).…”

“…A plant’s nutrient uptake phenomenon can be approximated by the Michaelis–Menten equation ( Clarkson, 1985 ; Le Bot et al, 1998 ; Cott et al, 2018 ), and a system that follows this mechanism can have a steady-state solution according to the conditions of input variables and parameters ( Golicnik, 2011 ).…”

Differential Nutrient Uptake by Saltmarsh Plants Is Modified by Increasing Salinity

“…For example, high salinity inhibits ammonium assimilation by Spartina alterniflora (Bradley and Morris, 1991 ); small additions of ammonium can offset salinity stress (MacTavish and Cohen, 2017 ), but a lack of a combined effect was also observed (Alldred et al, 2017 ). On the other hand, reports on nutrient uptake kinetics per se of halophytic species are scarce (Bradley and Morris, 1991 ; Mozdzer et al, 2010 , 2011 ; Cott et al, 2018 ). As far as we know, there is no information on nitrogen and phosphorus uptake kinetics in the genera Sarcocornia, Atriplex , and Arthrocnemum , common in Mediterranean salt marshes, except for the work of Muñoz and Niell ( 2009 ).…”