AUTHOR=Shi Baoku , Wang Yunbo , Meng Bo , Zhong Shangzhi , Sun Wei 

TITLE=Effects of Nitrogen Addition on the Drought Susceptibility of the Leymus chinensis Meadow Ecosystem Vary with Drought Duration

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00254

DOI=10.3389/fpls.2018.00254

ISSN=1664-462X

ABSTRACT=<p>It is not clear yet how extreme drought and nitrogen (N) deposition influence grassland ecosystem functions when they are considered together, especially in complex field conditions. To explore the response of the <italic>Leymus chinensis</italic> meadow ecosystem to manipulated extreme drought (45 days), N addition and their interaction, we measured leaf photosynthetic characteristics, aboveground phytomass on the community level and ecosystem C exchange in different treatments at the middle and the end of the drought period. The extreme drought treatment decreased the leaf net CO<sub>2</sub> assimilation rate and ecosystem C exchange [gross ecosystem productivity (GEP), ecosystem respiration and net ecosystem CO<sub>2</sub> exchange]. In contrast, the N addition treatment increased aboveground phytomass, GEP and net ecosystem CO<sub>2</sub> exchange. The effects of N addition on the drought susceptibility of the <italic>L. chinensis</italic> meadow ecosystem varied with drought severity. The N addition treatment alleviated drought-induced suppression of CO<sub>2</sub> exchange at the leaf and ecosystem levels in the middle of the drought period, whereas it exacerbated drought-induced suppression of the CO<sub>2</sub> exchange and aboveground phytomass on the community level at the end of the drought period. Given that dominance by <italic>L. chinensis</italic> is a characteristic of the studied ecosystem, knowledge of the traits of <italic>L. chinensis</italic> and its response to multiple global change drivers will be crucial for predicting future ecosystem functions. Furthermore, increasing N deposition may affect the response of the <italic>L. chinensis</italic> meadow ecosystem to further droughts by increasing carbon allocation to roots and therefore root–shoot ratios.</p>