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

Abstract

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 Leymus chinensis 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 CO2 assimilation rate and ecosystem C exchange [gross ecosystem productivity (GEP), ecosystem respiration and net ecosystem CO2 exchange]. In contrast, the N addition treatment increased aboveground phytomass, GEP and net ecosystem CO2 exchange. The effects of N addition on the drought susceptibility of the L. chinensis meadow ecosystem varied with drought severity. The N addition treatment alleviated drought-induced suppression of CO2 exchange at the leaf and ecosystem levels in the middle of the drought period, whereas it exacerbated drought-induced suppression of the CO2 exchange and aboveground phytomass on the community level at the end of the drought period. Given that dominance by L. chinensis is a characteristic of the studied ecosystem, knowledge of the traits of L. chinensis 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 L. chinensis meadow ecosystem to further droughts by increasing carbon allocation to roots and therefore root–shoot ratios.

Towards comparable assessment of the soil nutrient status across scales—Review and development of nutrient metrics

“…Positive warming effects on plant growth can be intensified by enhanced nutrient availability following increases in mineralization (Dieleman et al, 2012;Strömgren & Linder, 2002), and nutrients can be important modulators of ecosystem responses to altered rainfall. The latter can follow from changes in nutrient dynamics (Dreesen, De Boeck, Janssens, & Nijs, 2012;Ren et al, 2017;White, Moore, & Craig, 2004), as well as from differences in plant carbon allocation associated with the nutrient status of an ecosystem (Gessler, Schaub, & McDowell, 2017;Shi, Wang, Meng, Zhong, & Sun, 2018;Wang, Meng, et al, 2018).…”

Root and shoot responses of upland New Rice for Africa varieties to fluctuating soil moisture conditions as affected by different levels of nitrogen fertilization

“…Moreover, under fluctuating soil moisture conditions shoot and root growth tended to be higher when the amount of nitrogen fertilizer was greater (Table 1). In previous studies by Shi, Wang, Meng, Zhong, and Sun (2018) and Wu et al (2018), nitrogen application could mitigate the negative effects of water deficit on shoot and root growth under drought. The findings of the present study suggest that N application could alleviate the stress caused by fluctuating soil moisture conditions.…”

Short-Term Nitrogen Addition Does Not Significantly Alter the Effects of Seasonal Drought on Leaf Functional Traits in Machilus pauhoi Kanehira Seedlings

“…Drought treatment significantly decreased A, E, Gs and ψ PD , mainly due to the fact that drought-associated soil water shortage leads to CO 2 limitation through stomata closure (a decrease in Gs) and metabolic constraints [35,60]. Specifically, soil water shortage attributed to drought has a negative effect on N metabolism by regulating the activities of crucial enzymes that participate in N assimilation and catabolism, which results in damage to cell membranes and further decreases photosynthetic capacity [35,61].…”

“…Elevated A can be explained in two ways. Firstly, it may have increased the leaf chlorophyll content [35,63]. Secondly, it may have increased the LNC possibly fixed in photosynthetic pigments and enzymes, resulting in a higher A [63].…”

“…Firstly, co-occurring drivers can have additive effects (i.e., no statistically significant effect of the interaction between drought and N deposition is detected) [30], which can be predicted from single-factor studies [31]. Secondly, the combination of drought and N deposition may not be additive, but instead may have non-additive effects on plants (i.e., the interaction is statistically significant), meaning that opposite or synergistic interaction effects may occur through multi-factor approaches [2,3,20,30,[32][33][34][35]. Many studies have reported that N deposition increases plant sensitivity to drought stress [2,3,32,34,36,37], because high productivity caused by N fertilization may decrease plants' drought resistance and increase mortality [30].…”