Effects of nitrogen addition and drought stress on carbon, nitrogen and phosphorus stoichiometry of Bothriochloa ischaemum

Objectives Both nitrogen and water shortage are the main limiting factors for plant growth in arid and semiarid ecosystems. Study the carbon (C), nitrogen (N) and phosphorus (P) stoichiometric characteristics of plant under nitrogen deposition and drought stress will help understanding the response characteristics of arid and semiarid ecosystems to global changes. Methods A pot experiment was conducted inside a phytotron using Bothriochloa ischaemum as tested martials. N application rates of 0, 2.5 and 5.0 g/(m2a) were designed, representing CK, low N and high N rate; and water supply levels of field capacity of 75%-80%, 55%-60% and 35%-40% were setup, representing drought stress level of well-watered, moderate drought stress and severe drought stress in turn. The contents of C, N and P in the shoot and root were determined and the C, N, and P stoichiometry were calculated. Results N addition and drought stress had no significant influence on C concentration in the aboveground and root of B. ischaemum. N addition increased the N concentration by 9.7%-48.8% (P 0.001) in the shoot, while drought stress decreased it by 2.8%-28.3% (P 0.001). Nitrogen addition and drought stress had significant interactive effects on the root N concentration, N addition increased the N concentration by 25.0%-26.1% (P 0.01) under well-watered condition and had no significant influence on it under drought stress condition. N addition and drought stress significantly decreased the P concentration by 17.4%-31.8% and 12.0%-22.1% in shoot. N addition and drought stress had significant interactive effects on the C:N ratio in shoot, N addition increased the C:N ratio by 24.9%-32.9% (P 0.05) under drought stress, but not under well-watered condition. The C:N ratio in the root of B. ischaemum was decreased by 19.8%-24.5% (P 0.05) by N addition under well watered condition. N addition and drought stress decreased the C:P ratio by 24.4%-42.3% and 12.2%-31.0% in the shoot of B. ischaemum, respectively, but not in the root. N addition significantly increased the N:P ratio in the aboveground part of B. ischaemum, drought stress did not. N addition and drought stress had significant interactive influence on the N:P ratio in the root of B. ischaemum, N addition increased the N:P ratio by 26.8%-54.8% (P 0.05) under well-watered condition and had no significant influence on it under drought stress condition.Conclusions N addition will increase the C:P and N:P ratio in the aboveground part of B. ischaemum under drought stress, intimating that the growth of B. ischaemum would be restrained by both N and P on the Loess Plateau with the aggravation of drought stress and N deposition to some extent.