Suppression of methane uptake by precipitation pulses and long-term nitrogen addition in a semi-arid meadow steppe in northeast China.

In the context of global change, the frequency of precipitation pulses is expected to decrease while nitrogen (N) addition is expected to increase, which will have a crucial effect on soil C cycling processes as well as methane (CH) fluxes. The interactive effects of precipitation pulses and N addition on ecosystem CH fluxes, however, remain largely unknown in grassland. In this study, a series of precipitation pulses (0, 5, 10, 20, and 50 mm) and long-term N addition (0 and 10 g N m yr, 10 years) was simulated to investigate their effects on CH fluxes in a semi-arid grassland.

Drought sensitivity of aboveground productivity in Leymus chinensis meadow steppe depends on drought timing.

There is limited understanding of the combined effects of discrete climate extremes and chronic environmental changes on ecosystem processes and functioning. We assessed the interactions of extreme drought timing (45 days, in spring or summer) and nitrogen (N) addition in a full factorial field experiment in a Leymus chinensis-dominated meadow steppe in northeast China. We evaluated the resistance and recovery of the grassland (calculated in terms of aboveground biomass) to these two drought events.

Responses of hydrolytic enzyme activities in saline-alkaline soil to mixed inorganic and organic nitrogen addition.

The effects of manipulating nitrogen (N) deposition, with the use of a single form of N, on soil enzyme activities have been extensively studied. However, the impacts varying the N type (organic vs. inorganic) on soil hydrolytic enzyme activities have been less studied.

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

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 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 assimilation rate and ecosystem C exchange [gross ecosystem productivity (GEP), ecosystem respiration and net ecosystem CO exchange].