Differential responses of heterotrophic and autotrophic respiration to nitrogen addition and precipitation changes in a Tibetan alpine steppe

Abstract

Soil respiration (Rs) is an important source of atmospheric CO2 flux and is sensitive to changes in soil nutrient and water contents. Despite extensive studies on the effects of enhanced atmospheric nitrogen (N) deposition and changes in precipitation (P) on Rs, few studies have taken into account the effects of interactions between these factors on Rs of alpine grasslands. To address these questions, we investigated the effects of N addition (10 g N m−2 yr−1), changes in precipitation (±50% precipitation), and their interaction on soil respiration and its components, including heterotrophic respiration (Rh) and autotrophic respiration (Ra),in a Tibetan alpine steppe during three consecutive growing seasons. We found that Rs differed in its response to N addition and precipitation regimes. Specifically, decreased precipitation led to a significant reduction in Rs during the last two years, whereas N addition minimally impacted Rs. Another important finding was that soil respiration components differed in their response to N addition and precipitation regimes. Nitrogen addition significantly enhanced Ra, whereas Rh was not altered in response to N addition. By contrast, the precipitation regime led to marked changes in Rh, but exhibited marginally significant effects on Ra. Therefore, our findings highlighted that soil respiration differed in its response to N addition and precipitation regimes mainly due to the different responses of soil respiration components to these factors. Therefore, carbon dynamics should take soil respiration components into account under global change scenarios.

Precipitation and nitrogen addition enhance biomass allocation to aboveground in an alpine steppe

“…Aboveground biomass was sampled in mid‐August annually by clipping all plants within three 0.25 m × 0.25 m quadrates that were randomly placed within each plot and not overlapped spatially among years. Briefly, shoots were cut at the soil surface and oven‐dried at 65°C for 72 hr before they were weighed (Li et al, ). Thereafter, to assess the effect of altered precipitation, N addition, and their interaction on over all belowground biomass and aboveground biomass at different soil layer, we collected belowground biomass using three 8‐cm‐diameter soil cores from each plot in mid‐August 2016.…”

“…Briefly, shoots were cut at the soil surface and oven-dried at 65°C for 72 hr before they were weighed (Li et al, 2018). Thereafter, to assess the effect of altered precipitation, N addition, and their interaction on over all belowground biomass and aboveground biomass at different soil layer, we collected belowground biomass using three 8-cm-diameter soil cores from each plot in mid-August 2016.…”

“…For example, during the period 1990–2003, atmospheric N deposition has increased substantially from 8.7 to 13.8 kg N ha −1 year −1 in the region (Lü & Tian, ). Our precious studies have shown that altered precipitation and enhanced N deposition had a marked influence on aboveground community biomass (Li et al, ). However, we less known their responses of community BGB and allocation between AGB and BGB to altered Precip, enhanced N deposition, and their interaction in the alpine steppe.…”

Nitrogen addition reduces soil respiration but increases the relative contribution of heterotrophic component in an alpine meadow

“…Due to different turnover times and controlling factors of plant and soil C pools (Wang, Sun, et al, ), R a and R h have showed differential responses to N enrichment (Fang et al, ; Li et al, ; Zeng, Zhang, & Wang, ). Multiple lines of evidence indicate that N application generally decreases R h when the added N exceeds microbial demand (Fang et al, ; Liu & Greaver, ; Peng, Li, et al, ), which has been explained by the decrease in soil microbial biomass (Treseder, ), inhibition of extracellular enzyme activities (Jian et al, ; Ramirez, Craine, & Fierer, ; Wang, Liu, & Bai, ), alterations in soil microbial abundance and composition (Zhang, Chen, & Ruan, ), and the increase in microbial C use efficiency (Finn et al, ; Liu, Qiao, Yang, Bai, & Liu, ).…”

“…Multiple lines of evidence indicate that N application generally decreases R h when the added N exceeds microbial demand (Fang et al, ; Liu & Greaver, ; Peng, Li, et al, ), which has been explained by the decrease in soil microbial biomass (Treseder, ), inhibition of extracellular enzyme activities (Jian et al, ; Ramirez, Craine, & Fierer, ; Wang, Liu, & Bai, ), alterations in soil microbial abundance and composition (Zhang, Chen, & Ruan, ), and the increase in microbial C use efficiency (Finn et al, ; Liu, Qiao, Yang, Bai, & Liu, ). The effect of N enrichment on R a is disparate, showing a positive (Fang et al, ; Li et al, ), neutral (Ren et al, ) or negative effect (Wei et al, ). A recent global synthesis revealed that N addition decreased R h by 8.1% and increased R a by 21.6%, resulting in no response of R s across all the terrestrial ecosystems (Zhang et al, ).…”