Differential effects of warming and nitrogen fertilization on soil respiration and microbial dynamics in switchgrass croplands

Abstract

The mechanistic understanding of warming and nitrogen (N) fertilization, alone or in combination, on microbially mediated decomposition is limited. In this study, soil samples were collected from previously harvested switchgrass (Panicum virgatum L.) plots that had been treated with high N fertilizer (HN: 67 kg N ha−1) and those that had received no N fertilizer (NN) over a 3‐year period. The samples were incubated for 180 days at 15 °C and 20 °C, during which heterotrophic respiration, δ13C of CO2, microbial biomass (MB), specific soil respiration rate (Rs: respiration per unit of microbial biomass), and exoenzyme activities were quantified at 10 different collections time. Employing switchgrass tissues (referred to as litter) with naturally abundant 13C allowed us to partition CO2 respiration derived from soil and amended litter. Cumulative soil respiration increased significantly by 16.4% and 4.2% under warming and N fertilization, respectively. Respiration derived from soil was elevated significantly with warming, while oxidase, the agent for recalcitrant soil substrate decomposition, was not significantly affected by warming. Warming, however, significantly enhanced MB and Rs indicating a decrease in microbial growth efficiency (MGE). On the contrary, respiration derived from amended litter was elevated with N fertilization, which was consistent with the significantly elevated hydrolase. N fertilization, however, had little effect on MB and Rs, suggesting little change in microbial physiology. Temperature and N fertilization showed minimal interactive effects likely due to little differences in soil N availability between NN and HN samples, which is partly attributable to switchgrass biomass N accumulation (equivalent to ~53% of fertilizer N). Overall, the differential individual effects of warming and N fertilization may be driven by physiological adaptation and stimulated exoenzyme kinetics, respectively. The study shed insights on distinct microbial acquisition of different substrates under global temperature increase and N enrichment.

The continent-scale variations in soil microbial respiration in forest ecosystems: diverged pattern and mechanism

“…In this study, we investigated Rm along a 4,200 km and found that Rm ranged from 3.3 to 98.2 mg C kg -1 soil with a mean of 20.7 mg C kg -1 soil within 3-day incubation ( Fig. 2a), which was within the general range of the Rm measured in laboratory (Li et al, 2018;Priess & Folster, 2001). Our results suggested that Rm values had large spatial variations across China forest ecosystems.…”

Effects of nitrogen fertilization and bioenergy crop type on topsoil organic carbon and total Nitrogen contents in middle Tennessee USA

“…Added together with other cellulosic biofuel crops, these dedicated energy crops will contribute to more than 30% of biofuel plant biomass in the coming decades [2,4]. N fertilizers generally increase bioenergy crop yields [5,6], but many studies report highly varied magnitudes and signals of soil C and N contents in response to N fertilization [7][8][9][10]. Few studies have compared the root traits in different bioenergy crops and no study has investigated the role of root traits in mediating bioenergy crop and soil responses to N fertilization.…”

Responses of soil respiration to nitrogen addition in the Sanjiang Plain wetland, northeastern China

“…The effect of N addition on SR has been widely studied in forest ecosystems [12,14,17,23,24], agricultural ecosystems [29–31] and grassland ecosystem [13,18,19,21,22,25]. However, there is a lack of report for wetland ecosystems [32,33].…”