Contrasting effects of ammonium and nitrate additions on the biomass of soil microbial communities and enzyme activities in subtropical China

Abstract

Abstract. The nitrate to ammonium ratios in nitrogen (N) compounds in wet atmospheric deposits have increased over the recent past, which is a cause for some concern as the individual effects of nitrate and ammonium deposition on the biomass of different soil microbial communities and enzyme activities are still poorly defined. We established a field experiment and applied ammonium (NH 4 Cl) and nitrate (NaNO 3 ) at monthly intervals over a period of 4 years. We collected soil samples from the ammonium and nitrate treatments and control plots in three different seasons, namely spring, summer, and fall, to evaluate the how the biomass of different soil microbial communities and enzyme activities responded to the ammonium (NH 4 Cl) and nitrate (NaNO 3 ) applications. Our results showed that the total contents of phospholipid fatty acids (PLFAs) decreased by 24 and 11 % in the ammonium and nitrate treatments, respectively. The inhibitory effects of ammonium on Gram-positive bacteria (G + ) and bacteria, fungi, actinomycetes, and arbuscular mycorrhizal fungi (AMF) PLFA contents ranged from 14 to 40 % across the three seasons. We also observed that the absolute activities of C, N, and P hydrolyses and oxidases were inhibited by ammonium and nitrate, but that nitrate had stronger inhibitory effects on the activities of acid phosphatase (AP) than ammonium. The activities of Nacquisition specific enzymes (enzyme activities normalized by total PLFA contents) were about 21 and 43 % lower in the ammonium and nitrate treatments than in the control, respectively. However, the activities of P-acquisition specific enzymes were about 19 % higher in the ammonium treatment than in the control. Using redundancy analysis (RDA), we found that the measured C, N, and P hydrolysis and polyphenol oxidase (PPO) activities were positively correlated with the soil pH and ammonium contents, but were negatively correlated with the nitrate

Nitrogen fertilization changes the molecular composition of soil organic matter in a subtropical plantation forest

“…Furthermore, accelerated nitrification is the decisive cause of soil acidification under N enrichment, because the oxidation of NH 4 + or NH 3 to NO 3 − produces much H + (Lu, Mao, Gilliam, Luo, & Mo, ). Similar results of NO 3 − accumulation and acidification in the subtropical forest soils were reported by other researchers (Zhang et al., ; Zhao, Zhang, Müller, & Cai, ). Another alternative explanation is the increase in base cation (e.g., Ca 2+ , Mg 2+ ) leaching due to NO 3 − loss, which reduces soil acid neutralizing capacity (Lu et al., ).…”

“…At the same site, Zhang et al. () reported that low levels of NH 4 Cl and NaNO 3 fertilization (40 kg N ha −1 yr −1 ) accelerated soil NO 3 − accumulation and soil acidification, which, in turn, inhibited the enzyme activity of C hydrolysis (e.g., α‐1–4‐glucosidase and β‐1–4‐glucosidase). This suggests a slower decomposition of carbohydrates (DeForest, Zak, Pregitzer, & Burton, ).…”

“…Compared with the control, the higher relative abundance of furfural under N enrichment indicates a decrease in glycanolytic activity, which is associated with degradation of polysaccharides and storage of carbohydrates (Saiya-Cork, Sinsabaugh, & Zak, 2002). At the same site, Zhang et al (2017) reported that low levels of NH 4 Cl and NaNO 3 fertilization (40 kg N ha −1 yr −1 ) accelerated soil NO 3 − accumulation and soil acidification, which, in turn, inhibited the enzyme activity of C hydrolysis (e.g., α-1-4-glucosidase and β-1-4-glucosidase). This suggests a slower decomposition of carbohydrates (DeForest, Zak, Pregitzer, & Burton, 2004).…”

Different Molecular Characterization of Soil Particulate Fractions under N Deposition in a Subtropical Forest

“…On the one hand, previous studies demonstrated the selective stabilization of O-alkyl C such as carbohydrates could defend against microbial attack through interactions with pedogenic oxides under mineral N application [78]. On the other hand, the glycanolytic activity (e.g., α-1-4-glucosidase and β-1-4-glucosidase) associated with degradation of polysaccharide was inhibited under N enrichment in our study site [79], thus leading to an accumulation of carbohydrates. Naafs et al [80] also pointed out that the polysaccharides was accumulated due to reduced bacterial activity.…”

Litter Management as a Key Factor Relieves Soil Respiration Decay in an Urban-Adjacent Camphor Forest under a Short-Term Nitrogen Increment

“…The mechanism for this phenomenon is not clear, but one probable explanation is that some other nutrient elements (i.e., C and P) from litter become limited factors when N was satisfied [51]. Furthermore, Zhang, et al [52] reported that carbon hydrolysis and polyphenol oxidase activities were positively correlated with (NH 4 -N), which was only influenced by litter treatments. Thus, litter may play an important role in this experiment.…”