Soil biochemical responses to nitrogen addition in a secondary evergreen broad-leaved forest ecosystem

Abstract

In order to investigate the effects of N deposition on soil biochemistry in secondary forests, one N addition experiment was conducted in a secondary evergreen broad-leaved forest in the western edge of Sichuan Basin, with the highest level of background N deposition (about 95 kg N ha−1 yr−1) in China. Three N treatment levels (+0, +50, +150 kg N ha−1 yr−1) were monthly added to soil surface in this forest beginning in April 2013. Soil biochemistry and root biomass of the 0–10 cm soil horizon were measured from May 2014 to April 2015. Soil respiration was measured for two years (September 2013 to August 2015). It was showed that N additions were correlated to significantly lower soil pH, microbial biomass C (MBC) concentration, MBC/microbial biomass N (MBN) ratio, root biomass, and soil respiration rate, and significantly higher concentrations of ammonium (NH4 +) and nitrate (NO3 −). These results indicate that N additions had a significant effect on the size of soil microbial community. In addition, soil C storage may potentially increase due to the dropped soil C release under N addition.

Simulated nitrogen deposition significantly reduces soil respiration in an evergreen broadleaf forest in western China

“…In this study, after two years of simulated N deposition, the MBC and MBN values in the L, M, and H treatments were significantly lower than those in the Ctr treatment ( Fig 6A and 6B ). Simulated N deposition significantly decreased MBC and MBN in our study, and this result is in line with previous studies in other forest ecosystems [ 9 , 22 , 26 , 27 , 65 ]. Furthermore, we also found that N deposition significantly decreased the concentration of DOC ( Fig 6C ).…”

“…Previous studies found that fine root biomass is significantly and positively correlated with soil respiration [ 52 , 59 , 60 ]. Similar to the results of this study, many previous studies found that N deposition can decrease root biomass, which leads to less input from belowground roots to the soil [ 22 , 27 , 28 , 61 ]. In our study, we found that fine root biomass was significantly reduced by simulated N deposition ( P < 0.05, Fig 6E ).…”

“…As intended, simulated N deposition significantly decreased soil respiration, and this was most pronounced in the M and H treatments ( Fig 3 and Table 1 ), which induced decreases in CO 2 transfer from the soil to the atmosphere. Recently, a study conducted in a secondary evergreen broad-leaved forest in the rainy area of western China also found that N deposition (150 kg N ha −1 ·a −1 ) significantly decreased soil respiration [ 22 , 52 ]. These findings agree with several studies that revealed that N deposition leads to short-term decreases in soil respiration [ 26 – 28 , 53 ]; however, these results are contradictory to the results of other studies [ 18 , 23 , 54 – 56 ].…”

“…The rainy area of western China is a large ecotone on the western edge of the Sichuan Basin that spans 400–450 km north to south and 50–70 km east to west with an area of approximately 25,000 km 2 ( Fig 1 ) [ 19 – 21 ]. Due to the high elevation and the effect of the East Asian Monsoon and Indian Monsoon, warm moist air from the Sichuan Basin is readily condensed into rain on the western edge of the basin, resulting in abundant rainfall [ 19 , 22 ]. Due to the climate and topography, this area receives considerable N deposition from the Sichuan Basin [ 13 , 23 ].…”

Only Minor Changes in the Soil Microbiome of a Sub-alpine Forest After 20 Years of Moderately Increased Nitrogen Loads

“…All these mentioned reasons explain why we found no or only minor changes of the soil microbial communities to the moderate long-term N addition at this forest site. The bacterial and fungal abundance remained unchanged, which is in agreement with others (Peng et al, 2017;Forstner et al, 2019b). Similarly, Hesse et al (2015) found no change in fungal biomass in a natural maple forest in USA treated with N for 16 years.…”