Gross nitrogen transformation rates in semiarid tropical soils under different salinity and vegetation conditions

Abstract

Exacerbated inundations and saltwater intrusions due to sea‐level rise can significantly alter the ecology of low‐lying coastal drylands by affecting their nutrient cycling and productivity. During the present study, controls on production and consumption of nitrogen in soils of semiarid tropical climate with different levels of vegetation–salinity–moisture condition were investigated using 15N isotope dilution experiments. For this purpose, soils were collected from five land types including two in salt flat and one each in grassland (GL), wetland (WL), and an agricultural field. Soils with no vegetation, high salinity, and high moisture (salt flats) showed significant decline in gross production of nitrogen (mineralization rate: 0.21 ± 0.10 mg N·kg−1·d−1; nitrification rate: 0.27 ± 0.17 mg N·kg−1·d−1) compared to soils with vegetation, low salinity, and low moisture (GL, WL, and agricultural) (mineralization rate: 2.47 ± 1.74 mg N·kg−1·d−1; nitrification rate: 1.43 ± 1.30 mg N·kg−1·d−1). Backward stepwise regression analysis of the results indicated salinity to be the most important factor controlling nitrogen transformation rates. It is likely that soils undergoing frequent seawater exposure or excessive evaporation may experience slowdown in nitrogen cycling due to salinization leading to reduced nutrient production and consumption. Due to climate change, the areal extent of coastal drylands undergoing such decline in nutrient production is likely to increase, eventually leading to loss of productivity and desertification.

Higher N Addition and Mowing Interactively Improved Net Primary Productivity by Stimulating Gross Nitrification in a Temperate Steppe of Northern China

“…Mowing is one of the most important management mechanisms in the grassland ecosystems of northern China that directly or indirectly affects net primary productivity by influencing microbial activity and N turnover rates [ 17 ]. Previous studies reported that mowing also strongly affected nutrient cycling processes because mowing removed aboveground biomass and decreased litter biomass [ 15 , 23 ], which could increase soil surface temperature and decrease soil moisture content and further affect the bacterial and fungi composition and then stimulate N turnover processes [ 24 , 25 , 26 , 27 ]. Some studies showed that mowing reduced root biomass and soil total N concentrations [ 28 , 29 ], which was likely due to the loss of N through aboveground biomass harvesting.…”