Increase in pH stimulates mineralization of ‘native’ organic carbon and nitrogen in naturally salt-affected sandy soils

Abstract

Large amounts of terrestrial organic C and N reserves lie in salt-affected environments, and their dynamics are not well understood. This study was conducted to investigate how the contents and dynamics of 'native' organic C and N in sandy soils under different plant species found in a salt-affected ecosystem were related to salinity and pH. Increasing soil pH was associated with significant decreases in total soil organic C and C/N ratio; particulate (0.05-2 mm) organic C, N and C/N; and the C/N ratio in mineral-associated (<0.05 mm) fraction. In addition, mineral-associated organic C and N significantly increased with an increase in clay content of sandy soils. During 90-day incubation, total CO 2 -C production per unit of soil organic C was dependent on pH [CO 2 -C production (g kg -1 organic C) = 22.5 pH -119, R 2 = 0.79]. Similarly, increased pH was associated with increased release of mineral N from soils during 10-day incubation. Soil microbial biomass C and N were also positively related to pH. Metabolic quotient increased with an increase in soil pH, suggesting that increasing alkalinity in the salt-affected soil favoured the survival of a bacterial-dominated microbial community with low assimilation efficiency of organic C. As a result, increased CO 2 -C and mineral N were produced in alkaline saline soils (pH up to 10.0). This pH-stimulated mineralization of organic C and N mainly occurred in particulate but not in mineral-associated organic matter fractions. Our findings imply that, in addition to decreased plant productivity and the litter input, pH-stimulated mineralization of organic matter would also be responsible for a decreased amount of organic matter in alkaline salt-affected sandy soils.

Soil quality indices; special focus on salt-affected soil: review and case study in Northern Egypt.

“…Biodiv. Soil Security Vol.1 (2017) HEBA ELBASIOUNY et al drastic in soils prone to secondary salinization due to poor irrigation and improper drainage management (Rietz and Haynes, 2003;Li et al, 2007). Secondary salinization can accelerate land degradation by excessive salt concentration which leads to dispersion, surface sealing and crust formation and structural changes.…”

“…Land area affected by salinization is as high as 30% or more in countries such as Egypt, Iran and Argentina (Qadir et al, 2006;Abdelfattah et al, 2009). Salt-affected soils occupy approximately 955 Mg ha in the world, 10% of total surface of dry lands (Li et al, 2007). Therefore, there is an urgent need to monitor and identify salt-affected soils, and assess the extent and severity of degradation for obtaining acceptable estimates of available resources for sustainable soil uses and management (Mashali, 1999;Abdelfattah et al, 2009;Farifteh, 2007;Farifteh, 2008).…”

Film fully-mulched ridge-furrow cropping affects soil biochemical properties and maize nutrient uptake in a rainfed semi-arid environment

“…At harvest, soil C and N mineralization was performed on fresh soil samples (< 2 mm) randomly taken from five narrow ridges in the top 20 cm layer at 25°C in the dark (Li et al 2007b). After adjusting the moisture to 60% waterholding capacity, soil (equivalent to 50 g oven-dried weight) was filled into a small cup.…”

Aspect-vegetation complex effects on biochemical characteristics and decomposability of soil organic carbon on the eastern Qinghai-Tibetan Plateau

“…This was confirmed by consistent change patterns of total CO 2 − C evolution and labile OC fractions between soil depths and vegetations types and by close correlations between OC mineralization and labile OC fractions in soil OC across soil samples and sites at either 18 or 25°C incubation temperature. In addition, it is known that increase in soil pH (Li et al 2007c) and decrease in C/N ratio (Giardina et al 2001;von Lützow et al 2002) favor soil OC mineralization. Thus, the higher soil pH and lower C/N ratio under meadows might have also helped increase soil OC decomposability compared with shrublands.…”