Relative availability of inorganic N-pools shifts under land use change: An unexplored variable in soil carbon dynamics
Graphical abstract
Introduction
Soil organic carbon (SOC) and its fractions are considered as good indicators of soil quality and environmental stability (Saha et al., 2011), therefore their monitoring and management in human-induced land use change (LUC) is important for global C cycle (Wei et al., 2013). Globally, soil holds around 1500 Pg of soil organic C representing twice and thrice as much C as in atmosphere and aboveground biomass, respectively (Batjes, 1996, Lal, 2008, Schmidt et al., 2011). LUC in the form of conversion of forest to grassland and/or cropland induces heavy changes in SOC dynamics (Helfrich et al., 2006), leading to C losses in the order of 10–55% (Helfrich et al., 2006, Perrin et al., 2014), however its mechanistic understanding is still limited in tropics (Lal, 2012, Perrin et al., 2014). LUC enhances the soil greenhouse gaseous emissions by releasing stored soil C to the atmosphere, particularly in tropics, thus impacts global climate change and food security (Lal, 2004, IPCC, 2007, Don et al., 2011). Globally, tropics shares 32% of C present in the world soil, of which around 40% is present in the forest soils (Eswaran et al., 1993) where the current rate of C loss due to LUC is about 1.6 ± 0.8 Pg C y−1 (Smith, 2008). Scientists working on global warming and climate change have identified soil as a major source and sink for atmospheric CO2 (Schmidt et al., 2011, USEPA, 2011, Sanford et al., 2012). Therefore, the quantification of different SOC pools and soil CO2 emissions and its governing factors are necessary for the mechanistic understanding of how LUC affects the SOC dynamics for the management implications.
Land use change plays a regulatory role in SOC dynamics affecting microbial composition and activity in bulk soil as well as within aggregates (Wagai et al., 1998, Helgason et al., 2010, Wallenius et al., 2011, Cui et al., 2014). Land use majorly predicts the short term soil CO2 flux (SCE) affecting soil microbial properties (Iqbal et al., 2009). However, microbial attributes have not been found to be related with C mineralization in most of the studies (Strickland et al., 2010). Soil microbial biomass (SMB) act as a source and sink of available nutrients, thus defines nutrient transformation in terrestrial ecosystems (Singh et al., 1989). Any changes in it may also affect the cycling of SOC. It is highly responsive to changes in land use and management than SOC (Henneron et al., 2015). Generally, it tends to decline with LUC from forest to grassland and/or cropland and offers a method in assessing the soil quality in different vegetation types (Groffman et al., 2001).
Land use change causes a loss of soil structure, but limited studies have focused on the effect of changes in aggregate size distribution and characteristics on soil physical, chemical and biological properties (Conant et al., 2004, Cui et al., 2014). Land use with minimum disturbance favors a better soil aggregation/structure (Liu et al., 2010) and conversion to appropriate land uses may recover the soil structure and quality (Li and Pang, 2010, Sanford et al., 2012). Soil aggregation is intrinsically linked with C accumulation (Six et al., 2000a, Six et al., 2000b). Further, the soil aggregation is reported to have dominance over microbial-mediated decomposition processes in terrestrial ecosystems (Six et al., 2004). Moreover, soil aggregation not only physically protects soil organic matter (SOM), but influences microbial community structure, limits oxygen diffusion, regulates water flow, determines nutrient adsorption and desorption, and reduces run-off and erosion (Six et al., 2004). Under LUC, the architecture of the pore network is much affected (Ruamps et al., 2011). The localization and accessibility of the organics stored in soil micropores inside aggregates has been found to be a function of complex biophysical interactions under changing microclimatic conditions during soil development (Simpson et al., 2004). All of these processes have profound cumulative effects on SOM dynamics and nutrient cycling. Further, Six et al. (1998) reported that soil management systems that promote aggregate destruction, principally of macro-aggregates, increase SOM decomposition rates due to the exposure of previously protected organic matter in the aggregates. The turnover of macro-aggregate, which contains greater amount of C than micro-aggregate, is fast under human management (Smith et al., 2015). The faster turnover greatly affects the C and N distribution across aggregate-size fractions (Li and Pang, 2010). The stability and turnover of macro-aggregate has been reported to define the characteristics of micro-aggregates as well (Elliott and Coleman, 1988). Therefore, LUC probably influence SOM decomposition rates affecting aggregate turnover, probably by affecting the architecture of aggregates (Cui et al., 2014, Rabbi et al., 2014a, Rabbi et al., 2014b). Further, the identification of major driver of aggregate dynamics and C distribution within aggregate fractions with LUC would be pivotal as an indicator variable for the shift in SOC dynamics.
Pools and turnover of SOC are highly sensitive to LUC. LUC defines soil structural dynamics by affecting the qualitative and quantitative distribution of input C across aggregate size fractions. However, investigation of qualitative and quantitative effects of LUC on SOC is limited (Poeplau and Don, 2013). Attempts have been made to identify SOC fractions highly sensitive to LUC than bulk SOC, for an early detection of overall stock change (Lobe et al., 2011). Therefore, the process of C dynamics can be better understood by the differences in SOC and its fractions among different land uses (Saha et al., 2011). Soil C loss is decomposition-dependent, affected chiefly by quality of the substrate and microbial communities (Chapela et al., 2001). Recent researches have shown that molecular structure alone does not control SOM stability but environmental and biological control predominates (Schmidt et al., 2011). It is hypothesized that the turnover of aggregate-associated C is dependent on soil structural development and its dynamics would be mediated by the availability of soil nutrient pool. In addition, relative availability of soil inorganic N-species (i.e. soil nitrate-N and ammonium-N) on SOC dynamics has not been performed. Therefore, the present study investigates that how the changes in soil physicochemical, microbial and aggregate attributes with LUC affect SOC dynamics to find out a possible ecological indicator of change in the soil processes. Therefore, the objectives of present study were: (1) to study the quantitative and qualitative shift in nutrient, microbial and aggregate characteristics with LUC and (2) how these changes mechanistically govern SOC dynamics with special reference to relative availability of inorganic N pools.
Section snippets
Description of experimental sites
The study was conducted at the experimental plots in the Banaras Hindu University campus, Varanasi, India during the peak of winter season of 2011–2012. The study sites comprise three separate patches of secondary forest (SF), grassland (GL) and agricultural plots (CL) each. These adjacent land uses were selected in this study as they represent the major land use types in recent times. These land use types have been created due to conversion of native forest vegetation during the year
Effect of land use change on soil physicochemical properties
Land use change has resulted into various observable changes in soil physicochemical properties. With the change to GL and CL from SF, a significant increase in soil pH, bulk density (11 and 18%) and soil NO3−-N (340 and 592%) content, whereas a significant decrease in soil porosity, SOC (31 and 42%) and SON (7 and 35%) was observed (Table 1), respectively. However, increase in BD (7%) and soil NO3−-N (57%) whereas decrease in SOC (16%) and SON (30%) was observed from GL to CL. Moreover, SMC,
Effect of land use change on SOC and SCE
Land use change dramatically affects SOC dynamics modifying soil properties and thus contributes to increased concentration of atmospheric CO2 (Campos, 2006). Most of the previous studies have indicated that LUC results in the shifts in soil physical, chemical, and biological properties (Aon et al., 2001). It is in conformity with the significant change in the SOC with the land use change in our study. However, similar SOC in SF and GL, as observed in the present study, has been reported
Conclusion
Land use change shows a distinct qualitative and quantitative change in soil nutrient availability, microbial properties and aggregate characteristics. In the present study, shift in aggregate distribution toward smaller size fractions at the cost of macro-aggregate fraction with land use change and simultaneous increase in SCE (opposite to SOC) signifies the importance of macro-aggregate in SOC dynamics. Moreover, the concurrent shift in microbial attributes seems to govern SOC dynamics
Acknowledgements
Authors are grateful to J. S. Singh, Emeritus Professor, Department of Botany, Banaras Hindu University, Varanasi, for his valuable suggestions for improving the manuscript. Authors are also highly thankful to Council of Scientific and Industrial Research (CSIR) and University Grants Commission (UGC), New Delhi, India, for funding support as research fellowships. The precious comments given by the unknown reviewers for the improvement in manuscript are also highly acknowledged.
References (84)
- et al.
Spatio-temporal patterns of soil microbial and enzymatic activities in an agricultural soil
Appl. Soil Ecol.
(2001) - et al.
Soil aggregation and organic matter in a sandy clay loam soil of the Indian Himalayas under different tillage and crop regimes
Agric. Ecosyst. Environ.
(2009) - et al.
Chloroform fumigation and the release of soil nitrogen: a rapid direct extraction method to measure microbial biomass N in soil
Soil Biol. Biochem.
(1985) - et al.
Methods for physical separation and characterization of soil organic matter fractions
Geoderma
(1993) - et al.
Ectomycorrhizal fungi introduced with exotic pine plantations induce soil carbon depletion
Soil Biol. Biochem.
(2001) - et al.
Effects of land-use intensification on soil carbon and ecosystem services in Brigalow (Acacia harpophylla) landscapes of southeast Queensland, Australia
Agric. Ecosyst. Environ.
(2006) - et al.
Physical and chemical stabilization of soil organic carbon along a 500-year cultivated soil chronosequence originating from estuarine wetlands: temporal patterns and land use effects
Agric. Ecosyst. Environ.
(2014) - et al.
Carbon losses from soil and its consequences for land-use management
Sci. Total Environ.
(2007) - et al.
Soil organic matter in soil physical fractions in adjacent semi-natural and cultivated stands in temperate Atlantic forests
Soil Biol. Biochem.
(2009) - et al.
Soil microbial biomass and activity in tropical riparian forests
Soil Biol. Biochem.
(2001)
Soil aggregation: influence on microbial biomass and implications for biological processes
Soil Biol. Biochem.
Effect of land use on the composition of soil organic matter in density and aggregate fractions as revealed by solid-state 13C NMR spectroscopy
Geoderma
No-till soil management increases microbial biomass and alters community profiles in soil aggregates
Appl. Soil Ecol.
Microbial biomass, and dissolved organic carbon and nitrogen strongly affect soil respiration in different land uses: a case study at Three Gorges Reservoir Area, South China
Agric. Ecosyst. Environ.
Carbon dioxide emissions from Ultisol under different land uses in mid-subtropical China
Geoderma
Land use effects on soil quality in a tropical forest ecosystem of Bangladesh
Agric. Ecosyst. Environ.
Storage of organic carbon in aggregate and density fractions of silty soils under different types of land use
Geoderma
Soil organic matter fractions as early indicators for carbon stock changes under different land-use?
Geoderma
Effect of land-use conversion on C and N distribution in aggregate fractions of soils in the southern Loess Plateau, China
Land Use Policy
Impact of land use and soil fertility on distributions of soil aggregate fractions and some nutrients
Pedosphere
Aggregate dynamics and associated soil organic matter contents as influenced by prolonged arable cropping in the South African Highveld
Geoderma
Effect of ammonium and nitrate addition on carbon mineralization in wetland soil
Soil Biol. Biochem.
Microbial indicators related to soil carbon in Mediterranean land use systems
Soil Till. Res.
Soil aggregate size distribution mediates microbial climate change feedbacks
Soil Biol. Biochem.
Conversion of forest to agriculture in Amazonia with the chop-and-mulch method: does it improve the soil carbon stock?
Agric. Ecosyst. Environ.
Sensitivity of soil organic carbon stocks and fractions to different land-use changes across Europe
Geoderma
Soil organic carbon mineralization rates in aggregates under contrasting land uses
Geoderma
The relationships between land uses, soil management practices, and soil carbon fractions in South Eastern Australia
Agric. Ecosyst. Environ.
Microbiological indicators of soil quality and degradation following conversion of native forests to continuous croplands
Ecol. Ind.
Microbial biogeography at the soil pore scale
Soil Biol. Biochem.
Soil carbon lost from Mollisols of the North Central U.S.A. with 20 years of agricultural best management practices
Agric. Ecosyst. Environ.
Microbial biomass and activity in an agricultural soil with different organic matter contents
Soil Biol. Biochem.
Microbial biomass associated with water-stable aggregates in forest, savanna and cropland soils of a seasonally dry tropical region, India
Soil Biol. Biochem.
A history of research on the link between (micro) aggregates, soil biota, and soil organic matter dynamics
Soil Tillage Res.
Soil macroaggregate turnover and microaggregate formation: a mechanism for C sequestration under no-tillage agriculture
Soil Biol. Biochem.
When does organic carbon induce aggregate stability in vertosols?
Agric. Ecosyst. Environ.
Soil carbon efflux and sequestration as a function of relative availability of inorganic N pools in dry tropical agroecosystem
Appl. Soil Ecol.
Microbial C, N and P in dry tropical forest soils: effects of alternate land uses and nutrient flux
Soil Biol. Biochem.
Rates of in situ carbon mineralization in relation to land-use, microbial community and edaphic characteristics
Soil Biol. Biochem.
The effect of organic matter on the structure of soils of different land uses
Soil Till. Res.
An extraction method for measuring soil microbial biomass C
Soil Biol. Biochem.
Land use and environmental factors influencing soil surface CO2 flux and microbial biomass in natural and managed ecosystems in southern Wisconsin
Soil Biol. Biochem.
Cited by (48)
Nitrogen addition may promote soil organic carbon storage and CO<inf>2</inf> emission but reduce dissolved organic carbon in Zoige peatland
2022, Journal of Environmental ManagementCitation Excerpt :Notably, the reduced N-acquiring enzyme activities (i.e., NAG and LAP) after N addition in W and T soils (Fig. 3) indirectly verified that N addition possibly alleviated microbial N limitation. Moreover, the significantly negative relationships between N-acquiring enzyme activities (i.e., NAG, LAP) and SOC (Fig. S4) further emphasized the importance of N availability in C sequestration in the studied area (Srivastava et al., 2016). The importance of N availability in controlling C storage has been recognized (Fernández-Martínez et al., 2014; Argiroff et al., 2019; Kicklighter et al., 2019; Srivastava et al., 2020).
Effect of alternate partial root-zone drying (PRD) on soil nitrogen availability to alfalfa
2021, Agricultural Water ManagementCitation Excerpt :In cropland ecosystems, soil N availability is usually estimated by the soil NH4+-N concentration and NO3−-N concentration (Stevens et al., 2010), whereas some studies have considered the NO3−-N/NH4+-N ratio a better indicator than their concentrations to estimate the soil N availability to crops (Li et al., 2019). Considering the NO3−-N/NH4+-N ratio can not only reflect the soil NO3−-N and NH4+-N supply for plant growth (Davidson et al., 2007), and the dominant form of soil inorganic N (Xiao et al., 2018) but may reflect the soil N in relation to C dynamics (Srivastava et al., 2016). Furthermore, recent studies have argued that the soil NO3−-N stock and NH4+-N stock are suitable for evaluating N availability to crops (Alam et al., 2020; Wang et al., 2020c; Zhou et al., 2020) since the soil NO3−-N stock and NH4+-N stock represent the soil inorganic N supply in the long-term (Bell et al., 2012).
Spatio-temporal variability in soil CO<inf>2</inf> efflux and regulatory physicochemical parameters from the tropical urban natural and anthropogenic land use classes
2021, Journal of Environmental ManagementCitation Excerpt :Such high level of heterogeneity in soil properties under urban land uses has also been reported by previous studies (Livesley et al., 2016). Our results, in particular, showed that the variation in SCE was mainly triggered by the spatial and seasonal variations in soil temperature, soil moisture and nutrient availability, which was in agreement with previous studies conducted in different ecosystems (Vargas et al., 2011; Davidson et al., 2012; Srivastava et al., 2016). SEM model 1 (Fig. 7a) results also support this consensus by showing standardized path coefficients of 0.60, 0.59 and 0.22 for soil temperature, moisture and SOC content, respectively, for overall dataset.