Elsevier

Geoderma

Volumes 193–194, February 2013, Pages 213-221
Geoderma

Carbon dynamics of soil organic matter in bulk soil and aggregate fraction during secondary succession in a Mediterranean environment

https://doi.org/10.1016/j.geoderma.2012.08.036Get rights and content

Abstract

Clarifying which factors cause an increase or decrease in soil organic carbon (SOC) after agricultural abandonment requires integration of data on the temporal dynamics of the plant community and SOC. A chronosequence of abandoned vineyards was studied on a volcanic island (Pantelleria, Italy). Vegetation in the abandoned fields was initially dominated by annual and perennial herbs, then by Hyparrhenia hirta (L.) Stapf, and finally by woody communities. As a consequence, the dominant photosynthetic pathway changed from C3 to C4 and then back to C3. Conversion of a plant community dominated by one photosynthetic pathway to another changes the 13C/12C ratio of inputs to SOC. Using the time since abandonment and the shift in belowground δ13C of SOC relative to the aboveground δ13C plant community, we estimated C3-C and C4-C changes during secondary succession.

SOC content (g kg 1) increased linearly (R2 = 0.89 and 0.73 for 0–15 and 15–30 cm soil depth) with the age of abandonment, increasing from 12 g kg 1 in cultivated vineyards to as high as 26 g kg 1 in the last stage of the succession. δ13C increased in the bulk soil and its three aggregate fractions (> 250, 250–25, and < 25 μm) during succession, but the effect of soil depth and its interaction with succession age were significant only for soil aggregate fractions. Polynomial curves described the change in δ13C over the chronosequence for both depths. δ13C in the bulk soil had increased from − 28‰ to − 24‰ by 35 years after abandonment for both depths but then decreased to − 26‰ at 60 years after abandonment (corresponding with maturity of the woody plant community). Overall, the results indicate that abandoned vineyards on volcanic soil in a semi-arid environment are C sinks and that C storage in these soils is closely related to plant succession.

Highlights

► Volcanic soils of semi-arid vine old fields may be C sinks. ► Soil organic carbon increases linearly with abandonment age. ► Soil organic carbon increases the most in the micro-aggregate fraction. ► With increasing time since abandonment, micro-aggregate mass increases. ► New C replaces old C in all soil aggregate fractions, except for the smallest one.

Introduction

Because of human activities, the concentration of atmospheric CO2 is increasing rapidly while the long-term storage capacity of terrestrial and ocean ecosystems is declining (Canadell et al., 2007). Understanding the role played by soil in global C dynamics requires estimation of soil carbon (C) stocks. Because more C is stored in the soil than in vegetation or the atmosphere (Eswaran et al., 2000), changes in soil C content could greatly affect the atmosphere (Lal, 2004).

The effects of the conversion of native vegetation to cropland or pasture on C storage are well known (Del Galdo et al., 2003, Desjardins et al., 2004, Romkens et al., 1999). In contrast, less is known about the dynamics of soil organic carbon (SOC) after agricultural abandonment, and this is especially true for Mediterranean areas (Alberti et al., 2011, La Mantia et al., 2007). Soil carbon dynamics after the abandonment of cultivated land is connected to the development of the natural vegetation through secondary succession processes (Kosmas et al., 2000, Martinez-Fernandez et al., 1995, Van Rompaey et al., 2001). There is some evidence that abandonment of agricultural land and the subsequent regeneration of forests through secondary succession may return C storage to the pre-agricultural levels, although the rate of recovery depends on the time one considers and whether the land was previously used for crops or pasture (Guo and Gifford, 2002, Post and Kwon, 2000).

A major factor affecting the dynamics of SOC after the abandonment of an agricultural land is climate (Alberti et al., 2011). Jinbo et al. (2007) found that abandonment led to an increase in SOC in a favourable (medium rainfall and high temperatures that supported high primary productivity) climate but a decrease in SOC in an unfavourable climate. This finding, however, was not confirmed by other experimental evidence. For example, abandonment under climatic conditions that limit primary production (as in Mediterranean climate) caused an increase in the soil C stock (Alberti et al., 2011). Similarly, a lack of soil disturbance in a semi-arid environment resulted in an increase of C in the soil surface (Alvaro-Fuentes et al., 2009).

Furthermore, the increase of SOC content is determined by the incorporation of new organic matter in the coarse fraction and the reduction of mineralisation processes in the finest ones (Barbera et al., 2012, Ouédraogo et al., 2005). While during the early stages of secondary succession the increase of carbon stock is mainly due to anthropic disturbance reduction, in the older stages of succession it is caused by an increasing plant productivity, which is generally found along secondary succession in mesic Mediterranean conditions, and which has been confirmed also during old field succession on Pantelleria Island (La Mantia et al., 2007, La Mantia et al., 2008). It is not clear whether SOC content can continue to increase as a function of time since agricultural abandonment or whether there is some limit. Whether SOC accumulates or decreases greatly depends on how interactions between climate and soil type affect SOC mineralisation rates and/or accumulation in soil.

SOC mineralisation can be reduced within soil aggregates in comparison to bulk soil, and the formation and turnover of soil aggregates are affected by agricultural abandonment and other changes in land management (Schimel, 1995). There is still lack of knowledge on how management conditions and their abandonment affect aggregate formation and the protection of SOC. Generally, micro-aggregates (< 250 μm) (Tisdall and Oades, 1982) are relatively stable and are bound by persistent polysaccharide-based glues produced by roots and microbes and by calcium bridges. On the other hand, micro-aggregates are bound into macro-aggregates (> 250 μm) by a network of roots and hyphae. Therefore, macro-aggregate stability is thought to respond more rapidly to changes in land use. Several authors have reported that the aggregate stability and SOC content of stable macro-aggregates were higher in native grassland than in cultivated fields (Cambardella and Elliot, 1992, Six et al., 2002). Others reported a higher mean residence time of SOC for reduced-tilled soils (Collins et al., 1999, Six et al., 2002), and the increased residence time was attributed to an increased physical protection of soil aggregates in the absence of disturbance.

As noted, the physical protection of SOC provided by aggregates favours SOC accumulation whereas cultivation tends to break aggregates apart and therefore increases SOC mineralisation. The inclusion of SOC in soil aggregates and the mineralisation of SOC in broken aggregates are accompanied by changes in the chemical structure of SOC. These processes have been studied with the aid of δ13C analysis (Buzek et al., 2009, Desjardins et al., 1994, Desjardins et al., 2004, Desjardins et al., 2006, Wookey et al., 2002).

After agricultural abandonment, old fields are spontaneously colonised by various plants, a gradual process during which different plant communities develop (secondary succession). In general, annual and perennial herb communities dominate early and are then partially or completely replaced by perennial grasses, shrubs, and/or trees. If during succession there is a switch between C3 and C4 photosynthetic pathways, the 13C/12C ratio (δ13C) of inputs to SOC is modified. Using the time since perturbation and the shift in belowground δ13C of SOC relative to the aboveground δ13C of the plant community, researchers can estimate the SOC turnover rate (Wolf et al., 1994). SOC turnover rates have been estimated when C4-dominated natural grasslands were converted to C3 annual crops and perennial pastures (Balesdent et al., 1990, Follet et al., 1997), or when C3-dominated natural forests and grasslands were converted to C4 annual crops and perennial pastures (Balesdent et al., 1987, Gregorich et al., 1995, Jastrow et al., 1996), but no data are available for secondary successions characterised by a C3–C4–C3 pathway. When separated on the basis of chemical composition, aggregate size, or particle density, SOC aggregate fractions have been shown to differ in age and thus in turnover rate (Balesdent et al., 1990, Jastrow et al., 1996).

The present study analyses the change in soil carbon stock along a secondary succession after agricultural abandonment describing differences in SOC turnover rates along succession for all soil aggregate fractions. The study of soil carbon dynamics linked to spontaneous secondary succession processes has been identified as a priority in policy-oriented research since data on natural post-abandonment soil evolution is lacking (Zanchi et al., 2007). Furthermore, the present study evaluates SOC turnover using changes in the natural abundance of δ13C. This evaluation contributes to the knowledge on aggregate formation and the protection of SOC under different management systems, and provides data on SOC turnover along a C3–C4–C3 succession pathway.

Section snippets

Study and sampling area

The study was carried out in cultivated and abandoned terraced vineyards on Pantelleria Island (Italy), which is situated in the rift of the Sicilian Channel (83 km2 surface area; 36°44′ N, 11°57′ E) (Fig. 1a). Pantelleria is of volcanic origin, its highest summit is Montagna Grande (836 m a.s.l.), and its surface rocks are mainly acidic, silicic vulcanites (pantellerites and trachytes). The most frequent soils are Lithosols, Regosols (mainly escalic), and Cambisols (mainly vitric). The island is

Total C and N

SOC content (g kg 1) increased linearly (R2 = 0.89 and 0.73 for 0–15 and 15–30 cm soil depth) with the age of abandonment; it increased from 12 g kg 1 in the cultivated vineyard (terrace 1) to 26 g kg 1 in the vineyard abandoned 60 years earlier (terrace 7) (Table 2, Fig. 2a). There was no interaction between age and depth, and SOC content was greater near the surface (0–15 cm) than deeper (15–30 cm) in the soil (Fig. 2a); after 60 years of abandonment, SOC content was 28 g kg 1 at 0–15 cm and 26 g kg 1 at 15–30

Discussion

In the semi-arid Mediterranean environment, where climate is one of the major driving forces for determining both rate of vegetation community turnover within secondary succession, and the period necessary to complete conversion (new steady state), knowledge of C stock and the resilience of the soil must be increased. The results of the current study indicate that, following abandonment of vineyards on volcanic soil in a semi-arid Mediterranean area, the soil acts as a C sink. This finding is

Conclusions

In this study, we evaluate the SOC incorporation in bulk soil and aggregate fraction after vineyard abandonment and consequent natural vegetation encroachment, using an approach based on natural differences in δ13C of plants with C3 and C4 photosynthesis. Our findings have some implications for the understanding of carbon turnover and organic matter stabilisation in semi-arid Mediterranean environments. The study of a C3-C4–C3 succession pathway has enabled us to put into evidence the quantity

Acknowledgements

This work was financially supported by the Italian government through the PRIN project “The impacts of secondary succession processes on carbon storage in soil and biomass and on biodiversity and the role of dispersal centers and vectors for recolonisation processes”. We are grateful to Bruce Jaffee for revising the English version of the manuscript.

References (52)

  • J. Rühl et al.

    An empirical test of neighbourhood effect and safe-site effect in abandoned Mediterranean vineyards

    Acta Oecologica

    (2011)
  • A.J.J. Van Rompaey et al.

    The impacts of land use policy on the soil erosion risk: a case study in central Belgium

    Agriculture, Ecosystems and Environment

    (2001)
  • G. Alberti et al.

    Regional Environmental Change

    (2011)
  • J. Alvaro-Fuentes et al.

    Soil aggregation and soil organic carbon stabilization: effects of management in semiarid Mediterranean agroecosystems

    Soil Science Society of America Journal

    (2009)
  • M. Arianoutsou

    Timing of litter production in a maquis ecosystem of North-Eastern Greece

    Acta oecologica Oecologia Plantarum

    (1989)
  • J. Balesdent et al.

    Natural 13C abundance as a tracer for soil organic matter dynamics studies

    Soil Biology and Biochemistry

    (1990)
  • V. Barbera et al.

    Long-term cropping systems and tillage management effects on soil organic carbon stock and steady state level of C sequestration rates in a semiarid environment

    Land Degradation & Development

    (2012)
  • B. Bonet

    Secondary succession of semi-arid Mediterranean old-fields in south-eastern Spain: insights for conservation and restoration of degraded lands

    Journal of Arid Environments

    (2004)
  • C.A. Cambardella et al.

    Particulate soil organic matter changes across a grassland cultivation sequence

    Soil Science Society of America Journal

    (1992)
  • J.G. Canadell et al.

    Contributions to accelerating atmospheric CO2 growth from economic activity, carbon intensity, and efficiency of natural sinks

    Proceedings of the National Academy of Sciences of the United States of America

    (2007)
  • H.P. Collins et al.

    Soil carbon dynamics in corn-based agroecosystems: results from carbon-13 natural abundance

    Soil Science Society of America Journal

    (1999)
  • I. Del Galdo et al.

    Assessing the impact of land-use change on soil C sequestration in agricultural soils by means of organic matter fractionation and stable C isotopes

    Global Change Biology

    (2003)
  • H. Eswaran et al.

    Global carbon stocks

  • R.F. Follet et al.

    Carbon isotope ratios of Great Plains soils and in wheat-fallow systems

    Soil Science Society of America Journal

    (1997)
  • E.G. Gregorich et al.

    Turnover of soil organic matter and storage of corn residue carbon estimated from natural 13C abundance

    Canadian Journal of Soil Science

    (1995)
  • L.B. Guo et al.

    Soil carbon sequestration and land-use change: a meta analysis

    Global Change Biology

    (2002)
  • Cited by (0)

    View full text