Biogeochemical factors contributing to enhanced carbon storage following afforestation of a semi-arid shrubland

J. M. Grünzweig (1, 2) , I. Gelfand (2) , D. Yakir (2)

1 Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture
2 Department of Environmental Sciences and Energy Research

Ecosystems in dry regions are generally low in productivity and carbon (C) storage. We report, however, large increases in C sequestration following afforestation of a semi-arid shrubland with Pinus halepensis trees. Using C and nitrogen (N) inventories, based in part on site-specific allometric equations, we measured an increase in the standing ecosystem C stock from 2380 g C m^?2 in the shrubland to 5840 g C m^?2 in the forest after 35 years, with no significant change in N stocks. The total amount of C produced by the forest was estimated as 6250 g C m^?2. Carbon sequestration following afforestation was associated with increased N use efficiency as reflected by an overall increase in C/N ratio from 7.6 in the shrubland to 16.6 in the forest. The C accumulation rate in the forest was particularly high for soil organic C (SOC; increase of 1760 g C m^?2 or 50 g C m^?2 yr^?1), which was associated with the following factors: 1) Analysis of a small ¹³C signal within this pure C₃ system combined with size fractionation of soil organic matter indicated a significant addition of new SOC derived from forest vegetation (68% of total forest SOC) and a considerable portion of the old original shrubland SOC (53%) still remaining in the forest. 2) A large part of both new and old SOC appeared to be protected from decomposition as about 60% of SOC under both land-use types were in mineral-associated fractions. 3) A short-term decomposition study indicated decreased decomposition of lower-quality litter and SOC in the forest, based on reduced decay rates of up to 90% for forest compared to shrubland litter. 4) Forest soil included a significant component of live and dead roots. Our results showed the considerable potential for C sequestration, particularly in soils, following afforestation in semi-arid regions, which is particularly relevant in light of persistent predictions of drying trends in the Mediterranean and other regions.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Interfaces continentales, environnement; Océan, Atmosphère; Sciences de la Terre

J. M. Grünzweig, I. Gelfand, D. Yakir. Biogeochemical factors contributing to enhanced carbon storage following afforestation of a semi-arid shrubland. Biogeosciences Discussions, 2007, 4 (4), pp.2111-2145. ⟨hal-00297901⟩