Losses of soil carbon by converting tropical forest to plantations: erosion and decomposition estimated by δ¹³C

Abstract

Indonesia lost more tropical forest than all of Brazil in 2012, mainly driven by the rubber, oil palm, and timber industries. Nonetheless, the effects of converting forest to oil palm and rubber plantations on soil organic carbon (SOC) stocks remain unclear. We analyzed SOC losses after lowland rainforest conversion to oil palm, intensive rubber, and extensive rubber plantations in Jambi Province on Sumatra Island. The focus was on two processes: (1) erosion and (2) decomposition of soil organic matter. Carbon contents in the Ah horizon under oil palm and rubber plantations were strongly reduced up to 70% and 62%, respectively. The decrease was lower under extensive rubber plantations (41%). On average, converting forest to plantations led to a loss of 10 Mg C ha À1 after about 15 years of conversion.The C content in the subsoil was similar under the forest and the plantations. We therefore assumed that a shift to higher d 13C values in plantation subsoil corresponds to the losses from the upper soil layer by erosion. Erosion was estimated by comparing the d 13 C profiles in the soils under forest and under plantations. The estimated erosion was the strongest in oil palm (35 AE 8 cm) and rubber (33 AE 10 cm) plantations. The 13 C enrichment of SOC used as a proxy of its turnover indicates a decrease of SOC decomposition rate in the Ah horizon under oil palm plantations after forest conversion. Nonetheless, based on the lack of C input from litter, we expect further losses of SOC in oil palm plantations, which are a less sustainable land use compared to rubber plantations. We conclude that d 13 C depth profiles may be a powerful tool to disentangle soil erosion and SOC mineralization after the conversion of natural ecosystems conversion to intensive plantations when soils show gradual increase of d 13C values with depth.

Carbon and nitrogen stocks in dead wood of tropical lowland forests as dependent on wood decay stages and land-use intensity

“…Conversion of natural forest into jungle rubber systems may not only impact the microclimate conditions, but may likely alter also other environmental factors such as soil organic matter composition, which therefore alter the microbial and fungal community as well which in turn will influence the dead wood degradation. These findings are strongly supported by Guillaume et al (2015) who reported loss of soil organic C and soil organic N in the top soil of jungle rubber at the same study sites. The reduced soil organic matters give evidence that decreased stocks of dead wood in the jungle rubber may be one of the factors leading to reduced C and N input to the soil.…”

Land use change decreases soil carbon stocks in Tibetan grasslands

“…2c) due to C depletion by enhanced decomposition. The relationship between δ 13 C and the logarithm of C content can reflect SOC turnover (Garten 2006;Guillaume et al 2015). In this study, the steeper slope of cropland than that of Kobresia pasture in the top 15-cm depth demonstrates increased decomposition (Fig.…”

“…The standard errors of means are presented in figures. Two-way analysis of variance (ANOVA) was used to estimate the effect of land use and soil depth on SOC, total N, microbial biomass C and N, as well as soil δ 13 C and δ 15 N. One-way ANOVA was used to estimate the effect of land use on stocks of SOC and microbial biomass C. Linear regression was used to correlate SOC and total N, microbial biomass N or soil δ 13 C. Linear regression was also used to correlate log SOC% and soil δ 13 C for each land use type for estimation of SOC turnover (Garten 2006;Guillaume et al 2015), as well as to assess the increase of δ 13 C (Δδ 13 C) and the decrease of SOC (ΔSOC) caused by land use changes from grassland to cropland or Elymus pasture. All statistical analyses were performed with SPSS 16.0 software (SPSS Inc., Chicago, IL, USA).…”

“…Consequently, even small changes in the soil organic C (SOC) pool would have large effects on atmospheric CO 2 and produce potential feedbacks to climate (Kirschbaum 2004;Heimann and Reichstein 2008;Cotrufo et al 2011;Stockmann et al 2013). Land use change is one of the most important factors strongly affecting SOC stocks and dynamics on earth (Jendinson et al 1991;Stockmann et al 2013;Guillaume et al 2015). Therefore, understanding how land use changes affect SOC dynamics is important to clarify feedbacks to climate (Stockmann et al 2013).…”

“…Consequently, isotopic enrichment occurs and reflects increased decomposition of soil organic matter. Therefore, we combined direct measurements of SOC with soil δ 13 C and δ 15 N as well as microbial biomass C and N contents to analyze the mechanisms of C and N losses (Guillaume et al 2015). To achieve more detailed information regarding the effects of land use on SOC, we analyzed soil samples at 5-cm intervals up to 30-cm depth.…”