Carbon sequestration potential in perennial bioenergy crops: the importance of organic matter inputs and its physical protection

Abstract

To date, only few studies have compared the soil organic carbon (SOC) sequestration potential between perennial woody and herbaceous crops. The main objective of this study was to assess the effect of perennial woody (poplar, black locust, willow) and herbaceous (giant reed, miscanthus, switchgrass) crops on SOC stock and its stabilization level after 6 years from plantation on an arable field. Seven SOC fractions related to different soil stabilization mechanisms were isolated by a combination of physical and chemical fractionation methods: unprotected (cPOM and fPOM), physically protected (iPOM), physically and chemically protected (HC-ls + c), chemically protected (HC-ds + c), and biochemically protected (NHC-ds + c and NHC-ls + c). The continuous C input to the soil and the minimal soil disturbance increased SOC stocks in the top 10 cm of soil, but not in deeper soil layers (10-30; 30-60; and 60-100 cm ) presumably due to a higher C input from leaf-litter. The conversion from an arable maize monoculture to perennial bioenergy crops increased the organic C associated to the most labile organic matter (POM) fractions, which accounted for 38% of the total SOC stock across bioenergy crops, while no significant increments were observed in more recalcitrant (silt-and clay-sized) fractions, highlighting that the POM fractions were the most prone to land-use change. The iPOM fraction increased under all perennial bioenergy species compared to the arable field. In addition, the iPOM was higher under woody crops than under herbaceous ones because of the additional C inputs from leaflitter that occurred in the former. Conversion from arable cropping systems to perennial bioenergy crops can effectively increase the SOC stock and enlarge the SOC fraction that is physically protected within soil microaggregates.

Factors influencing soil aggregation and particulate organic matter responses to bioenergy crops across a topographic gradient

“…Increases in unprotected POM-C pools were observed over the duration of this study in all cropping systems (Fig. 3), indicating the sensitivity of these pools to changes in land use (Chimento et al, 2014). The strong relationship between root productivity and frPOM-C (Fig.…”

“…Many prior studies have investigated impacts of land cover (John et al, 2005;Leifeld and Kögel-Knabner, 2005;Marquez et al, 1999;Yamashita et al, 2006;Chimento et al, 2014), and topography (Garten and Ashwood, 2002;Cambardella et al, 2004;Hook and Burke, 2000) on POM-C pools. Of these, few have quantified the impacts on functionally different (protected vs. unprotected) POM fractions.…”

“…Maximizing this C storage benefit necessitates understanding how cropping systems that produce bioenergy feedstocks alter belowground C cycling across agroecosystems (Anderson-Teixera et al, 2013;Blanco-Canqui, 2010;Tiemann and Grandy, 2015). Perennial crops, such as switchgrass and short-rotation woody crops, are expected to influence carbon cycling and the overall potential environmental benefits of bioenergy much differently relative to annual crops (Chimento et al, 2014;Robertson et al, 2011), with the realized improvements to ecosystem functioning likely dependent on the location of crops within landscapes (Dale et al, 2011). Sites poorly suited for annual row crops due to edaphic limitations or susceptibility to erosion and flooding have the potential to produce significant biomass from perennial vegetation (Campbell et al, 2008;Gelfand et al, 2013;Tilman et al, 2006).…”

Ideas and perspectives: Can we use the soil carbon saturation deficit to quantitatively assess the soil carbon storage potential, or should we explore other strategies?

“…Moreover, several authors observed that increases in SOC stocks following a land management change were mostly due to an increase in sand-size particulate organic matter (e.g. Feng et al, 2014;Cardinael et al, 2015;Chimento et al, 2016). As a result, a significant part of SOC stock increase induced by the implementation of farming methods known to promote soil carbon stocks is expected to occur mostly in the soil >20 µm fraction.…”

Yields and quality of biomasses and grain in Cynara cardunculus L. grown in southern Italy, as affected by genotype and environmental conditions

“…Anyway, in this three years period, the cardoon cropping system didn't show the positive effect on C storage into the soil that we could expect considering the absence of soil tillage. On the contrary other perennial crops, such as giant reed, showed a soil C increase that was considered an effect of the contribution of leaf fall, root exudates and turnover (Fagnano et al, 2015;Harper et al, 2012;Felten and Hemmerling, 2012;Chimento et al, 2016).…”