Comparison of ecosystem-scale carbon fluxes at agroforestry and adjacent monocropping sites in Germany

Abstract Agroforestry (AF) systems, such as short rotation alley-cropping systems are considered to improve carbon (C) sequestration compared to conventional land use without trees, while also providing environmental co-benefits, such as improved biodiversity and reduced soil erosion. Supporting ecosystem-scale measurements of C uptake are, however, largely lacking. In this study, we aim to quantify the continuous C uptake of four temperate AF and four adjacent monocropping (MC) sites in northern Germany for over two years using lower-cost eddy covariance (LC-EC) measurements. Based on the LC-EC measurements we showed that the net ecosystem production (NEP) of the AF sites was significantly higher compared to the adjacent MC. At the grassland site the AF NEP was on average 444 g C $$\hbox {m}^{-2}\,\hbox {y}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mtext>m</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace/> <mml:msup> <mml:mtext>y</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> higher compared to the adjacent MC across years. At the three cropland sites the differences between AF and MC varied from year to year, but on average the NEP was 37–205 g C $$\hbox {m}^{-2}\,\hbox {y}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mtext>m</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace/> <mml:msup> <mml:mtext>y</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> higher at the AF sites. The gross primary production and ecosystem respiration were between 151–390 and 114–185 g C $$\hbox {m}^{-2}\,\hbox {y}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mtext>m</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace/> <mml:msup> <mml:mtext>y</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> higher at the AF cropland sites, and 291 and 735 g C $$\hbox {m}^{-2}\,\hbox {y}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mtext>m</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace/> <mml:msup> <mml:mtext>y</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> lower at the AF grassland site compared to the adjacent MC, respectively. With our comparison study, it was shown that the harvest of the tree strips did not seem to systematically affect the ecosystem-scale C uptake of the AF. Finally, on the long-term it is expected that the AF sequester more C compared to the MC sites, due to the more complex landscape and additional litter fall at the AF.