Major contribution of grass roots to soil carbon pools and CO 2 fluxes in a mesic savanna
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Major contribution of grass roots to soil carbon pools and CO2 fluxes in a mesic savanna Edmund February & Johanna Pausch & Steven I. Higgins
Received: 14 February 2020 / Accepted: 24 July 2020 # Springer Nature Switzerland AG 2020
Abstract Aims There is a trend of increasing woody biomass in tropical savannas. Here we ask what effect this increase may have on soil carbon pools and fluxes. Methods Using a field experiment we determine the amount of soil carbon directly under grasses, a juvenile tree among grasses and a juvenile tree with no grasses. We also measure CO2 efflux at the soil surface and use gas wells to extract CO2 from several soil depths. Results Our results show that grasses contribute substantially more than trees to both soil carbon and soil respiration. Grasses also make a disproportionate contribution to the δ13C value of SOC in the tree only treatments. The surface gas efflux data show that soil respiration increased with an increase in volumetric soil moisture and temperature and plots with both grasses and trees had higher respiration rates than plots with Responsible Editor: Simon Jeffery Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11104-020-04649-3) contains supplementary material, which is available to authorized users. E. February (*) Department Biological Sciences, University of Cape Town, Private bag, Rondebosch 7701, South Africa e-mail: [email protected] J. Pausch Agroecology, University of Bayreuth, Universitätsstr. 30, Bayreuth 95440, Germany S. I. Higgins Plant Ecology, University of Bayreuth, Universitätsstr. 30, Bayreuth 95440, Germany
trees only or with grasses only. Conclusions The highest soil respiration is in the top 20 cm of the soil with grasses the primary contributors to both δ13CSOC and δ13CR. Any increase in woody biomass will result in a decline in SOM turnover and nitrogen mineralization rates resulting in higher SOC pools. The associated increases in SOC and above ground biomass will however be associated with negative economic and biodiversity impacts. Keywords Savanna . Soil respiration . CO2 flux . Soil Organic Carbon.
Introduction Tropical savanna is typically composed of a discontinuous layer of C3 trees interspersed among a continuous layer of C4 grasses (Frost et al. 1986). Changes in the relative proportion of these two plant life forms may alter savanna structure considerably from a few scattered trees as in the Kalahari to the well wooded Miombo of Central Africa (Chidumayo 1990; Dean et al. 1999). The combination of C3 trees and C4 grasses can be found across a rainfall gradient from around 280 mm in the southern Kalahari in southern Africa to 2500 mm in the South American Llanos (Lehmann et al. 2014). The defining feature for these ecosystems however is that this rainfall is distinctly seasonal with a 5–8 month warm wet season followed by a cool dry season when soil moisture may drop below wilting point (February and Higgins 2016). The high moisture deficit
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