Belowground Ecosystem Recovery During Grassland Restoration: South African Highveld Compared to US Tallgrass Prairie

Abstract

Conversion of cultivated land to grassland is globally practiced to reverse soil degradation, but belowground ecosystem response to restoration has never been compared between old and new world temperate grasslands. We used a chronosequence approach to model change in root biomass and quality (indexed by C:N ratio), microbial biomass and composition [indexed by phospholipid fatty acids (PLFAs)], soil aggregate structure, and soil C and N stocks in the South African Highveld and compared recovery of these variables to a grassland restoration chronosequence in the US tallgrass prairie. We hypothesized soil C recovery, and mechanisms promoting soil C and N accrual would be convergent between these distant temperate grasslands with similar growing season precipitation, history of cultivation, and undergoing restoration with C 4 -grasses. Total PLFA richness and concentrations of most microbial groups rose to represent uncultivated grassland in the highveld (similar to tallgrass prairie), but in contrast to tallgrass prairie, the fungi:bacteria ratio did not increase with restoration age. In the highveld, root biomass accumulation was lower, but root quality became more representative of the never-cultivated grassland than in restorations in tallgrass prairie. Soil aggregate recovery was slightly faster in tallgrass prairie, and the pattern of macroaggregate C recovery was divergent due to less depletion in cultivated soil and higher stock of C in the uncultivated soil relative to the highveld. More rapid restoration of total soil C and N stocks in the highveld was attributed to greater soil C saturation deficit at the onset of restoration, development of higher quality root systems that promote the microbial biomass and soil aggregation, and climate conditions (distinct periodicity of rainfall and high aridity) that likely impose more limitation to decomposition relative to the tallgrass prairie ecosystem.

Characterization of organic matter fractions in the top layer of soils under different land uses in Central‐Eastern Europe

“…Zhang et al. (); Baer, Bach, Meyer, Du Preez, and Six (); and Li et al. () reported that tillage is the main initial cause of SOC loss in arable lands.…”

Soil Organic Carbon Accumulation in Abandoned Croplands on the Loess Plateau

“…Different responses of carbon sequestration also appreciated within a time span of 30–40 years (Deng et al, ). Several studies have presented a linear model of SOC accumulation following the cessation of cultivation (McLauchlan et al, ; Deng et al, ), while an asymptotic curve has been reported for the secondary pasture soils in the South African Highveld and US tallgrass prairie (Baer et al, ; Preger et al, ). It is assumed that the surface soil is most affected by land use changes (Guo & Gifford, ; DeGryze et al, ) and after new plantations (Rodrigo Comino et al, , ).…”

More than a century of Grain for Green Program is expected to restore soil carbon stock on alpine grassland revealed by field 13 C pulse labeling

“…Several studies have estimated the time to restore degraded ecosystems or specific soil characteristics, and have predicted that it would take from 30 yr to more than 200 yr to restore nitrogen, total C or SOC (Baer et al, 2015;Craft et al, 2002), and 16-30 yr to restore SOC, total nitrogen, and phosphorus concentrations in a degraded alkaline grassland in Jilin, China . A synthesis of China's GfGP showed that the C stock tended to stabilize after 30 yr of conversion from cropland (Deng et al, 2014).…”

“…A synthesis of China's GfGP showed that the C stock tended to stabilize after 30 yr of conversion from cropland (Deng et al, 2014). The studies referred to were based on the assumption that soil characteristics would change at a constant rate using either the best fit exponential model of C changes measured during the history (9-15 yr) of restoration (Baer et al, 2015;Craft et al, 2002;Li et al, 2014) or a linear model for up to 30 yr of history (Deng et al, 2014).…”

“…However, previous studies of C stocks and sequestration have mostly been based on satellite images, existing large-scale datasets (Delang and Yuan, 2015) and estimates from inventories of different C pools Wang et al, 2002;Wang et al, 2011;Wang et al, 2005;Zhao et al, 2014). For example, the C sequestration or accumulation rate of soil has been estimated from C stocks in the plant-soil system and age after conversion from cropland, and has been used to calculate the time needed for recovery of the SOC stocks of degraded marsh (Craft et al, 2002), degraded alkaline grassland , and cultivated grasslands (Baer et al, 2015). To date, there have been no direct quantitative evaluations of photoassimilate partitioning and ecosystem C sequestration in grassland under the GfGP management, and there is little information available about the restoration time required by the GfGP, especially based upon the processes of photoassimilate partitioning.…”