Soil nutrients increase long‐term soil carbon gains threefold on retired farmland

Abstract

Abandoned agricultural lands often accumulate soil carbon (C) following depletion of soil C by cultivation. The potential for this recovery to provide significant C storage benefits depends on the rate of soil C accumulation, which, in turn, may depend on nutrient supply rates. We tracked soil C for almost four decades following intensive agricultural soil disturbance along an experimentally imposed gradient in nitrogen (N) added annually in combination with other macro‐ and micro‐nutrients. Soil %C accumulated over the course of the study in unfertilized control plots leading to a gain of 6.1 Mg C ha−1 in the top 20 cm of soil. Nutrient addition increased soil %C accumulation leading to a gain of 17.8 Mg C ha−1 in fertilized plots, nearly a threefold increase over the control plots. These results demonstrate that substantial increases in soil C in successional grasslands following agricultural abandonment occur over decadal timescales, and that C gain is increased by high supply rates of soil nutrients. In addition, soil %C continued to increase for decades under elevated nutrient supply, suggesting that short‐term nutrient addition experiments underestimate the effects of soil nutrients on soil C accumulation.

Increased precipitation and nitrogen addition accelerate the temporal increase in soil respiration during 8‐year old‐field grassland succession

“…Therefore, N addition can quickly promote growth of dominant grass species (Xia & Wan, 2008) and accelerate the plant community composition shift from grass–forb codominance to grass dominance. The greater increase in grass biomass by N addition may overwhelmingly offset the decrease in forb biomass, and finally result in an increased litter input and thus soil organic C supply for soil microbial respiration, which is consistent with a previous study (Seabloom et al, 2021). The positive relationships of the changes in soil respiration with those in the heterotrophic component (Figure 5b) and the path analyses under the N addition treatment (Figure 7a,b) in this study provided further supports for the above arguments.…”

“…Nitrogen addition usually increases ecosystem productivity (Fay et al, 2015) and stimulates soil C recovery in grasslands following disturbance (Fornara & Tilman, 2012; Seabloom et al, 2021), which can subsequently affect soil C release (Zhou et al, 2014). Nevertheless, plant functional groups with inherent differences in N‐use strategy may exacerbate competitive interactions (Midolo et al, 2019) and mediate the successional processes (Kimball et al, 2014; Seabloom et al, 2020).…”

“…However, no change in plant composition and relative biomass under N addition after 4 years of succession is observed in a semi‐arid grassland (Bai et al, 2015). The inconsistent findings of N addition effects on aboveground and belowground processes during community succession, including acceleration (Pickett et al, 2009; Seabloom et al, 2021; Sparrius et al, 2013), delay (Carson & Barrett, 1988; Inouye & Tilman, 1995; Kimball et al, 2014; McLendon & Redente, 1992; Seabloom et al, 2020), and neutral change (Bai et al, 2015; Huberty et al, 1998), pose major challenges in predicting how plant community change affects temporal variation of soil respiration under N addition.…”

“…Nitrogen addition usually increases ecosystem productivity (Fay et al, 2015) and stimulates soil C recovery in grasslands following disturbance (Fornara & Tilman, 2012;Seabloom et al, 2021), which can subsequently affect soil C release (Zhou et al, 2014).…”

Soil carbon stocks in temperate grasslands differ strongly across sites but are insensitive to decade‐long fertilization

“…Enhanced soil C storage may occur only when macro-and micronutrients are applied in concert (Crowther et al, 2019;Fornara et al, 2013;Kaspari, 2021;Pastore et al, 2021;Seabloom et al, 2021b), consistent with the notion that nutrient co-limitation is common across grasslands (Fay et al, 2015;Harpole et al, 2011). Moreover, fertilization effects on soil C storage may be particularly weak in mineral soils in both forests and grasslands.…”