Humus Chemistry—Genesis, Composition, Reactions

Effects of Litterfall on the Accumulation of Extracted Soil Humic Substances in Subalpine Forests

“…We found that soil HA content and HA/FA ratio significantly decreased in mixed forests after 1 year of continuous litterfall input, but FA content was not affected by litter input. Moreover, the reduction in the soil HA content of mixed forest was more than total extracted humus, which may be due to the conversion of HA and FA (Stevenson, 1994) or the priority synthesis of FA in the synthesis of humus (Dou et al, 2007;Ni et al, 2014Ni et al, , 2016. The effect of seasonal litterfall input on the soil HA was similar to that of the total extracted humus (Figure 4).…”

“…Litterfall transfers approximately one third of the global annual C uptake (approximately 18 Pg•C•year −1 ) to soil surface (Grace, 2004;Malhi et al, 2011), although the amount of this C that is sequestered in soils is not fully understood. Humic substances in the soil are in a dynamic process of continuous decomposition and synthesis (Stevenson, 1994), and the amount depends on the relative amounts of the formation and degradation of humic substances (Dou et al, 2007). Our results partly supported our hypothesis that retained litter may decrease soil humic substances content, but this effect may be regulated by litter types and litter production in different periods.…”

“…Litterfall had no significant effect on the HA/FA ratios in the coniferous and mixed forests among the different periods, while litterfall significantly decreased the ratio in the broadleaved forest in the early growing season. This result might be due to the fact that litterfall promoted the conversion between HA and FA (Stevenson, 1994). Furthermore, litterfall had no significant effect on the content of soil humic substances in winter.…”

“…Humus is the main component of soil organic matter (Kogel-Knabner, 2000) and is important for soil fertility and nutrient cycling (Ponge, 1999;Ono et al, 2011;Chertov and Komarov, 2013). As a basic carrier of nutrients and carbon, forest litterfall plays an essential role in the formation of soil humus (Stevenson, 1994;Prescott et al, 2000;Neumann et al, 2018). Different kinds of litterfall have different chemical compositions and qualities that might determine the development processes of humus in soil (Wei et al, 2018;Zanella et al, 2018a,b).…”

“…High temperatures and year-round low temperatures will prevent the accumulation of soil HA (Wen, 1984). Studies have shown that climate, substrate quality, and the soil environment determine whether the formation of humic substances is dominated by HA or FA (Stevenson, 1994) due to their special properties of acid solubility and alkali solubility (Prescott et al, 2000;Ponge and Chevalier, 2006). However, there are still many unclear factors regarding the formation and transformation of humic substances.…”