# The Role of Cryptogams in Soil Property Regulation and Vascular Plant Regeneration: A Review
## 2 Effects of Cryptogam on Soil Properties
### Effects of Cryptogam on Soil Fertility and Nutrients Availability
#### 2.2.2 Effects of Cryptogam on Soil Nitrogen Content and Availability  
Similar to soil C, N in soil is also mainly derived from living plant secretions and dead residues [51], and also somewhat from atmospheric N deposition [60]. Thus, similar to soil C, in harsh environments such as deserts [15; 18], sandy lands [14], drylands [52], \begin{table}
\begin{tabular}{c c c c c} \hline
**Geomorphic Feature** & **Cryptogam Species** & \begin{tabular}{c} **Effects of Cryptogam on** \\ **Soil Water Content** \\ \end{tabular} & \
\begin{tabular}{c} **Annual** \\ **Precipitation (mm)** \\ \end{tabular} & **References** \\ \hline Alpine stepe & Lichen–moss crusts and moss crusts & Decreasing & 403.8 & [6] \\ Wind–Water Erosion & Cyanobacteria and moss biocrusts & Decreasing & 409 & [7] \\ Crisscross Region & & & & \\ Semiarid watershed on & & & & \\ the Loess Plateau & & & & \\ The Loess Plateau & & & & \\ Sandland & & & & \\ The Loess Plateau & & & & \\ \multicolumn{4}{l}{} \\ \multirow{2}{*}{Haleakala’s crater} & \multirow{2}{*}{
\begin{tabular}{c} _Grimnia toraquata_ \\ \end{tabular} } & \multirow{2}{*}{Increasing} & \multirow{2}{*}{More than 600} & \multirow{2}{*}{[8]} \\  & & & & \\ \multicolumn{4}{l}{} \\ \multirow{2}{*}{Sand dune} & \multirow{2}{*}{Green algae crust, lichen–moss mat} & \multirow{2}{*}{Increasing or having} & \multirow{2}{*}{1100} & \multirow{2}{*}{[9]} \\  & and moss mat & & & \\ \hline \end{tabular}  
\end{table} 
Table 1: Cont. karts [61; 62], waste tailings [53], and high-altitude [55] regions, cryptogam secretions and dead residues are the most important sources of soil N. Therefore, the soil covered by cryptogams has a higher TN content. In forest ecosystems, due to the absorption and retention of N by moss, the soil will reduce the acquisition of N in a short period of time, but this part of N will still be returned to the soil after the death of moss [63]. As such, from a long-term perspective, moss reduces the loss of N in the ecosystem and is conducive to the accumulation of soil N. In addition, in nitrogen-poor boreals, feather moss secrete chemicals to attract nitrogen-fixing cyanobacteria as a source of N [64]. When feather mosses die and decompose, the obtained N is released into the soil. Studies of boreal forest burned areas have found that moss layers accelerate the decomposition rate of vascular plant litter and cause more N to be retained in the litter [65], promoting N accumulation in ecosystems. In urbanized areas, moss can absorb excess N in the air and soil, forming a small N sink to prevent N loss or N pollution [66]. In the face of environmental erosion, moss-covered soils can maintain a higher TN content [67]. In addition to the effects on soil TN content, cryptogam also exerts important effects on the transformation, availability, and form of N in soil. In desert areas, moss crust contributes to the transformation of soil N, resulting in increased contents of NH4\({}^{+}\)-N and NO3\({}^{-}\)-N in the soil, but lichen crust does not improve the transformation of N [16; 25]. In addition, some studies have found that the influence of moss crust on the content of various forms of N in the soil in desert areas is regulated by water conditions. In the case of drought, it leads to the accumulation of NH4\({}^{+}\)-N. Conversely, in humid environments, it increases the content of NO3\({}^{-}\)-N in the soil [68]. In karst areas, in addition to increasing soil TN, NH4\({}^{+}\)-N, and NO3\({}^{-}\)-N contents, moss crust can also significantly increase urease activity, soil microbial biomass, and diversity [61]. If the moss crust is destroyed and removed, this positive effect quickly fades [20; 21]. This suggests that moss has the potential to increase soil N availability in karst areas. In temperate forests, moss have been found to favor soil NH4\({}^{+}\)-N accumulation but reduce soil nitrate nitrogen content [69], and the effect of moss on soil nutrient content is strongly influenced by seasons (monsoon season and winter seasons are significantly different) [70].