# 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
In boreal forests, mosses promote NH4\({}^{+}\)-N accumulation, while lichens increase NO3\({}^{-}\)-N content in soil [28]. In the Loess Plateau area of China, researchers have not only found that the soil AN content under the moss layer is higher [71] but also that the artificial cultivation of the moss crust can directly increase soil AN [72]. However, in subpolar birch forests, moss causes a decrease in soil temperature and prevents atmospheric nitrogen deposition into the soil, resulting in decreases in soil nitrogen availability, limiting nitrogen cycling, and ultimately leading to a decrease in soil NH4\({}^{+}\)-N and DON content [29]. 2.3 Effects of Cryptogam on the Content and Availability of Phosphorus, Potassium and Micronutrients in Soil  
P in soil mainly comes from the weathering of parent material [73], and the dynamics of P in soil mainly include weathering generation, absorption, and utilization by plants, in addition to adsorption and loss [74]. Similar to P, K in soil is also mainly derived from the weathering of the parent material, but the difference is that K in soil is more easily lost via precipitation than P [75]. In desert ecosystems, due to the lack of parent material, lichen or moss crust usually increases TOC and TN, but not TP and TK, contents in soil [14; 15; 16; 17; 26; 76]. Only several studies have found that biological soil crust increases soil TP [18; 27] and TK [19; 23] contents. In rocky desertification areas (including karst areas) with sufficient parent material, moss crust is found to increase soil TP [20; 21; 61] and TK [22] contents. In both stand and burned areas of boreal forest, moss accelerate the decomposition rate of vascular plant litter but reduce the loss of P in litter [57; 65], thereby alleviating the loss of P in the ecosystem and facilitating its accumulation in the soil. Moss layers are also found to be conducive to the accumulation of soil TP and TK in grasslands [77]. In the face of erosion, soil covered by moss also retains a higher TP and TK content [67]. In general, cryptogam can promote the accumulation of TP and TK in soil, possessing a better-promoting effect than that of lichen [23]. These studies suggest that the effect of cryptogams on soil P and K content is mainly achieved by influencing the weathering of the parent material and the decomposition of litter. Cryptogams have more influence on soil P and K availability than on TP and TK. In desert scenarios, lichen and lichen crust significantly increase soil AP [15; 17; 26] and AK contents [18; 27]. However, this effect is limited to the topsoil (no more than 5 cm deep). In addition, moss has been found to increase soil PO\({}_{4}\)\({}^{3-}\)-P content in deserts [76]. Other studies have shown that in semi-arid deserts, the moss layer accumulates some AP in the dry season. When the rainy season comes, this part of AP will be leached into the soil by precipitation [31], resulting in an increase in soil AP content. However, in sandy land, moss can only increase AK content and decrease AP content in surface (0-2 cm) soil [14]. In drylands, both lichen and moss have enhanced soil acid phosphatase activity [52], suggesting that both of them have the potential to improve soil P availability. Moss also enhances the availability of soil P and K in rocky desertification areas [22; 78]. Mosses and lichens have been found to improve soil P availability in grasslands and high-latitude areas [54; 77]. To sum up, in most ecosystems, cryptogams play a role in improving the content and availability of soil C, N, P, and K (Table 2), and there are important interactions between these elements in the soil. For example, cryptogam plants lead to increases in soil N content and availability, elevating plant primary productivity and providing more organic carbon sources for the soil. However, soil N has a complex effect on C accumulation. Some studies found that more N would inhibit soil C accumulation [79], while others found that soil N had a positive effect on soil C accumulation [80], or otherwise no effect [81].