# The Role of Cryptogams in Soil Property Regulation and Vascular Plant Regeneration: A Review
## 3 Effects of Cryptogam on Vascular Plants Regeneration
### Cryptogam Indirectly Affects Vascular Plant Regeneration by Regulating Soil Conditions  
A large number of studies have found that cryptogam affects the regeneration of vascular plants by regulating soil water status. In the absence of other water sources in areas with \(<\)500 mm annual precipitation, cryptogams can inhibit vascular plant regeneration by reducing soil water content. For example, in sandy environments, natural lichen and hyrophyte crusts limit the regeneration of _Artemisia ordosica_ by reducing soil water content [112]. Studies in semi-arid regions have also found that moss crust reduces soil water content, thereby inhibiting _Artemisia ordosica_ regeneration [4]. A study of _Echinops gmelinii_ regeneration in the Tengger Desert showed that, although moss crust significantly increased soil nutrient content (TOC, TN, TP, and TK), the regeneration capacity was still decreased, an effect caused by the moss-based redistribution of soil water [19]. However, when the annual precipitation was higher than 600 mm or there was artificial irrigation, cryptogams all had the effect of increasing soil water content to promote vascular plant regeneration. For example, in boreal forests with annual precipitation of more than 1000 mm, moss layers created a better soil water and temperature environment, which promoted the regeneration of _Abies balsamea_[38]. Researchers also found in evergreen broad-leaved forests that the moss layer is conducive to the accumulation of soil water and nutrients, thus promoting the regeneration of vascular plants [113]. In a study in the Tengger Desert in China, the same artificial irrigation was applied to soils with different biological crusting, and we found that moss crust improved the ability of soil to capture seeds. Due to the fact that moss crust limits water infiltration, the topsoil has a higher water content and promotes the germination of captured seeds. Moreover, the longer the moss crust development time, the better the soil water condition is and the higher the germination rate of seeds will be [114,115]. [PERSON] separately designed the arid and humid environmental conditions in the greenhouse experiment, finding that moss only promoted the growth of _Leptochloa crinite_ in the humid environment due to increasing soil moisture [68]. In greenhouse experiments, moss promoted the development of _Populus tremula_, _Salix apnea_, and _Betula pendula_ due to their ability to hold soil water for longer [37]. In addition, some studies found that the effect of moss on soil water content depends on the height and density of moss. In the mid-altitude mountain area with 437 mm of precipitation, excessive moss height (>5 cm) or density (>50%) will significantly reduce soil water content and inhibit vascular plant regeneration. However, low moss height or density will increase soil water content and promote vascular plant regeneration [34]. In addition, some studies have found that the effect of moss on soil water content depends on the height and density of the moss. In the mid-altitude mountain area with 437 mm of annual precipitation, excessively tall (>5 cm) or dense (>50%) moss will significantly reduce soil water content and inhibit vascular plant regeneration. However, low moss height or density will increase soil water content and promote vascular plant regeneration [34]. In addition, as mentioned above, cryptogams tend to lead to increased soil nutrient content and availability, providing more nutrients for vascular plant growth and promoting vascular plant regeneration. In greenhouse experiments, lichen crust promotes seed germination and the seedling growth of _Bromus tectorum_ by increasing soil fertility [17]. In a study of the regeneration of two native species and one exotic species in different bio-crusted soils, lichen and moss crusts 2343 were found to increase soil nutrient content and promote seedling growth [26]. In deserts, moss crust improved soil fertility and led to increased seed germination rates and seedling growth for _Leptochloa crinita_[68].