Zhang Qing, Li Jiwen, Zhang Shujun, Li Yonggang, Wu Nan, Zhou Xiaobing, Yin Benfeng, Zhang Yuanming
State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, China.
Key Laboratory of Crop Nutrition and Fertilization, Ministry of Agricultural/Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, China.
Front Plant Sci. 2023 Mar 6;14:1137754. doi: 10.3389/fpls.2023.1137754. eCollection 2023.
The biological soil crust, a widespread phenomenon in arid and semi-arid regions, influences many ecological functions, such as soil stability, surface hydrology, and biogeochemical cycling. Global climate change has significantly altered winter and spring freeze-thaw cycles (FTCs) in mid and high-latitude deserts. However, it is unclear how these changes will affect the biological soil crust and its influence on nutrient cycling and soil enzyme activity.
We conducted this study in the Gurbantunggut Desert, a typical temperate desert, using the moss crust as an example of an evolved biological soil crust. Simulating the effects of different FTC frequencies (0, 5, and 15 times) on soil carbon, nitrogen, phosphorus-related nutrients, and extracellular enzyme activities allowed us to understand the relationship between soil environmental factors and nutrient multifunctionality during FTC changes.
The results showed that recurrent FTCs significantly increased the accumulation of carbon and phosphorus nutrients in the soil and decreased the effectiveness of nitrogen nutrients. These changes gradually stabilized after 15 FTCs, with available nutrients showing greater sensitivity than the previous full nutrient level. FTCs inhibited carbon, nitrogen, and phosphorus cycle-related hydrolase activities and promoted carbon cycle-related oxidase activities in the crust layer. However, in the 0-3 cm layer, the carbon and phosphorus cycle-related hydrolase activities increased, while peroxidase and urease activities decreased. Overall, the nutrient contents and enzyme activities associated with the carbon, nitrogen, and phosphorus cycles were lower in the 0-3 cm layer than in the crust layer. In addition, the multifunctionality of nutrients in the soil decreased after 15 FTCs in the crust layer and increased after 5 FTCs in the 0-3 cm layer. Structural equation modeling showed that FTC, soil water content, pH, available nutrients, and extracellular enzyme activity had opposite effects on nutrient multifunctionality in different soil layers. The change in nutrient multifunctionality in the crust layer was primarily caused by changes in total nutrients, while soil water content played a greater role in the 0-3 cm layer. Regardless of the soil layer, the contribution of total nutrients was much higher than the contribution of available nutrients and extracellular enzyme activity. In conclusion, it is essential to consider different soil layers when studying the effects of global climate change on the nutrient cycling of the biological soil crust.
生物土壤结皮是干旱和半干旱地区普遍存在的现象，影响着许多生态功能，如土壤稳定性、地表水文学和生物地球化学循环。全球气候变化显著改变了中高纬度沙漠地区冬春季节的冻融循环（FTC）。然而，目前尚不清楚这些变化将如何影响生物土壤结皮及其对养分循环和土壤酶活性的影响。
我们以古尔班通古特沙漠（典型的温带沙漠）为例，以苔藓结皮作为已演化的生物土壤结皮的代表进行了本研究。通过模拟不同冻融循环频率（0次、5次和15次）对土壤碳、氮、磷相关养分及胞外酶活性的影响，来了解冻融循环变化过程中土壤环境因子与养分多功能性之间的关系。
结果表明，反复的冻融循环显著增加了土壤中碳和磷养分的积累，降低了氮养分的有效性。这些变化在15次冻融循环后逐渐稳定，速效养分比之前的全养分水平表现出更高的敏感性。冻融循环抑制了结皮层中与碳、氮和磷循环相关的水解酶活性，促进了与碳循环相关的氧化酶活性。然而，在0-3厘米土层中，与碳和磷循环相关的水解酶活性增加，而过氧化物酶和脲酶活性降低。总体而言，0-3厘米土层中与碳、氮和磷循环相关的养分含量和酶活性低于结皮层。此外，结皮层在经历15次冻融循环后土壤养分多功能性降低，而0-3厘米土层在经历5次冻融循环后土壤养分多功能性增加。结构方程模型表明，冻融循环、土壤含水量、pH值、速效养分和胞外酶活性对不同土层的养分多功能性有相反的影响。结皮层养分多功能性的变化主要由总养分的变化引起，而土壤含水量在0-3厘米土层中起更大作用。无论土层如何，总养分的贡献远高于速效养分和胞外酶活性的贡献。总之，在研究全球气候变化对生物土壤结皮养分循环的影响时，考虑不同土层至关重要。
