DataSheet1_Soil extracellular enzyme activity reflects the change of nitrogen to phosphorus limitation of microorganisms during vegetation restoration in semi-arid sandy land of northern China.docx

Soil extracellular enzyme activity (EEA) and enzyme stoichiometry are indicators of soil nutrient availability and microbial substrate limitation. However, the patterns in soil enzyme activities and stoichiometry, and their key drivers remain unclear during vegetation restoration in degraded sandy land. Here, soil ecosystems at five restoration stages of degraded sandy land were selected for investigation and we quantified the microbial nutrient limitation using EEA stoichiometry. The average C:N:P ratio for the nutrient-acquisition enzymes was 1:0.88:0.86, which differed from the global ratio of 1:1:1, indicating stronger microbial C limitation than N or P limitation. With vegetation restoration, the enzyme N:P ratio decreased, but the angle term used in vector analysis increased, indicating that the restored grassland transitioned from N-restricted (angle < 45°) to P-restricted (angle > 45°). Plant C inputs increased the soil nutrient content and significantly decreased the microbial C and N limitation but increased P limitation due to nutrient competition between plants and soil microorganisms. Decreased soil water levels caused by vegetation transpiration may have shifted the microbial limitation from N to P. The decreased fungi:bacteria ratio strengthened the microbial C and N or P limitations. On the basis of these findings, as measures to alleviate the associated nutrient limitations, we would recommend supplementation with phosphorus in the potential and slight stages of rocky desertification and the supplementary application of nitrogen in the moderate and severe stages during the restoration of degraded sandy ecosystems.

土壤细胞外酶活性（EEA）及其化学计量学构成了评估土壤养分可利用性和微生物底物限制的指标。然而，在沙质退化土地植被恢复过程中，土壤酶活性和化学计量学的模式及其主要驱动因素尚不明确。本研究选取了五个不同恢复阶段的沙质退化土地土壤生态系统进行调查研究，并利用EEA化学计量学量化了微生物养分限制。营养获取酶的平均碳氮磷比（C:N:P）为1:0.88:0.86，与全球平均值1:1:1存在差异，表明微生物碳限制强于氮或磷限制。随着植被恢复，酶的氮磷比下降，但矢量分析中使用的角度值上升，这表明恢复后的草地已从氮限制（角度<45°）转变为磷限制（角度>45°）。植物碳输入的增加提升了土壤养分含量，显著降低了微生物碳和氮限制，但同时也因植物与土壤微生物之间的养分竞争而加剧了磷限制。植被蒸腾作用导致的土壤水分降低可能将微生物限制从氮转变为磷。真菌与细菌比值的下降强化了微生物碳、氮或磷限制。基于这些发现，为缓解相关的养分限制，我们建议在潜在的轻微沙漠化阶段补充磷，在中等至严重沙漠化阶段恢复退化沙质生态系统时补充氮肥。