Abstract:

Soil is the fundamental medium of terrestrial ecosystems and a key element in maintaining vegetation growth, nutrient cycling, and ecological stability. It not only provides support and water and nutrient sources for plant roots, but also serves as an important carrier for biogeochemical cycles and energy conversion. The changes in soil quality directly affect the productivity, structural stability, and response capacity of the ecosystem to external disturbances. In recent years, the saline-alkali land problem, which is widespread in arid and semi-arid areas, has become a major environmental obstacle restricting regional ecological restoration, agricultural production, and sustainable land use. The accumulation of salt could damage soil structure, inhibit microbial activity, and reduce nutrient availability, thereby leading to soil degradation, restricted vegetation growth, and a decline in ecosystem function. In this context, scientifically assessing the soil quality of saline-alkali land, identifying key limiting factors, and revealing their ecological regulation mechanisms are of great theoretical and practical significance for formulating land improvement measures, enhancing ecosystem service functions, and promoting regional ecological restoration. However, traditional soil quality assessment systems often relied solely on physical, chemical, and biological indicators, focusing on the quantitative characterization of internal soil properties, while neglecting the role of soil as a core component of the ecosystem in maintaining ecological services such as the carbon cycle, water retention, and habitat supply. This single-dimensional assessment method was difficult to comprehensively reflect the ecological essence of soil functions and their response characteristics to environmental changes. Therefore, constructing a comprehensive soil quality assessment framework that could take ecosystem service functions into account is of significant scientific value for revealing the mechanism of ecological degradation in saline-alkali land and promoting sustainable land management in arid areas. In this study, the Kekeya saline-alkali land in southern Xinjiang was selected as the study area. Ecosystem services, including habitat quality, carbon sequestration capacity, soil retention, and water yield services, were introduced into the regional soil quality evaluation system, and the physical, chemical, biological, and ecological attributes of the soil were comprehensively considered. Based on the analysis of each index, the minimum data set for soil quality assessment was constructed using principal component analysis and correlation screening. The magnitude and spatial distribution of the soil quality index (SQI) were calculated and revealed, and the interrelationship between soil quality and vegetation characteristic index was explored. The specific research results showed that: 1) the spatial distribution of regional habitat quality services and carbon sequestration capacity services was relatively similar. In the regions with relatively high vegetation coverage in the central area, the habitat quality and carbon sequestration values were relatively high, while in the unused land, they were relatively low. Soil retention service was relatively high in low-lying areas and relatively low in flat areas. The distribution of regional water production service shared certain similarities with the distribution of precipitation, generally showing a higher distribution in the west and a lower distribution in the east. In addition, the average total amount of total soluble salts in the regional soil was 56.73 g∙kg⁻¹, and the average pH value was 8.20, indicating a relatively strong soil salinity and alkalinity. The soil moisture content in the region was less than 20%, and the overall situation was relatively dry. The diversity of soil bacteria in the region was approximately 10 times that of fungi. It was indicated that in the saline-alkali land of arid regions, the diversity of soil bacteria was much higher than that of fungi. 2) Among all the indicators, the correlation coefficient between the soil organic matter and the total humus carbon was the highest. The cumulative contribution rate of the principal components reached 82.36%. The minimum dataset for soil quality assessment included carbon sequestration, soil retention, water yield, bulk weight, porosity, total nitrogen, potassium, pH, organic matter, and dissolved organic carbon ten indicators. Among them, the weight of organic matter was the highest (0.120), followed by total nitrogen (0.116), while the lowest weight was that of soil retention (0.085). It was indicated that soil organic matter and total nitrogen in the region were the main controlling factors of soil quality. Through calculation, it was found that the SQI in the region was generally low, with an average value of 0.28 and generally ranging from 0.20 to 0.30. The soil quality was relatively high in the middle, while it was relatively low in the west and east. 3) The spatial differentiation of various vegetation indicators in the region was also quite obvious. Among them, SQI had the most significant correlation with vegetation coverage (r=0.501). However, SQI did not show a significant correlation with other vegetation structure indices. It indicated that vegetation coverage could sensitively reflect changes in soil quality, while the response of vegetation community structure was relatively lagging. In addition, the spatial distribution of high SQI areas and high coverage areas in the region was also relatively consistent, revealing the positive feedback mechanism between soil and vegetation coverage. Vegetation improved the microclimate, promoted leaching of salts, and enhanced soil fertility, while the improved soil in turn promoted the recovery and stability of vegetation. In summary, in this study, a new framework for comprehensive evaluation of soil quality in saline-alkali land that integrates ecosystem services was established. Based on the traditional physical, chemical and biological index systems, it systematically introduces key ecosystem services such as habitat quality, carbon sequestration capacity, soil retention, and water yield, achieving a transformation from single element evaluation to comprehensive characterization of multi-dimensional ecological processes. The results clarify the dominant role of organic matter and total nitrogen in the evolution of soil quality, reveal the interaction mechanism among soil physical and chemical properties and ecological services, and elucidate the feedback relationship between soil quality improvement and vegetation restoration. This framework not only enriches the theoretical system of soil quality assessment in saline-alkali land, but also provides operational technical paths and scientific basis for the sustainable land use, ecosystem health assessment, and restoration of degraded ecosystems in arid and semi-arid areas. It has significant practical significance for the construction of regional ecological security patterns and the high-quality development of oasis ecosystems.

Key words: ecosystem services, saline-alkali land, soil quality assessment, principal component analysis, minimum data set, vegetation characteristics

摘要：

土壤是植被生长和生态系统健康的基础，开展盐碱地土壤质量评估对地区土地生产力提高和生态环境保护至关重要。该研究以南疆柯柯牙盐碱地为研究对象，将地区生态系统服务与土壤物理、化学和生物指标相结合，利用主成分分析和相关性分析法构建最小数据集对地区土壤质量进行评价，并探讨土壤质量与植被特征的相互关系。结果表明：地区生态系统服务具有明显的空间异质性。土壤水溶性盐总质量分数和pH分别为56.73 g∙kg⁻¹和8.20，土壤盐碱化程度较高。在各指标中，土壤有机质与腐殖质总碳量之间的正相关性最强。构建的土壤质量评价的最小数据集包括固碳量、土壤保持、产水量、容重、孔隙度、全氮、全钾、pH、有机质和溶解性有机碳等10个指标。其中，有机质权重最高，为0.120；产水量的权重最低，为0.085。地区土壤质量相对较差，土壤质量指数（SQI）平均值为0.28，总体位于0.20－0.30之间。土壤质量在中部相对较高，而在西部和东部相对较低。此外，在各植被特征中，SQI与植被覆盖度之间具有最显著的相关性，而SQI与Shannon-Wiener多样性指数、Simpson多样性指数和Pielou均匀度指数并未出现显著的相关性。该研究可为地区盐碱地的土壤质量提升与生态环境改善提供一定的参考。

关键词: 生态系统服务, 盐碱地, 土壤质量评价, 主成分分析, 最小数据集, 植被特征