Effects of different ecological transition patterns on soil aggregate stability and cementing substances in jujube economic forest in the Lvliang Mountain

The ecological transformation of abandoned jujube forests in the Lvliang Mountain is an important part of the ecological restoration of the Loess Plateau. Soil aggregates are the basic unit of soil structure, and their composition and stability are important indicators for evaluating soil quality, and soil cementing material is an important material basis for the formation of aggregates. This study reveals the formation mechanism of soil aggregates by investigating the changes in the content of soil aggregates and cementing material in different ecological transition modes of red jujube economic forests in the Lvliang Mountain. Taking jujube forest abandonment as the control (CK), four different ecological transition model plots were selected as the research objects, including Medicago sativa (AL), medicinal herbs (MM), Pinus tabuliformis (CP) and Platycladus orientalis (PO), the distribution proportion and stability characteristics of water-stable aggregates with particle size <0.053、0.053~0.25、0.25~2 mm and >2mm were analyzed. The contents of six aggregate organic cementing substances and inorganic cementing material calcium carbonate were determined in soil organic carbon, fulvic acid, humic acid, polysaccharide, total glomalin-related soil protein and the easily extractable glomalin-related soil protein. The response relationship between the distribution ratio and stability of aggregates and aggregate cemented substances was explored through redundancy analysis. The results showed that: 1) Compared with CK, ecological transition increased the content of >2 mm and 0.25~2 mm agglomerates, with increments of 1.61% to 5.29% and 1.59% to 5.45%, In addition, the mean weight diameter and geometric mean diameter of the agglomerates also increased, with increments of 0.05 to 0.16 mm and 0.02 to 0.08 mm, respectively, and the CP mode performed best; the rate of agglomerate destruction decreased, ranging from 24.85% to 66.15%. 2) Compared with CK, the contents of six organic cementing substances were increased by the four ecological transition modes, and the content of calcium carbonate in inorganic cementing substances was reduced. 3) The explanation rates of humic acid and easily extractable glomalin-related soil protein for the distribution proportion and stability of aggregates were 59.0% and 14.8%, respectively, reaching a significant level (P<0.05), and the contribution rate of humic acid was the highest, which was 71.0%. In summary, different modes of ecological transformation improved the stability of soil aggregates and the content of organic cementing materials, among which the CP mode had the best effect, and humic acid was the most significant cementing material affecting the distribution ratio and stability of soil aggregates. The results of the study are important for guiding the ecological transformation of abandoned jujube forests and promoting ecological restoration in the Loess Plateau region.