The aim of this study was to explore the soil microbial composition and diversity differences of Pinus sylvestris var. mongolica plantations with different stand ages, which has great significance in maintaining the microecological balance and sustainable management of soil.

The 8 a, 15 a, 30 a, 36 a, 42 a, 49 a and 56 a P. sylvestris plantations were selected as the research objects. By using Illumina MeSeq high-throughput sequencing technology, this article studied the community composition and diversity characteristics of soil bacteria and fungi in stands of different ages.

1) 32 phyla, 80 classes, 154 orders, 308 families, and 531 genera of bacteria were detected in the soil of P. sylvestris plantation of different stand ages. The dominant phyla were Actinobacteria (32.71%±3.74%), Proteobacteria (23.14%±2.13%), Acidobacteria (16.22%±2.75%), and Chloroflexi (9.00%±1.23%). The relative abundance of Firmicutes increased to 7.16% and 7.47% in 49 a and 56 a, respectively. After afforestation, the relative abundance of bacteria in the soil increased gradually with the increase of stand age and Crossiella spp. appeared in the P. sylvestris plantation.2) 6 phyla, 25 classes, 88 orders, 184 families, and 369 genera of fungi were detected in the soil of P. sylvestris plantation of different stand ages. The dominant phylum was Ascomycota (70.12%±11.17%). The relative abundance of Zygomycota increased to 15.20% and 23.42% in 49 a and 56 a, respectively. The evolution rate of soil fungi accelerated with the increase of stand age, and 42-56 a was the fastest, followed by 8 a-36 a, while ck was the slowest. The number of beneficial fungi in soil increased with the increase of stand age, but the mycorrhizal fungi gradually decreased. The number of unique OTUs in 8a was the largest, which was 1.46-2.54 times higher than that of other forest ages. The number of unique OTUs ranged from 67 to 71 in 36 a-49 a, while it was 41 in 56 a.

The soil microbial community structure of the P. sylvestris plantation in sandy land was gradually improved with the increase of stand age. However, the soil microbial diversity in soil decreased at the age of 56 years. The forest age of 56 may be the turning point of the decline of P. sylvestris plantation.

To study the change process of soil nutrients and enzyme activities in different forest ages of Pinus tabulaeformis in Horqin sandy land, so as to provide a reference for vegetation restoration in this area.

Taking the shifting sandy land as the control (0 a), the sand-fixing 18, 34, 48, 56 a Chinese pine plantation land was selected as the research objects, and the soil samples were collected in layers for the determination of soil chemical properties and enzyme activities. The redundancy analysis method was used to explore the change process of soil enzyme activity at different forest ages and its relationship with soil physical and chemical properties.

Compared with the control, the contents of organic matter, total nitrogen, total phosphorus and available potassium increased significantly with the increase of stand age, but total potassium and available nitrogen had no obvious changes. The activities of catalase, dehydrogenase, urease, neutral phosphatase and neutral protease in the 0-2 cm soil layer under different forest ages were significantly higher than that of the control with obvious superficial polymerization, sucrase activity was the highest at 18 a and then decreased. Stand age, soil layer and their interaction significantly affected soil enzyme activity. Redundancy analysis showed that soil total nitrogen, total potassium, available phosphorus, available potassium and soil urease, dehydrogenase, and catalase all had extremely significant positive correlations. The accumulation of 7 chemical properties in the first two axes explained 76.06% of soil enzyme activity, and the order of importance to soil enzyme activity was total nitrogen, available phosphorus, total potassium, organic matter, total phosphorus, available potassium, and available nitrogen. Total nitrogen is the key factor affecting the difference of soil enzyme activity.

The Chinese pine plantation can effectively improve the sandy soil fertility and soil enzyme activity, and the improvement effect will increase with the increase of the forest age.