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Purpose: To understand the effects of poplar–intercropping systems on soil nutrients and soil enzyme activities, and further analyzed the relationship between soil enzyme activities and soil nutrients. Methods: Three different planting systems were chosen: a monoculture wheat (Triticum aestivum) system (W), a narrowly spaced poplar (Populus deltoides)–wheat intercropping system (PWN), and a widely spaced poplar–wheat intercropping system (PWW). The chemical properties (soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP) and available potassium (AK)) and four enzymatic activities (urease, catalase, sucrase and alkaline phosphatase) in four soil layers (0–20, 20–40, 40–60 and 60–100 cm) of two sampling sites (1.5 and 3.5 m from tree row) in the three planting systems were investigated. Results: The SOM, TN, TP, TK, AP, AK concentrations and four soil enzyme activities were higher in the intercropping systems than in the monoculture wheat system, especially the PWN system. In the vertical direction, the soil nutrient concentrations and soil enzyme activities decreased with soil depth (P < 0.001), except AK and catalase. In the horizontal direction, the SOM, TN, TP, TK concentrations and four soil enzyme activities decreased with greater of distance from the poplar row, but the distribution trend was the opposite for AN, AP and AK. The correlation analysis revealed that the soil enzyme activities were significantly correlated with the SOM, TN, TP, AN and AP concentrations in the three planting systems (P < 0.01). Conclusion: In conclusion, agroforestry systems can significantly increase soil nutrient status and soil enzyme activities and can be an efficient method for improving soil health conditions. Additionally, compared with the wide poplar spacing in the intercropping system, the reasonably dense planting of intercropped poplar had more obvious effects on improving soil enzyme activities and soil nutrients. [ABSTRACT FROM AUTHOR]

Artificial pruning is an important silvicultural practice that can produce clear wood in poplar plantations. This study focused on the growth of poplar, understory vegetation diversity and soil properties in response to different pruning intensities in poplar plantations. We implemented three different pruning treatments based on the height-to-crown base (HCB) to tree height (H) ratio in Populus deltoides 'Nanlin 3804′ plantations: CK (no pruning), a 1/3 pruning treatment and a 1/2 pruning treatment. The poplar growth conditions, understory vegetation biodiversity and soil properties were investigated for one year after pruning. Compared with CK, the 1/2 pruning treatment significantly decreased the increment of diameter at breast height (DBHi) and stem volume increment (Vi) by 16.4% and 12.8%, respectively. Meanwhile, pruning significantly promoted understory vegetation biomass and increased the Shannon–Weiner diversity index of understory vegetation, and these variables were positively correlated with pruning intensity. The 1/2 pruning treatment significantly reduced the contents of soil nitrate nitrogen (NO3-N), total inorganic nitrogen (IN) and microbial biomass nitrogen (MBN) by 21.9%, 13.9% and 22.4%, respectively. However, the 1/3 pruning treatment had no significant influence. Pruning mainlyaffectedthe soil enzyme activity in the surface (0–10 cm) layer. The 1/3 and 1/2 pruning treatments significantly decreased soil urease activity by 20.1% and 15.0%, respectively. Furthermore, nonmetric multidimensional scaling analysis showed that the seasonal variation in soil properties was significant, and significant differences among pruning treatments were mainly observed in July and October. Redundancy analysis showed that the growth of aboveground vegetation was significantly correlated with soil properties, particularly soil IN content and urease activity. Therefore, the results highlighted that pruning could promote the growth of understory vegetation and accelerate the transformation of soil nutrients. The 1/2 pruning treatment significantly inhibited the growth of poplar in terms of DBH and V, while the 1/3 pruning treatment promoted the growth of poplar in the short term. Overall, we think that the 1/3 pruning intensity is more suitable for pruning practice. [ABSTRACT FROM AUTHOR]

The main objective of this study was to compare the effects of two densities (278 stems·ha−1 with two spacings of 6 m × 6 m or 4.5 m × 8 m, 400 stems·ha−1 with two spacings of 5 m × 5 m or 3 m × 8 m) and three poplar clones (NL95, NL895, and NL797) on productivity and carbon (C) sequestration of poplar ecosystems. The results showed that planting density significantly affected the biomass of a single tree. The mean tree biomass of clone NL95 was higher in all spacings than that of the other clones, with a significant difference for the 6 m × 6 m spacing. The biomass of poplar trees ranged from 78.9 to 110.3 Mg·ha−1, with the highest tree biomass observed in the square configuration. Soil C concentration (0–100 cm) increased after 12 years of management. Soil C storage ranged from 138.1 to 164.3 Mg C·ha−1, and the highest soil C storage was in the NL797 poplar plantation with 6 m × 6 m spacing. Our results suggested that clones NL95 and NL797 should be chosen for planting, with a planting density of 278 stems·ha−1 and spacing of 6 m × 6 m. [ABSTRACT FROM AUTHOR]