Effects of root pruning on the physicochemical properties and microbial activities of poplar rhizosphere soil

Abstract

This study aimed to determine the effects of root pruning on the physicochemical characteristics and microbial activities of poplar rhizosphere soil. The root systems of 5-year-old poplar (Populus×euramericana cv. ‘Neva’) trees were manually pruned at 6, 8, or 10 times diameter at breast height (DBH) from the trunk (severe, moderate, and light, respectively) along both inter-row sides. Moderate root pruning significantly increased the concentrations of amino acids, organic acids, and total sugars in the root exudates and decreased the pH of rhizosphere soil. This treatment also increased the contents of available nitrogen, phosphorus, potassium, and total organic carbon as well as high-, medium-, and low-activity organic carbon in rhizosphere soil. Moreover, moderate pruning increased the contents of microbial biomass carbon and nitrogen, and enhanced basal respiration, in addition to decreasing the metabolic quotients in rhizosphere soil by 8.9%, 5.0%, and 11.4% compared with control, light, and severe root pruning treatments, respectively. Moderate pruning increased the growth rates of DBH, tree height, and volume to the highest levels. Furthermore, these indices were not significantly different between the light root pruning and control groups, but varied significantly between severe and moderate root-pruning treatments. Thus, root pruning, depending on the distance from the trunk, significantly influences the physicochemical properties and microbial activities in poplar rhizosphere soil.

Regulatory effects of root pruning on leaf nutrients, photosynthesis, and growth of trees in a closed-canopy poplar plantation

“…Populus × euramericana cv. ‘Neva’ is one of the most suitable species for afforestation and woody production in arid and semiarid areas of China [ 5 ]. The successful establishment and rapid growth of the trees depend on the fast growth and nutrient-absorbing ability of the root system.…”

“…On subsequent survey dates, the N and P concentrations of leaves in the 8–2 treatment had increased and were significantly higher compared with other treatments, which was in part agreement with a previous study [ 4 ]. Compared with the 8–4 treatment, the same strength of root pruning on two sides of the tree in the 8–2 treatment not only stimulated the growth of new roots [ 5 ], but also increased the absorption area of the roots ( Fig 3 ), which subsequently increased the nutrient uptake [ 9 , 25 ].…”

“…With the increase of growth time, the lateral roots of poplar gradually expand and inevitably intermingle with those of neighboring trees after canopy closure. Interweaved roots inhibit the growth of poplar, and is beneficial to the spread of pests and diseases, and thus, significantly reduce root vitality during this period [ 4 – 5 ]. In addition, the amount of fine roots decreased when poplars were at the stage of canopy closing, thereby significantly suppressing the ability of the poplar root system to absorb water and nutrients [ 5 – 7 ].…”

“…Interweaved roots inhibit the growth of poplar, and is beneficial to the spread of pests and diseases, and thus, significantly reduce root vitality during this period [ 4 – 5 ]. In addition, the amount of fine roots decreased when poplars were at the stage of canopy closing, thereby significantly suppressing the ability of the poplar root system to absorb water and nutrients [ 5 – 7 ]. Therefore, how to improve root system vitality in poplar closed-canopy plantations is particularly important for tree growth and, thus, the economic return of such plantations.…”

“…Our previous research on canopy-closed poplar trees reported that removing some roots at a distance of 8 times the diameter at breast height (DBH) from trunk on both inter-row sides of the trees improved tree growth and rhizosphere soil fertility [ 4 – 5 ]. However, it is currently unknown whether cutting roots of poplars on four sides at a certain distance from trunk will have improved results compared with pruning roots on two sides.…”