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

A plantation of 5-year-old poplar Populus × euramericana cv. 'Neva' was used to study the regulatory effects of root pruning on nutrients, photosynthetic characteristics, and water-use efficiency (WUE) of leaves and growth rates of diameter at breast height (DBH; 1.3 m), tree height, and volume. Six root-pruning treatments were conducted with different combinations of intensity (at a distance of six, eight or ten times DBH from the trunk) and orientation (on two or four sides of the trees). Results showed that the N, P, K, photosynthetic rate, transpiration rate, and stomatal conductance of leaves were all significantly decreased by root pruning over the initial period following root pruning (30 days), but increased in the subsequent investigations. The values of the above indexes peaked in 8-2 treatment (i.e., eight times DBH distance on two sides). The leaf WUE in 8-2 treatment, and average growth rates of DBH, tree height and volume, were the highest among all treatments within 3 years of root pruning. The results indicated that the root pruning based on the appropriate selection of intensity and orientation had significant positive effects on leaf nutrients, photosynthesis, and growth of trees in a closed-canopy poplar plantation.

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

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.

[Effects of gel made by super absorbent polymers and urea on fine root growth and nitrogen use efficiency of Platycladus orientalis bareroot seedlings.] / 保水剂-å°¿ç´ å‡èƒ¶å¯¹ä¾§æŸè£¸æ ¹è‹—ç»†æ ¹ç”Ÿé•¿å’Œæ°®ç´ åˆ©ç”¨çŽ‡çš„å½±å“.

A pot experiment including five treatments, i.e., CK (neither fertilizer nor super absorbent polymers), U (urea alone), S [super absorbent polymers (SAP) alone], SUM (SAP mixed with urea) and SUG (gel made of SAP and urea) was conducted to evaluate their effects on fine root morphological characteristics, fine root absorption area, fine root nitrogen metabolism and nitrogen use efficiency of Platycladus orientalis bareroot seedlings. Results showed that compared with U treatment, the SUG treatment significantly increased the biomass, length, specific root length, surface area and volume of fine root. The total absorption area and active absorption area of fine root were also increased remarkably under the SUG treatment. The specific root length in the SUG treatment was increased by 34.7%, 37.9%, 41.1% and 12.4% compared with the treatments of CK, U, S and SUM, respectively. Compared with the U treatment, the activities of nitrate reductase, glutamine synthase, glutamate synthase and glutamate dehydrogenase in fine root of the SUG treatment was improved by 41.2%, 76.6%, 30.7% and 125.8%, respectively, while the ratio of GS to GDH decreased. Not only the ground diameter and plant height, but also the dry matter accumulation of aboveground and underground parts was remarkably enhanced under the SUG treatment. The nitrogen use efficiency was 40.7% in the SUG treatment, being 118.8% and 44.5% higher than the U and SUM treatments, respectively. Gel made of SAP and urea was able to significantly increase the nitrogen use efficiency, promote the growth and enhance the ability of drought resistance by improving the morphological characteristics, enhancing the absorption area and key enzymes activities of nitrogen metabolism in the fine root of P. orientalis bareroot seedlings.

[Effects of drought stress on the growth, photosynthetic characteristics, and active oxygen metabolism of poplar seedlings].

A pot experiment was conducted to study the effects of different water treatments (normal irrigation, light drought, moderate drought, and severe drought) on the growth, gas exchange, chlorophyll fluorescence characteristics, and active oxygen metabolism of poplar ( Populus x euramericana cv. 'Neva') seedlings in the experimental nursery of Shandong Forestry Academy from April to October, 2011. As compared with those under normal irrigation, the growth of the seedling' s basal diameter under light, moderate, and severe drought stress decreased by 12.8%, 44.5%, and 65.6%, and the height growth decreased by 12.2%, 43.1%, and 57.2%, respectively. With the increasing extent and duration of drought stress, the maximal photochemical efficiency of PS II , quantum yield, photochemical quenching coefficient, net photosynthetic rate, and stomatal conductance of the seedling leaves decreased gradually under light drought stress, while decreased rapidly under both moderate and severe drought stress. The non-photochemical quenching coefficient increased significantly under light drought stress, but decreased after an initial increase under moderate and severe drought. The leaf superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities under drought stress decreased after an initial increase, but definite differences existed in the responses of the three enzymes to drought stress and reactive oxygen. The leaf relative electric conductivity and malondialdehyde (MDA) content under drought stress increased significantly, plasma membrane was damaged, and massive ions leaked out. The most serious damage of plasma membrane was found under severe stress. Under light drought stress, the seedlings had higher photosynthetic efficiency and stronger oxidative enzyme defense system; under moderate and severe drought stress, the photosynthetic efficiency decreased significantly, and the oxidative enzyme defense system was damaged remarkably.