Effects of root pruning on the growth and rhizosphere soil characteristics of short-rotation closed-canopy poplar

Abstract

When poplar trees planted at a high density are canopy-closed in plantation after 4-5 years of growth, the roots of adjacent trees will inevitably intermingle together, which possibly restricts the nutrient uptake by root system. Root pruning might stimulate the emergence of fine roots and benefit the tree growth of short-rotation poplar at the stage of canopy closing. The aim of this study is to evaluate the effects of root pruning on DBH (diameter at breast height, 1.3 m), tree height, nutrients (N, P and K) and hormones (indoleacetic acid and cytokinin) in poplar leaves, gas exchange variables (photosynthetic rate and stomatal conductance), and rhizosphere soil characteristics. Field experiment was carried out with four-yearold poplar (Populus × euramericana cv. 'Neva') planted in a fluvo-aquic loam soil in Shandong province, China in early April, 2008. Three root pruning treatments (severe, moderate and light degree) were conducted at the distances of 6, 8 and 10 times DBH on both inter-row sides of the trees to the depth of 30 cm, respectively. The results showed that the growth performance was obtained in the following order of treatments: moderate > light = control > severe. In the rhizophere soil, moderate and light pruning increased the microbial populations, enzymatic activities, and the concentrations of available N, P, K and organic matter. Generally, root pruning to improve tree growth and rhizosphere soil fertility can be recommended in canopy-closed poplar plantation. The appropriate selection of root pruning intensity is a pivotal factor for the effectiveness of this technique.Key words: root pruning method; poplar plantation; growth performance; rhizosphere soil fertility. ResumenEfectos de la poda de raíces sobre el crecimiento y las características de la rizosfera del suelo de los álamos de corta rotación en la etapa del dosel cerradoCuando los chopos plantados a alta densidad cierran el dosel de copas después de 4-5 años, las raíces de árboles adyacentes inevitablemente se mezclan, lo que posiblemente limita la absorción de nutrientes por el sistema radicular. La poda de raíces podría estimular la aparición de raíces finas y beneficiar al crecimiento de los álamos de corta rotación en la etapa del dosel cerrado. El objetivo de este estudio es evaluar los efectos de la poda de raíces en el DAP (diámetro a la altura del pecho, 1,3 m), altura de los árboles, los nutrientes (N, P y K) y las hormonas (ácido indolacético y citoquininas) en las hojas, variables de intercambio gaseoso (tasa de fotosíntesis y conductancia estomática) y característi-cas de la rizosfera del suelo. El experimento de campo se llevó a cabo con chopos (Populus × euramericana cv. 'Neva') de cuatro años de edad plantadas en un suelo franco fluvo-ácuico en la provincia de Shandong, China, a principios de abril de 2008. Se efectuaron tres tratamientos de poda de raíces (severa, moderada y el grado de luz) a distancias de 6, 8 y 10 veces DAP en ambos lados entre las filas de los árboles a la profundidad de 30 cm. Los res...

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

“…This decrease in pH improved the solubility of phosphorus, potassium, and some salt ions [ 14 ], thereby increasing the contents of available phosphorus and potassium in the rhizosphere soil. This effect could also increase the concentration of nutrient ions in the rhizosphere soil, enhancing soil fertility and facilitating the absorption and utilization of nutrients by the root systems of poplar [ 4 , 6 ]. Previous studies on apple [ 36 ] and wheat [ 37 ] reported similar conclusions.…”

“…In contrast to the control group, light root pruning had no significant effects on the ecological environment of poplar rhizosphere soil; an effect that was significant as a result of moderate root pruning but reversed by severe root pruning. This was mainly because moderate root pruning promoted the germination of a large number of fine roots from the incision (Figs 4 – 6 ), thereby significantly enhancing root activity and producing abundant root exudates [ 4 ]. Light root pruning had a limited stimulation effect on the incision because of the large distance between the point of root pruning and the trunk; by contrast, severe root pruning severely damaged the root system because of the short distance between the point of pruning and the trunk, delaying the recovery of the root system [ 7 ].…”

“…Root pruning caused the disturbances to the soil-plant system and therefore induced the changes in microbial biomass in the rhizosphere solution [ 14 ]. Du et al [ 4 ] reported that moderate root pruning increased the microbial population in rhizosphere soil, which had a beneficial effect on MBC and MBN. This experimental result was also observed in our study.…”

“…Soil conditions, such as soil nutrients, water content, and aeration status, directly influence the growth, distribution, absorption function, and metabolic function of root systems, which then affect the growth, development, and output of the aboveground parts of the plant [ 2 ]. Poplar is the main afforestation tree species of fast-growing and high-yielding plantation projects in China [ 3 ].Poplar trees are mainly planted at a density of 830–1100 trees per ha in China [ 3 ].As the poplar tree grows, the lateral roots gradually expand and inevitably intermingle with those of adjacent trees when the canopy of the poplar plantation is closed [ 4 ]. The interwoven roots slow down the growth of the poplar tree and promote the spread of pests and diseases, thereby significantly reducing the root activity [ 5 ].…”

“…The interwoven roots slow down the growth of the poplar tree and promote the spread of pests and diseases, thereby significantly reducing the root activity [ 5 ]. Moreover, the amount of fine roots sharply decreases, suppressing the ability of the root system to absorb water and nutrients [ 4 , 6 ]. Therefore, methods for improving root system activity in closed-canopy poplar plantations must be developed to promote tree growth.…”