Fine-Root Responses of Populus tomentosa Forests to Stand Density

Abstract

Stand density directly affects the distribution of ecological factors such as light, heat, and water in forest communities and changes the diversity and structure of undergrowth species, thereby affecting soil health. Fine roots can provide water and nutrients to plants rapidly in the fierce competition of soil resources, so as to get rid of environmental factors. This study examined the fine-root responses of the Populus tomentosa clone S86 to three stand densities (plant × row spacing: 2 × 2 m, 4 × 3 m, 4 × 5 m). We measured the biomass, morphology, and nitrogen content of lower- (1–3 order) and higher-order (>3 order) fine roots, and analyzed soil chemical properties in 10–30 cm. The soil from the density (2 × 2 m) stands showed lower soil organic matter content, available nitrogen, available phosphorous, and available potassium than others. Obviously, lower and higher-order fine roots were different: biomass of the >3 order accounted for 77–87% of the total biomass, 1–3-order fine-root diameter around 0.28–0.38 mm, while >3-order fine root were 1.28–1.69 mm; the length of 1–3-order fine root was longer than the >3 order, and root length density, specific root length, and nutrient content between the 1–3 and >3 orders were different. At 2 × 2 m, 1–3-order fine-root biomass was the highest, 132.5 g/m3, and the 1–3-order fine-root length, diameter, surface, root length density was also the highest; at the same time, the 1–3-order fine-root total nitrogen and organic matter content was also the highest, while the >3 order was highest under 4 × 3 m or 4 × 5 m. The findings of this study show that stand density affected the available nutrient content of the soil. When soil resources were poor, the biomass, morphology, and chemical content of fine roots were adjusted to increase the nutrient absorption rate, particularly in the lower-order roots.

Short-term effects of organic amendments on soil fertility and root growth of rubber trees on Hainan Island, China

“…Tree root systems are vitally important for the proper functioning of forest ecosystems because of their pivotal roles in the absorption of soil nutrients and water, soil organic matter stock, and for maintaining plant growth, tree stability and stem straightness (Lindström and Rune 1999;Collins and Bras 2007;Xi et al 2011;Pransiska et al 2016;Bo et al 2018;Wang and Xie 2018). Fine roots (diameter < 2 mm) are the most active segments of root systems and respond rapidly to variations in the soil environment (Hendrick and Pregitzer 1992;Lukac and Godbold 2010;Montagnoli et al 2012;Jha 2018;Liu et al 2018).…”

“…Fertilization is one of the most important practices to maintain tree growth and rubber yield because root morphology depends significantly on nutrient availability (Fransen et al 1998). Trees increase their number of fine roots to absorb more soil nutrients (Bo et al 2018). Normally, rubber planters are encouraged to apply chemical fertilizer and organic materials to an excavated fertilization cave (typically 100-200 cm long × 60 cm wide × 40 cm deep) between rows by taking advantage of the physiological plasticity of roots to obtain nutrients.…”

Response of density-related fine root production to soil and leaf traits in coniferous and broad-leaved plantations in the semiarid loess hilly region of China

“…Stand density influences soil environments by affecting the availability of nutrients (Bo et al 2018), and is regarded as In black locust plantations, soil C and N contents showed a cumulative trend in low stand densities, peaked at density class III, then decreased slightly with increasing density. Organic C and N content were closely related on a small scale to stand density (Chen 2006).…”

“…In forest plantations, stand density is a major index representing resource use conditions and interactions among and between trees and environments; thus, it is of major consideration in management practices. Stand density determines stand spatial structure and directly affects the distribution of light, heat, moisture, and other ecological factors affecting the growth of individual trees and of the plantation (Cai et al 2016;Hakkenberg et al 2016;Bo et al 2018). The effect of stand density on fine root dynamics has been studied in natural forests coupled with species richness (He et al 2005;Marquard et al 2009;Zeng et al 2020).…”

Abiotic and biotic factors controlling fine root biomass, carbon and nutrients in closed-canopy hybrid poplar stands on post-agricultural land

“…Higher soil P was related to higher fine root P concentration in P . tomentosa plantations, but inconsistent trends where observed for fine root N and potassium (K) 51 . Yet, N-fertilization led to a 3-fold increase in fine root N concentrations in P .…”