Abstract
Fine roots (< 2 mm in diameter) play an important role in belowground ecosystem processes, and their physiological ecology is easily altered by nitrogen deposition. To better understand the response of physiological and ecological processes of fine roots to nitrogen deposition, a manipulation experiment was conducted to investigate the effects of exogenous nitrogen addition (control (0 kg ha−1 a−1), low (5 kg ha−1 a−1), moderate (10 kg ha−1 a−1), and high nitrogen (20 kg ha−1 a−1)) on the biomass, morphological characteristics, chemical elements and nonstructural carbohydrates of fine roots in a Picea schrenkiana forest. We found that most fine roots were located in the 0–20 cm of soil layer across all nitrogen treatment groups (42.81–52.09% of the total biomass). Compared with the control, the biomass, specific root length and specific root area of the fine roots increased in the medium nitrogen treatment, whereas the fine roots biomass was lower in the high nitrogen treatment than in the other treatments. In fine roots, nitrogen addition promotes the absorption of nitrogen and phosphorus and their stoichiometric ratio, while reducing the content of nonstructural carbohydrates. The content of nonstructural carbohydrates in the small-diameter roots (< 1 mm in diamter) in each nitrogen treatment group was lower than that in the large-diameter roots. Correlation analysis showed that soil carbon and nitrogen were positively correlated with fine root biomass and specific root length and negatively correlated with the nonstructural carbohydrates. Our findings demonstrate that medium nitrogen addition is conducive to the development of fine root morphology, while excessive nitrogen can suppress the growth of root systems.
Highlights
Fine roots (< 2 mm in diameter) are the main organ through which plants absorb nutrients and water; these structures play a key role in carbon (C) distribution and nutrient cycling of terrestrial e cosystems[1,2]
Ostonen et al.[10] found that the root tissue density (RTD) and specific root length (SRL) of Norway spruce decreased with increasing soil N availability, but Comas and Eissenstat[18] found that RTD was significantly negatively correlated with SRL in temperate forests
The fine root biomass showed a slight increase in the medium nitrogen (MN) addition treatment (Fig. 1a)
Summary
Fine roots (< 2 mm in diameter) are the main organ through which plants absorb nutrients and water; these structures play a key role in carbon (C) distribution and nutrient cycling of terrestrial e cosystems[1,2]. Fine roots are the most active part of the root system and are sensitive to variations in soil and atmospheric environments due to nitrogen (N) deposition[3]. Extensive studies have shown that fine root morphology is closely related to the changes in soil nutrient availability caused by N. deposition, the degree of many responses is still c ontroversial[13,14]. The discrepancies in the responses of fine root morphology to N deposition may be ascribed to plant species (such as carbon allocation strategies), habitat conditions, and soil environments. The vertical distribution of fine roots and their response to N addition determine the strategies plants use to obtain soil resources and reflect the adaptability of plants to the environment. Knowing how the morphological and chemical properties of fine roots in different diameter classes and soil layers change with N deposition is helpful for understanding the mechanisms of plant adaptation strategies to environmental changes in arid zones
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