Differential Variation in Non-structural Carbohydrates in Root Branch Orders of Fraxinus mandshurica Rupr. Seedlings Across Different Drought Intensities and Soil Substrates

Abstract

Non-structural carbohydrates (NSCs) facilitate plant adaptation to drought stress, characterize tree growth and survival ability, and buffer against external disturbances. Previous studies have focused on the distribution and dynamics of NSCs among different plant organs under drought conditions. However, discussion about the NSC levels of fine roots in different root branch orders is limited, especially the relationship between fine root trait variation and NSC content. The objective of the study was to shed light on the synergistic variation in fine root traits and NSC content in different root branch orders under different drought and soil substrate conditions. The 2-year-old Fraxinus mandshurica Rupr. potted seedlings were planted in three different soil substrates (humus, loam, and sandy–loam soil) and subjected to four drought intensities (CK, mild drought, moderate drought, and severe drought) for 2 months. With increasing drought intensity, the biomass of fine roots decreased significantly. Under the same drought intensity, seedlings in sandy–loam soil had higher root biomass, and the coefficient of variation of 5th-order roots (37.4, 44.5, and 53% in humus, loam, and sandy–loam soil, respectively) was higher than that of lower-order roots. All branch order roots of seedlings in humus soil had the largest specific root length (SRL) and specific root surface area (SRA), in addition to the lowest diameter. With increasing drought intensity, the SRL and average diameter (AD) of all root branch orders increased and decreased, respectively. The fine roots in humus soil had a higher soluble sugar (SS) content and lower starch (ST) content compared to the loam and sandy–loam soil. Additionally, the SS and ST contents of fine roots showed decreasing and increasing tendencies with increasing drought intensities, respectively. SS and ST explained the highest degree of the total variation in fine root traits, which were 32 and 32.1%, respectively. With increasing root order, the explanation of the variation in root traits by ST decreased (only 6.8% for 5th-order roots). The observed response in terms of morphological traits of different fine root branch orders of F. mandshurica seedlings to resource fluctuations ensures the maintenance of a low cost-benefit ratio in the root system development.

Drought- and soil substrate-induced variations in root nonstructural carbohydrates result from fine root morphological and anatomical traits of Juglans mandshurica seedlings

“…In this study, the SRL and RTD of the first two root orders exhibited a strong association with the variation in fine root NSC content. In contrast to our previous studies [ 29 , 30 ], fine root diameter did not significantly explain the variation in the higher content of fine root NSCs. Wang et al [ 63 ] showed that the average root elongation rate was significantly negatively correlated with soluble sugar and positively correlated with starch content.…”

“…Previous studies have found that seedlings of the drought-tolerant species Pinus tabuliformis invest more carbon in lower-order roots to facilitate plants to absorb more water and nutrients to survive under harsh conditions [ 27 ]. Similar results were also presented in our recent study on Fraxinus mandshurica [ 30 ], after 60 days of drought, the lower-order roots of F. mandshurica seedlings had higher NSC contents than those of higher-order roots. This result implies that when carbon is limited, F. mandshurica seedlings preferentially allocate carbon to thinner roots rather than thicker roots.…”

“…These pots were thereafter controlled daily to maintain a constant weight until the experiment ended in September 2017. A detailed description of the drought control is provided in our previous study [ 29 , 30 ].…”

“…Yang et al [ 28 ] found that the sensitivity of the root NSC concentration of Phyllostachys edulis seedlings to drought supported the plasticity of root architecture to some extent in allocating more carbon to structure low-cost roots. Our previous study demonstrated that the root morphological traits but not chemical traits, explain the variation in NSC contents induced by drought [ 29 , 30 ]. Given the heterogeneity of morphological and physiological function among branch orders [ 9 ], however, fewer works on the modifications of NSCs induced by drought have focused on the changes in root morphology and anatomy.…”

Fertilization reduces root architecture plasticity in Ulmus pumila used for afforesting Mongolian semi-arid steppe

“…We therefore might speculate that the reduction of rooting depth occurring in our study site due to fertilization and characterized by sandy soils would lead to a future forest stand more susceptible to anchorage failure. In addition, papers in a recent topic collection reported that variations in rooting depth may be a key functional trait for determining plant survival and growth in drought-prone regions ( Ji et al, 2021 ; Lihui et al, 2021 ; Montagnoli et al, 2022 ). The shallow root system as observed in our study could be more vulnerable to drought stress since the ability to capture water and nutrients at deeper soil layers would be quite reduced.…”