Cover crops are widely used to increase the quantity of organic carbon (C) returned to the soil between cash crops. Roots play an important role in increasing soil organic carbon (SOC) levels, but the root traits that impact SOC likely vary widely among cover crop species and this variation has yet to be characterized. Recently, cover crop mixtures have expanded in popularity as a way to increase the diversity of cover crop benefits. We tested the quantity, quality and spatial distribution of roots in three monocultures and one mixture to increase our understanding of root trait variation among species, and how that variation impacts mixture design. Root cores were taken from in-row and between-row locations to a depth of 40 cm from cover crops planted after winter wheat during the 2016–2017 growing season. These samples were taken from a larger maize–soybean–winter wheat organic grain rotation experiment (2012–2018) located in central Pennsylvania, USA. Cover crop treatments included monocultures of triticale (X Triticosecale Wittmack cv. ‘Trical 815’), canola (Brassica napus L. cv. ‘Wichita’), crimson clover (Trifolium incarnatum L. cv. ‘Dixie’) and a five species mixture dominated by those three species. Additionally, cumulative carbon (C) inputs were assessed for the entire rotation to determine cover crop and cash crop root C contributions. Root biomass C vertical and horizontal distribution, root-to-shoot (R:S) ratio, and root carbon-to-nitrogen (C:N) ratio differed among cover crop treatments. Triticale produced more root biomass in the between-row space at all depth intervals compared to other cover crop treatments. The five species mixture had more total 0–5 cm and between-row 0–5 cm root biomass than crimson clover in spring 2017. Cover crop and cash crop roots increased cumulative C estimates by between 37% (crimson clover) and 46% (triticale) compared to shoot C alone. Cover crop root trait information can inform the belowground benefits from combining different species into cover crop mixtures. Crimson clover produced less root biomass, surface root biomass and between-row root biomass than other cover crop treatments. Therefore, combining crimson clover with grass and certain brassica species can improve total root biomass production, and root distribution compared to crimson clover monocultures, whereas reducing the C:N ratio of roots compared to grass species monocultures. The five species mixture led to greater cumulative carbon inputs compared to monoculture treatments, which was due to greater cover crop biomass C and its influence on the following corn crop's biomass C.

Drought stress negatively affects the cotton production all over the world. The negative impact of drought varies for different species due to some morphological and root attributes that help some species to better stand under drought. But the extent of disturbance varies for different cotton species. To find out such variation, two cotton species (Gossypium hirsutum and Gossypium arboreum) were studied under normal and drought conditions for 2 years. Two genotypes for each species were included, i.e. PC-1 and COMILLA (G. arboreum) and IUB-13 and IUB-65 (G. hirsutum). The experiment was laid out under a completely randomized design following factorial arrangement. Genotype × treatment × year interaction of cotton genotypes was studied for different root, morphological, physiological and fibre-related traits. Traits such as above ground dry biomass, above ground fresh biomass, chlorophyll contents, leaf area, seed cotton yield, sympodial branches/plant, fibre strength and ginning out-turn were higher in G. hirsutum genotypes as compared to G. arboreum genotypes. However less reduction under drought in all above mentioned traits was recorded for G. arboreum, than G. hirsutum. Furthermore, root traits; primary root length, lateral root numbers, root fresh weight and root dry weight were enriched under drought condition in G. arboreum genotypes than in G. hirsutum genotypes, which is a clear manifestation of higher drought tolerance ability in G. arboreum genotypes transferrable to G. hirsutum genotypes through interspecific crossing or other means.

The relationships between arbuscular mycorrhizal fungi and root morphological characteristics were studied under greenhouse conditions of 78 tropical native woody species and 47 seedling species collected in the field. Seedlings of native woody pioneer and early secondary species that generally exhibited fine roots with a dense cover of long root hairs showed higher mycorrhizal response and root mycorrhizal colonization than late-secondary and climax species with coarse roots with a sparse cover of short root hairs. Root-hair length and incidence decreased with the progression among the successional groups while fine-root diameter increased, both in the greenhouse and in the field. The mycorrhizal response was highly correlated to root mycorrhizal colonization in the greenhouse and in the field. These parameters were inversely correlated with the seed mass and fine-root diameter, but directly correlated with root-hair incidence, both in the greenhouse and in the field. Mycorrhizal response and root mycorrhizal colonization were also directly correlated with the root-hair length and root/shoot ratio of uninoculated plants. The seedling mycorrhizal status of the early successional woody species suggests that the root traits of these fast-growing species can be more receptive to attraction, infection and colonization by arbuscular mycorrhizas than root traits of late-successional species.