Root Structure and Function of Grapevine Rootstocks (Vitis) in Response io Salinity

Purpose Accessing freshwater resources becomes more complex in arid and semi-arid areas due to increased demands and declining water quality. Alternative water sources for agriculture such as saline and recycled water are currently being used. A better understanding of roots' response to irrigation with saline water is crucial for future agriculture in arid and semi-arid areas. Methods Three grapevine (Vitis) rootstocks were examined, and their roots' responses to salinity were studied. The rootstocks were planted in pots filled with sand and were grown in a commercial net house subjected to two salinity treatments: 10 mM and 30 mM NaCl (EC = 2 and 4 ds m-1, respectively). We measured root morphologic and anatomic properties at the end of the experiment. Results The specific root area increased in response to salinity due to reduced root tissue density. In addition, a reduction in the average root diameter also affected the specific root area by increasing the surface area to volume ratio. Plant biomass was allocated primarily to the shoot in all three rootstocks, reducing the root to shoot ratio. At the same time, the bottom part of the root zone was more affected by salinity. SO4 showed improved chloride and sodium exclusion, concomitant with a significant increase in its narrow roots' contribution to the surface area. Conclusion Narrow roots play a more prominent role in the acquisition of water and nutrients as salinity increases. Furthermore, a decrease in root tissue density and average diameter may contribute to salt exclusion from the roots.

Root Porosity Contributes to Root Trait Space of Wetland Monocotyledons Independently of Economics Traits.

Aims Root aerenchyma, a key adaptive trait to anoxic soils has rarely been integrated into trait-based plant ecology. This study aims to evaluate the relationship between root porosity and root economics-related traits among wetland plants, focusing on the effect of aerenchyma on root tissue density, a central trait in plant economics spectrum.Methods Root porosity, root tissue density with air-space included or excluded (RTD and RTDA), and other root economics-related traits were measured separately for basal and lateral roots of 16 garden-grown Ontario wetland monocots with contrasting root longevities.Results Interspecific variation in root porosity was unrelated to root economics traits and did not differ between species with long-lived or short-lived roots. Consequently, RTDA better differentiated between species with contrasting root longevities than RTD did, consistently both for basal and lateral roots. Root dry matter content (RDMC) accurately predicted RTDA. A principal component analysis showed that in the root adaptive trait space of wetland plants, the first dimension is defined by economics-related traits, the second dimension by lateral root porosity and the ratio of lateral to basal root length, and the third dimension by basal root porosity.Conclusions Interspecific variation in the aerenchyma content is independent of root economics: Wetland plants can construct economically conservative or acquisitive roots of any porosity. Consequently, to consistently express root functional relationships among wetland plant species, root tissue density should be expressed with RTDA, i.e., excluding the air space, or with the more easily measured RDMC.

Shifts in fine root traits within and among species along a fine-scale hydrological gradient

Background and Aims Lessons from above-ground trait ecology and resource economics theory may not be directly translatable to below-ground traits due to differences in function, trade-offs and environmental constraints. Here we examine root functional traits within and across species along a fine-scale hydrological gradient. We ask two related questions: (1) What is the relative magnitude of trait variation across the gradient for within- versus among-species variation? (2) Do correlations among below-ground plant traits conform with predictions from resource-economic spectrum theory? Methods We sampled four below-ground fine-root traits (specific root length, branching intensity, root tissue density and root dry matter content) and four above-ground traits (specific leaf area, leaf size, plant height and leaf dry matter content) in vascular plants along a fine-scale hydrological gradient within a wet heathland community in south-eastern Australia. Below-ground and above-ground traits were sampled both within and among species. Key Results Root traits shifted both within and among species across the hydrological gradient. Within- and among-species patterns for root tissue density showed similar declines towards the wetter end of the gradient. Other root traits showed a variety of patterns with respect to within- and among-species variation. Filtering of species has a stronger effect compared with the average within-species shift: the slopes of the relationships between soil moisture and traits were steeper across species than slopes of within species. Between species, below-ground traits were only weakly linked to each other and to above-ground traits, but these weak links did in some cases correspond with predictions from economic theory. Conclusions One of the challenges of research on root traits has been considerable intraspecific variation. Here we show that part of intraspecific root trait variation is structured by a fine-scale hydrological gradient, and that the variation aligns with among-species trends in some cases. Patterns in root tissue density are especially intriguing and may play an important role in species and individual response to moisture conditions. Given the importance of roots in the uptake of resources, and in carbon and nutrient turnover, it is vital that we establish patterns of root trait variation across environmental gradients.

Does root respiration in Australian rainforest tree seedlings acclimate to experimental warming?

Plant respiration can acclimate to changing environmental conditions and vary between species as well as biome types, although belowground respiration responses to ongoing climate warming are not well understood. Understanding the thermal acclimation capacity of root respiration (Rroot) in relation to increasing temperatures is therefore critical in elucidating a key uncertainty in plant function in response to warming. However, the degree of temperature acclimation of Rroot in rainforest trees and how root chemical and morphological traits are related to acclimation is unknown. Here we investigated the extent to which respiration of fine roots (≤2 mm) of four tropical and four warm-temperate rainforest tree seedlings differed in response to warmer growth temperatures (control and +6 °C), including temperature sensitivity (Q10) and the degree of acclimation of Rroot. Regardless of biome type, we found no consistent pattern in the short-term temperature responses of Rroot to elevated growth temperature: a significant reduction in the temperature response of Rroot to +6 °C treatment was only observed for a tropical species, Cryptocarya mackinnoniana, whereas the other seven species had either some stimulation or no alteration. Across species, Rroot was positively correlated with root tissue nitrogen concentration (mg g−1), while Q10 was positively correlated with root tissue density (g cm−3). Warming increased root tissue density by 20.8% but did not alter root nitrogen across species. We conclude that thermal acclimation capacity of Rroot to warming is species-specific and suggest that root tissue density is a useful predictor of Rroot and its thermal responses in rainforest tree seedlings.

A split supply of bio-organic and chemical fertilizer synergistically affects root system architecture and improves above-ground growth in pear tree (Pyrus pyrifolia Nakai)

Background: Root system architecture (RSA) is highly plastic, responding to nutrient availability and the heterogeneity of the soil environment. However, the linkage of root morphology to anatomy and root nutrient, and its implication for root function at the heterogeneous application of bio-organic and chemical fertilizer have not yet been defined, especially for pear trees.Results: In this study, a split-root experiment was conducted using 1-year old ‘Cuiguan’ trees. No fertilizer (NF), chemical fertilizer (CF), and bio-organic fertilizer (BIO) were paired to test six combinations: NF-NF, NF-CF, NF-BIO, CF-CF, BIO-BIO, and BIO-CF. Root morphological, anatomical traits and root nutrient concentrations, and their relationships were determined. Trees receiving BIO had significantly higher lateral root numbers, activity, total lateral root length, and specific root length than trees receiving no BIO, while the effects on root tissue density were the direct opposite. Compared with CF-CF treatment, root xylem thickness, stele diameter, vessel diameter, and number of vessels all increased in response to BIO-CF treatment. Root growth was synergistically promoted in BIO-CF, with increased special root length and root nitrogen concentration, but root tissue density and the carbon:nitrogen ratio were reduced. Intriguingly, the synergistic effect resulted in greater trunk girth without sacrificing height, compared to trees receiving CF or BIO alone.Conclusions: The combination of BIO and CF improves root traits and tree growth, suggesting that using bio-organic fertilizer as a supplement to reduce the application rate of chemical fertilizer is beneficial to orchard ecosystems.

The root economics spectrum: divergence of absorptive root strategies with root diameter

Plant roots usually vary along a dominant ecological axis, the root economics spectrum (RES), depicting a tradeoff between resource acquisition and conservation. For absorptive roots, which are mainly responsible for resource acquisition, we hypothesized that root strategies as predicted from the RES shift with increasing root diameter. To test this hypothesis, we used seven contrasting plant species for which we separated absorptive roots into two categories: thin roots (< 247 μm diameter) and thick roots. For each category, we analyzed a~range of root traits closely related to resource acquisition and conservation, including root tissue density, carbon (C) and nitrogen (N) fractions as well as root anatomical traits. The results showed that trait relationships for thin absorptive roots followed the expectations from the RES while no clear trait relationships were found in support of the RES for thick absorptive roots. Our results suggest divergence of absorptive root strategies in relation to root diameter, which runs against a single economics spectrum for absorptive roots.