Oxygen transport in soil and the vertical distribution of roots

Soil Research ◽  
2007 ◽  
Vol 45 (2) ◽  
pp. 101 ◽  
Author(s):  
F. J. Cook ◽  
J. H. Knight ◽  
F. M. Kelliher

An analytical solution for steady-state oxygen transport in soils including 2 sink terms, viz roots and microbes with the corresponding vertical distribution scaling lengths forming a ratio p, showed p governed the critical air-filled porosity, θc, needed by most plants. For low temperature and p, θc was <0.1 but at higher temperatures and p = 1, θc was >0.15 m3/m3. When root length density at the surface was 104 m/m3 and p > 3, θc was 0.25 m3/m3, more than half the pore space. Few combinations of soil and climate regularly meet this condition. However, for sandy soils and seasonally warm, arid regions, the theory is consistent with observation, in that plants may have some deep roots. Critical θc values are used to formulate theoretical solutions in a forward mode, so different levels of oxygen uptake by roots may be compared to microbial activity. The proportion of respiration by plant roots increases rapidly with p up to p ≈2. Synthesis of vertical root biomass density, L [= L0 exp(–z/Zr), z is the depth positive down (m)] (m/m3), data using an exponential function to represent the distribution suggested that, on average, 70 ± 10% of fine roots in 10 terrestrial biomes were located in the upper 0.1 m of soil. Integrated over the root-zone, LT is given by the product of the function’s 2 parameters, the surface value of L, L0 (m/m3), and length scale, Zr (m). As postulated, negative correlations were obtained between L0 and Zr. For a maize (Zea mays L.) crop, significantly different distributions were measured during relatively dry and wet seasons and predicted by our model. For woody and herbaceous plants, Zr (the value determines the rate of decrease in L with depth) averaged 0.3 and 0.2 m, respectively, while the corresponding averages for Rm0 [= L0.ρr, ρr is root density (kg/m)] were 2.7 and 1.1 kg/m3.

2020 ◽  
Author(s):  
Camilla Rasmussen ◽  
Eva Rosenqvist ◽  
Fulai Liu ◽  
Dorte Bodin Dresbøll ◽  
Kristian Thorup-Kristensen ◽  
...  

&lt;p&gt;Minimizing water limitation during growth of agricultural crops is crucial to unlocking full yield potentials. Crop yield losses vary according to timing and severity of water limitations, but even short-term droughts can be a major cause of yield losses. While the potential influence of deep roots on water uptake has been highlighted numerous times, the actual contribution of deep roots to water uptake is yet to be revealed. The objective of this study is to get an understanding of what limits deep water uptake by deep-rooted crops under topsoil water limitations.&lt;/p&gt;&lt;p&gt;We found that deep-rooted crops experience water limitations despite access to water stored in the deep soil and we hypothesize that deep water uptake by deep-rooted crops is limited by 1) the hydraulic conductivity of the deeper part of the root zone, arising from limited root length density in combination with the hydraulic resistance of the roots or 2) by a hormonal response arising from the plant sensing dry conditions in the shallow soil leading to stomata closure, to conserve water. The two hypotheses can of course not be valid simultaneously, but both might be valid under certain conditions, at certain times or for certain species.&lt;/p&gt;&lt;p&gt;In a large-scale semi-field setup, we grow oil seed rape and by combining measures of root development, root hydraulic conductivity, transpiration, stomatal conductance, ABA concentrations and soil water content from a large scale semi-field setup with a mechanistic 3-D root-soil modelling approach (R-SWMS), we are able to us distinguish various scenarios and to evaluate what limits deep water uptake.&lt;/p&gt;


2021 ◽  
Author(s):  
Inés M. Alonso-Crespo ◽  
Emanuela W.A. Weidlich ◽  
Vicky M. Temperton ◽  
Benjamin M. Delory

The order of arrival of plant species during assembly can affect the structure and functioning of grassland communities. These so-called priority effects have been extensively studied aboveground, but we still do not know how they affect the vertical distribution of roots in the soil and the rooting depth of plant communities. To test this hypothesis, we manipulated the order of arrival of three plant functional groups (forbs, grasses and legumes) in a rhizobox experiment. Priority effects were created by sowing one functional group 10 days before the other two. Rhizoboxes in which all functional groups were sown simultaneously were used as controls. During the experiment, the mean rooting depth of plant communities was monitored using image analysis and a new methodological approach using deep learning (RootPainter) for root segmentation. At harvest, we measured aboveground (community and species level) and belowground (community level) biomass, and assessed the vertical distribution of the root biomass in different soil layers. At the community level, all scenarios where one functional group was sown before the other two had similar shoot and root productivity. At the species level, two forbs (Achillea millefolium and Centaurea jacea) benefited from arriving early, and one legume (Trifolium pratense) had a disadvantage when it was sown after the grasses. Priority effect treatments also affected the vertical distribution of roots. When grasses were sown first, plant communities rooted more shallowly than when forbs or legumes were sown first,. In addition, roots moved down the soil profile 24% more slowly in grasses-first communities. Our results highlight that plant functional group order of arrival in grassland communities can affect the vertical distribution of roots in the soil and this may have implications for species coexistence.


1974 ◽  
Vol 4 (2) ◽  
pp. 175-178
Author(s):  
Jack R. Sutherland

Soil samples were collected throughout the year to determine the vertical distribution of Xiphinemabakeri nematodes in soil in a Douglas-fir [Pseudotsugamenziesii (Mirb.) Franco] nursery and to monitor seasonal changes in nematode distribution pattern. Root distribution, moisture content, available pore space, and osmotic pressure were also determined for soil samples taken at various depths to see if they were related to nematode distribution. More than 90% of the nematodes were present in the upper 20 cm of soil, especially from 0 to 10 cm, and this percentage did not change with season. Nematode distribution was related only to root distribution. The significance of the results for nematode control practices is discussed.


Tellus B ◽  
2011 ◽  
Vol 63 (1) ◽  
Author(s):  
Abhay Devasthale ◽  
Michael Tjernström ◽  
Karl-Göran Karlsson ◽  
Manu Anna Thomas ◽  
Colin Jones ◽  
...  

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