Investigation of plant growth and transpiration-induced matric suction under mixed grass–tree conditions

Abstract

Investigation of plant growth and transpiration-induced matric suction under mixed grass-tree conditions Ni, J. J.; Leung, Anthony; Ng, C. W. W.; So, P. S. General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain.• You may freely distribute the URL identifying the publication in the public portal. Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractAlthough evapotranspiration-induced matric suction for single species has been widely studied, little is known about how mixed-species planting would affect the plant growth and induced matric suction. This study aims to explore the effects of grass-tree interaction on their growth and induced matric suction during evapotranspiration (ET) and rainfalls. Field monitoring was carried out to measure matric suction responses in compacted soil that was vegetated with (i) single tree species, Schefflera heptaphylla and (ii) mixed species of the trees and a grass species, Cynodon dactylon. In each condition, three tree spacings (120, 180 and 240 mm) were planted. When tree spacing increased from 120 to 240 mm, the peak tree root area index (RAI, for fine roots with diameter < 2 mm) decreased by 16%, but the peak grass RAI increased by 29%. At mixed planting plots, the ET-induced peak matric suction for tree spacing of 240 mm was 20% higher than that for spacing of 180 mm because of increased contribution of grass root-water uptake as the trees were more widely spaced. Without grass, a reverse trend was observed as tree-tree interaction reduced at wide spacings. The peak ET-induced matric suction had a significant linear correlation with RAI. During rainfalls, the highest matric suction was preserved for the case of 240 mm spacing due to the greatest reduction of soil hydraulic conductivity by roots.

Investigating plant root effects on soil electrical conductivity: An integrated field monitoring and statistical modelling approach

“…In response to rainfall, soil water content increased correspondingly. This is contradictory to previous laboratory and field test results (Simon and Collison, 2002;Garg et al, 2015;Ni et al, 2017), which consistently showed that water content in the vegetated soil was lower than that in the bare soil. Soil water content was found to decrease after rainfall due to evaporation (E) and ET from bare and tree-covered soils, respectively.…”

Unsaturated hydraulic properties of vegetated soil under single and mixed planting conditions

“…Plant roots cause changes in soil matric suction (Simon & Collison, 2002;Veylon et al, 2015;Ng et al, 2016a;Ni et al, 2017) through evapotranspiration and soil hydraulic properties, including soil water retention curve (SWRC) and soil hydraulic conductivity function (SHCF). Some studies (Table 1) showed an increase in water retention capability when plant roots are present in the soil (Scanlan & Hinz, 2010;Rahardjo et al, 2014;Leung et al, 2015;Ng et al, 2016a, b;Jotisankasa & Siririrattanachat, 2017), probably because of the blockage of soil pore space by roots (Buczko et al, 2007).…”

“…Some studies (Table 1) showed an increase in water retention capability when plant roots are present in the soil (Scanlan & Hinz, 2010;Rahardjo et al, 2014;Leung et al, 2015;Ng et al, 2016a, b;Jotisankasa & Siririrattanachat, 2017), probably because of the blockage of soil pore space by roots (Buczko et al, 2007). However, some studies reported an opposite result Jotisankasa and Sirirattanachat, 2017), arguably because of the formation of soil cracks due to, for instances, repeated soil shrinkage, swelling and root decay and growth (Vergani & Graf, 2015;Ng et al, 2016a;Ni et al, 2017;Leung et al, 2017).…”

Quantification of root reinforcement in bio-slope stabilization: laboratory and field studies

“…A major benefit in the mechanical aspect of plants on slope stability is via root soil reinforcement, which is considered as an additional soil strength or root cohesion [11][12][13][14]. Plants can provide additional slope stabilization effect further through transpiration, whereby soil moisture is extracted from the ground, thus increasing the soil suction and shear strength [15][16]. The roots can also affect soil's hydraulic conductivities, soil-water retention, and infiltration capacity in several opposing ways depending on root contents and growing stage [15,17].…”

“…Plants can provide additional slope stabilization effect further through transpiration, whereby soil moisture is extracted from the ground, thus increasing the soil suction and shear strength [15][16]. The roots can also affect soil's hydraulic conductivities, soil-water retention, and infiltration capacity in several opposing ways depending on root contents and growing stage [15,17]. Active growing roots tend to decrease permeability while decaying roots can increase macrovoid content, soil permeability, and infiltration into the soil.…”