Aquaporin‐mediated changes in hydraulic conductivity of deep tree roots accessed via caves

Abstract

Although deep roots can contribute substantially to wholetree water use, little is known about deep root functioning because of limited access for in situ measurements. We used a cave system on the Edwards Plateau of central Texas to investigate the physiology of water transport in roots at 18-20 m depth for two common tree species, Quercus fusiformis and Bumelia lanuginosa. Using sap flow and water potential measurements on deep roots, we found that calculated root hydraulic conductivity (RHC) fluctuated diurnally for both species and decreased under shading for B. lanuginosa. To assess whether these dynamic changes in RHC were regulated during initial water absorption by fine roots, we used an ultra-low flowmeter and hydroxyl radical inhibition to measure in situ fine root hydraulic conductivity (FRHC) and aquaporin contribution to FRHC (AQPC), respectively. During the summer, FRHC and AQPC were found to cycle diurnally in both species, with peaks corresponding to the period of highest transpirational demand at midday. During whole-tree shade treatments, B. lanuginosa FRHC ceased diurnal cycling and decreased by 75 and 35% at midday and midnight, respectively, while AQPC decreased by 41 and 30% during both time periods. A controlled growth-chamber study using hydroponically grown saplings confirmed daily cycling and shade-induced reductions in FRHC and AQPC. Winter measurements showed that the evergreen Q. fusiformis maintained high FRHC and AQPC throughout the year, while the deciduous B. lanuginosa ceased diurnal cycling and exhibited its lowest annual values for both parameters in winter. Adjustments in FRHC and AQPC to changing canopy water demands may help the trees maintain the use of reliable water resources from depth and contribute to the success of these species in this semi-arid environment.

Vascular Function in Grape Berries across Development and Its Relevance to Apparent Hydraulic Isolation

“…Aquaporins are a family of transmembrane proteins considered to be largely responsible for the high permeability to water exhibited by plasma membranes. The regulation of R h by aquaporins is now well documented in roots (Martre et al, 2001;McElrone et al, 2007;Vandeleur et al, 2009), and oxidative gating of aquaporins has been reported to reduce hydraulic conductivity by 90% in cells of the giant algae Chara (Henzler et al, 2004). The results of previous work suggest that aquaporins play an important role in the regulation of water movement during the development of flowers, seeds, and fruits (Maurel et al, 1995;Gao et al, 1999;Picaud et al, 2003;Shiota et al, 2006;Zhou et al, 2007).…”

Vegetation in karst terrain of southwestern China allocates more biomass to roots

“…Plants growing in tiny, shallow soils and rocky habitats tend to allocate more resources to roots to maintain and physically support the ecosystem. However, dominant canopy tree species in karst forests have low net photosynthetic rate and low light photosynthetic productivity (Yang, 2011), but changes of hydraulic conductivity of deep tree roots may help the trees maintain the use of reliable water resources from depth (McElrone et al, 2007). Such ecophysiological evidences imply that karst forests have lower growth rate and lower biomass and productivity, but in such a shallow-water lacking environment more roots are developed to elevate deeper groundwater.…”

Soil water potential determines the presence of hydraulic lift of Populus euphratica Olivier across growing seasons in an arid desert region

“…Specifically, plants spent their energy on active transport of water when they suffered from the extreme environment, e.g. the storage water in plants was insufficient to meet their metabolic activities, or plants urgently needed to lift water from groundwater into shallow soils via plant stems to absorb minerals (McElrone et al 2007;Prieto et al 2012;Johnson et al 2014). Within the HL process, it may be not enough water potential difference to lift water from deep soil layers or groundwater to shallow soil layers due to transpiration shutoff at night (Prieto et al 2012).…”