Water acquisition, sharing and redistribution by roots: applications to agroforestry systems

J Bayala,I Prieto

doi:10.1007/s11104-019-04173-z

Abstract

AimsIn the face of problems caused by ‘intensive agriculture’ dominated by large areas of monocultures, mixed intercropping mimicking natural ecosystems has been reported to constitute a viable solution to increase and stabilize productivity. When designing such systems, root niche separation was thought to be a prerequisite to optimize production.MethodsThis paper reviews the beneficial and adverse effects of trees and crops on water acquisition and redistribution in agroforestry ecosystems using the concepts of competition and facilitation between plants in link with root functional traits.ResultsThe results of the review showed that the reality was more complex leading agroforestry practitioners to adopt management practices to induce a separation in root activities thus avoid competition, particularly for water. Water uptake by plant roots is triggered by the water potential difference between the soil and the atmosphere when leaf stomata are open and depends largely on the root exploration capacity of the plant. Thus, root water uptake dynamics are strongly related to root-length densities and root surface areas. In addition, plants with deep roots are able to lift up or redistribute water to the upper layers through a process known as hydraulic lift, potentially acting as “bioirrigators” to adjacent plants. The redistributed water could be of importance not only in regulating plant water status, e.g. by enhancing transpiration, but also in increasing the survival and growth of associated crops in mixed systems.ConclusionsEven though some more work is still needed to assess the volume of water transferred to neighbors, hydraulic lift could constitute an ecological viable mechanism to buffer against droughts and ensure productivity in regions with erratic rainfall. Giving the difficulty in measuring the above-mentioned aspects in the field, modeling of some of the most relevant parameters to quantify them might inform the design of future empirical studies.

Highlights

In the face of the world current challenges to sustain good living conditions including increasing population numbers, a changing climate or the degrading agro-ecosystems associated with a declining agricultural productivity, there is a need for approaches that could ensure food security
Agroforestry or the combination of trees with agricultural crops or pasture, was listed among the climate smart technologies (Dinesh et al 2017). This is due, in large part, to the fact that intercropping has the potential to promote an efficient use of two limiting factors for plant growth, i.e. water and nutrients, by an improved acquisition of these resources through complementary root distributions, water sharing mechanisms such as hydraulic redistribution (HR), common mycorrhizal networks, and/or reduced runoff leading to increased water infiltration (Bayala and Wallace 2015; Brooker et al 2015; Mao et al 2012; Prieto et al 2012b)
The safety-net hypothesis, i.e. intercepting mobile nutrients leaching from crop root zones, is complementary to the nutrient pump hypothesis which refers to the taking-up of nutrients, generally relatively immobile, from deep soil layers, their incorporation in aboveground plant tissues and their transfer to upper soil layers through leaf shedding and decomposition (Ong and Leakey 1999; van Noordwijk and Ong 1999; Jobbagy and Jackson 2004)

Summary

Results

The results of the review showed that the reality was more complex leading agroforestry practitioners to adopt management practices to induce a separation in root activities avoid competition, for water. Water uptake by plant roots is triggered by the water potential difference between the soil and the atmosphere when leaf stomata are open and depends largely on the root exploration capacity of the plant. Root water uptake dynamics are strongly related to root-length densities and root surface areas. Plants with deep roots are able to lift up or redistribute water to the upper layers through a process known as hydraulic lift, potentially acting as “bioirrigators” to adjacent plants. The redistributed water could be of importance in regulating plant water status, e.g. by enhancing transpiration, and in increasing the survival and growth of associated crops in mixed systems

Conclusions

Introduction

Conclusion