Intercrops improve the drought resistance of young rubber trees

Abstract

The expansion of rubber cultivation into drought prone areas calls for innovative management to increase the drought resistance of the trees. The competition for water exerted by an intercrop in the upper soil layers will likely stimulate the growth of young rubber tree roots into deeper soil layers where water availability is more stable. This study examined the effects of a legume (Pueraria phaseoloides) and a grass (Vetiveria zizanoides) intercrop, on the fine root traits of young rubber trees (Hevea brasiliensis Müll. Arg.) established along a toposequence covering a range of soil depths in northeast Thailand. Two plots with and without the intercrops were set up in a 3-year-old rubber plantation. Tree girth, mortality rate, nutrient content in the leaves, predawn leaf water potential, and soil water content profiles were monitored over four successive years. Fine root length density, specific root length, fine root biomass, and fine root diameter of the rubber trees were measured in the fourth year. In shallow soils, the trees with the legume intercrop had a higher growth rate, a higher leaf nutrient content, and a higher fine root length density in the deepest soil layers than the controls, supporting the hypothesis of an adaptive root response, increasing drought resistance. However, the trees with the grass intercrop did not show this effect. In deep soils, specific root length was highest without the intercrops, and the soil water profile and predawn leaf water potential suggested that trees with intercrops benefited from increased water extraction below 110 cm depth. We showed, for the first time, that rubber tree root traits can be manipulated through intercropping to improve drought resistance. However, our results suggest intercropping might not reduce risks of tree mortality caused by drought in the shallowest soils of the subhumid area of northeast Thailand.

Root foraging of birch and larch in heterogeneous soil nutrient patches under water deficit

“…Tree roots are capable of responding to drought through a variety of strategies including belowground biomass adjustment, anatomical alteration, physiological acclimation, and morphological growth [ 6 ]. A drought event can stimulate tree roots to penetrate downwards and explore deeper soils by elongating the root axis and enlarging the diameter and surface area of the root system [ 7 , 8 ]. More roots arranged in deeper soils can compensate for declining shallow roots in severe droughts [ 8 ] and avoid competition for water in topsoil [ 7 ].…”

“…A drought event can stimulate tree roots to penetrate downwards and explore deeper soils by elongating the root axis and enlarging the diameter and surface area of the root system [ 7 , 8 ]. More roots arranged in deeper soils can compensate for declining shallow roots in severe droughts [ 8 ] and avoid competition for water in topsoil [ 7 ]. Tree root systems can also increase the branching of lateral fine roots by continuously egressing new roots to arrange the belowground system and help increasing soil porosity [ 9 ].…”

“…Regarding the similar response to soil heterogeneous condition across multiple herbaceous plant species [ 12 , 23 , 38 ], our objective was to assess fine root foraging behavior and N utilization in the two tree species. It was hypothesized that: (i) root foraging precision and plasticity will show the same response for both birch and larch, and (ii) root foraging behavior will be promoted by drought [ 7 , 8 ].…”

Intercropping of Maize (Zea mays) and Cotton (Gossypium hirsutum L.) vs. Monoculture: Plant Growth, Root Development, and Yield

“…Li et al (2001) pointed out the subtotal crop yield at maturity in intercropping of two crops was higher overall than the sum of crop yields when individually culturing them. Clermont-Dauphin et al (2018) found that intercropping with other species could alter the root traits of rubber trees and improve its drought resistance. In our experimental study, it is possible that the root morphology of intercropped maize and cotton had mutual influence on the plant growth and yield formation.…”

Economic outcomes of rubber-based agroforestry systems: a systematic review and narrative synthesis

“…While great ecological and biophysical benefits of rubber agroforestry are well established (Drescher et al 2016;Clermont-Dauphin et al 2018;Warren-Thomas et al 2015), worldwide production of natural rubber is increasingly in monoculture systems (Langenberger et al 2017). This trend toward monoculture rubber is especially noted in Asia (Drescher et al 2016).…”