Below‐ and above‐ground growth and biomass allocation in maize and Sorghum halepense in response to soil water competition

Abstract

The aim of this study was to establish the morphological or physiological nature of the changes in growth parameters of maize and Sorghum halepense plants growing under competition for water. Plant growth analysis studies in semi-controlled conditions in plastic containers were conducted in two consecutive years. The competition treatments were established 4 weeks after emergence of both species and lasted for 4 weeks. Treatments of low (75% of field capacity) and very low water availability (irrigation withheld) were established. The variables obtained were: relative growth rate (RGR), leaf area ratio (LAR), net assimilation rate (NAR), specific leaf area (SLA), leaf mass fraction (LMF), rhizome mass fraction (rizMF), root length ratio (RLR), root mass fraction (RMF), specific root length (SRL) and length of fine roots (VfRL). The RGR of S. halepense was less affected by the two levels of competition than that of either of two maize hybrids. The weed was able to maintain its ability to grow, due to the maintenance of NAR during competition. A similar contribution of biomass from leaves and rhizomes to roots was observed in S. halepense, favouring the formation of very fine roots. In contrast, in maize, the decrease in RGR was due to a decline in NAR and there was no formation of fine roots to maintain water absorption during competition. The greater increase both in biomass partitioned to roots and root length by S. halepense, might negatively impact maize ability to compete for water during the critical competition period.