Effect of different water supply regimes on growth and size hierarchy in spring wheat populations under mulched with clear plastic film

This study was conducted to determine the effect of water supply regimes and plastic film mulching on the harvest index (HI), reproductive allocation (RA) and size hierarchy in spring wheat (Triticum aestivum L.) populations, and to explore their mechanism in relation to size hierarchy and life-history strategies. The grain yield, biological yield (aboveground biomass), HI and RA of spring wheat decreased significantly (p < 0.001) along the water control gradient (irrigative amount decreased 132 → 66 → 0 mm) either mulching or non-mulching, size hierarchy (as measured by the Gini coefficient (G) of aboveground biomass per plant) always increased. HI and RA in mulching treatment were significantly lower than non-mulching (p < 0.05). Meanwhile, the number and weight of barren shoots and the ratio of barren shoot biomass to total shoot biomass were significantly greater (p < 0.05) in mulched populations than non-mulched controls both at booting, flowering and ripening stages. RA and HI were both negatively correlated to average G of the populations. These results suggested that size hierarchies in spring wheat populations are closely correlated with the water regime in the field, and that under greater drought stress there are relatively smaller plants with lower HI (size-dependent reproductive allocation). Size hierarchy is an index of competitive status in plant populations under stress environments. Agriculturally, greater size hierarchy may result in growth redundancy, which is detrimental to reproductive allocation and consequently, grain yield. The results support the view that stand uniformity in field crops is an important mechanism for increasing grain yield. From tilling to ripening stages, the tendency of Gini coefficient (G) shows obvious differences between mulched populations and non-mulched controls. At booting and flowering, the G was significantly higher in mulched populations than non-mulched controls, and it was just contrary at ripening. Appreciable growth redundancy occurred in spring wheat populations mulched with plastic film, which may result from the exacerbated interplant competition and self-thinning. Thus, spring wheat cultivation with plastic film mulching does not always mean high-efficiency, although there is a remarkable increase in grain yields.