Weed ecology is affected by succession in differently aged gardens of Citrus sinensis and C. reticulata

Abstract

The concepts of destruction and rebuilding in the succession play an important role in agro-ecology. Agricultural ecosystems are always affected by tillage, soil preparation, harvest, burning, and arboriculture. A common practice in the northern province of Mazandaran (Iran) is to replace rice (Oryza sativa L.) cultivation with Citrus farming. It can be accordingly interesting to investigate the ecology of weed community specifically the dominance and characters during the different stages of succession, using constitutive and physiological aspects. In a 2-year research work, some functional (species composition and stability) and physiological characteristics (relative growth rate, biomass, and N and P uptake) of different weeds in the initial and final stages of secondary succession in Citrus gardens were compared. Three young (Citrus sinensis L.) and three old Citrus (Citrus reticulata Blanco) gardens (with the average age of 2 and 29 years, respectively), were selected in the suburb of Qaemshahr city (Iran), the centre of Citrus production. In each garden, three main fixed plots (30 m2), with five subplots (1 m2) and destructive quadrates in each one, were prepared and used for the experiment (January 2013–August 2014). Weed composition was monthly recorded. The concept of dominance diversity was used to estimate the community consistency. Thirty-three weed species were identified among which the Poaceae and Asteraceae families were the dominant ones. In the young gardens, the number of weed species was twice more than the old ones. Poa nemoralis as a perennial and sciophytes species were plentiful in the old gardens. Just in the young gardens, the weed species were moved by pappus. There was a linear and stable regression between weed frequency and dominance in the final sampling. Higher relative growth rate as well as higher N and P uptake was resulted in the young gardens. Seed size and growth rate were correlated in the young gardens, and the smaller seeds resulted in a higher rate of weed survival. Parameters including weed dominance, functional and physiological characteristics, seed size, and the environment may determine weed ecology and survival at different stages of succession in Citrus gardens.