Seasonal variation in soil CO2 emission and leaf gas exchange of well‐managed commercial Citrus sinensis (L.) orchards
Lawrence Munjonji, Kingsley Kwabena Ayisi, T. P. Mafeo, Thabang Maphanga, Kabisheng Mabitsela
Abstract
Abstract Purpose To investigate whether soil clay content, cultivar and seasonal variation have any effect on soil CO 2 emission rates and leaf CO 2 assimilation rates in a drip-irrigated commercial Citrus sinensis orchard. Methods The study was carried out in the field as a randomised complete block design in a 2 × 2 factorial consisting of two soil types and two citrus cultivars on a drip-irrigated commercial Citrus sinensis orchards with 2-week interval measurements of soil CO 2 emission and leaf gas exchanges for a year. Results Soil clay content did not influence plant CO 2 assimilation rates and soil CO 2 emission rates in irrigated citrus. However, seasonal variation significantly influenced both processes. Soil CO 2 emission rates were highest in summer and were more than double the rates observed in winter while leaf CO 2 assimilation rates were highest in autumn and four times higher than the winter season rates. Mean seasonal soil CO 2 emission rates were strongly influenced by mean minimum seasonal temperatures while leaf CO 2 assimilation rates only showed a relatively weak relationship with mean maximum seasonal temperatures. Conclusions Soil clay content did not influence soil CO 2 emission and assimilation rates in drip irrigated citrus suggesting a non-significant effect of clay content for soils subjected to similar management practices. Citrus CO 2 assimilation rate peaks in the autumn while soil CO 2 emission rates peak in summer. A snapshot analysis of CO 2 sequestration rates suggests that irrigated citrus orchards are net sinks of CO 2 in summer, autumn and winter season.