Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/23/2001
Publication Date: N/A
Interpretive Summary: Root systems represent a tremendous carbohydrate cost to plants. Although plants require roots for water and nutrient uptake, when more carbohydrates are invested in roots, fewer carbohydrates will be available for shoot growth and yield. Root carbohydrate requirements vary with soil conditions. The majority of roots in citrus are near the soil surface, a region where conditions are frequently dry and temperatures fluctuate considerably. To better understand carbohydrate costs associated with citrus roots in different environments, relationships between root carbohydrate use (measured as respiration) and soil conditions were developed. We found that root respiration was higher in warm wet soils than in cooler soils. However, after 3-4 days, citrus roots adapted to temperatures above 23 degrees Celsius, thereby reducing their metabolism under these conditions. We also found that root respiration decreased in dry soil. Using these data, a model was constructed to predict citrus root respiration based on temperature and soil moisture. Root respiration predicted by the model was similar to respiration measured in a citrus grove. In conjunction with other available models, this model can be used to predict the effects of various soil management practices (e.g., irrigation, mulching) on tree growth and fruit yield in citrus.
Technical Abstract: In citrus, the majority of fine roots are distributed near the soil surface, a region where conditions are frequently dry and temperatures fluctuate considerably. To develop a better understanding of the relationship between changes in soil conditions and a plant's belowground respiratory costs, the effects of temperature and soil drying on citrus root respiration were quantified in controlled greenhouse experiments. Chambers designed for measuring respiration of individual roots were used. Under moist soil conditions, root respiration in citrus increased exponentially with changes in soil temperature (Q10 = 1.8 to 2.0), provided the changes in temperature were short term. However, when soil temperatures were held constant, the response of root respiration to increasing temperatures could not be defined exponentially. This was because citrus root acclimated to controlled temperatures above 23 degrees C, thereby reducing their metabolism in warmer soils. Under drying soil conditions, root respiration decreased gradually at 6% soil water content and reached a minimum at <2% soil water content. Using greenhouse data from this study, a model was constructed to predict diurnal patterns of fine root respiration based on temperature and soil water content. The model was then tested and validated in the field using data obtained by CO2 trapping on root systems of mature citrus trees. The trees were grown at a site where soil temperature and water content were experimentally manipulated. Respiration rates predicted by the model were in general agreement with observed rates, which indicates the model may be used to estimate entire root system respiration in citrus.