Early Pinus caribaea var hondurensis root development .1. Influence of matric suction

This paper reports 2 experiments that examine the influence of matric suction on radicle elongation in Pinus caribaea var. hondurensis. Experiment 1 where mechanical impedance of root development was negligible and aeration was not limiting, and experiment 2 in low strength soils where both air-filled porosity and moisture were allowed to vary. In experiment 1, radicles were grown between sheets of Whatman No. 42 filter paper. The known wetting characteristic of this paper was used to prepare known pretrial suctions and define postharvest suctions. The midpoint of the pretrial-postharvest suction range was defined as nominal matric suction. Relationships between radicle elongation and nominal matric suction were developed for 6 P. caribaea var. hondurensis families. As matric suction increased from 0.0065 to 3.13 MPa, radicle elongation after 48 h of growth decreased monotonically to zero. Over the range of matric suctions, there was no critical level, below which radicle elongation was unaffected by increasing suction. It was concluded that radicles were able to sense, and respond to, increasing suction. Significant family x matric suction interactions were observed. In experiment 2, radicles were grown in 2 low-strength repacked soils. An optimal level of matric suction for radicle elongation was observed in both soils. At suctions below and above the optima, inadequate air-filled porosity and moisture stress respectively adversely impacted upon elongation. The 2 experiments demonstrated that matric suction affects radicle elongation both directly and indirectly through interaction with other physical soil properties. Although increasing suction reduces radicle elongation, there may be a 'non-limiting' range of suctions in soil media over which radical elongation is relatively unaffected due to a concomitant improvement in aeration.