(324) Irrigation Effects on Fine Root Dynamics in Peach (Prunus persica)

We are using a minirhizotron camera system to observe fine root dynamics beneath irrigated and nonirrigated peach trees. Our long term goals are: 1) to relate the timing of fine root production to tree phenology, soil water content, and soil temperature; and 2) to determine how fine root architecture and demography differ between trees with and without supplemental irrigation. In early 2002, minirhizotrons were constructed and installed beneath each of 72 open-center, 4-year-old `Redglobe' peach trees at the Musser Fruit Research Farm near Clemson University. Beginning in May 2002, videotaped images from each minirhizotron were collected at 2-week intervals; notes on tree phenology were also recorded biweekly. Videotapes were digitized in the lab, and information on root length, diameter, appearance and longevity was extracted from the images. Soil temperature and volumetric water content were measured in the orchard throughout the growing season. In the 2 years following minirhizotron installation, irrigated trees allocated a significantly greater percentage of their fine root length to the upper soil layers and exhibited less root branching than nonirrigated trees. Fine roots produced by irrigated trees lived significantly longer: irrigated trees had a median root life span of 165 days, while nonirrigated trees had a median root life span of only 115 days (P< 0.001; proportional hazards regression). Fine roots from irrigated trees remained in the physiologically active “white” state for an average of 10 days longer than roots from nonirrigated trees (P< 0.001). Data from 2002–03 indicate that the trees produce new root flushes at least three times during the year, with a significant flush occurring immediately after harvest.

Rapid fine root disappearance in a pine woodland: a substantial carbon flux

Fine root production and mortality are difficult to estimate accurately, because some fine roots die within days of being produced, and many apparently healthy roots disappear rapidly with no obvious period of senescence. Such root dynamics are difficult to analyze without very fine-scaled temporal observations. To capture the behavior of short-lived and rapidly disappearing roots, we sampled minirhizotron tubes weekly for 11 months in a Pinus palustris Mill. woodland. Fine root ([Formula: see text]2 mm diameter) length production and length mortality during this period were 1.57 ± 0.23 mm·cm–2 (mean ± SE) and 1.19 ± 0.17 mm·cm–2, respectively. Depending on the type of estimate used, rapid disappearance accounted for between 21 and 37% of total fine root mortality. Rapidly disappearing roots had relatively short life-spans, a median of just 10.5 days. Monthly sampling of the same data set underestimated length production by 15%, overestimated median root life-span by 60%, and obscured causes of root loss. If short-lived roots are not accounted for, total net primary productivity in temperate forests may be underestimated by as much as 10%. We propose that belowground herbivory is the leading explanation for this rapid disappearance.