EFFECTS OF SOIL COMPACTION AND ORGANIC MAl-l-ER REMOVAL ON MORPHOLOGY OF SECONDARY ROOTS OF LOBLOLLY PINE

Root studies are being used to monftor possible changes in growth of loblolly pines on a long-term serf productivity study site. Here, we report the results of a preliminary look at roots in the sixth growrng season, Roots were collected from loblolly pines grown in soil that was first subjected to three levels of compaction (none, moderate, severe) and three levels of organic matter removal (stem only, total tree, and total aboveground biomass). Roots were fixed, sectioned, and stained for examination by light microscope. The proportion of roots with bark formation decreased from 70 percent in uncompacted soil to 43 percent in severely compacted soil. Depletion of starch grains was significantly fess In samples from uncompacted soil than in compacted soil. INTRODUCTION year-old loblolly pine stand on the site was harvested in Management p rac t i ces tha t change so i l p roper t ies may 1989. The compaction treatments (none, moderate, and affect growth and health of secondary roots and eventually severe) and organic matter treatments (stem only, total the long-term productivity of the site. The USDA Forest tree, and total aboveground biomass) were applied soon Service’s long-term soil productivity (LTSP) study, which after harvest. The ‘plots were planted with containerized has recently been installed at several sites in the United seedlings from 10 open-pollinated loblolly pine families in States and Canada (Tiarks and others 1993) is designed to February 1990. Soil bulk densities were measured with a measure such changes over a rotation. Its primary purpose core sampler at planting and at stand age 5. Tree volumes is to monitor changes in productivity and soil processes. were calculated on the basis of pine heights and diameter Three levels of soil compaction, three levels of organic at breast height (d.b.h.) measured at age 6 (Schmitt and matter removal, and two levels of vegetation control were Bower 1970) . applied (Powers and others 1990). Ultimately, interpretation of the relationship between these treatments and Roots were sampled twice in the sixth growing season. In productivity will require the linking of changes in soil the first sampling (March 24, 1995) roots from 10 trees properties to soil processes, including root growth and were collected in the plots representing the extremes of the heal th. treatments (OM,C, and OM,C,). In the second sampling (October 10, 1995) we sampled roots of five pines per Anatomical study of roots is particularly useful for treatment. There were 9 different treatments, and an assess ing roo t hea l th (Wa lk inshaw 1995) . So i l compac t ion average of 14 roots per tree was collected at each affects root health and subsequent crop production in sampling. The March sampling yielded 264 root specimens annua l c rops (A l lmaras and o thers 1988, Fe ldman 1984) . and the October sampling 753. Root samples were from Compacted soils have fewer and smaller pores, and such pines randomly selected from among the families. To conditions damage roots and alter their morphology. ensure that nonpine roots were not included in the Loblolly pine roots less than about 5 millimeter (mm) in samples, we collected only in subplots that had received diameter appear to be particularly vulnerable to soil he rb ic ide t rea tment . compact ion (Cope land 1952) . Shedd ing o f dead cor tex reduces root diameter and eliminates large numbers of root Roots were collected in a 25centimeter (cm) by 25-cm hairs in loblolly and other conifers (Kozlowski and Scholtes area located about 1 meter (m) from the stem of a pine. All 1948, Leshem 1974). Many injuries develop after the period soil and roots between a depth of 2 cm and a depth of 20 of roo t ex tens ion dur ing secondary roo t deve lopment cm were collected and the roots gently shaken to remove (Coutts 1987). excess soil. The center 2 to 4 cm of each root was excised and placed into formalin-acetic acid-alcohol (FAA) fixative The objectives of the present study were to evaluate the for 14 days (Sass 1951). Fixed root specimens were re-cut usefulness of root morphology variables as indicators of to 1 to 3 mm, dehydrated in alcohol series, embedded in root health, and to measure the effects of soil compaction paraffin, and cut into 7 micrometers (m) to 10 m transverse and organ ic res idue remova l on anatomy o f secondary sections. Sections were stained by hematoxylin-eosin, roots. Papan ico laou ’s schedu le , o r the ac id -sch i f f p rocedure (Haas 1980). Three to nine stained sections were prepared METHODS from each root, but only the first usable section from each The root samples used were collected at the LTSP site root was read. Observations on root sections were at 100 located in Rapides Parish, LA, (Tiarks and others 1991) at to 500 diameters with a photomicroscope. Halogen and the beginning and end of the sixth growing season. A 40. polarized light sources and neutral density filters were used ’ Plant Pathologist and Soif Scientist, respectively, USDA Forest Service, Southern Research Station, 2500 Shreveport Highway, Pineviffe, LA 7 1 3 6 0 . In: Haldrop, Thomas A., ed. 1998. Pmcedhgs of the dnth biennial 418 southern siividtural fe~eafch conference; 1997 mmar~ 2527; Clemson, SC. Gen. Tech. Rep. SRS-20. Asheville, NC: U.S. Departrent ofAgrkulture,PorestSe~ice, Southern Researd Station. p. 418-421. II to differentiate tannin and cellulose:lignin complexes. The percentage of roots meeting the criteria for a variable was calculated by tree. If the cambium appeared dead and tannin accumulation was excessive, the root was considered to be dead and not used in further analysis. No dead roots were found in the March sampling and only four roots were dead in the October sampling. Variables for Histological Observations Based on past observations of root samples from Louisiana (2,619 roots), Mississippi (623 roots), and North Carolina (1,221 roots), 10 variables were selected for further testing. They were :