EFFECTS OF SOIL COMPACTION AND VESICULAR-ARBUSCULAR MYCORRHIZAE ON ROOT DYNAMICS OF YELLOW-POPLAR AND SWEETGUM SEEDLINGS

GERRY LYNN SIMMONS, Purdue University

Abstract

Greenhouse and field studies were conducted to determine the influence of changes in soil physical properties associated with increasing compaction on root dynamics of yellow-poplar (Liriodendron tulipifera L.) and sweetgum (Liquidambar styraciflua L) seedlings grown in association with the mycorrhizal fungi Glomus macrocarpum Tul. and Tul. or G. fasciculatum (Thaxt) Gerd. and Trappe. In the greenhouse studies, seedlings were transplanted into pots containing silt loam soil compacted to bulk densities of 1.25, 1.40, or 1.55 Mg m$\sp{-3}$ and grown for three months. Seedlings were inoculated with fungal chlamydospores or distilled water during transplanting. In the first study, the minimum soil water potential was $-10$ kPa. In the second study, minimum soil water potentials were $-10$ or $-300$ kPa. At both water potentials, total weight and length of lateral roots, fibrosity of the root system, stem height, and total biomass of seedlings for both tree species decreased significantly when bulk density increased from 1.40 to 1.55 Mg m$\sp{-3}$. Root limiting values for bulk density, mechanical resistance, and air-filled porosity were 1.55 Mg m$\sp{-3}$, 4180 kPa, and 0.06 m$\sp{3}$ m$\sp{-3}$, respectively. Critical values for bulk density and resistance were greatest and critical values for air-filled porosity were least for sweetgum seedlings inoculated with G. fasciculatum. The root growth model, ROOTCOMP, accurately predicted total root length for each tree-fungal association for the range of soil conditions tested in the second greenhouse study. Inoculated yellow-poplar seedlings had greater root weight at each bulk density than noninoculated seedlings. Mycorrhizal effects on root length of yellow-poplar were variable, and fibrosity was not significantly affected by mycorrhizal treatment. Mycorrhizal dependency values for yellow-poplar did not differ between fungal species. At $-10$ kPa, sweetgum seedlings inoculated with G. fasciculatum had the greatest root weight, length, and fibrosity, and the highest mycorrhizal dependency values at each bulk density. At $-300$ kPa, sweetgum seedlings inoculated with G. fasciculatum had the greatest root growth at the low and medium bulk densities. In the field study, mycorrhizal treatments did not significantly affect first year root growth at either site. Root growth of both tree species was greater at Site 1 due to lower bulk densities and a higher soil moisture content. In general, root growth at both sites decreased at surface bulk densities greater than 1.30 Mg m$\sp{-3}$.

Degree

Ph.D.

Subject Area

Forestry

COinS