Effects of subsoiling on lateral roots, sucrose metabolizing enzymes, and soil ergosterol in two Jeffrey pine stands.

We determined the effects of subsoiling on woody lateral roots and enzyme activities involved in stem carbon metabolism of 90- to 100-year-old Jeffrey pine (Pinus jeffreyi Grev. and Balf.) growing on the eastern side of the California Sierra Nevada Range. Twelve 1.0-ha plots were established on each of two sites. Four site treatments-thinning and subsoiling entire plots, thinning and no subsoiling, thinning and subsoiling skid trails only, and no thinning or subsoiling (undisturbed control)-were replicated three times on each site. Root excavations and assays of stem cambium sucrose metabolizing enzymes were carried out during the summer and fall of 1994 and 1995. Subsoiled plots had more roots < 1 cm in diameter exhibiting dieback than undisturbed plots. No relationship was found for stem cambial sucrose synthase (SS) activity among treatments or sites; however, a strong seasonal pattern was observed. Activity of pyrophosphate-dependent phosphofructokinase (PPi-PFK) was seasonal, whereas ATP-dependent phosphofructokinase (ATP-PFK) activity was constant throughout the seasons. Neither of the PFK activities responded to treatment or site. Among plots, ergosterol, a surrogate for estimating live fungal biomass, was present in highest concentrations in soil and rhizosphere samples from subsoiled plots.