Lawrence W. Parker

Diurnal migration and responses to simulated rainfall in desert soil microarthropods and nematodes

Abstract Diurnal patterns of microarthropod abundance in surface leaf litter were related to its moisture content. Leaf litter moisture was nearly 7% by weight at 0800h but fell to less than 1% by mid-day. Oribatid and tydeid mites moved into litter in the early morning and back into the soil before mid-day. There were no significant differences in numbers of nematodes in litter or soil and 78–98% of the nematodes were anhydrobiotic (coiled) in soil and litter at all times sampled. Following simulated rainfall there were fewer microarthropods in litter at mid-day in the absence of marked decreases in soil and litter moisture content. During drying, there were gradual reductions in numbers and species diversity of litter microarthropods. Nematode numbers did not change as litter dried. Anhydrobiotic nematodes in the soil increased from 14% on day 1 to 85% on day 4. Between 24 and 36 h after simulated rainfall, the proportion of anhydrobiotic litter nematodes increased from 35 to 80%,. Within 1 h after simulated rainfall, there were marked increases in numbers and diversity of microarthropods in surface litter. No collembolans were extracted from dry litter controls but the wet litter was dominated by isotomid, sminthurid and onychiurid collembolans. There were increases in numbers and diversity of oribatid, tydeid and gamasid mites in the wet surface litter within l h after wetting compared to controls.

Soil respiration in a chihuahuan desert rangeland

Abstract Soil respiration of a desert soil was measured at the New Mexico State University Ranch in Southern New Mexico. Respiration rates were highest during late July and August after summer rains. Soil respiration data were used to estimate soil organic matter turnover which was 54 yr using summer data and 20 yr using both summer and winter data. The long turnover estimate for summer measurements resulted from temperatures above optimum in June and July. Diurnal soil respiration was also measured after a simulated 2.54 cm rain event. For both wetted and dry soils, temperature controlled the patterns of soil respiration with an optimum of near 41°C. Activation energy values decreased from 84.91 to 39.5 kJ mol −1 when the soil was wetted. A light-dark container method was tested as a possible means of estimating algal uptake of CO 2 , however, the method was not feasible for desert soils.

Effects of organic amendments on soil biota on a degraded rangeland.

Rehabilitation of degraded rangeland requires rebuilding the soil, including soil biota. In this study wheat straw, bark and wood chips, and dried municipal sludge were placed on native range plots in northcentral New Mexico. Organic amendments had little or no effects on decomposition of straw, litter respiration, soil respiration, biomass of soil microflora, and populations of most of the soil biota in the second year of the study. The differences in soil nematode and microarthropod population densities and straw decomposition occurred only in the bark and wood chip mulched plots in year 1. The absence of differences in year 2 may have been the result of below-average rainfall. The wood chip bark mulch was visibily present at the end of year 2 but the other mulches were not. There may be long-term benefits from application of recalcitrant mulches like wood chips and bark, but the less recalcitrant mulching materials like straw and low application rates of sludge produce no measurable benefit.

Effects of Initial Litter Accumulation and Climate on Litter Disappearance in a Desert Ecosystem

We examined monthly litter disappearance from initial concentrations of 50g, lOOg, 150g and 200g * m2. Approximately 35%-50% of the litter disappeared each month from May-September. In March and April litterfall input exceeded litter loss. Litter loss was consistently higher in the lOOg * m-2 accumulation than from the other concentrations. Stepwise regression analysis showed that litter loss varied as a function of soil temperature at 15 cm (r2 = 0.40) and that initial litter quantity was the second most important variable (increased r2 to 0.45). Monthly litter disappearance was apparently independent of monthly rainfall. Abiotic variables gave an r2 of 0.48, suggesting that much of the seasonal variation in litter disappearance is attributable to the soil biota. Suppression of microarthropods by treating the soil with chlordane insecticide resulted in marked reduction in litter disappearance.

Contributions of soil fauna to decomposition and mineralization processes in semiarid and arid ecosystems

Abstract This review examines the following questions: (1) do soil fauna play an important regulatory role in decomposition and mineralization processes in arid and semiarid ecosystems? (2) if important, what are the mechanisms of the rate regulation, and (3) what are the management implications of these relationships? Because termites process more than half of the surface litter in hot deserts, this review focuses on faunal effects on buried litter and roots. Elimination of soil arthropods reduced rates of mass loss and coupled mass loss to soil moisture. With arthropods present soil moisture accounted for less than 50% of the variation in mass loss. Other experiments demonstrated that regulation of mass loss results from predatory mites regulating the population density of grazers, thereby preventing overgrazing of the fungi and bacteria. The regulation of microbial grazers by soil microarthropods also affects rates of mineralization and nutrient immobilization. Populations of small fungus grazing mites...

Decomposition and soil biota after reclamation of coal mine spoils in an arid region

SummaryWe compared soil biota and buried wheat straw decomposition on sites subject to topsoiling plus straw mulch reclamation procedures 1–4 years prior to our study and on an unmined site. Rates of straw decomposition were highest on the unmined site. Decomposition rates were higher on the 1- and 2-year-old sites than on the 3- and 4-year-old reclaimed spoil. Microarthropod population densities and number of taxa were greater from decomposing straw on the unmined site and lowest from straw on the 1- and 2-year-old areas. Soil bacteria, fungi, and protozoan populations on buried straw on the oldest reclaimed sites were generally equal to those on the unmined area. Nematode populations on buried straw in the unmined site and 1- and 2-year-old reclaimed sites were similar. Populations of denitrifying bacteria were larger on recently reclaimed sites than on 3- and 4-year-old sites. Decomposition and nitrogen mineralization varied as a function of the diversity and abundance of soil microarthropods. Soil microfauna can serve as an index of soil development in a disturbed arid soil.