Robert L. Tate

Effects of pine roots on microorganisms, fauna, and nitrogen availability in two soil horizons of a coniferous forest spodosol

SummaryWe investigated the effects of pitch pine seedling roots on extractable N, microbial growth rate, biomass C and N, and nematodes and microarthropods in microcosms with either organic (41% C, 1.14% N) or mineral (0.05% C, 0.01% N) horizon soils of a spondosol. Root quantity was manipulated by varying plant density (0, 1, 2, or 4 seedlings) and rhizosphere soil was separated from non-rhizosphere soil by a 1.2 μm mesh fabric. In the rhizosphere of organic soil horizons, moisture, microbial growth rate, biomass C and N, and extractable N declined as root density was increased, but there was little effect on nematodes or microarthropods. High levels of extractable N remained after 5 months, suggesting that N mineralization was stimulated during the incubation. In the rhizosphere of mineral soil horizons, microbial growth rate, and nematode and microarthropod abundances increased at higher root density, and in the absence of roots faunal abundance approached zero. Faunal activity was concentrated in the rhizosphere compared to non-rhizosphere soil. In organic soil horizons, roots may limit microbial activity by reducing soil moisture and/or N availability. However, in mineral soil horizons, where nutrient levels are very low, root inputs can stimulate microbial growth and faunal abundance by providing important substrates for microbial growth. Our results demonstrate a rhizosphere effect for soil fauna in the mineral soil, and thus extends the rhizosphere concept to components of the soil community other than microbes for forest ecosystems. Although our results need to be verified by field manipulations, we suggest that the effects of pine roots on nutrient cycling processes in coniferous forests can vary with soil nutrient content and, therefore, position in the soil profile.

Microscopic observations of bacterial sorption in soil cores

Abstract Bacterial cells may be immobilized in soil through adsorption to a variety of soil particles. These associations affect the interaction of native soil microbes with their nutrient sources and control at least in part the distribution of foreign bacteria entering the soil system. To observe the relationship between soil structure and adsorption of amended bacterial cells, a series of intact cores of Freehold fine sandy loam were inoculated with suspensions of Arthrobacter crystallopoietes cells at concentrations ranging from 106 to 108 cells per ml. The cells were cultivated in a glucose-based medium to induce spherical cell formation. Following inoculation, the soil cores were rinsed with sterile water (30–40 ml h–1), flushed with thiazine red R to stain the bacterial cells, and then prepared for examination by common micromorphological techniques. The use of fluorescence, polarizing, and reflected light microscopy of soil thin sections, allowed direct, qualitative determinations of microbial distribution and associations with soil components. A. crystallopoietes cells were detected throughout the length of the soil columns. Soil pores did not appear to be clogged by the spherical A. crystallopoietes cells. Adsorption of amended bacteria was governed by the presence of both variably charged mineral oxides and organic matter within the intergrain microaggregates and occurred along coated mineral surfaces. Amendment of non-inoculated soil columns with 0.2% (w/v) solution of glucose demonstrated that the staining and sectioning procedure was sufficiently sensitive to detect growth of indigenous bacterial populations and their distributions within the soil matrix.

Nitrogen mineralization rates of the acidic, xeric soils of the New Jersey Pinelands: field rates

Using the buried-bag procedure, we quantified nitrogen mineralization rates in the xeric, acidic Lakehurst, and Atsion sands of the New Jersey Pine Barrens. Average annual nitrogen yields in the upper 15 cm for the Lakehurst and the Atsion sands were 38.4 and 53.0 kg N/ha, corresponding to 4.5 and 2.5% of the total nitrogen, respectively. Net nitrogen mineralization in both soils exhibited distinct seasonal patterns with maxima in summer and minimum rates in the winter. Nitrification accounted for only 5% of the total N mineralized in both soils. This is consistent with the finding of low populations of autotrophic nitrifiera in these soils.

Microbial Biomass Measurement In Acidic Soil: Effect Of Fungal; Bacterial Activity Ratios And Of Soil Amendment

The chloroform fumigation-incubation method for estimating soil microbial biomass is applicable to most soils; but, problems are associated with its use with extremely acidic soils and with soils amended with carbonaceous substrates. To evaluate the basis for these difficulties, this project was commenced with the objectives of (a) evaluating the variation in the fungal respiration in fumigated and native acidic forest soil and of (b) assessing the effect of chloroform fumigation on microbial respiration and invertase activity in this soil amended with glucose or corn stover. The soil samples were collected from the O-horizon (pH 3.5) and A-horizon (pH 3.5) of a Lakehurst soil series (a mesic coated Haplaquodic quartzipsamment). Cycloheximide and streptomycin inhibition of glucose respiration indicated that in native O-horizon soil, the fungal to bacterial activity ratio was approximately 82:12. During the incubation period following fumigation, fungal activity ranged from 92 to 99% of total glucose respiration in fumigated O-horizon soil samples and 83 to 90% in the nonfumigated soils. Comparable values for the A-horizon soils were 85 to 90% in the fumigated soils and 33 to 84% in the native samples. Return of glucose metabolism to pre-fumigation rates occurred within 2 days after fumigation in the chloroform treated O-horizon soils whereas 10 days were required in the A-horizon soils. Chloroform fumigation of soils receiving corn stover or glucose caused a greater production of CO2 and more invertase activity due to the amendment than was detected in comparable nonfumigated soil samples. These data suggest that differences in basic microbial population activity ratios between chloroform-fumigated acidic soils and unfumigated control soil samples contribute to the difficulties of applying the chloroform fumigation-incubation method to extremely acidic soils and that the method is likely invalid for use with extremely acidic soils receiving inputs of carbonaceous compounds.

Nitrogen mineralization rates of the acidic, xeric soils of the New Jersey Pinelands: laboratory studies

In a series of laboratory incubation studies, we evaluated the effects of temperature, moisture, and nitrogen amendment on nitrogen mineralization rates in the acidic Lakehurst and Atsion sands of the New Jersey Pinelands. The average potentially mineralizable nitrogen (No) values for the Lakehurst and Atsion sands were 87 and 94 μg/g (170 and 630 kg N/ha), respectively. Mineralization constants (k) were 0.0501 and 0.0756/wk at 25 and 35°C, respectively, for the Lakehurst sand and 0.0327 and 0.0452/wk for the Atsion sand. Maximum mineralization occurred at 35°C for both soils with Q10 values ranging from 1.8 to 2.1. Optimal soil moisture tensions for nitrogen mineralization were between −0.01 and −0.03 MPa. A soil moisture tension of −0.1 MPa reduced nitrogen mineralization with the Lakehurst sand, but not with the Atsion sand. Amendment of the soil with ammonium sulfate increased mineralization with the Atsion sand, but had no effect on the Lakehurst soil. Conversely, ammonium chloride amendment increased the nitrogen mineralization rates in the Lakehurst, but not the Atsion sand. Urea amendment inhibited nitrogen mineralization with both soils. No nitrate accumulation was observed in any of the nitrogen-amended samples.

Function Of Protease And Phosphatase Activities In Subsidence Of Pahokee Muck1

To elucidate the biochemical mechanisms involved in subsidence of Histosols, I examined the role of protease and phosphatase activities in organic matter oxidation in Pahokee muck of the Everglades Agricultural Area. I studied the variation of enzyme levels in relation to the availability of organic matter (both exogenously supplied and native) and the parameters of development of enzymatic activities during reestablishment of microbial communities in steam-sterilized muck. In sterilized soils, protease and phosphatase activity development was compared with changes in endogenous respiration, glucose respiration, and polyphenol oxidase activity. Both protease and phosphatase activities were stimulated by augmented availability of metabolizable organic matter. This was shown through amendment of muck with dried, ground sugarcane (Saccharum spp. L.) leaves and through enhanced availability of native soil organic matter (suspension in water and mixing with sand). In the presence of plant debris, the augmented enzyme levels were maintained for up to 15d before a significant decline in activity was observed. Protease, phosphatase, and polyphenol oxidase activities, endogenous respiration, and glucose respiration increased immediately upon inoculation of sterile muck with fresh muck (1g fresh/10 g sterile muck). Greater activity was developed in sterile muck from a St. Augustinegrass (Stenotaphrum secundatum (Walt) Kuntz) field than in sterile muck from an uncropped (bare) field. Phosphatase activity was enhanced in both types of sterile muck by amendment with glucose, whereas protease activity was stimulated by this amendment only in the sterile muck from the uncropped field. Augmented protease, phosphatase, and polyphenol oxidase activities were maintained for several weeks in the recolonized sterile muck, while the respiratory activities peaked within 3d of inoculation, then declined. These data suggest that protease and phosphatase activities are involved in oxidation of both readily available and humified soil organic matter. Hence, a role of these enzymic activities in Histosol subsidence is proposed.

SOURCE AND ROLE OF PEROXIDASE IN SOIL ORGANIC MATTER OXIDATION IN PAHOKEE MUCK

We examined the source of peroxidase (E.C. 1.11.1.7) activity in Pahokee muck, its role in subsidence of this organic soil, the effect of exogenous nutrients in soil peroxidase levels, and oxidation of humic acid by peroxidase produced by a fungus native to Pahokee muck. Amendment of soil with ammonium, phosphate, glucose, or vitamin-free casamino acids had no effect on peroxidase activity. Amendment with glucose plus ammonium, yeast extract, or ground sugarcane leaves increased peroxidase levels two-to threefold. Solubilization of the native soil organic matter or amendment of the soil with ethylenediaminetetraacetic acid (EDTA) also stimulated the enzymic activity. A peroxidase-producing fungus was isolated from the soil. The peroxidase synthesized by this fungus increased the E4/E6 ratio of the purified humic acid. These data suggest that soil peroxidase of Pahokee muck is produced by the microbial community and that this enzyme functions in humic acid oxidation.

NITRITE PRODUCTION IN PAHOKEE MUCK: FREQUENCY OF OCCURRENCE AND SOURCE

We examined nitrite production in Pahokee muck, a drained Histosol, collected in the Everglades agricultural area. Soil nitrite levels ranged from 0 to 21.8 and 0 to 5.10 micrograms of nitrite-nitrogen per cubic centimeter in surface (0 to 10 cm) soils in 1977–78 and 1980, respectively. In 1980, 83 percent (n = 125) of the samples contained less than 0.5 μg nitrite-N/cm3, with 33 percent containing no detectable nitrite. No effect of crop on mean nitrite levels was detected. Nitrite concentrations generally correlated with nitrate and, in some cases, soil moisture, but not ammonium. In laboratory studies, maximum nitrite accumulated in muck samples amended with nitrate plus glucose and incubated anaerobically. No nitrite was detected in unamended samples incubated aerobically. These data suggest denitrification as the source of nitrite in Pahokee muck.

Red Soils of South China: Management, Properties, and Sustainability Challenges

S oils are major determinants of societal development, stability, and sustainability. Indeed, the nature of specific regional soils can determine the success or failure of societal development. An example of such a highly important regional soil is the red soils of south China, which covers approximately 102 million ha (approximately 27% of the total cultivated land of China) in the tropical and subtropical regions of China and supports approximately 43% of the country’s population (see “Coadaptation of Plants to Multiple Stresses in Acidic Soils” by X. Q. Zhao et al. in this issue). This special issue of Soil Science is the product of discussions of soil science research in the red soils of south China and their unique properties with our newest editorial board members with strong ties to the region, Dr. Weilin Huang and Dr. Fangbai Li. The red soils of south China provide an outstanding opportunity for study of the role of a fragile soil system in the feeding of a major portion of the world’s population and the optimization of management for enhancement of soil productivity and sustainability. Realization of the importance of the field and laboratory research is predicated on the maxim that goals for local soil development should not be imposed upon the soil system, but rather soil management must be predicated on the nature and properties of the underlying soils. This requires a clear understanding of essential soil properties and their susceptibility to a changing environment. Soil management failures certainly have local implications, but with expanding national and international economies, local and regional soil management decisions can have major impacts on the maintenance of a sound, resilient worldwide food supply network. Thus, it is with great pleasure that Soil Science presents current examples of the studies of these red soils of China, the complications associated with their management, and the challenges for stewardship directed at maintaining system productivity as well as sustainability. The selections offered in this issue provide an understanding of the unique properties, their impact on the larger national plan for soil stewardship, and the difficulties that arise from past soil management. Examples of current research

From the Editor’s Desk: Complexity and Nonlinearity in Soil Science

The desire for simple solutions to society’s problems, especially as they involve the two big ‘‘E’s’’Vthe environment and the economyVcould be said to be endemic to our species. Development of linear solutions to complex problems is certainly an admirable goal, but as we delve deeper into the driving forces behind the issues, complexity emerges as the rule, not the exception. Simple answers to scientific concerns, especially environmental processes directly impacting society, could possibly have been considered to be an achievable goal for society at one time, and such solutions may even be sought by at least a portion of the scientific community today. Unfortunately, as our understanding of the multitude of interactive processes impacting our world increases, achievement of simple answers becomes even more elusive. To a large degree, the rate of evolution of our understanding of processes driving complex environmental systems has been controlled by our analytical capabilities as well as our computing power. This limited perspective may have resulted in a simplistic view, per chance superficially aesthetic view, of our ecosystems. An example of the evolution of the appreciation of the complex could be exemplified by a simple example taken from a prime emphasis of soil science research throughout the existence of our specialtyVoptimizing crop yields. Consider the conception of an intensively cultivated, agricultural field through the ages. Initially, the magnificently beautiful depiction of the uniformity of the agricultural soil in an artist’s rendering of the aesthetics of the farm scene is at least in part supported by both the scientific and societal concepts of an ideal food production systemVclean soil, low weed intrusion, high crop yields. Management decisions were based on the grower’s experience as informed by specialists in soil fertility. Soil appeared to be minimally impacted by variation in environmental parameters. Cropping schemes involved assembly of a relatively small number of management plans involving variations in fertility and water control, possibly driven by slight variations in topography or soil type. Today, we must appreciate the fact that the seemingly uniform system of monoculture is really reliant on the existence of a mosaic of highly variable microsites, all contributing essential ecosystem services to the function of what was previously depicted as a uniform system. This microheterogeneity (complexity, if you please) is now understood as essential to the concurrent occurrence of such life-sustaining processes as nitrification and denitrification within the microsites of that seemingly uniform field. Uniformity of the beauty of the simple has evolved to a deeper appreciation of the essentiality of the diverse. Therefore, it could easily be concluded that our understanding of the processes in any system, albeit soil, water, or air, is truly delimited by the limitations of the analytical tools and skills available for study of environmental processes and the mathematical models that we use to describe them. In the past, scientific insights have been generally described by the linear variation of a few major soil properties. But, as our purview of the interacting processes (physical, chemical, and biological) of the soil systems grows from the micro to the macro, we have become more aware of the fact that a clear understanding of ecosystems requires an appreciation of the nonlinearity and complexity of their interactions and their variation within the highly variable mosaic comprising the whole soil. Were this simply a scientific issue, the task would be much simpler. But for a constructive response of society to scientific issues, this nonlinearity of complex processes must also be explained to a society that is more comfortable thinking linearly about simply defined issues. Thus, understanding and progress in application of true scientific insights into environmental processes and their importance to society are critical. Therefore, the importance of nonlinearity in complex soil systems is clearly a timely topic for a special issue of Soil Science. Soil Science presents this special issue with the objective of providing insight into current international research being conducted at levels ranging from the microsite to the total soil system. It is our hope that our readers will find the research exemplified herein enlightening and that the information will provide seeds for further development in this essential area of study. The inspiration and selection of many of the participants in this project stem from presentations at the EDITORIAL