Robert J. Zasoski

Tannins in nutrient dynamics of forest ecosystems - a review

Tannins make up a significant portion of forest carbon pools and foliage and bark may contain up to 40% tannin. Like many other plant secondary compounds, tannins were believed to function primarily as herbivore deterrents. However, recent evidence casts doubts on their universal effectiveness against herbivory. Alternatively, tannins may play an important role in plant–plant and plant–litter–soil interactions. The convergent evolution of tannin-rich plant communities on highly acidic and infertile soils throughout the world, and the intraspecific variation in tannin concentrations along edaphic gradients suggests that tannins can affect nutrient cycles. This paper reviews nutrient dynamics in forest ecosystems in relation to tannins. Tannins comprise a complex class of organic compounds whose concentration and chemistry differ greatly both among and within plant species. Because the function and reactivity of tannins are strongly controlled by their chemical structure, the effects of tannins on forest ecosystem processes are expected to vary widely. Tannins can affect nutrient cycling by hindering decomposition rates, complexing proteins, inducing toxicity to microbial populations and inhibiting enzyme activities. As a result, tannins may reduce nutrient losses in infertile ecosystems and may alter N cycling to enhance the level of organic versus mineral N forms. The ecological consequences of elevated tannin levels may include allelopathic responses, changes in soil quality and reduced ecosystem productivity. These effects may alter or control successional pathways. While a great deal of research has addressed tannins and their role in nutrient dynamics, there are many facets of tannin biogeochemistry that are not known. This lack of information hinders a complete synthesis of tannin effects on forest ecosystem processes and nutrient cycling. Areas of study that would help clarify the role of tannins in forest ecosystems include improved characterization and quantification techniques, enhanced understanding of structure-activity relationships, investigation of the fate of tannins in soil, further determination of the influence of environmental factors on plant tannin production and decomposition, and additional information on the effects of tannins on soil organisms.

A rapid nitric‐perchloric acid digestion method for multi‐element tissue analysis

Abstract A procedure has been developed for multi‐element analysis of nitric‐perchloric tissue digests. Both plant and animal tissues appear to be quantitatively digested. The recommended procedure is rapid, requires a minimum of glassware manipulation and reagent addition. Analysis of National Bureau of Standards reference material, SRM 1571 (Orchard Leaves) and SRM 1577 (Bovine Liver) was satisfactory for all elements sought.

Mapping soil micronutrients

Abstract Soils vary widely in their micronutrient content and in their ability to supply micronutrients in quantities sufficient for optimal crop growth. Soils deficient in their ability to supply micronutrients to crops are alarmingly widespread across the globe, and this problem is aggravated by the fact that many modern cultivars of major crops are highly sensitive to low micronutrient levels. Original geologic substrate and subsequent geochemical and pedogenic regimes determine total levels of micronutrients in soils. Total levels are rarely indicative of plant availability, however, because availability depends on soil pH, organic matter content, adsorptive surfaces, and other physical, chemical, and biological conditions in the rhizosphere. Micronutrient availability to plants can be measured in direct uptake experiments, or estimated with techniques that correlate quantities of micronutrients extracted chemically from soils to plant uptake and response to micronutrient fertilization. Rational management of micronutrient fertility and toxicity requires an understanding of how total and plant-available soil micronutrients vary across the land. A variety of approaches have been used to survey and map the geographic distribution of soil micronutrient content and availability at scales ranging from global to sites within single production fields. Soil micronutrient maps covering large areas improve our understanding of the nature and extent of micronutrient problems, and aid in determining their relationships with climate, soil properties, and soil genetic characteristics determined at similar scales, for example, Soil Taxonomy to the order, sub-order, or great group levels. Intermediate scale maps can be useful in delineating specific areas where deficiencies or toxicities are likely for agriculture, and in determining localized soil characteristics that may be associated with such problems. Highly detailed maps of soil micronutrient content and availability in individual fields are being developed for site-specific precision agriculture. Soil micronutrient maps have fostered discovery of relationships between soil micronutrient content and availability and some human and livestock health problems such as goiter, Keshan and Kaschin–Beck diseases, and cancer. Advances including the global positioning system (GPS), geographic information systems (GIS), inductively coupled plasma (ICP) spectrometry, geostatistics, and precision agriculture facilitate soil micronutrient mapping and provide quantitative support for decision and policy making to improve agricultural approaches to balanced micronutrient nutrition.

Contribution of amino compounds to dissolved organic nitrogen in forest soils

Dissolved organic nitrogen (DON) may play an important role in plantnutrition and nitrogen fluxes in forest ecosystems. In spite of the apparentimportance of DON, there is a paucity of information concerning its chemicalcomposition. However, it is exactly this chemical characterization that isrequired to understand the importance of DON in ecosystem processes. Theprimaryobjective of this study was to characterize the distribution of free aminoacidsand hydrolyzable peptides/proteins in the DON fraction of Oa horizon leachatesalong an extreme edaphic gradient in northern California. Insitu soil solutions were extracted by centrifugation from Oahorizonscollected beneath Pinus muricata (Bishop pine) andCupressus pygmaea (pygmy cypress) on slightlyacidic/fertile and highly acidic/infertile sites. DON accounted for 77 to99% of the total dissolved nitrogen in Oa horizon leachates. Nitrogen infree amino acids and alkyl amines ranged from 0.04–0.07 mgN/L on the low fertility site to 0.45–0.49 mg N/L onthe high fertility site, and accounted for 1.5 to 10.6% of the DON fraction.Serine, glutamic acid, leucine, ornithine, alanine, aspartic acid andmethylamine were generally the most abundant free amino compounds. Combinedamino acids released by acid hydrolysis accounted for 48 to 74% of theDON, suggesting that proteins and peptides were the main contributor to DON inOa horizon leachates. Together, nitrogen from free andcombined amino compounds accounted for 59 to 78% of the DON. Most of theDON was found in the hydrophobic fraction, which suggests the presence ofprotein/peptide-polyphenol complexes or amino compounds associated withhumic substances. Because free and combined amino acids can be an importantnitrogen source for some plants, soil DON may play an important role in plantnutrition and ecosystem function.

Linking chemical reactivity and protein precipitation to structural characteristics of foliar tannins

Tannins influence ecosystem function by affecting decomposition rates, nutrient cycling, and herbivory. To determine the role of tannins in ecological processes, it is important to quantify their abundance and understand how structural properties affect reactivity. In this study, purified tannins from the foliage of nine species growing in the pygmy forest of the northern California coast were examined for chemical reactivity, protein precipitation capacity (PPC), and structural characteristics (13C NMR). Reactivity of purified tannins varied among species 1.5-fold for the Folin total phenol assay, and 7-fold and 3-fold, respectively, for the acid butanol and vanillin condensed tannin assays. There was about a 5-fold difference in PPC. Variation in chemical reactivity and PPC can be largely explained by differences in structural characteristics of the tannins determined by 13C NMR. In particular, the condensed versus hydrolyzable tannin content, as well as the hydroxylation pattern of the B-ring and stereochemistry at the C-2–C-3 position appear to influence reactivity. Due to the large differences in chemical reactivity among species, it is necessary to use a well-characterized purified tannin from the species of interest to convert assay values to concentrations. Our results suggest that structural characteristics of tannins play an important role in regulating their reactivity in ecological processes.

Zinc uptake by corn as affected by vesicular-arbuscular mycorrhizae

Pot-grown mycorrhizal and non-mycorrhizal sweet corn were grown in a low Zn soil. All treatments received a complete nutrient solution with or without Zn. Treatments were harvested sequentially to detemine temporal mycorrhizal effects on: (a) tissue and water soluble Zn and (b) differential uptake of P and Zn. Plants grown with supplemental Zn had greater growth and Zn tissue concentration than those not receiving Zn. With no supplemental Zn, mycorrhizal treatments had greater growth and Zn concentration than non-mycorrhizal treatments. There was no indication of nutrient interaction between Zn and P. Over the range of tissue Zn found, there appeared to be no advantage to water soluble Zn analysis over total Zn in assessing plant Zn status.

Effects of vesicular-arbuscular mycorrhizal inoculation at different soil P availabilities on growth and nutrient uptake of in vitro propagated coffee (Coffea arabica L.) plants

Abstract In a pot experiment, the growth and the nutrient status of in vitro propagated coffee (Coffea arabica L.) microcuttings were investigated for 5 months following vesicular-arbuscular mycorrhizal (VAM) inoculation with either Acaulospora melleae or Glomus clarum at four soil P availabilities. Control plants remained P-deficient even at the highest soil P availability while mycorrhizal plants were P-sufficient at all soil P availabilities. Growth of control plants was only improved at the highest soil P availability. In P-deficient soil, neither of the two VAM species improved plant growth. Plant growth increased by 50% following inoculation with either A. melleae or G. clarum when P availability went from deficient to low. No further plant growth improvement was induced by either VAM species at intermediate and high soil P levels. Nevertheless, growth of plants inoculated with G. clarum was still significantly greater than that of non-mycorrhizal plants at the highest soil P availability. Root colonization by G. clarum increased with increasing soil P availability while root colonization by A. mellea decreased with soil P level increasing above low P availability. Soil P availability also affected Zn nutrition through its influence on VAM symbiosis. With increasing soil P availability, foliar Zn status increased with G. clarum or decreased with A. mellea in parallel to root colonization by VAM. This study demonstrates the beneficial effects of VAM inoculation on in vitro propagated Arabica coffee microcuttings, as shown previously for seedlings. This study also demonstrates differences in tolerance to soil P availability between VAM species, most likely resulting from their differing abilities to enhance coffee foliar P status.

Interaction of lime, organic matter and fertilizer on growth and uptake of arsenic and mercury by Zorro fescue (Vulpia myuros L.)

The Sulphur Bank Mercury Mine (SBMM) is an abandoned open pit mine located on the eastern shores of Clear Lake, California. Revegetation efforts have been difficult because the mine-soils at SBMM have low pH, low fertility and elevated As and Hg concentrations. In a greenhouse study, we examined the interactions of lime, N, P and OM additions with respect to plant growth, and As and Hg uptake. Three selected acidic mine-soils from the site containing high (164 mg/kg) (S-H), medium (123 mg/kg) (S-M) and low (31 mg/kg) (S-L) total As content were planted to the Eurasian annual grass, Zorro fescue (Vulpia myuros L.). The Hg concentrations for these soils varied between 1700 and 3000 mg/kg with S-L > S-H ≅ S-M. A factorial design used 3 soils, 2 lime, 2 N, 2 P and 2 OM treatments with treatments replicated three times. Multiple regression analyses indicated a strong relationship between As plant uptake, root length density (RLD) and soluble As. A highly significant linear relationship between Hg uptake and RLD for plants growing on the three soils illustrated the importance of plant root characteristics in influencing Hg uptake. Soluble As decreased in the order S-H > S-M > S-L in positive correlation with P and DOC but in inverse relationship to oxalate extractable Fe. Lime and OM additions correlated negatively with soluble Hg and Hg tissue concentration due to either Hg adsorption to OM or to inorganic surfaces. Addition of lime increased dry matter yield and Hg uptake in all three soils.

Effects of VA-mycorrhizae and nitrogen sources on rhizosphere soil characteristics, growth and nutrient acquisition of coffee seedlings (Coffea arabica L.)

Effects of N sources (ammonium, nitrate and ammonitrate) and VA mycorrhizae (Glomus intraradices) on rhizosphere soil characteristics (pH, exchangeable acidity, exchangeable cations, inorganic N concentrations) growth and nutrient acquisition of coffee seedlings (Coffea arabica L. cv guatemala) were investigated in a pot study with an acid soil (Red Bluff Loam) sterilized by autoclaving. Ammonium addition decreased rhizosphere pH while nitrate and ammonitrate additions both increased rhizosphere pH. Mycorrhizae induced a higher pH, a lower exchangeable acidity and higher values of exchangeable cations in the rhizosphere. Ammonium addition resulted in a lower mycorrhizal infection than the two other N sources. Mycorrhizal plants grew better and accumulated more N, Ca and Mg than non-mycorrhizal plants.

Effects of solution pH, temperature, nitrate/ammonium ratios, and inhibitors on ammonium and nitrate uptake by Arabica coffee in short‐term solution culture

Abstract Solution pH, temperature, nitrate (NO3 ‐)/yammonium (NH4 +) ratios, and inhibitors effects on the NO3 ‐ and NH4 + uptake rates of coffee (Coffea arabica L.) roots were investigated in short‐term solution culture. At intermediate pH values (4.25 to 5.75) typical of coffee soils, NH4 + and NO3 ‐ uptake rates were similar and nearly independent of pH. Nitrate uptake varied more with temperature than did ammonium. Nitrate uptake increased from 0.05 to 1.01 μmol g‐1 FWh‐1 between 4 and 16°C, and increased three‐fold between 16 to 22°C. Between 4 to 22°C, NH4 + uptake rate increased more gradually from 1.00 to 3.25 μmol g‐1 FW h‐1. In the 22–40°C temperature range, NH4 + and NO3 ‐ uptake rates were similar (averaging 3.65 and 3.56 umol g‐1 FW h‐1, respectively). At concentrations ranging from 0.5 to 3 mM, NO3 ‐ did not influence NH4 + uptake rate. However, NO3 ‐ uptake was significantly reduced when NH4 + was present at 3 mM concentration. Most importantly, total uptake (NO3 ‐+NH4 +) at any NO3 ‐/NH4 +...