R. Paul Schreiner

Mycorrhizal Interactions in Sustainable Agriculture

AbstractVesicular-arbuscular mycorrhizal (VAM) fungi are an intimate link between the roots of most crop plants and soils, thereby affecting the development of host plants and host soils. The role of VAM fungi in improving plant nutrition and their interactions with other soil biota have been investigated with reference to host plant growth, but little is known about how these interactions affect soil structure. The impact of cultural practices and the particular role that VAM fungi play in improving soil structure are discussed in the context of sustainable farming.

The diversity of arbuscular mycorrhizal fungi amplified from grapevine roots (Vitis vinifera L.) in Oregon vineyards is seasonally stable and influenced by soil and vine age

The diversity of arbuscular mycorrhizal fungi (AMF) in 10 Oregon vineyards was assessed by examining spores in soil and amplifying mycorrhizal DNA from roots. Seventeen spore morphotypes were found in soil, including seven species in the Acaulosporaceae. Eighteen phylotypes were amplified from grape roots with AM1 and NS31 primers, and clones were dominated by Glomus spp. (> 99%). A few clones (< 1%) representing a single phylotype within Gigasporaceae, and a single clone within Archaeosporaceae were amplified from roots with AM1-NS31 primers. A separate experiment employing known proportions of grape roots colonized by Glomus intraradices or by Gigaspora rosea showed that fungi within Gigasporaceae might be underrepresented in clone abundance when Glomus spp. co-occur in roots. No clones representing fungi within the Acaulosporaceae were amplified from vineyards, although specific fungi within Acaulosporaceae were shown to colonize Pinot noir roots in sterilized soil and were amplified from these roots. Four Glomus phylotypes, including G. intraradices, were found in roots from all 10 vineyards, and these fungi accounted for 81% of clones. AMF phylotypes amplified from roots did not change during the growing season, although six phylotypes varied with soil type. The presence of three phylotypes was affected by vineyard age, and phylotype richness appeared to decline as vineyard age increased beyond 20 y. PCA analysis supported the hypothesis that the AMF community is different in red-hill soils than in valley soils and indicated certain phylotypes might be associated with lower soil and vine nutrient status. However, the changes in the AMF community in grape roots across vineyards were subtle because most root samples were dominated by the same three or four phylotypes. A separate analysis using primers to amplify AMF from the Archeasporaceae/Paraglomeraceae showed most root samples also were colonized by at least one Paraglomus or Archaeospora phylotype.

Plant and soil response to single and mixed species of arbuscular mycorrhizal fungi under fungicide stress

Abstract Defining sustainable agricultural practices requires an understanding of both above- and below-ground consequences to management strategies. While alternatives to biocides are sought for the control of weeds, insects and pathogens, biocide use will continue with the goal of reducing quantities used in an integrated approach. The impact of three fungicides on plant growth, seed yield, seed nutrient composition, and on soil aggregation as mediated by arbuscular mycorrhizal (AM) fungi was studied in a silty-clay loam soil with a high extractable P concentration. Shoot dry mass, seed yield and seed nutrient (N, P, K) contents of pea (Pisum sativum L.) plants were enhanced by three AM fungi and a mixture of three fungi compared with nonAM plants. Each AM fungus produced a distinct pattern of shoot responses of plants, but the mixed inoculum treatment was as good or better than each single species for all of the above-ground measures of plant performance. Soil aggregation was improved by two of the three AM fungi as individual inocula, and was further increased in the mixed inoculum treatment. Two of the three fungicides reduced shoot dry mass and seed yield, but none of the fungicides affected soil aggregation. Fungicides inhibited mycorrhiza formation least in the mixed inoculum treatment which gave the best overall plant and soil responses. Since the three fungi together were more tolerant of fungicides than each fungus alone, it appeared that as a community, AM fungi modified and alleviated fungicide stress, resulting in high levels of plant performance and soil aggregation.

Mycorrhizal fungi effects on nutrient composition and yield of soybean seeds

Abstract Nutrient composition and yield of soybean [Glycine max (L.) Merr] seeds are heritable traits affected by environmental factors. This study determined the effects of arbuscular‐mycorrhizal (AM) fungi on seed protein, lipid, and phosphorus (P) composition and yield in soybean grown under a high nitrogen (N) regime. Plants were grown in pot cultures without AM fungi in P‐fertilized (+P) or unfertilized (‐P) soil, or in ‐P soil inoculated with one of the AM fungi Glomus mosseae (Nicol. & Gerd.) Gerd, and Trappe (Gm), Glomus etunicatum Becker and Gerd.(Ge), or Gigaspora rosea Nicol. and Schenck (Gr). Seed yields of+AM plants, as a group, were halfway between those of the +P and ‐P plants. Seed size was highest in Gm plants. Differences in protein concentrations between Ge and Gr and the other treatments were highly significant. Seed P and protein concentrations were not significantly correlated (p=0.162), but a highly significant (r =‐0.949) negative correlation between seed P and lipid concentrations...

Mycorrhizal Colonization in Dryland Vineyards of the Willamette Valley, Oregon

Abstract Arbuscular mycorrhizal fungi (AMF) enhance the growth of numerous plants, including grapevines, by increasing the absorptive surface area between roots and soil. A survey of commercial vineyards in Oregon was conducted to assess the levels of root colonization by AMF at two times during the growing season. Grapevines sampled, ranged in age from 2 to 29 years old and were growing in 10 different soil types from 3 soil orders. AMF colonization of fine (feeder) roots of vines was generally high, averaging 73% and 69% of root length colonized at bloom and veraison, respectively. Vine age, soil type, cultivar, trellis type and vine row aspect did not influence colonization of roots by AMF. In-row cultivation reduced AMF colonization at bloom, and foliar application of soluble phosphorus fertilizers reduced arbuscules (the site of nutrient transfer in mycorrhizas) in roots at veraison. The proportion of roots colonized by AMF at bloom was negatively correlated to leaf N concentrations and positively correlated to soil and leaf K concentrations. The proportion of roots containing arbuscules at bloom was positively correlated to soil pH and leaf K concentrations, but negatively correlated to leaf P and N concentrations. AMF colonization of roots was negatively correlated to soil moisture at veraison. Root colonization by AMF in Oregons dryland vineyards appears to be reduced by cultivation and foliar P application, but may be enhanced by increasing soil pH.

N, P, and K Supply to Pinot noir Grapevines: Impact on Vine Nutrient Status, Growth, Physiology, and Yield

Pinot noir grapevines (self-rooted Pommard clone) were grown in a pot-in-pot sand culture vineyard to examine the impact of low N, P, and K supply on vine growth and physiology. Four-year-old vines were given either full nutrition (Control) or reduced levels of each N, P, and K supplied at 50%, 20%, or 10% of the Control rate with all other nutrients held constant over three years (2006–2008). Vine growth, nutrient status, photosynthetic parameters, yield, and berry quality were monitored. The N, P, and K status of vines was reduced by each of the intended treatments, although N and P concentrations in leaf blades and petioles were reduced earlier and to a greater extent than K. Low N treatments reduced dormant season cane weights in all years, shoot lengths and leaf area in 2008, and fruit yield in 2008. Yield reduction under low N supply in 2008 was primarily a result of reduced berry size. Low N also reduced single leaf photosynthesis and quantum efficiency of photosystem II in 2008, while low P and K did not. Juice YAN (yeast assimilable nitrogen) levels were greatly reduced by low N supply in 2007 and 2008, although YAN was lower in 2007 across all treatments. Low P and low K supply did not alter growth or yield. Low P supply reduced juice P concentrations, but low K supply did not alter juice K. Reduced yield, growth, and juice YAN levels in low N treatments provide a framework to refine leaf blade and petiole N standards for Pinot noir grown in the region, but limiting levels of P and K were not as clearly defined.

N, P, and K Supply to Pinot noir Grapevines: Impact on Berry Phenolics and Free Amino Acids

Understanding the direct role that macronutrient supply (N, P, and K) has on berry chemistry was evaluated in Pinot noir grapevines grown in sand culture. Self-rooted Pinot noir vines were grown for three years with either full nutrition (Control) or three reduced levels of either N, P, or K supply while holding all other nutrients constant. Vines were managed to minimize differences in vine water status (altering irrigation to achieve similar daily soil moisture content) and fruit cluster solar exposure (altering leaf pulling to achieve similar cluster irradiance) due to varying nutrient supply so that indirect effects on berry chemistry could be largely eliminated. Berry chemistry was evaluated in the second and third years after different nutrient supply treatments were imposed. Results showed that low N, but not low P or K, altered berry free amino acid (FAA) and phenolic profiles. Low N supply reduced FAA and yeast assimilable nitrogen (YAN) in both years by up to 70% and altered certain FAAs more than others, thus changing berry FAA profile. The concentration of sugars, anthocyanins, and flavonol-glycosides increased in low N vines during the third season, but the increase in sugars and anthocyanins was attributed to the decline in berry size that year. Condensed tannins and total phenolic acids were increased in low N vines across both years, independent of changes in berry size. Results indicated that low N supply altered YAN to the greatest degree, while anthocyanin enhancement did not occur until yield and berry size were also reduced. Increased concentrations of tannins and phenolic acids in berries occurred in response to low N supply independent of reductions in yield and berry size.

Consequences of Mesocriconema xenoplax Parasitism on Pinot noir Grapevines Grafted on Rootstocks of Varying Susceptibility

Pinot noir grapevines grafted to five rootstocks (Vitis vinifera) and a self-rooted control known to vary in resistance to ring nematode (Mesocriconema xenoplax) were studied over four years to evaluate durability of resistance to ring nematode and to better understand how ring nematode parasitism affects below- and aboveground vine growth and physiology. Ring nematode populations in infested microplots of all three susceptible vines (self-rooted, 3309C, 1103P) increased rapidly during the second year and remained high throughout the study, while nematodes increased in two of the previously resistant rootstocks (110R, 101-14) during the third year. Only 420A remained resistant through the entire 4-year period. The impact of ring nematode parasitism on vines was most apparent in the susceptible rootstocks and self-rooted vines with reductions in fine root growth and colonization by arbuscular mycorrhizal fungi (AMF) occurring as early as the second year. Reductions in both fine root production and AMF colonization due to ring nematode were greater in subsequent years in the susceptible vines. The frequency of fine roots containing vesicles of AMF was reduced in all five rootstocks that supported a population increase of ring nematode (only 420A was unaffected). Ring nematode did not alter aboveground vine performance until the third or fourth growing season, when shoot lengths and pruning weights were reduced in the three susceptible vines. Ring nematode did not alter shoot growth in any of the three resistant rootstocks, nor did it affect leaf gas exchange or leaf water potential in any vines in any year. However, by year four ring nematode reduced fruit yield as a main effect across all rootstock treatments.

Nitrogen Requirements of Pinot noir Based on Growth Parameters, Must Composition, and Fermentation Behavior

A study to reassess the nitrogen (N) requirements for Pinot noir was carried out using a pot-in-pot vineyard where N inputs were carefully controlled. Pinot noir grafted on 101-14 rootstock was exposed to five levels of N supply beginning in their fourth growing season, and vine productivity, berry chemistry, and must fermentation dynamics were studied over three years. N supply altered the N status of vines in accordance with expectations. Varying N had a greater impact on vegetative growth parameters than upon reproductive responses. For example, at veraison, leaf area of vines exposed to the three lowest rates of N was reduced in all years, but yield was only reduced at the lowest N rate in the first year and at the two lowest N rates in subsequent years. Fruitfulness and fruit set were reduced slightly by low N, while flower number of inflorescences was unaffected. Effects on berry maturity indices at harvest were generally small, but effects on must yeast assimilable nitrogen (YAN) concentrations were large. YAN was reduced from ~200 mg N/L in the Control to as low as 25 mg N/L at the lowest N rate after three years. Treatments with lower YAN required more time to complete alcoholic fermentation, particularly those with YAN below 100 mg N/L. However, all musts fermented to dryness. Reducing vegetative growth of Pinot noir can be achieved prior to reducing yield by reducing N status when vines are cropped at levels typical for premium wine production in the region. YAN levels as low as 100 mg N/L may be a better production target for wineries to achieve minimum fermentation requirements of Pinot noir.

Soil Nitrogen, Phosphorus, and Potassium Alter β-Damascenone and Other Volatiles in Pinot noir Berries

The aim of this work was to evaluate the volatile composition of grape berries in vines subjected to varying levels of nitrogen (N), phosphorus (P), and potassium (K) supply. Pinot noir grapevines were grown in a pot-in-pot system for three years and fertigated with varying levels of N, P, or K while holding all other nutrients constant. N was varied from 7.50 mM total N supply (Control) to as low as 1.125 mM total N in five discreet levels, while P and K supply were each varied over four levels, with the lowest rate (0 mM) applied during fertigation events. Free and bound volatiles in berries were determined in each year. Variation in N supply had a greater impact on the volatile composition of berries than did variation in P or K supply. Reducing N supply to vines resulted in lower total (free + bound) β-damascenone and C-6 compounds in berries in all three years, and low K supply resulted in lower total β-damascenone in two of three years. Nutrient supply had a relatively small impact on monoterpenes and other volatile compounds in Pinot noir berries.