Jonathan R. Cumming

Nitrification potentials and landscape, soil and vegetation characteristics in two Central Appalachian watersheds differing in NO3- export

Two watersheds within 1 km of each other in the Central Appalachian mountains of West Virginia have similar management histories and receive 13 kg of N in atmospheric deposition, but NO3 � export from one watershed (W4) has increased over the last 30 years, and is now approximately five times greater than NO3 � export from the other (W10). We measured net nitrification potentials (NNP) and other landscape, soil, and plant community variables (1) to determine whether differences in leaching could be attributed to differences in NNP, (2) to identify other significant differences between the watersheds, (3) to identify variables that could account for both between- and within-watershed variability in NNP, and (4) to identify readily measured variables that distinguish plots with relatively high or low NNP. NNPs in W4 were 0.84 kg N ha � 1 per day, approximately three times higher than those on W10. Watershed 4 lay at a slightly higher elevation, had gentler slopes, a thinner forest floor, lower C:N in the 0‐10 cm soil layer, lower tree density, greater basal area in Acer saccharum, less basal area in Quercus prinus and Amelanchier arborea, more frequent occurrences of A. saccharum seedlings, Laportea canadensis, Polystichum acrostichoides, Trillium sp., Uvularia sessilifolia and Viola spp., and fewer occurrences of Gaultheria procumbens, and Viburnum acerifolum. NNPs were correlated with many soil characteristics related to base cation supply, C:N and water holding capacity (WHC). Several two- and three-variable regression models, which were mostly based on soil characteristics, accounted for a large proportion of the variability in NNP (adjusted R 2 > 0:60), as well as for the difference between watershed means (t-test of residuals indicate no significant difference). A regression model based on basal area of A. saccharum and A. rubrum and the presence or absence of Trillium accounted for 50% of the variability in NNP. At this highdeposition site, plots with soils that had higher pHs, greater base cation supply and WHC, and lower C:N were more susceptible to NO3 � leaching and N saturation. # 2002 Elsevier Science B.V. All rights reserved.

The role of arbuscular mycorrhizas in decreasing aluminium phytotoxicity in acidic soils: a review

Soil acidity is an impediment to agricultural production on a significant portion of arable land worldwide. Low productivity of these soils is mainly due to nutrient limitation and the presence of high levels of aluminium (Al), which causes deleterious effects on plant physiology and growth. In response to acidic soil stress, plants have evolved various mechanisms to tolerate high concentrations of Al in the soil solution. These strategies for Al detoxification include mechanisms that reduce the activity of Al3+ and its toxicity, either externally through exudation of Al-chelating compounds such as organic acids into the rhizosphere or internally through the accumulation of Al–organic acid complexes sequestered within plant cells. Additionally, root colonization by symbiotic arbuscular mycorrhizal (AM) fungi increases plant resistance to acidity and phytotoxic levels of Al in the soil environment. In this review, the role of the AM symbiosis in increasing the Al resistance of plants in natural and agricultural ecosystems under phytotoxic conditions of Al is discussed. Mechanisms of Al resistance induced by AM fungi in host plants and variation in resistance among AM fungi that contribute to detoxifying Al in the rhizosphere environment are considered with respect to altering Al bioavailability.

The influence of phosphorus availability and Laccaria bicolor symbiosis on phosphate acquisition, antioxidant enzyme activity, and rhizospheric carbon flux in Populus tremuloides

Many forest tree species are dependent on their symbiotic interaction with ectomycorrhizal (ECM) fungi for phosphorus (P) uptake from forest soils where P availability is often limited. The ECM fungal association benefits the host plant under P limitation through enhanced soil exploration and increased P acquisition by mycorrhizas. To study the P starvation response (PSR) and its modification by ECM fungi in Populus tremuloides, a comparison was made between nonmycorrhizal (NM) and mycorrhizal with Laccaria bicolor (Myc) seedlings grown under different concentrations of phosphate (Pi) in sand culture. Although differences in growth between NM and Myc plants were small, Myc plants were more effective at acquiring P from low Pi treatments, with significantly lower km values for root and leaf P accumulation. Pi limitation significantly increased the activity of catalase, ascorbate peroxidase, and guaiacol-dependent peroxidase in leaves and roots to greater extents in NM than Myc P. tremuloides. Phosphoenolpyruvate carboxylase activity also increased in NM plants under P limitation, but was unchanged in Myc plants. Formate, citrate, malonate, lactate, malate, and oxalate and total organic carbon exudation by roots was stimulated by P limitation to a greater extent in NM than Myc plants. Colonization by L. bicolor reduced the solution Pi concentration thresholds where PSR physiological changes occurred, indicating that enhanced Pi acquisition by P. tremuloides colonized by L. bicolor altered host P homeostasis and plant stress responses to P limitation. Understanding these plant–symbiont interactions facilitates the selection of more P-efficient forest trees and strategies for tree plantation production on marginal soils.

Relative quantification of membrane-associated calcium in red spruce mesophyll cells

Abstract We describe a method for localizing and comparing relative amounts of plasma membrane-associated calcium ions (mCa) in complex tissues and verify the procedure for mesophyll cells of red spruce (Picea rubens Sarg.) needles. This technique incorporates epifluorescence microscopy using the fluorescent probe chlorotetracycline (CTC) with computer image processing and analysis. Using an appropriate standardization for image brightness, the procedure allows relative quantitative comparison of CTC-fluorescence in the plasma membrane-cell wall region that corresponds to relative amounts of mCa. The technique effectively discerned mCa differences among red spruce needle sections exposed to treatments designed to alter mCa levels in vitro. Estimates of mCa for nine red spruce seedlings, were highly repeatable over a 6 week period in late summer. This repeatability verifies that the described methods produce reliable and reproducible estimates of foliar mCa in woody plant foliage. By incorporating image analysis, this technique allows for relative quantitative estimates of mCa specific to the physiologically-important and labile pool of Ca associated with the plasma membrane-wall complex. Such measurements have not previously been reported for woody plant tissues and thus may provide new insights into the relative roles and responsiveness of mCa vs total foliar Ca pools.

Phosphorus disequilibrium in the tripartite plant-ectomycorrhiza-plant growth promoting rhizobacterial association

Plant roots and rhizospheres are colonized by an extensive and diverse microbial community. These microbes may form mutualistic, commensal, and/or pathogenic relationships and influence agricultural and forest productivity. Symbiotic ectomycorrhizal (EcM) fungi colonize the roots of many tree species, and the literature on these associations extensively describes their influence on plant nutrient relations and response to environmental stress. Similarly, soil bacteria ubiquitously colonize roots and rhizospheres and many of these bacteria may also play roles in influencing tree productivity. In particular, plant growth promoting rhizobacteria (PGPR) positively affect plant growth by altering nutrient availability in soils and inducing changes in plant hormone balance, plant stress resistance, and immunity pathways. In nature, EcM fungi and soil PGPR co-exist and the interaction and composition of this multi-tiered rhizosphere community aids in the acquisition of nutrient resources from soils as well as host plant response to environmental stress. The assembly of EcM communities is influenced by tree species and environmental conditions, and the tree and EcM species further influence PGPR community structure. Functionally, these symbiotic associations exhibit unique expression profiles and ecophysiological activities within the tripartite association. EcM and PGPR mediate production of complex arrays of exudates, including organic acids, siderophores, enzymes, and other organic compounds, which alter nutrient equilibria in soils, leading to increased access to phosphorus (P) and other macro- and micronutrients. As a metaorganism, the tripartite ectomycorrhizas increase the ecological breadth of host trees and influence the structure and function of forested ecosystems.

Phosphorus acquisition by three wheat cultivars contrasting in aluminium tolerance growing in an aluminium-rich volcanic soil

Abstract. Phosphorus (P) deficiency and aluminium (Al) phytotoxicity are major limitations for crop yield in acid soils. To ameliorate such limitations, agricultural management includes application of lime and P fertilisers, and the use of Al-tolerant plant genotypes. The mechanisms of Al tolerance and P efficiency may be closely related through strategies that decrease the toxicity of the Al3+ ion and increase P availability in soils. However, the effects of soils with high Al saturation on P acquisition by wheat have been little studied under field conditions. The aim of this work was to study Al–P interactions on wheat genotypes of contrasting Al tolerance when grown under field conditions in a volcanic soil with high Al saturation (32%) and low pH (5.0). A field-plot experiment was performed with winter wheat genotypes, two Al-tolerant (TCRB14 and TINB14) and one Al-sensitive (STKI14), with application of 0, 44 and 88 kg P ha–1. At the end of tillering and after physiological maturity (90 and 210 days after sowing), plants were harvested and yield and P and Al concentrations in shoots and roots were measured. Soil acid phosphatase, root arbuscular mycorrhizal (AM) colonisation, AM spore number and soil glomalin were determined. Shoot and root production and P uptake were higher in Al-tolerant genotypes than the sensitive genotype. In addition, root AM colonisation and soil acid phosphatase activity were also higher in tolerant genotypes. By contrast, Al concentration in shoots and roots was higher in the sensitive genotype with a concomitant decrease in P concentration. Grain yield of Al-tolerant genotypes was higher than of the Al-sensitive genotype with and without P fertiliser. Overall, the Al-tolerant genotypes were more effective at P acquisition from soil as well as from P fertiliser added, suggesting that plant traits such as Al tolerance, P efficiency, and AM colonisation potential co-operate in overcoming adverse acid soil conditions.

Diversity of Arbuscular Mycorrhizal Fungi in Acidic Soils and Their Contribution to Aluminum Phytotoxicity Alleviation

Acidic conditions limit crop production on 40 % of the world’s soils. These soils are characterized by a pH between 4.5 and 5.5, low phosphorus (P) availability, high contents of aluminum (Al) and manganese (Mn), and low soil basic cations. Edaphic conditions of acidic soils limit plant growth, mainly due to Al3+ phytotoxicity, which reduces water and nutrient acquisition from soils and severely limits root growth of sensitive species. However, the association of symbiotic arbuscular mycorrhizal (AM) fungi with plant roots often modifies plant response to acid soil factors through enhanced P acquisition and reduced Al exposure. Several management practices are implemented to mitigate the negative effects of acidic soils on plant growth, among which are lime application, P fertilization, and the use of Al-tolerant plants. In this regard, the inoculation with AM fungi appears as another management alternative, because of the well-documented AM contribution to plants growing in acidic soils. Several reports have demonstrated that AM fungal structures and glomalin-related soil protein (GRSP) protect plants against stress produced by high levels of Al. However, there is broad functional diversity among AM fungal genera or species in their capacity to confer Al-resistance to host plants in acidic soils. Therefore, the aim of this review is to summarize AM fungal diversity present in acidic soils as well as relate their presence with the potential to alleviate Al phytotoxicity.

Assessing urban forest effects and values: Morgantown's Urban Forest

An analysis of the community forest in Morgantown, WV, was undertaken in 2004 to characterize the structural and functional attributes of this forest resource. The assessment revealed that this city has about 658,000 trees with canopies that cover 35.5 percent of the area. The most common tree species are sugar maple, black cherry, and hawthorn. The urban forest currently stores about 93,000 tons of carbon valued at

Carbon allocation and partitioning in Populus tremuloides are modulated by ectomycorrhizal fungi under phosphorus limitation

1.9 million. In addition, these trees remove about 2,900 tons of carbon per year (

Pseudomonas fluorescens Transportome Is Linked to Strain-Specific Plant Growth Promotion in Aspen Seedlings under Nutrient Stress

60,000 per year), with trees and shrubs removing about 104 tons of air pollution per year (