Astrid Volder

• PhD. Utrecht University, Netherlands
• Perennial root systems at University of California, Davis

Changes in function as an individual root ages has important implications for understanding resource acquisition, competitive ability and optimal lifespan. Both nitrate uptake and respiration rates of differently aged fine roots of grape (Vitis rupestris x V. riparia cv. 3309 C) were measured. The resulting data were then used to simulate nitrate u...

We investigated seasonal root production and root turnover of fertilized and well-watered monocultures of Phalaris for 2 years using minirhizotrons installed in six newly designed temperature gradient tunnels, combined with sequential soil coring. Elevated atmospheric CO2 treatments were combined with two cutting frequencies and three warming scena...

Premise: While root-order approaches to fine-root classification have shown wide utility among wild plants, they have seen limited use for perennial crop plants. Moreover, inadequate characterization of fine roots across species of domesticated perennial crops has led to a knowledge gap in the understanding of evolutionary and functional patterns...

We only have a limited understanding of the nutrient uptake physiology of individual roots as they age. Despite this shortcoming, the importance of nutrient uptake processes to our understanding of plant nutrition and nutrient cycling cannot be underestimated. In this study, we used a 15 N depletion method that allowed for the measurement of nitrat...

California signed the Sustainable Groundwater Management Act (SGMA) into law in 2014. SGMA requires groundwater-dependent regions to halt overdraft and develop plans to reach an annual balance of pumping and recharge. Groundwater aquifers can be recharged by flooding agricultural fields when fallow, but this has not been an option for perennial cro...

Arbuscular mycorrhizal fungi (AMF) are mutualistic fungi that play important roles in plant nutrition and soil ecosystem functions. While AMF are known to benefit diverse host plants under a range of conditions, little is known about their presence in commercial almond orchards and how frequently used management practices regulate AMF root colonisa...

Leaf temperature (TL) is tightly coupled with the rate of transpirational water loss from the leaf. The temperatures of wet and dry reference leaf surfaces (Twet and Tdry, respectively) are commonly used to normalize temperature measurements for current environmental conditions and then calculate a crop water stress index (CWSI). Since it is often...

Information on root growth patterns is crucial to understand cultivar adaptations to deficit irrigation, particularly for subsurface drip-irrigated crops, where root systems are more confined than furrow or sprinkler systems. A 2-year field experiment evaluated the effect of deficit irrigation (50% vs. 100% crop evapotranspiration, ETc) on root gro...

The inclusion of a smother crop used as a cash crop in an intercropping system may be an effective cultural control strategy for the management of weeds in organic production systems. In addition, a multilayered canopy created when intercropping species with different growth forms may limit germination cues for weed seeds and can allow for a more e...

Saline irrigation water can lead to salt buildup and reduced crop yields. Halophytic plants are known to accumulate excess salts in tissues, removing them from the immediate environment. This two-phase experiment explored the feasibility of intercropping watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai var. lanatus) with halophytic species...

Interspecies specific interactions are generally regarded as drivers of plant productivity in multispecies agroe-cosystems. Complementary use of resource in diverse communities can enhance community productivity through optimal use of plant-available resources and positive interactions such as facilitation can ameliorate high abiotic stress conditi...

A greenhouse study was conducted to evaluate the growth and development of poinsettia ‘Prestige Red’ (Euphorbia pulcherrima) grown in a commercial peat-based potting mix (Sunshine Mix #1) amended with biochar at 0%, 20%, 40%, 60%, 80%, or 100% (by volume) at four different fertigation regimes: F1: 100 to 200 mg·L⁻¹ nitrogen (N), F2: 200 to 300 mg·L...

In a two year minirhizotron study (2011 and 2012), the root growth, yield and fruit quality responses of six melon genotypes to two locations with different soil types were investigated. The field experiments were conducted in south Texas at two locations viz. Uvalde with clayey (hyperthermic aridic calciustolls) and Weslaco with sandy loam (hypert...

Open field irrigated agriculture in arid to semi-arid regions of the world is seriously affected by frequent and severe droughts, limited water resources, and increased regulations restricting ground water use. Integrated strategies for melon (Cucumis melo L.) production can be applied to increase water savings without reducing marketable yields an...

A greenhouse experiment was conducted to evaluate the effects of water stress on leaf water potential, plant growth, and photosynthesis in purple passionflower (Passiflora incarnata). Twenty 4-L pots with two plants in each pot were arranged in a completely randomized design. Ten pots received a daily irrigation dose of 100% evapotrans-piration (ET...

Subtropical and tropical climates are becoming more vulnerable to drought and salinity problems. Of the crops produced in these climates, citrus is especially sensitive to increasing salinity. In times of water scarcity and periodic drought alternative water sources that may be lower in quality may be required for irrigation, leading to reduced yie...

Forecasting the effects of climate change on nitrogen (N) cycling in pastures requires an understanding of changes in tissue N. We examined the effects of elevated atmospheric CO2 concentration, atmospheric warming and simulated grazing (clipping frequency) on above and belowground tissue N concentrations and C:N ratios of a C3 pasture grass. Phala...

In natural ecosystems, plant communities composed of functionally diverse species produce more biomass overall than less diverse communities. This increased biomass production is thought to occur due to complementary use of resources such as nutrients and water, and facilitation during sub-optimal environmental conditions. Using the same concept in...

Abstract: Increasing concentrations of greenhouse gases are projected to elevate global surface air temperatures by 1.5 to 4.5 °C by the end of the century, and magnify the intensity and variability of seasonal precipitation distribution. The mid-latitude savannas of North America are predicted to experience substantial modification in precipitatio...

Background/Question/Methods Fully understanding the combined effect of elevated CO2 and climate warming on nitrogen (N) cycling in pastures requires an understanding of changes in tissue N and C:N ratios in response to climate and management treatments. In addition, it requires a full accounting of above- and belowground biomass production. We ex...

In multispecies systems, facilitation and complementarity can offset some of the negative effects of interspecies competition. This can lead to more efficient use of resources by the plant community as a whole, resulting in an increase in productivity. Overyielding, a phenomenon whereby plant production in mixture exceeds that of production in mono...

Water scarcity associated with intense and frequent droughts has increased the need for the implementation of drought adaptation strategies that can save water and sustain crop productivity in water limited environments. A two season (2011 and 2012) study evaluated root growth, yield and fruit quality responses of cvs. Mission (muskmelon; reticulat...

The presence of vegetation is thought to reduce loss of soil substrate after roof installation; however, few attempts have been made to quantify this effect. Twelve green roof modules placed at a 2% slope were used to quantify the effect of wind, precipitation intensity ,vegetation and vegetation type on modular green roof substrate depth. The pres...

As climate change impacts rainfall distribution and frequency many agricultural producers are turning to alternative water sources as supplemental irrigation. Often these sources are of low quality and high in salinity. Glycophytic crops, which include most agricultural crop species, are negatively impacted by salt stress. This results in a dramati...

Fluctuations in rainfall, increased drought stress, limited water availability, and low-quality irrigation water are major concerns for agricultural producers. Low-quality irrigation water and drought increase salinity in soils, which results in yield reductions of salt-sensitive crops such as watermelon. The objectives of this project were to eval...

Background/Question/Methods Crop rotations during the heat of Texas’ summers are limited due to the poor availability of crops that can withstand the high temperatures. Additionally, management practices that enhance or sustain soil and crop productivity while reducing inputs can increase producer profit and reduce the potential for nutrient runo...

Increased continuous irrigation due to drought conditions and above average temperatures, and resulting salt buildup in soils, can lead to a decline in yields in salt-sensitive species such as watermelon. This greenhouse investigation is phase one of a two-phase study aimed at assessing the potential benefits of utilizing halophytic species as comp...

Fine root morphology is strongly affected by genotype, environment, and the interaction between genotype and environment. In surveys of herbaceous plants it has been shown that plants from competitive resource rich habitats generally produce fine roots with greater length per unit root dry mass (specific root length, SRL). Few studies have explored...

Water stress alters biomass allocation strategies of crop plants, resulting in changes in root growth patterns in time and space. Understanding these changes will assist in screening cultivars for drought tolerance traits in melons. This study was conducted to investigate the effect of deficit irrigation (50% vs. 100% crop evapotranspiration, ETc)...

Green roofs can improve urban environments by reducing the amount of runoff and in some cases improve the quality of runoff leaving urban areas. Water quality and soil chemistry of four green roofs in Houston that harvest and recycle rainwater and irrigation runoff were investigated. The green roofs vary in age from 2.5 to 8 years. Continuous recyc...

After an outbreak of blotch leafminer (Cameraria caryaefoliella) on field-grown pecan (Carya illinoinensis) trees in 2010, an experiment was conducted to evaluate the consequences of the injury on carbon assimilation and photosynthetic efficiency, and, in particular, to assess if low-to-moderate injury induces a compensatory increase in photosynthe...

Root zones of mature Sweetgum paved with either pervious or impervious concrete after 15-18 years of tree growth exhibited much reduced standing fine root length compared to unpaved plots 3 years after pavement installation. The objective of this paper was to determine whether these observed reductions in standing root length were due to reduced ro...

Savanna tree-grass interactions may be particularly sensitive to climate change. Establishment of two tree canopy dominants, post oak (Quercus stellata) and eastern redcedar (Juniperus virginiana), grown with the dominant C4 perennial grass (Schizachyrium scoparium) in southern oak savanna of the United States were evaluated under four climatic sce...

We conducted a study to determine if inoculation with arbuscular mycorrhizal fungi (AMF) would enhance the tolerance of vinca [Catharanthus roseus (L.) G. Don] plants to sodium chloride (NaCl)-induced salinity in irrigation water. Vinca tolerated salinity levels up to 40 mM. Chlorophyll concentration, proline synthesis, and total antioxidant activi...

The quantification of ecological services from green roofs in Texas is emergent and proving advantageous. Identification of candidate plant species for green roofs in Texas and similar hot and humid subtropical climates is limited. Three extensive green roof systems and research sites in Texas employed different water conserving techniques ranging...

Background and aims The application of green roof technology has become more common in the central, northwestern and eastern USA, and is now being employed across the southern USA as well. However, there is little research in the literature that evaluated plant survival on unirrigated green roofs in subtropical climates that experience frequent dro...

Planting depth (location of root collar in relation to substrate surface grade) varies in the container production industry. Optimum planting depth varies for different species. Most container-produced plants are grown in a soilless media to allow better aeration and drainage conditions, so the effects of planting depth observed in landscape establ...

In recent years, increased awareness of the potential interactions between rising atmospheric CO2 concentrations ([ CO2 ]) and temperature has illustrated the importance of multifactorial ecosystem manipulation experiments for validating Earth System models. To address the urgent need for increased understanding of responses in multifactorial exper...

Citrus production in Texas, currently valued at approximately $75 million, is the third largest citrus industry in the U.S., with Hidalgo and Cameron Counties in the Lower Rio Grande Valley (LRGV) accounting for more than 98% of bearing acres. In recent years, the citrus industry in the U.S. and the LRGV in particular, has been facing numerous chal...

There are numerous benefits to preserving existing mature trees in urbanizing areas, such as larger amounts of shade, greater transpirational cooling and greater air pollution removal. However, covering root zones of mature trees with gas and water impervious materials often leads to rapid death of mature trees in urbanizing areas as result of anox...

Cultivar evaluations for drought tolerance and irrigation management are very important in water-limited, arid regions of the United States. This study was conducted to investigate the effect of deficit irrigation (50% vs. 100% crop evapotranspiration, ETc) on three melon (Cucumis melo L.) cultivars (Mission and Da Vinci, reticulatus type and Super...

Modular green roofs were investigated to better understand surface and membrane level temperature expectations of unirrigated green roofs during hot summer conditions in south-central Texas. We used three succulent monocultures, Sedum kamtschaticum, Delosperma cooperi, Talinum calycinum syn. Phemeranthus calycinus and one unplanted control module,...

The effect of planting depth, defined as the location of the root collar relative to soil surface, is of particular concern for tree growth, development, and performance in the landscape and seems to be dependent on soil conditions. The objective of this study was to determine the effect of three planting depths and four soil amendments on live oak...

Mature trees with large canopies help reduce problems of excessive heat and surface runoff in urban areas through shading, transpirational cooling, and interception and absorption of precipitation. Trees in paved impervious areas often suffer from a poor root zone environment. The objective of this experiment was to test if use of pervious concrete...

Increasing concentrations of greenhouse gases are projected to elevate global surface air temperatures by 1.1 to 6.4°C by the end of the century, and potentially magnify the intensity and variability of seasonal precipitation distribution. The mid-latitude grasslands and savannas of North America are predicted to experience a shift towards drier su...

Background/Question/Methods There are numerous benefits to preserving existing mature trees in urbanizing areas, such as larger amounts of shade, greater transpirational cooling and greater air pollution removal. However, covering root zones of mature trees with gas and water impervious materials often leads to rapid death of mature trees in urba...

In this paper, we examined twelve riparian forests along urban-rural gradients in Austin, TX (USA), on the relationship among watershed urbanization and the invasion of alien woody species. We assessed the degree of biological invasion by measuring relative alien cover (RAC) of the riparian forests. We also measured environmental variables (15 in t...

Installation of intensive and extensive green roofs is becoming popular for reducing runoff from impervious surfaces in many cities around the world. Most studies on runoff quality from green roofs have been conducted in cooler northern climates. We examined the losses and gains of nutrients, cations and selected anions in planted and unplanted gro...

Background/Question/Methods Climate change is predicted to alter tree establishment in savannas as tree and grass species differentially respond to warming and altered rainfall patterns. Yet, tree-grass interactions and linkages to tree establishment in response to climate change drivers remain largely unknown, but key to predicting vegetation chan...

Humans significantly affect their ecosystem. Nowhere is this more evident than in our towns and cities around the world. We have options when it comes to the sustainability of our cities. We have to pay attention to meeting the needs of today without compromising the needs of the future. However, to truly understand those options, we need to have t...

Ecosystem services have been defined as the benefits that human populations derive directly or indirectly from ecosystem functions. These services range from the obvious, such as provision of food and fiber and timber for homes, to the less obvious, such as microbial nutrient cycling in soil and environmental cooling by vegetation. This chapter dis...

A green roof is a vegetated roof or deck designed to provide urban greening for buildings, people, or the environment. Made popular across Europe over the past few decades, green roofs are now becoming more familiar to North Americans as some cities have built green roof pilot projects and adopted incentives for using green roofs or even require th...

Tree transplanting practices influence plant survival, establishment, and subsequent landscape value. The inability to adequately quantify effects of transplanting practices threatens long-term sustainability of landscape trees. Planting depth [i.e., location of the root collar relative to soil grade (soil surface)], is of particular concern for tr...

Planting depth during container production may influence plant growth, establishment, and subsequent landscape value. A lack of knowledge about the effects of common transplanting practices may lead to suboptimal performance of planted landscape trees. Planting depth, i.e., location of the root collar relative to soil grade, is of particular concer...

During the development of parking lots and pedestrian areas, mature trees are often removed from the site and replaced with saplings after development is completed. This research aims to study the possibility of using pervious porous concrete as an alternative pavement that may help to keep existing mature trees, and all the benefits they can provi...

Climate warming and drought may alter tree establishment in savannas through differential responses of tree seedlings and grass to intermittent rainfall events. We investigated leaf gas exchange responses of dominant post oak savanna tree (Quercus stellata and Juniperus virginiana) and grass (Schizachyrium scoparium, C4 grass) species to summer rai...

Background/Question/Methods Southern oak savanna may be especially responsive to rainfall redistribution and climate warming during tree establishment as tree and grass species compete for water and other resources. Quercus stellata (post oak) and Juniperus virginiana (juniper) are the dominant C3 trees and Schizachyrium scoparium (little bluestem...

Background/Question/Methods We measured soil respiration rates to study effects of tree-grass interactions and climate change on root and soil microbial activity in southern oak savanna. Quercus stellata (post oak, deciduous) and Juniperus virginiana (juniper, evergreen) are the dominant C3 trees and Schizachyrium scoparium (little bluestem) the d...

Placing impermeable pavement around existing trees can cause declines in tree growth and health due to reduced water infiltration and soil surface gas exchange.Using pervious concrete, with greater water infiltration and gas permeability, could be a good alternative. The purpose of this study was to test soil respiration, root growth and soil extra...

Pecan is an important nut crop grown throughout much of the southern U.S, with New Mexico, Georgia, and Texas ranked as the leading producers. The commercial pecan nursery industry currently relies on improved cultivars grafted on rootstocks derived from open-pollinated seeds. Seedstocks are chosen in relation to their geographical origin and gener...

We only have a limited understanding of the nutrient uptake physiology of individual roots as they age. Despite this shortcoming, the importance of nutrient uptake processes to our understanding of plant nutrition and nutrient cycling cannot be underestimated. In this study, we used a ¹⁵N depletion method that allowed for the measurement of nitrate...

An experiment was conducted to investigate the morphologic characteristics and photosynthetic response of sun and shade leaves of mature pecan [Carya illinoinensis (Wangenh.) K. Koch] trees. Treatments were established according to leaf type (sun or shade leaves) and cultivar (Pawnee and Stuart). Sun leaves were chosen from those growing on exterio...

Coupled surface-atmosphere models are being used with increased frequency to make predictions of tropospheric chemistry on a 'future' earth characterized by a warmer climate and elevated atmospheric CO2 concentration. One of the key inputs to these models is the emission of isoprene from forest ecosystems. Most models in current use rely on a schem...

Summary • This study examined the effects of warming, elevated atmospheric CO2 and cutting regimen on the growth of Phalaris aquatica cv. Holdfast swards. • Six temperature gradient tunnels (TGT) were used to manipulate both air temperature and atmospheric CO2 concentrations (ambient and 750 ppm). Within each tunnel, there were three temperature tr...

Polar-desert plants experience low average air temperatures during their short growing season (4–8 °C mean July temperature). In addition, low availability of inorganic nitrogen in the soil may also limit plant growth. Our goals were to elucidate which N sources can be acquired by polar-desert plants, and how growth and N-uptake are affected by low...

The effects of prolonged exposure to dry surface soil on the capacity of roots to take up water and phosphorus were examined in mycorrhizal sour orange (Citrus aurantium L,) seedlings grown in pots with upper and lower portions separated hydraulically. In the first experiment, upper portions of the pots were either irrigated every 2-3 d, droughted...

Aquatic seedlings of Ranunculus peltatus Schrank were subjected to three levels of droughl (dry, saturated and flooded) at two different phenological stages, vegetative stage and at onset of flowering. Changes in growth form, timing of flowering, number of flowers and fiuits and the number of seeds per fruit were monitored to test the effect of dro...