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Interspecies specific interactions are generally regarded as drivers of plant productivity in multispecies agroecosystems. 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 conditions. We studied the effects on physiological response, leaf traits and water use efficiency of a multifunctional species intercropping system consisting of peanut (Arachis hypogaea L.), watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai], okra [Abelmoschus esculentus (L.) Moench], cowpea [Vigna unguiculata (L.) Walp.], and pepper (Capsicum annuum L.) planted alone or in various intercropping combinations in a low fertilizer input system in the peak of summer heat in Texas. Differences in gas exchange measurements were detected only in watermelon in year 2 of the study when okra was the dominant crop. This same year watermelon specific leaf area (SLA) was significantly higher when okra was present in a treatment and particularly in the three and four species combinations, Wpwo and Wpwoc, 27.5 and 31.0 m2 kg−1, respectively, as compared to watermelon grown in monoculture, strip intercropped with peanut (Spw) and within row intercropped with peanut (Wpw), 20.4, 20.1, and 19.8 m2 kg−1, respectively. This corresponds with an increase watermelon leaf N concentration and a decrease in leaf C:N ratio in Wpwo and Wpwoc treatments. No differences in d13C composition, a measure of water use efficiency over the leaf lifespan, were detected across cropping system for each species. Water use efficiency based on per plant production (WUEyield) indicated an increase in water use efficiency in dominant crops such as watermelon in 2011 and okra in 2012, but a reduction in WUEyield subordinate crops such as cowpea and pepper both years of the study. Peanut grown in monoculture and strip intercropped with watermelon had significantly lower leaf water potential values in 2012, −2.2 and −2.1 MPa, respectively, as compared to intercropping systems increasing in level of integration (Wpw = − 1.1, Wpwo = − 0.6, Wpwoc = − 1.3, Wall = −1.1 MPa), indicating peanut benefited from alterations to microclimate and facilitative interactions with companion crops in some intercropping systems through a reduction in plant water stress. The results from this study suggest there may be a benefit to a multifunctional intercropping system in the form of increased food production per unit of water input in dominant crops and reduced water stress for some component species. This is important to producers; showing a method to increase overall crop production without increasing water inputs.

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 (hyperthermic typic calciustolls) type soils, with subsurface drip irrigated using black plastic mulch. Root length intensity ( L a , cm cm −2 ), marketable (MFY), total fruit yield (TFY; t ha −1 ), fruit firmness (N) and soluble solids content (SSC; °Bx) of four TAMU inbreds and two commercial hybrids, Mission and Journey were measured. Root length intensity was lower in 2011 than in 2012, possibly due to the variations in climatic, and soil conditions, and minirhizotron tube artifacts. Sandy loam soil produced 77% higher L a (1.6 vs. 0.9 cm cm −2 ) as compared to clay soil. Under sandy loam soils, root growth distribution was deeper (40–70 cm) while it was confined at the depth of drip tape ( L a to most popular commercial cultivar Mission and higher L a than Journey. These results reveal that under high input intensive production systems large root systems may not be required for high yielding potential, however under sandy loam soils cultivars vary in their root distribution patterns across soil depth. Further, the great rooting ability of TAMU breeding lines under different soil types and equivalent yield potential to commercial hybrids confirms their suitability as a potential parent for developing genetically improved and stable cultivars for a wide range of environments.

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 yield unless a mechanism of increasing salinity tolerance is found. The salinity tolerance of citrus rootstocks differs depending on species and cultivar in their ability to exclude or sequester toxic ions. Identifying rootstocks that are more salt tolerant is important to citrus production in susceptible areas. ‘Olinda’ Valencia trees budded to three rootstocks (sour orange [SO], C22, and C146) and the ungrafted rootstocks were subjected to 6 months of saline irrigation. Simulated brackish water at 1, 3, 5, and 10 dS m −1 along with a 0 dS m −1 control were used to irrigate trees over the course of the study. Throughout this time period chlorophyll fluorescence, stomatal conductance, electrolyte leakage, and SPAD were measured to identify how trees responded to different levels of salinity stress. Chlorophyll fluorescence, stomatal control, and SPAD decreased with increased salinity, while electrolyte leakage increased. These responses were more pronounced in grafted trees than ungrafted trees. C22 and C146 rootstocks showed more tolerance to increases in salinity than the SO rootstocks. The ‘Olinda’ Valencia scion reduces rootstock tolerance to salinity, however, trees grafted to the C22 and C146 rootstocks showed more salinity tolerance than those grafted to SO rootstocks. This study emphasizes that both rootstock and scion should be considered when selecting trees for saline conditions.

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 impractical to directly measure Tdry and Twet, the goals of this work were to: i) determine a suitable artificial reference surface that makes application of the CWSI faster and easier in the field, ii) develop a model for Tdry and Twet based on the reference surface temperature that allows for calculation of standard CWSIs, iii) test the technique for a range of weather conditions and tree species, and iv) analyze the sensitivity of these two models to Tdry and Twet, and their impact on the estimation of four different CWSIs. Our results showed that both Tdry and Twet are linearly related to the thermal temperature of green paper across a wide range of environmental conditions. Although there was a significant effect of the light conditions on Tdry and Twet, the same models could be used in both the sun and shade to relate Tdry and Twet to Tref. Moreover, results indicated that a new CWSI dependent only on TL and Twet was least sensitive to errors in Twet, but most sensitive to TL.

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 a crop setting may lead to increased yield (overyielding) in diverse cropping systems when compared to monocultures. Different combinations of peanut, watermelon, okra, cowpea, and pepper planted alone or in various intercropping combinations were investigated over two growing seasons in a low-input system in the peak of summer heat in Texas. Each species was selected to perform a specific function within the system. Results from land equivalent ratio (LER) indicate that the within-row combination with peanut, watermelon and okra (Wpwo) and peanut, watermelon, okra and cowpea (Wpwoc) consistently overyielded in 2011 and 2012. LER values were 1.17 each for Wpwo and Wpwoc in 2011 and 1.17 and 1.20 in 2012, respectively. In 2011, watermelon was the dominant crop and was up-regulated in all intercropping combinations while all other component crops were down-regulated. Watermelon per plant production was significantly higher in the combination containing all species (Wall) when compared to its monoculture, 5.50 and 2.09 kgfruit plant−1, respectively. In 2012, okra was the dominant crop and was up-regulated in all intercropping combinations while watermelon, cowpea, and pepper were down-regulated. Okra per plant production was significantly higher in Wpwoc and Wall than in monoculture, 2.28, 2.46, and 1.13 kgfruit plant−1, respectively. These findings suggest that three and four species intercropping combinations, whereby each crop is selected to perform a specific function within the system, may provide small-scale sustainably-minded producers a model system that can be utilized in suboptimal conditions and allow them to reduce inputs while increasing overall yields.

As population and agricultural pressure on high quality fresh water resources increases, it becomes more important to identify rootstocks and production techniques that allow the usage of lower quality water in irrigated agriculture. Water of 0, 1, 3, 5 and 10 dS m −1 salinity was applied to grafted (with Olinda Valencia ( Citrus sinensis var. Olinda) scion) and ungrafted sour orange ( Citrus aurantium L.), C22, and C146 ( Citrus sunki Hort. Ex Tan. × Poncirus trifoliata L. Raf. ‘Swingle’) trees to evaluate the effect of grafting and rootstock variety on salinity tolerance. Grafted rootstocks had a lower survival rate at higher salinity concentration than ungrafted trees and effects were dependent upon tree variety. Height growth rate and standing leaf area of grafted citrus trees declined with increased salinity concentrations while the response of ungrafted and grafted citrus trees was variety dependent. Mortality increased and standing leaf area decreased with increasing tissue Na + and Cl − concentrations. Mortality in response to salinity was greater in grafted rootstocks than mortality of ungrafted trees. Overall, C22 and C146 rootstocks and ungrafted trees were found to be more tolerant of saline conditions than grafted SO rootstock or ungrafted SO trees.

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; reticulatus ), Da Vinci (tuscan; reticulatus ) and Super Nectar (honeydew; inodorus ) of melon ( Cucumis melo L.) to two irrigation rates (100% and 50% crop evapotranspiration (ETc)) on a silty clay soil under the semi-arid conditions of Texas. Deficit irrigation (50% ETc) increased root length density (RLD) in Mission, decreased in Da Vinci and did not affect in Super Nectar. Marketable fruit yield at 100% ETc irrigation was 77.1 t ha −1 in 2011 and 78.7 t ha −1 in 2012, but deficit irrigation caused a 30% decrease in marketable yield in both seasons, mainly due to a reduction in fruit size. Yield responses to deficit irrigation also varied with cultivar. A significant yield reduction of 43% in 2011 and 33% in 2012 was measured in Super Nectar, while for cvs. Mission and Da Vinci the reduction in yield was 24% and 30%, respectively in 2012. Deficit irrigation had no adverse impact on melon fruit quality; rather it increased total soluble solids content (23%) in Mission and β-carotene content (25%) in Da Vinci in 2011. At 50% ETc, agronomic water use efficiency (WUE; kg ha −1 mm −1 ) was improved in Mission (13%) in 2012 while it decreased in Super Nectar (21%) in 2011. These results showed that deficit irrigation can save 37–45% of irrigation water in Mission and Da Vinci cultivars ( reticulatus ) with a moderate reduction in economic yield. This practice may not be applicable for cv. Super Nectar ( inodorus ), as it reduced yield without improving water use efficiency.

As green roofs continue to grow in popularity more research will be needed in new ecoregions to support development of policy, regulation, and incentives. Extensive green roofs represent the majority of new construction each year and understanding their performance expectations is critical for regulation. In our experiment we tested the ability of three monocultures of low stature CAM plants (Sedum kamtschaticum, Delosperma cooperi and Talinum calycinum syn. Phemeranthus calycinus) to improve runoff reduction efficiency of un-irrigated modular extensive green roofs exposed to a range of precipitation event sizes in a warm and dry southern US climate. Stormwater runoff data were collected for 15 rainfall events that ranged from a minimum of 4.1 mm to a maximum of 102.9 mm. An average precipitation event retention efficiency of 78% was recorded. On average, the presence of T. calycinum enhanced retention efficiency by an additional 7.5% compared to unvegetated modules. Substrate volumetric water content affected retention capacity of unvegetated modules only.

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, each replicated 3 times. Media surface and below media temperatures were monitored, as well as soil water content and general weather conditions (RH, air temperature). Temperatures at the surface and below the media surface were compared with temperatures of a standard roof surface. We found that diurnal surface temperature reductions were very stable throughout the summer. Much larger temperature reductions were achieved below the modules than at the soil surface. Temperature reductions at the soil surface were predominantly driven by soil volumetric water content (VWC) and, to a lesser degree, air temperature while species and percent cover had small modifying effects through interactions with VWC and air temperature. Temperature reductions below the modules were driven by surface soil temperature, while increasing VWC led to a small decrease in temperature reductions at the membrane level. Mean daily temperature reductions achieved were 18.0 °C at the soil surface and 27.5 °C below the module, thus demonstrating that unirrigated, succulent-based green roofs can provide significant rooftop temperature reductions during hot, dry summer conditions.

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 establishment may be different from those seen in container-production. This study tested if inoculation with arbuscular mycorrhizal fungi (AMF) would enhance the tolerance of container-grown Ulmus parvifolia Jacq. (lacebark elm) to above and/or below grade planting depths. The AMF plants and non-AMF plants were planted into 2.1 L black plastic containers with their root collars at substrate surface (grade), 3 cm above grade, 1 cm above grade, 1 cm below grade, or 3 cm below grade under greenhouse conditions. Growth (stem diameter, total plant dry mass) and physiological responses (leaf nutrient concentration, chlorophyll concentration, total antioxidant and nitrate reductase activities, and total phenolic content) were measured. In general, AMF plants had greater growth when planted above or below grade when compared to non-AMF plants at the same planting depth, but this was not correlated with enhanced nutrient tissue levels. Non-AMF plants planted at grade had greater growth than AMF plants at grade. Planting at grade resulted in optimum growth for U. parvifolia. Poor transplanting techniques during container production (above or below grade) were partially alleviated by inoculating plants with AMF.

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 could be more beneficial for root growth and consequently a better alternative towards preserving existing mature trees during urban development. We measured root activity through CO 2 flux, and also measured root production of American sweetgum under impervious concrete, pervious concrete and no pavement conditions (control). Soil under impervious concrete had lower oxygen concentrations than soil under pervious concrete and control treatments, particularly under wet conditions. Soil under pervious concrete had a 0.020 m 3 m −3 (2% volumetric water content (VWC)) greater volumetric water content than soils paved with impervious concrete. Soil CO 2 efflux rates and soil CO 2 concentrations were extremely high under both concrete treatments. Standing live root length at the end of the experiment was greater under the control treatment than under both concrete treatments and these changes in root production were likely due to high soil CO 2 concentrations under both pervious and impervious concrete. The soil type at our site, which is a Ships clay with a very low permeability rate, may have limited CO 2 exchange through the pervious pavement. On this heavy clay soil, pervious concrete did not convey any measurable root growth benefits over impervious concrete.

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 (Quercus virginiana Mill.) growth and visual quality. Trees were planted with root collars at one of three planting depths (grade, 7.6 cm above grade, or 7.6 cm below grade). Soil amendments were: incorporated sand (30% by volume), incorporated composted peat (30% by volume), sandy topsoil in raised (20 cm) bed, and native sandy loam soil (control). Planting at grade or below grade resulted in 0% mortality, while planting live oak trees above grade resulted in 12.5% mortality. The container produced trees were top-heavy (high shoot:root ratio) and were thus susceptible to wind damage when planted above grade. Trunk diameter growth and relative growth rate were smaller when trees were planted with root collars below grade compared to those planted above grade or at grade. Visual quality of live oak roots was improved when trees were planted in raised beds with sandy topsoil compared to the control soil. Shoot visual quality was improved when trees were planted in the incorporated sand and raised beds with sandy topsoil compared to the control and incorporated peat sections. Thus, it is recommended to plant live oaks with the root collar at grade and in sandy top soils in raised beds to improve tree quality after establishment.

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 their use. Green roof standards and guidelines are also emerging to be used for governance and project specification. Although much is known about the application of green roofs across Europe, much less is known about their application across North America's diverse ecological regions. When considering the many decisions required in applying green roof technology to a specific place, there are few choices more critical to their success than the selection of appropriate vegetation. We conducted a review of green roof research to investigate what is known about the application of plants on green roofs across North America and their ecological implications. Results indicate that investigation sites across ecoregions begin to reveal differences in plant survival. Although ecological investigations are limited, their results show improved plant performance and ecological services with diverse green roofs. We conclude that as green roofs continue to become regulated and adopted in policy, further development of standards and guidelines is needed. To date, there is no common ground for reporting of green roof research, and we make recommendations for facilitating such efforts for improved research, policy development and their management across North America's diverse ecological regions.

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 provide, alive after site development. Three different pavement treatments: (1) no pavement; (2) impervious standard concrete; and, (3) pervious porous concrete were compared over 2 years to test their ability to modify growth and leaf gas exchange of existing 15–18-year-old American sweetgum ( Liquidamber styraciflua ) trees. Soil water and temperature dynamics of the pervious plots were closely correlated with those in the control plots. Plots treated with pervious concrete had greater soil water content than plots with standard concrete in the deeper soil layers in some seasons, but not during the summer. Tree diameter (dbh) relative growth rates were similar across the three pavement types. There was no effect of the treatments on leaf water potential or leaf gas exchange. The data presented in this paper suggest that pervious porous concrete does not provide additional benefits in ensuring growth and survival of pre-existing mature trees in new urban developments.

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 drought on reproduction. Plants that were transferred to a terrestrial, but water-saturated, environment at a vegetative stage rapidly changed from an aquatic, spreading, elongated growth form to a prostrate growth form and produced only slightly fewer seeds per pot (86) than the flooded control plants (93). Total seed production was decreased by 1000 seeds per pot in both saturated treatments compared to the control treatment. There was no significant difference in total seed production between plants encountering drought at a vegetative or a flowering stage (2471 vs. 2348 seeds per pot). Plants subjected to air drying of the soil (no water added) at both phenological stages changed growth form, but flower, fruit and seed production was negligible. The fact that total seed production was still relatively high under water-saturated conditions at both phenological stages may explains partially why this species is successful in temporary marshes where drought often occurs during its lifecycle. ~_3 1997 Elsevier Science B.V.