Winter injury to the root systems of fruit trees can cause significant tree losses and yield reductions in the northern regions of the United States and Canada. To compare the root and trunk cold temperature tolerance, a series of experiments were conducted using ungrafted apple rootstocks. ‘Geneva® 11’ (G.11), ‘Geneva® 30’ (G.30), ‘Geneva® 41’ (G.41), ‘P.2’, and ‘Budagovsky 9’ (B.9) apple (Malus ×domestica Borkh.) rootstocks had root tissue hardiness similar to ‘M.26’, but ‘Geneva® 935’ (G.935) had greater cold-hardiness than M.26 when based on shoot regrowth in ungrafted trees. The LT50 of M.26 and P.2 roots ranged from –12 to –14 °C. The LT50 was –13 °C for B.9, –13.4 to –14.6 °C for G.30, and –12 °C for G.11. The LT50 of G.41 was one of the highest in one experiment, –8 °C, and one of the lowest in another, colder than –15.0 °C. The LT50 of G.935 roots was the lowest and ranged from –16 to –19 °C. Compared with M.26, trunk cold-hardiness in December was greater in B.9 and P.2 and was similar in G.30. Cold-hardiness of G.11 in December was mixed with less injury in the xylem but more injury in the phloem compared with M.26. In October, M.26 and G.935 trunks had little injury after exposure to –24 °C.
Renae E. Moran, Youping Sun, Fang Geng, Donglin Zhang, and Gennaro Fazio
Ji-Jhong Chen, Jeanette Norton, Heidi Kratsch, Youping Sun, and Larry Rupp
Shepherdia ×utahensis ‘Torrey’ (hybrid buffaloberry) is an actinorhizal plant that can form symbiotic nodules with the actinobacterial genus Frankia. However, little research has been conducted to investigate the presence of Frankia in their nodules and the effects on plant growth. In this study, plants were grown in a Metro-Mix® 820 substrate and inoculated with soils collected from Mohave County, AZ, or in a low organic-matter substrate inoculated with soils from North Logan, UT. The presence of Frankia was quantified using PolF/PolR primers to amplify their nitrogenase (nifH) gene sequences. In the Metro-Mix 820 substrate, plants irrigated with nitrogen (N)-free Hoagland’s solution at pH 6.5 formed nodules at week 12 after experiment initiation, whereas those receiving the same solution with 2 mm ammonium nitrate (NH4NO3) appeared healthy, but no nodules formed. In the low organic-matter substrate, nodules formed in 5 weeks when plants were irrigated with N-free Hoagland’s solution at pH 7.5. Four 300-bp fragments of query sequences (SU1, SU2, SU3, and SU4) were obtained from nodules. When compared with nifH gene sequences reported in the literature using the Basic Local Alignment Search Tool (BLAST), more than 90% similarity to the nifH of Frankia spp. was obtained. The Frankia strains in the nodules shared nifH sequences similar to those of the same host-specific group of Shepherdia. Furthermore, Frankia strains with similar nifH genes have been reported in nodules of Shepherdia argentea (silver buffaloberry). Additionally, Frankia strains belonging to cluster 3 infective strains consisting of Elaeagnaceae and Rhamnaceae infective Frankia showed high similarity to the query sequences. This research demonstrates that nodulation of S. ×utahensis is inhibited at 2 mm NH4NO3. Apart from N, nodule formation may be associated with the substrate type and pH of the nutrient solution. Based on nifH gene sequence amplification, Frankia strains in the root nodules may have the potential to fix atmospheric nitrogen (N2). These Frankia strains have signature gene sequence characteristics of Elaeagnaceae-infective Frankia, suggesting that S. ×utahensis shares Frankia strains similar to its parents.
Ji-Jhong Chen, Heidi Kratsch, Jeanette Norton, Youping Sun, and Larry Rupp
Shepherdia ×utahensis ‘Torrey’ (‘Torrey’ hybrid buffaloberry) is an actinorhizal plant that can fix atmospheric nitrogen (N2) in symbiotic root nodules with Frankia. Actinorhizal plants with N2-fixing capacity are valuable in sustainable nursery production and urban landscape use. However, whether nodule formation occurs in S. ×utahensis ‘Torrey’ and its interaction with nitrogen (N) fertilization remain largely unknown. Increased mineral N in fertilizer or nutrient solution might inhibit nodulation and lead to excessive N leaching. In this study, S. ×utahensis ‘Torrey’ plants inoculated with soils containing Frankia were irrigated with an N-free nutrient solution with or without added 2 mm ammonium nitrate (NH4NO3) or with 0.0 to 8.4 g·L−1 controlled-release fertilizer (CRF; 15N–3.9P–10K) to study nodulation and plant morphological and physiological responses. The performance of inoculated plants treated with various amounts of CRF was compared with uninoculated plants treated with the manufacturer’s prescribed rate. Plant growth, gas exchange parameters, and shoot N content increased quadratically or linearly along with increasing CRF application rates (all P < 0.01). No parameters increased significantly at CRF doses greater than 2.1 g·L−1. Furthermore, the number of nodules per plant decreased quadratically (P = 0.0001) with increasing CRF application rates and nodule formation were completely inhibited at 2.9 g·L−1 CRF or by NH4NO3 at 2 mm. According to our results, nodulation of S. ×utahensis ‘Torrey’ was sensitive to N in the nutrient solution or in increasing CRF levels. Furthermore, plant growth, number of shoots, leaf area, leaf dry weight, stem dry weight, root dry weight, and N content of shoots of inoculated S. ×utahensis ‘Torrey’ plants treated with 2.1 g·L−1 CRF were similar to those of uninoculated plants treated with the manufacturer’s prescribed rate. Our results show that S. ×utahensis ‘Torrey’ plants inoculated with soil containing Frankia need less CRF than the prescribed rate to maintain plant quality, promote nodulation for N2 fixation, and reduce N leaching.
Haifeng Xing, Julie Hershkowitz, Asmita Paudel, Youping Sun, Ji Jhong Chen, Xin Dai, and Matthew Chappell
Reclaimed water provides a reliable and economical alternative source of irrigation water for landscape use but may have elevated levels of salts that are detrimental to sensitive landscape plants. Landscape professionals must use salt-tolerant plants in regions where reclaimed water is used. Ornamental grasses are commonly used as landscape plants in the Intermountain West of the United States due to low maintenance input, drought tolerance, and unique texture. Six ornamental grass species, including Acorus gramineus (Japanese rush), Andropogon ternarius (silver bluestem), Calamagrostis ×acutiflora (feather reed grass), Carex morrowii (Japanese sedge), Festuca glauca (blue fescue), and Sporobolus heterolepis (prairie dropseed), were evaluated for salinity tolerance. Plants were irrigated every 4 days with a fertilizer solution at an electrical conductivity (EC) of 1.2 dS·m–1 (control) or with a saline solution at an EC of 5.0 dS·m–1 (EC 5) or 10.0 dS·m–1 (EC 10). At 47 days, most species in EC 5 exhibited good visual quality with averaged visual scores greater than 4.6 (0 = dead, 5 = excellent). In EC 10, most A. gramineus plants died, but C. ×acutiflora, F. glauca, and S. heterolepis had no foliar salt damage. At 95 days, C. ×acutiflora, F. glauca, and S. heterolepis in EC 5 had good visual quality with averaged visual scores greater than 4.5. Acorus gramineus, A. ternarius, and C. morrowii showed foliar salt damage with averaged visual scores of 2.7, 3.2, and 3.4, respectively. In EC 10, A. gramineus died, and other grass species exhibited moderate to severe foliar salt damage, except C. ×acutiflora, which retained good visual quality. Plant height, leaf area, number of tillers, shoot dry weight, and/or gas exchange parameters also decreased depending on plant species, salinity level, and the duration of exposure to salinity stress. In conclusion, A. gramineus was the most salt-sensitive species, whereas C. ×acutiflora was the most salt-tolerant species. Festuca glauca and S. heterolepis were more tolerant to salinity than A. ternarius and C. morrowii. Calamagrostis ×acutiflora, F. glauca, and S. heterolepis appear to be more suitable for landscapes in which reclaimed water is used for irrigation. Plant responses to saline water irrigation in this research could also be applied to landscapes in salt-prone areas and coastal regions with saltwater intrusion into aquifers and landscapes affected by maritime salt spray.
Susmitha Nambuthiri, Robert L. Geneve, Youping Sun, Xueni Wang, R. Thomas Fernandez, Genhua Niu, Guihong Bi, and Amy Fulcher
The green industry has identified the use of biodegradable containers as an alternative to plastic containers as a way to improve the sustainability of current production systems. Field trials were conducted to evaluate the performance of four types of 1-gal nursery biocontainers [keratin (KR), wood pulp (WP), fabric (FB), and coir fiber (Coir)] in comparison with standard black plastic (Plastic) containers on substrate temperature, water use, and biomass production in aboveground nurseries. Locations in Kentucky, Michigan, Mississippi, and Texas were selected to conduct experiments during May to Oct. 2012 using ‘Green Velvet’ boxwood (Buxus sempervirens × B. microphylla) and ‘Dark Knight’ bluebeard (Caryopteris ×clandonensis) in 2013. In this article, we were focusing on the impact of alternative container materials on hourly substrate temperature variations and plant growth. Substrate temperature was on an average higher (about 6 °C) in Plastic containers (about 36 °C) compared with that in WP, FB, and Coir containers. However, substrate temperature in KR containers was similar to Plastic. Substrate temperature was also influenced by local weather conditions with the highest substrate temperatures recorded in Texas followed by Kentucky, Mississippi, and Michigan. Laboratory and controlled environment trials using test containers were conducted in Kentucky to evaluate sidewall porosity and evaporation loss to confirm field observations. Substrate temperature was similar under laboratory simulation compared with field studies with the highest substrate temperature observed in Plastic and KR, intermediate in WP and lowest in FB and Coir. Side wall temperature was higher in Plastic, KR, and FB compared with WP and Coir, while side wall water loss was greatest in FB, intermediate in WP and Coir, and lowest in plastic and KR. These observations suggest that the contribution of sidewall water loss to overall container evapotranspiration has a major influence on reducing substrate temperature. The porous nature of some of the alternative containers increased water use, but reduced heat stress and enhanced plant survival under hot summer conditions. The greater drying rate of alterative containers especially in hot and dry locations could demand increased irrigation volume, more frequent irrigation, or both, which could adversely affect the economic and environmental sustainability of alternative containers.
Tongyin Li, Guihong Bi, Genhua Niu, Susmitha S. Nambuthiri, Robert L. Geneve, Xueni Wang, R. Thomas Fernandez, Youping Sun, and Xiaojie Zhao
The performance of biocontainers as sustainable alternatives to the traditional petroleum-based plastic containers has been researched in recent years due to increasing environmental concern generated by widespread plastic disposal from green industry. However, research has been mainly focused on using biocontainers in short-term greenhouse production of bedding plants, with limited research investigating the use of biocontainers in long-term nursery production of woody crops. This project investigated the feasibility of using biocontainers in a pot-in-pot (PIP) nursery production system. Two paper (also referred as wood pulp) biocontainers were evaluated in comparison with a plastic container in a PIP system for 2 years at four locations (Holt, MI; Lexington, KY; Crystal Springs, MS; El Paso, TX). One-year-old river birch (Betula nigra) liners were used in this study. Results showed that biocontainers stayed intact at the end of the first growing season, but were penetrated to different degrees after the second growing season depending on the vigor of root growth at a given location and pot type. Plants showed different growth rates at different locations. However, at a given location, there were no differences in plant growth index (PGI) or plant biomass among plants grown in different container types. Daily water use (DWU) was not influenced by container type. Results suggest that both biocontainers tested have the potential to be alternatives to plastic containers for short-term (1 year) birch production in the PIP system. However, they may not be suitable for long-term (more than 1 year) PIP production due to root penetration at the end of the second growing season.
Xueni Wang, R. Thomas Fernandez, Bert M. Cregg, Rafael Auras, Amy Fulcher, Diana R. Cochran, Genhua Niu, Youping Sun, Guihong Bi, Susmitha Nambuthiri, and Robert L. Geneve
Containers made from natural fiber and recycled plastic are marketed as sustainable substitutes for traditional plastic containers in the nursery industry. However, growers’ acceptance of alternative containers is limited by the lack of information on how alternative containers impact plant growth and water use (WU). We conducted experiments in Michigan, Kentucky, Tennessee, Mississippi, and Texas to test plant growth and WU in five different alternative containers under nursery condition. In 2011, ‘Roemertwo’ wintercreeper (Euonymus fortunei) were planted in three types of #1 (≈1 gal) containers 1) black plastic (plastic), 2) wood pulp (WP), and 3) recycled paper (KF). In 2012, ‘Green Velvet’ boxwood (Buxus sempervirens × B. microphylla siebold var. koreana) was evaluated in 1) plastic, 2) WP, 3) fabric (FB), and 4) keratin (KT). In 2013, ‘Dark Knight’ bluebeard (Caryopteris ×clandonensis) was evaluated in 1) plastic, 2) WP, and 3) coir fiber (Coir). Plants grown in alternative containers generally had similar plant growth as plastic containers. ‘Roemertwo’ wintercreeper had high mortality while overwintering in alternative containers with no irrigation. Results from different states generally show plants grown in fiber containers such as WP, FB, and Coir used more water than those in plastic containers. Water use efficiency of plants grown in alternative containers vs. plastic containers depended on plant variety, container type, and climate.
Youping Sun, Genhua Niu, Andrew K. Koeser, Guihong Bi, Victoria Anderson, Krista Jacobsen, Renee Conneway, Sven Verlinden, Ryan Stewart, and Sarah T. Lovell
As the green industry is moving toward sustainability to meet the demands of society, the use of biocontainers as alternatives to petroleum-based plastic containers has drawn significant attention. Field trials of seven plantable biocontainers (coir, manure, peat, rice hull, soil wrap, straw, and wood fiber) were conducted in 2011 and 2012 at five locations in the United States to assess the influence of direct-plant biocontainers on plant growth and establishment and the rate of container decomposition in landscape. In 2011, container type did not affect the growth of any of the three species used in this study with an exception in one location. The three species were ‘Sunpatiens Compact Magenta’ new guinea impatiens (Impatiens ×hybrida), ‘Luscious Citrus’ lantana (Lantana camara), and ‘Senorita Rosalita’ cleome (Cleome ×hybrida). In 2012, the effect of container type on plant growth varied with location and species. Cleome, new guinea impatiens, and lantana plants grown in coir and straw containers were in general smaller than those in peat, plastic, rice hull, and wood fiber containers. After 3 to 4 months in the field, manure containers had on average the highest rate of decomposition at 88% for all five locations and two growing seasons. The levels of decomposition of other containers, straw, wood fiber, soil wrap, peat, coir, and rice hull were 47%, 46%, 42%, 38%, 25%, and 18%, respectively, in descending order. Plantable containers did not hinder plant establishment and posttransplant plant growth. The impact of container type on plant growth was smaller compared with that of location (climate). Similarly, the impact of plant species on pot decomposition was smaller compared with that of pot material.
Robin G. Brumfield, Alyssa J. DeVincentis, Xueni Wang, R. Thomas Fernandez, Susmitha Nambuthiri, Robert L. Geneve, Andrew K. Koeser, Guihong Bi, Tongyin Li, Youping Sun, Genhua Niu, Diana Cochran, Amy Fulcher, and J. Ryan Stewart
As high-input systems, plant production facilities for liner and container plants use large quantities of water, fertilizers, chemical pesticides, plastics, and labor. The use of renewable and biodegradable inputs for growing aesthetically pleasing and healthy plants could potentially improve the economic, environmental, and social sustainability of current production systems. However, costs for production components to integrate sustainable practices into established systems have not been fully explored to date. Our objectives were to determine the economic costs of commercial production systems using alternative containers in aboveground nursery systems. We determined the cost of production (COP) budgets for two woody plant species grown in several locations across the United States. Plants were grown in plastic pots and various alternative pots made from wood pulp (WP), fabric (FB), keratin (KT), and coconut fiber (coir). Cost of production inputs for aboveground nursery systems included the plant itself (liner), liner shipping costs, pot, pot shipping costs, substrate, substrate shipping costs, municipal water, and labor. Our results show that the main difference in the COP is the price of the pot. Although alternative containers could potentially increase water demands, water is currently an insignificant cost in relation to the entire production process. Use of alternative containers could reduce the carbon, water, and chemical footprints of nurseries and greenhouses; however, the cost of alternative containers must become more competitive with plastic to make them an acceptable routine choice for commercial growers.