Photosynthetic function in nut trees is closely related to nitrogen (N) nutrition because much of tree N is held within the leaf photosynthetic apparatus, but growing fruit and seeds also represent strong N sinks. When soil N availability is low, nut trees remobilize and translocate N from leaves to help satisfy N demand of developing fruit. Our objective was to describe shoot-level impacts of pecan [Carya illinoinensis (Wangenh.) K. Koch.] fruiting on leaf N and photosynthesis (Pn) during kernel fill under a range of tree N statuses. Our study was conducted in a mature ‘Western’ pecan orchard near Las Cruces, NM. In 2009, 15 trees showing a range of N deficiency symptom severity were grouped according to leaf SPAD into low, medium, and high N status categories. Differential N fertilizer rates were applied to the soil around high and medium N trees to accentuate differences in N status among the three categories. Light-saturated leaf Pn was measured on fruiting and non-fruiting shoots during kernel fill in 2009 and 2010. After measurement of Pn, the leaflet and its leaflet pair partner were collected, dried, and analyzed for tissue N. Leaf N concentration was significantly lower on fruiting shoots than non-fruiting shoots on all three sampling dates. The tree N status main effect was also significant, whereas the two-way interaction of shoot fruiting status and tree N status was not. Photosynthesis of leaves on fruiting shoots was significantly lower than that of non-fruiting shoots on all sampling dates. These data suggest that N demand by the growing kernel reduced N in leaves on the same shoot. Consequently, Pn of those leaves was reduced. The effect of tree N status and shoot fruiting status was best summarized with an additive model where there is a larger relative reduction in leaf N and Pn for fruiting shoots on trees with low N status.
Richard J. Heerema, Dawn VanLeeuwen, Rolston St. Hilaire, Vince P. Gutschick, and Bethany Cook
Marisa Y. Thompson, Jennifer J. Randall, Dawn VanLeeuwen, and Richard J. Heerema
Regarding pecan (Carya illinoinensis), alternate bearing, which is a biennial fluctuation of crop yield, is a major hindrance for the pecan industry. Little is known about the internal cues that trigger pecan shoots to become reproductive. This 2-year study approached the mysteries of alternate bearing of pecan by determining whether pecan homologs of three genes known to control floral initiation in other species are expressed differently at various times of the growing season or in distinct plant tissues, and whether expression of these genes can be manipulated by plant growth regulator (PGR) application when compared with an untreated control group. The flowering genes of interest were pecan homologs of leafy (CpLFY), apetala1 (CpAP1), and flowering locus t (CpFT). During year 1 (2014), PGRs ethephon and gibberellin GA3 were applied at the shoot level 1 week before each of three tissue sampling dates (13 June, 3 July, 29 July). During the following year (2015), two more PGRs were added to the study [a second double rate (2X) of gibberellin GA3 and ethylene inhibitor aminoethoxyvinylglycine (AVG)] for a total of four PGRs (applied on 10 June, 1 July, and 23 July) plus the untreated control. Experimental leaf and bud tissues were sampled from fruiting and nonfruiting shoots on mature ‘Western’ pecan trees and analyzed separately. Normalized expression levels of CpLFY and CpAP1 were significantly higher in buds than in leaves. Normalized expression of CpLFY in bud tissues differed statistically based on the sampling date in 2014, with the earliest date (13 June) having higher expression than the two later dates that year. In 2015, a treatment × date interaction revealed that, compared with the untreated control, CpLFY expression was significantly lower in shoots treated with both gibberellin GA3 dosages on 1 July. A few weeks later (23 July), CpLFY expression was lower in the 2X GA3 treatment group and higher in samples treated with AVG. In 2014, CpAP1 expression in buds was significant, with a treatment × date interaction in which ethephon increased CpAP1 expression, but only on one date (29 July). In 2015, bud CpAP1 expression was significantly higher in fruiting than in nonfruiting shoots; however, again, only on one date. The results reveal differential expression of these key flowering genes based on tissue type, sampling date, and fruiting status of the shoot and PGR treatment. Results suggest that more research of the effects of PGRs is necessary for understanding the flowering behavior of pecan and mitigating the intensity of alternate bearing.
Clare A. Bowen-O'Connor*, Rolston St. Hilaire, John Hubsten-berger, and Dawn VanLeeuwen
Bigtooth maple (Acer grandidentatum Nutt.) is indigenous to the southwestern United States. This species is not widely used in managed landscapes but the plant holds promise as a useful ornamental tree. Micropropagation might provide additional sources of selected genotypes for the nursery industry, but tissue culture has not been used successfully to propagate this species. We cultured double-node explants from greenhouse-grown, 2-year old seedlings of bigtooth maples that originated from Utah, Texas and New Mexico. Seedling height ranged from 15-90 cm. The shoot region was divided into three equal zones designated as terminal, intermediate and basal. Explants were selected from each of those zones. Explants were established on Murashige-Skoog (MS), Linsmaier-Skoog (LS), Woody Plant Medium (WPM) and Driver-Kuniyuki (DKW) tissue culture media. Shoot proliferation, area of the plate covered by callus and foliar pigment development (hue as determined by Royal Horticultural Society Color charts) were monitored for 17 weeks. Media affected shoot proliferation (P = 0.0042) but the zone of origin (P = 0.6664) of the explant did not. Callus area showed no significant difference among the four media and three zones (P = 0.2091) and averaged 3.60 centimeters2. After four subcultures, each lasting 30 days, explants on DKW media produced 10 shoots per explant. This media might hold promise for the micropropagation of bigtooth maple. Twenty-nine percent of all explants expressed foliar pigmentation, which ranged from red-purple to orange-red. Whether foliar pigment development in tissue culture correlates with expressed pigmentation in nature warrants further investigation.
Walter F. Ray, Geno A. Picchioni, Dawn M. VanLeeuwen, and Ryan M. Goss
Tall fescue (Festuca arundinacea) has desirable attributes as a cool-season turfgrass for the semiarid southwestern United States and the transition zone, but effects of cultural practices on newer cultivars within a desert climate are not adequately known. A field study was conducted between Sept. 1996 and Nov. 1997 to evaluate establishment of 15 turf-type tall fescue cultivars under two mowing heights (2 or 3 inches) and two different annual nitrogen (N), phosphorus (P), and potassium (K) application rates (N at 13.2 or 26.4 g·m−2, P at 0.9 or 1.8 g·m−2, and K at 11.0 or 22.0 g·m−2). The cultivars included ‘Amigo’, ‘Apache’, ‘Aztec’, ‘Bonanza’, ‘Chieftain’, ‘Cochise’, ‘Confederate’, ‘Coronado’, ‘Crossfire II’, ‘Falcon’, ‘Guardian’, ‘Kentucky 31’, ‘Leprechaun’, ‘Shortstop’, and ‘Virtue’. The fertilizer rate had no effect on turfgrass quality ratings throughout the establishment period, although overall quality was higher in Fall 1997 than during Spring and Summer 1997. The mowing height of 2 inches increased summer quality ratings of 11 of the 15 cultivars as compared with ratings under the 3-inch mowing height. The 2-inch mowing height improved fall quality ratings of seven of the 15 cultivars. No cultivars responded positively to the 3-inch mowing height. Consistently high summer through fall quality ratings were observed when ‘Apache’, ‘Aztec’, and ‘Crossfire II’ were mowed at the 2-inch height as compared with the other cultivar × mowing height treatment combinations. For turf-type tall fescue establishment in semiarid climates, findings support use of a 2-inch mowing height combined with the selective planting of ‘Apache’, ‘Aztec’, and ‘Crossfire II’ over other cultivar × mowing height combinations tested in the study.
Richard J. Heerema, Dawn VanLeeuwen, Marisa Y. Thompson, Joshua D. Sherman, Mary J. Comeau, and James L. Walworth
Zinc deficiency is common in pecan (Carya illinoinensis) grown in alkaline, calcareous soils. Zinc (Zn)-deficient pecan leaves exhibit interveinal chlorosis, decreased leaf thickness, and reduced photosynthetic capacity. Low photosynthesis (Pn) contributes to restricted vegetative growth, flowering, and fruiting of Zn-deficient pecan trees. Our objectives were to measure effects of soil-applied ethylenediaminetetraacetic acid (EDTA)-chelated Zn fertilizer on gas exchange of immature ‘Wichita’ pecan and characterize the relationship between leaf Zn concentration and Pn. The study orchard had alkaline and calcareous soils and was planted in Spring 2011. Zinc was applied throughout each growing season as Zn EDTA through microsprinklers at rates of 0 (Control), 2.2, or 4.4 kg·ha−1 Zn. Leaf gas exchange and SPAD were measured on one occasion in the 2012 growing season, four in 2013, and five in 2014. Soil Zn-EDTA applications significantly increased the leaf tissue Zn concentration throughout the study. On all measurement occasions, net Pn was significantly increased by soil-applied Zn EDTA compared with the control, but Pn was not different between the two soil-applied Zn-EDTA treatments. Leaf Pn in midseason did not increase at leaf tissue Zn concentrations above 14–22 mg·kg−1. Leaf SPAD consistently followed a similar pattern to Pn. Soil Zn-EDTA application increased leaf stomatal conductance (g S) compared with the Control early through midseason but not after August. Intercellular CO2 concentration was significantly lower for Zn-EDTA-treated trees than the Control even on dates when there was no significant difference in g s, which suggests that soil application of Zn-EDTA alleviated nonstomatal limitations to Pn caused by Zn deficiency.
Jacqueline Cormier, Robert Heyduck, Steven Guldan, Shengrui Yao, Dawn VanLeeuwen, and Ivette Guzman
A decrease in available farmland worldwide has prompted interest in polyculture systems such as intercropping where two or more crops are grown simultaneously on the same land to increase the yield per farm area. In Alcalde, NM, a year-round intercropping system was designed to evaluate organically produced blackberry cultivars (Rubus, subgenus Rubus) and winter greens in a high tunnel over a 2-year period. Two floricane fruiting blackberry cultivars, Chester Thornless and Triple Crown, were grown intercropped with ‘Red Russian’ kale (Brassica napus) and ‘Bloomsdale’ spinach (Spinacia oleracea) in a high tunnel. In an adjacent field, the planting of blackberry was repeated with no winter intercrop and no high tunnel. Both cultivars of blackberry were harvested July to September, and fresh weights were measured to determine suitability to the intercropping system in the high tunnel. Both species of winter greens were harvested January to April, and fresh yield weights were measured to discern fitness as possible intercrops in this system. Row covers were used for kale and spinach, and air temperatures were monitored November to April inside the high tunnel. High tunnel temperatures were within acceptable ranges for the production of greens with the use of rowcovers. Yield data from this study indicates that ‘Triple Crown’ blackberry outperformed ‘Chester Thornless’ blackberry in both the high tunnel and field trials with significant difference in the second season. Additionally, blackberry yields from both cultivars were observed to be higher in the field than in the high tunnel for both years. High temperature damage to high tunnel berry canes was noticed for both cultivars, with observed yield decreases in the second year in the high tunnel. Overall, this study indicates that the phenology and climate needs of the two winter greens and blackberry cultivars were not compatible for sustaining year-round organic high tunnel production.
Mark E. Uchanski, Dawn M. VanLeeuwen, Steven J. Guldan, Constance L. Falk, Manoj Shukla, and Juliette Enfield
Replicated temperature data from passively heated high tunnels are lacking, especially in the southwestern United States. Field studies were conducted over three seasons in two locations in New Mexico—a southern site in Las Cruces and a northern site in Alcalde—to characterize the crop environment in three high-tunnel designs during the winter growing season (October–March). High tunnels were 16 × 32 ft and oriented with the long edge running east to west. Heavyweight woven plastic covered the single-layer (SL) high-tunnel design. Double-layer designs (DL) were covered with a lightweight woven plastic on the bottom, followed by a second layer of the heavyweight plastic inflated with a fan. A heat sink was created using 16 55-gal barrels painted black, filled with water, and aligned along the north side of the double layer for the DL+B design. Soil temperature (3 inches deep) and air temperature (1 ft above the soil surface) were recorded inside the high tunnel, inside the high tunnel under a floating rowcover, and outside the high tunnel. In addition, photosynthetically active radiation (PAR) was recorded inside and outside the high tunnels during or near the winter solstice each year of the study. Daily air and soil temperature minimums were highest in the DL+B design and lowest in the SL design. Maximum air and soil temperatures did not significantly differ between high-tunnel designs, although the DL+B design measurements were consistently lower. During season 1, the SL design had significantly higher PAR transmission than the other two designs. In the northern location, the difference became insignificant during seasons 2 and 3, likely due to dust accumulation and plastic aging. In the southern location, the SL design maintained higher PAR transmission throughout the study, possibly due to plastic cleaning. Data collected in this study can help inform the decisions of high-tunnel growers and researchers in the region.