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
Rolston St. Hilaire, Carlos A. Fierro Berwart and Carlos A. Pérez-Muñoz
Mussaendas (Mussaenda spp.) are ornamental shrubs, and some cultivars are difficult to root. This study was conducted to explore how adventitious roots initiate and develop in the cultivar Rosea and to determine if anatomical events are associated with difficulty in rooting stem cuttings. Stem cuttings were treated with 5, 10, 15 mmol IBA, or distilled water, and sampled every 2 days over 26 days to observe adventitious root formation and development. Adventitious roots initiated from phloem parenchyma cells. Cuttings treated with 15 mmol IBA had a mean of 18 root primordia per basal 1 cm of cutting after 10 days. Primordia were absent in nontreated cuttings at 10 days. These results suggest that nontreated cuttings are difficult to root because few primordia are produced. Chemical name used: 1H-indole-3-butyric acid (IBA).
Malik G. Al-Ajlouni, Dawn M. VanLeeuwen, Michael N. DeMers and Rolston St. Hilaire
The apparent heterogeneity of human-generated materials in residential urban landscapes sustains concerns that the quantitative classification of urban residential landscapes is impossible. The objective of this research was to develop a method to quantitatively classify urban residential landscapes in a desert environment. Using a purposive sampling procedure, we studied the landscapable area around each of 54 residential homes in Las Cruces, NM. All materials in the landscape were identified, measured, and categorized. Using 30% as the cutoff to indicate that a material was dominant in the landscape, we classified 93% of all landscapes into nine common landscape types. Mulch-dominant landscapes were the most common, and landscape types differed between front- and backyards. Shrubs did not feature prominently in any of the common landscape types. Our classification method clearly identifies multiple landscape types, and for the first time, provides quantitative evidence that landscape types are distributed differently in front- and backyard landscapes in the desert environment of Las Cruces. Information on common landscape types will be valuable to landscape horticulturists wanting to craft water conservation plans that are landscape specific if the common landscape type can be linked to a landscape water budget.
Clare Bowen-O'Connor, John Hubstenberger, Dawn Van Leeuwen and Rolston St. Hilaire
Double-node microshoots of bigtooth maple (Acer grandidentatum Nutt.) were rooted in vitro on Driver-Kuniyuki Walnut (DKW) tissue culture media containing indole acetic acid (IAA). Microshoots represented six sources from three locations within Texas and New Mexico. Microshoots were placed in Phytatrays II™ containing DKW media with no plant growth regulator (DKW0) to reduce the high cytokinin levels used for shoot proliferation. Microshoots were induced to form roots for 15 days by placing them on DKW media containing IAA at 0.01, 1, 2.5, 5, 10, 15 or 20 μmol. Rooting frequency, the number of leaves and callus area were recorded every 30 days for 60 days. Rooting frequency increased up to 29% as IAA concentration increased (P= 0.004). However, as much as 71% of shoots for one of the three Guadalupe Mountain, Texas, sources rooted without auxin treatment after 30 days. The IAA concentration also affected the number of leaves per shoot (P= 0.0228) which averaged seven and callus area (P= <0.0001) which averaged 52 mm2. Average leaf size was 307 mm2. We conclude that IAA induces rooting in microshoots of bigtooth maple after 15 days of root induction. However, one source rooted without auxin treatment. The presence of callus does not interfere with root formation.
Rolston St. Hilaire, Michael A. Arnold, Don C. Wilkerson, Dale A. Devitt, Brian H. Hurd, Bruce J. Lesikar, Virginia I. Lohr, Chris A. Martin, Garry V. McDonald, Robert L. Morris, Dennis R. Pittenger, David A. Shaw and David F. Zoldoske
In the United States, urban population growth, improved living standards, limited development of new water supplies, and dwindling current water supplies are causing the demand for treated municipal water to exceed the supply. Although water used to irrigate the residential urban landscape will vary according to factors such as landscape type, management practices, and region, landscape irrigation can vary from 40% to 70% of household use of water. So, the efficient use of irrigation water in urban landscapes must be the primary focus of water conservation. In addition, plants in a typical residential landscape often are given more water than is required to maintain ecosystem services such as carbon regulation, climate control, and preservation of aesthetic appearance. This implies that improvements in the efficiency of landscape irrigation will yield significant water savings. Urban areas across the United States face different water supply and demand issues and a range of factors will affect how water is used in the urban landscape. The purpose of this review is to summarize how irrigation and water application technologies; landscape design and management strategies; the relationship among people, plants, and the urban landscape; the reuse of water resources; economic and noneconomic incentives; and policy and ordinances impact the efficient use of water in the urban landscape.