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A question that has plagued New Zealand botanists for many years is the occurrence of the divaricate growth form in several different plant families, and what selection pressure could have led to such parallel evolution. One prominent theory is that the divaricate habit is an adaptation to climatic extremes. This study aims to test if the 'self-shading' growth form of divaricates protects their internal leaves from photoinhibition under physiological drought and high irradiance. By being able to forego the costs of maintaining photoprotective mechanisms, they should have greater carbon gain than their non-divaricate congeners under these conditions. To test if divaricates are protected from the detrimental effects of photoinhibition, the water potentials, pigment and vitamin E concentrations, and photosynthetic rates of two divaricates species in their natural habitat were measured. Additionally, these parameters were recorded for the same divaricate species and their non-divaricate congeners under glasshouse conditions. In the field there were clear differences in several key parameters between divaricates under different levels of irradiance and water availability, and in most cases there was clear evidence of photoinbition. In the glasshouse, the maximum photosynthetic rates were significantly higher in divaricate leaves than in non-divaricate leaves, but there were no clear differences in the avoidance of photoinhibition between divaricates and non-divaricates. Interestingly, more pronounced responses to the different treatments were observed between genera than between the growth forms in the field and glasshouse experiments. The presence of photoinhibition and photoprotective mechanisms in divaricate leaves does not support the theory that the divaricate habit evolved as a physiological response to extreme climate conditions. The absence of a strong difference in the amount of photoinhibition between divariacte and non-divaricate congeners mean that high irradiance and drought stress are unlikely to have been a key factor in the evolution of the divaricate habit. That the within genus physiologies are more similar than within the growth forms would indicate that the divaricate habit possibly evolved after the evolution of the physiological responses of the genera.

Plant growth inhibitors were isolated from Haplopappus acradenius (Green) Blake and Baccharis sarothroides Gray, two desert species, found at the Boyce Thompson Southwestern Arboretum. Leaf and stem tissues of B. sarothroides were extracted with 80% methanol (v/v). This extract was reduced to an aqueous phase in vacuo and partitioned with ethyl acetate at pH 7.3 (NF, neutral fraction), pH 2.8 (AF, acidic fraction), and again at pH 2.8 following hydrolysis at pH 11 (HF, hydrolyzed fraction). Thin layer chromatography (TLC) on silica gel H in chloroform:ethyl acetate:formic acid (CHCl₃:EtOAc:HCOOH) produced a region between R(f)'s 0.5 to 0.6 from AF of B. sarothroides which inhibited wheat seed coleoptile and radicle growth 52.7% and 66.5%, respectively, using 500 ul of a 1.9 mg/ul extract. This section inhibited wheat coleoptile straight growth 38.6% at the same concentration. Additional TLC, UV spectrophotometry, spray reagents, NMR, and GC/MS indicated that the compound was 3,8-dihydroxy-5,6,7-trimethoxy-2-(4-methoxyphenyl)-4H-1-benzopyran-4-one at a concentration of 265 ug/g fresh weight. This compound significantly inhibited the wheat coleoptile straight growth bioassay 18.4% using 2 to 3 ug/ul. An 80% methanol extract of H. acradenius leaves evaporated in vacuo produced an aqueous insoluble brown resin. This resin dissolved in absolute methanol and separated by TLC in CHCl₃:EtOAc:HCOOH contained a region between R(f)'s 0.6 to 0.7 that inhibited wheat seed coleoptile growth 71.8% and radicle growth 90.7% using 200 ul of 1.5 mg/ul solution. Wheat coleoptile straight growth was inhibited 53.7% in this region at the same concentration. Further examination of this region by the same methods as those used for B. sarothroides indicated the presence of a C-12 alkenyl alcohol (2 mg/ml), an aromatic heterocyclic hydrocarbon (4 mg/ml), and an alkyl substituted version of 7-hydroxycoumarin (5 mg/ml) at a concentration of 0.7, 1.4, and 1.8 ug/g fresh weight, respectively. A combination of these compounds inhibited the wheat coleoptile straight growth bioassay 41.1% using 11 ug/ul. A 2 M HCl extract of H. acradenius was partitioned with diethyl ether, which was evaporated and the residue resuspended in 95% methanol. TLC in CHCl₃:EtOAc:HCOOH separated an area between R(f)'s 0.5 to 0.6 where wheat seed coleoptile growth was inhibited 49.7% and radicle growth was inhibited 54.6% using 1000 ul of a 3.3 mg/ul solution. Identified in this region was 7-hydroxycoumarin at a concentration of 150 ug/g fresh weight. The wheat coleoptile straight growth bioassy was inhibited 13.2% using 2 to 3 ug/ul.

Water availability is a critical limiting element in semi-arid ecosystem productivity and presents particular challenges in Sahelian countries such as Senegal. The landscapes are characterized by the presence of two common semi-arid shrubs (Piliostigma reticulatum and Guiera senegalensis), both of which may be important hydraulic regulators in these water-limited ecosystems. Dry season observations revealed higher moisture levels in soil surrounding the shrub shallower roots relative to bare soil. This observation led us to hypothesize that these shrubs may participate in a natural irrigation phenomenon termed as "hydraulic redistribution" (HR). This dissertation reports on three studies performed to ascertain the existence of and investigate the characteristics of this hypothesized phenomenon. The first study investigated seasonal variability in soil water and shrub root patterns. Soil moisture content declined steadily in the 0.9-1.2 m depth range and increased in the 0.2-0.4 m depth range, which supports the HR hypothesis. The second study quantified plot scale water balance fluxes. Notably, shrub water uptake from the water table served as a crucial contribution to the system water balance. The third study investigated the magnitude and dynamics of HR during the dry season. Crop-shrub associations were evaluated from measurements of soil moisture and potential, root sap flow and plant physiological measurements. This study proved the existence of HR and quantified the HR magnitude (~0.1 mm d⁻¹). For shrubs and annual crops in close association with shrubs, HR clearly provides a mechanism for drought-stress avoidance and maintenance of plant physiological functions. At the landscape scale, the interplay between shrub root morphology and HR may play a vital role in ecosystem function with practical implications for nutrient cycling and water balance in arid ecosystems. / Graduation date: 2006

A question that has plagued New Zealand botanists for many years is the occurrence of the divaricate growth form in several different plant families, and what selection pressure could have led to such parallel evolution. One prominent theory is that the divaricate habit is an adaptation to climatic extremes. This study aims to test if the 'self-shading' growth form of divaricates protects their internal leaves from photoinhibition under physiological drought and high irradiance. By being able to forego the costs of maintaining photoprotective mechanisms, they should have greater carbon gain than their non-divaricate congeners under these conditions. To test if divaricates are protected from the detrimental effects of photoinhibition, the water potentials, pigment and vitamin E concentrations, and photosynthetic rates of two divaricates species in their natural habitat were measured. Additionally, these parameters were recorded for the same divaricate species and their non-divaricate congeners under glasshouse conditions. In the field there were clear differences in several key parameters between divaricates under different levels of irradiance and water availability, and in most cases there was clear evidence of photoinbition. In the glasshouse, the maximum photosynthetic rates were significantly higher in divaricate leaves than in non-divaricate leaves, but there were no clear differences in the avoidance of photoinhibition between divaricates and non-divaricates. Interestingly, more pronounced responses to the different treatments were observed between genera than between the growth forms in the field and glasshouse experiments. The presence of photoinhibition and photoprotective mechanisms in divaricate leaves does not support the theory that the divaricate habit evolved as a physiological response to extreme climate conditions. The absence of a strong difference in the amount of photoinhibition between divariacte and non-divaricate congeners mean that high irradiance and drought stress are unlikely to have been a key factor in the evolution of the divaricate habit. That the within genus physiologies are more similar than within the growth forms would indicate that the divaricate habit possibly evolved after the evolution of the physiological responses of the genera.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 119-130). Also available on the World Wide Web.

2 p. / Originally Published: 2006 / Techniques and tips on watering trees and shrubs efficiently. Topics include weather, plant type, soil type and signs of under and over watering. Originally published 2006

Browse biomass production of Salix spp. and Betula glandulosa on a wetland in central British Columbia is estimated. Based on an extensive review of much of the literature pertaining to shrub biomass and shrub density estimation, a technique combining regression estimates of average stem biomass with a density estimate obtained using the corrected point distance method was applied. It was found that the best regression relationships were obtained using natural logarithmic transformations of the dimension and biomass variables. It was possible to obtain acceptable biomass equations for the four Salix species encountered without differentiating between the species. More accurate predictions of biomass were achieved using site specific equations and equations based on pooled site data than with general equations. It was concluded that the value of the approach taken is limited if site specific equations are required because of the considerable time required for sample collection and preparation. / Forestry, Faculty of / Graduate

The relationships between vegetation architecture and spider community attributes were examined in a big sage (Artemisia tridentata) community. Spiders were separated into guilds using similarities of species' hunting behavior. Shrub architecture was experimentally manipulated in the field by either clipping 50% of a shrub's foliage to decrease foliage density or tying together a shrub's branches to increase foliage density. Temporal patterns of spider species density, diversity (H') and evenness (J') showed midsummer peaks in both 1974 and 1975. Seasonal spider guild trends reflected the temporal prominence of a member species or genus. These temporally abundant species appeared to play a major functional role in this community. Shrub perturbations resulted in changes in spider species and guild densities. Spider species and guild density in the tied shrubs were significantly higher than that in the clipped or control shrubs sampled. Spider species diversity, density and guild density were also positively correlated with indicators of shrub volume and shrub foliage diversity. This suggests that structurally more complex shrubs (tied) can support greater spider species densities and diversity. Spider guild densities and IV's were significantly altered by changes of shrub architecture. The observed guild distribution were in agreement with known hunting behavior and life history data of the member species. The data suggest that architectural properties of habitat may be an important determinant of predatory invertebrate species diversity and distribution. Guild analysis may be useful in examining the roles of species groups in community studies.