S. Elwynn Taylor

Optimal Leaf Form

The size of leaves typical for specific climates has been studied for many years, and several investigators have considered the “leaf size class” as an indicator of climatic conditions (Raunkiaer, 1934). Bailey and Sinnott (1916) concluded that the form and size of leaves were more a result of environment than of genetic history, although the latter was certainly an influence. Benson et al. (1967) reported ecotypic differentiation of leaf form with respect to slope exposure for a hybrid population of Quercus douglassii × Q. turbinella. They suggested that hybrid variability may permit the rapid evolutionary selection of characters best suited for the particular microclimate. They reported that individuals found on the northeast slope had leaves of significantly larger dimension than did those growing on the more arid southwest slope (Fig. 5.1). It is generally considered that the reduction of leaf size in arid areas has the effect of conserving water, but quantitative evidence of the effects of leaf size has been available only recently.

Some Implications of Leaf Tearing in Musaceae

Leaf temperatures associated with torn and untorn leaves of Musaceae were taken in both dry and wet seasons at Barro Colorado Island, Canal Zone. Transpiration rates and leaf resistance to water—vapor diffusion were determined. Energy—budget analysis is used to describe the relationship of leaf dimension and leaf resistance to thermal survival and water usage. Gas—exchange theory is applied to predict the photosynthetic implications of leaf tearing. The analyses showed that leaves less than 10 cm wide are not subject to critical heat stress, have lower water loss, and higher ratios of photosynthesis to water expended than do leaves of widths greater than 10 cm. In wet season, leaves have lower resistance to the diffusion of water vapor and accordingly are less subject to excessive heating.

Obtaining weather data for input to crop disease-warning systems: leaf wetness duration as a case study

Os sistemas de alerta fitossanitario sao ferramentas de suporte a decisao desenvolvidos para ajudar os agricultures a determinar o melhor momento da aplicacao das medidas de controle para combater as doencas de plantas. As variaveis meteorologicas sao dados de entrada quase que obrigatorios desses sistemas. Este trabalho apresenta uma revisao sobre os meios pelos quais as variaveis meteorologicas sao coletadas para serem usadas como dados de entrada em sistemas de alerta fitossanitario e sobre os desafios associados a logistica de obtencao desses dados. Essa revisao compara o monitoramento meteorologico ao nivel do produtor, nas propriedades agricolas, com aquele feito ao nivel de redes de estacoes meteorologicas, assim como discute as vantagens e desvantagens entre medir e estimar tais variaveis meteorologicas. Especial enfase e dada a duracao do periodo de molhamento foliar (DPM), nao somente pela sua importância como dado de entrada em diversos sistemas de alerta fitossanitario, mas tambem pelo desafio de se obter dados acurados dessa variavel. Pode-se concluir, apos ampla discussao do assunto, que nao ha um metodo unico e melhor para se obter os dados meteorologicos para uso em sistemas de alerta fitossanitario; por outro lado, as circunstâncias a nivel local, regional e nacional provavelmente influenciam a estrategia de maior sucesso.

Adaptive Implications of Leaf Thickness for Sun‐ and Shade‐Grown Abutilon Theophrasti

Potentially adaptive effects of leaf thickness on photosynthesis and transpiration were studied for Abutilon theophrasti grown under high (600 μmol°m—2°s—1) and low (200 μmol°m—2°s—1) levels of photosynthetically active radiation. We determined the relationship of both surface area and volume of mesophyll cells of leaf thickness. Net photosynthesis and transpiration rates were measured on the third leaf of each seedling, under sunny (1200 μmol°m—2°s—1) and shaded (250 μmol°m—2°s—1) conditions. Plants grown under high light had greater mesophyll surface area and total mesophyll cell volume per unit leaf area than did plants grown under low light, and showed higher net photosynthesis under sunny conditions. There was little difference in transpiration rate between thick and thin leaves. Thick leaves and thin leaves showed similar net photosynthesis under shaded conditions. Consequently, the water use efficiency for thick leaves was greater than that for thin leaves under sunny conditions. Increased productivity without increased water use is potentially of adaptive significance in plants where the mesophyll of sun—grown leaves thickens.

Historical climate data management for agriculture: a microcomputer-based methodology

Abstract By using readily available microcomputer hardware and a commercial database management system, a tool was developed to improve access to and useability of historical climate data for agricultural applications. The menu-driven, user-friendly system provides quick summaries of maximum temperature, minimum temperature and precipitation data on a daily, weekly, monthly or 30-year normals basis and selective retrieval of weather records meeting certain user specified critical conditions. Data reports can be output to the computer screen, a printer or ASCII data files. The climate data information system was initially developed for 13 Iowa reporting stations and 34 years of daily temperature and precipitation data (1951–1984), but has also been adapted for 24 Illinois stations and as many as 89 years of data (1901–1989). The tool is being used by agricultural meteorologists, climatologists and State Extension staff to aid in climate-related agricultural research and information delivery.