Annual Plant Growth Research Articles

Monitoring root length density and root biomass in asparagus (Asparagus officinalis) with soil cores

Soil type, crop management practices, annual plant growth patterns, and seasonal changes in the soil environment all influence asparagus (Asparagus officinalis) roots. This study describes the dynamic changes in root growth that occur during the annual growth cycle of asparagus grown in two contrasting soil types and crop management systems. Root length density and biomass were estimated from soil cores (55 mm diam. × 0.2 m long) collected to 1 m in three locations adjacent to the row (0.15, 0.3, and 0.6 m from row centre). Samples were collected on six dates (early, or postharvest at early, mid, or late fern growth, and dormant period) between October 1999 and June 2000. Test sites varied with soil type (sandy loam or silt loam) and crop management system (normal 12‐week harvest or extended 15‐week harvest). Fleshy and fibrous roots were collected, root length density determined, and dry weights measured. Fleshy asparagus roots grew deeper in a sandy soil than in a silt soil, had higher dry matter content in silt than in sandy soil, and greater root length in a silt compared to a sandy soil. Fibrous root length density was greater during fern growth than during harvest, in a sandy versus a silt soil and at shallow versus deep sampling depths. Sampling date, soil depth, and sample location all significantly influenced asparagus fleshy and fibrous root biomass. Soil cores accurately estimated both total fleshy root length density and dry matter content when compared to the more time‐consuming complete root excavation. Results can be used to improve crop management practices, predict root biomass, and increase our understanding of the dynamics of root development in asparagus.

ESTIMATING ROOT LENGTH DENSITY AND BIOMASS IN ASPARAGUS

Soil type, crop management practices, annual plant growth patterns and seasonal changes in the soil environment all influence asparagus roots. This study describes the changes that occur in root growth over time in two contrasting soils and crop management systems. Soil cores (5.5-cm diameter x 20-cm long) were collected to one meter in on six dates (pre/postharvest, early/mid/late fern growth, and dormant period) and in three locations (15/30/60 cm from row) in 1999-2000. Sites varied with soil (sandy loam or silt loam) and by crop management system (normal 12-week harvest or extended 15-week harvest). Fibrous and fleshy roots were collected and root length density determined. Soil type significantly altered rooting depth (sandy>silt), dry matter content (silt>sandy) and root length density (silt>sandy) of fleshy roots. Fibrous root length density varied with sampling date (harvest silt) and sampling depth (shallow>deep). Sampling date, soil depth and sample location significantly influence asparagus fleshy and fibrous root biomass. Soil cores accurately estimated both total fleshy root length density and dry matter content when compared to the more time consuming complete root excavation. Results can be used to improve crop management practices, predict root biomass and increase our understanding of the dynamics of root development in asparagus.

Microhabitat to landscape impacts: crested porcupine digs in the Negev Desert highlands

Indian crested porcupines (Hystrix indica) are adaptable, generalist herbivores with wide environmental tolerances and a large geographic range. In the arid Negev Desert highlands of southern Israel, porcupines excavate and consume subterranean organs of 18 species of geophytes and hemicryptophytes in a variety of habitats. Their foraging generates a network of direct and indirect impacts on ecological processes. Porcupine digs varied in size according to depth of forage and substrate, and new digs averaged about 8 cm in depth, and 400 cm2and 940 cm3in surface area and volume, respectively. Digging rates also differed among habitats. In hilly watersheds, highest digging rates were in soil belts supporting the greatest cover of shrubs and geophytes. Dig densities peaked at > -031 dig m−2, impacting up to 4% of soil surfaces. Digs are temporary soil pockets (longevities of < -032 to > -0310 years) that trap soil, water, organic matter, and seeds. As highly productive microhabitats compared to surrounding soil matrix, they promote the germination and growth of annual plants including some porcupine forage species. Loose soil excavated by porcupines enhances soil erosion and transport, and may substantially enhance ecosystem flows of water, soil, and nutrients. Porcupine digging may help to maintain bare rock outcrops in Negev watersheds, thereby promoting large runoff flows that produce mesic patches and plant habitats. Runoff dynamics have greatly influenced past and present human exploitation of Negev landscapes. Recent experiments indicate that porcupine digs have important properties as small-scale landscape disturbances, and as sources and sinks of critical environmental resources. Additional research is needed to better define and predict porcupine digging impacts at several ecological levels, and as a basis for realistic management of Negev habitats and landscapes.

A Small Scale Biomass Fueled Gas Turbine Engine

A new generation of small scale (less than 20 MWe) biomass fueled, power plants are being developed based on a gas turbine (Brayton cycle) prime mover. These power plants are expected to increase the efficiency and lower the cost of generating power from fuels such as wood. The new power plants are also expected to economically utilize annual plant growth materials (such as rice hulls, cotton gin trash, nut shells, and various straws, grasses, and animal manures) that are not normally considered as fuel for power plants. This paper summarizes the new power generation concept with emphasis on the engineering challenges presented by the gas turbine component.

EL NIÑO EFFECTS ON THE DYNAMICS AND CONTROL OF ANISLAND ECOSYSTEM IN THE GULF OF CALIFORNIA

The tremendous increase in precipitation associated with the 1992–1993 El Niño profoundly affected terrestrial communities on arid islands in the Midriff region of the Gulf of California. In 1992, winter precipitation was 5.4 times the historical mean, and winter precipitation over the entire El Niño was the highest two-year amount ever recorded. Increased precipitation led to an explosion of annual plant growth on the previously barren (0–4% cover) islands: plant cover increased 10–160 times over what it had been. With the resumption of arid conditions in 1994, live plant cover returned to the low levels seen before the onset of El Niño. Insect abundance tracked this pulse in plant productivity and approximately doubled in 1992 and 1993 compared to 1991 levels. In 1994, the crash of annual plants caused insect densities to drop to the lowest levels recorded during the 5-yr study. El Niño also affected the composition of the insect assemblage. In the dry years 1990–1991, the assemblage was dominated by insects feeding on products originating in the ocean: detritivores/scavengers on shore drift of marine algae and carcasses, avian parasites, and detritivores of bird products. Herbivores were extremely rare. The heavy plant growth in 1992 stimulated large (40–190 times pre-El Niño levels) increases in herbivores. The great increases in land plant biomass and insect abundance are indicative of an important change in the dynamics of this system. Previously, most material flowing through the food webs of these islands originated directly or indirectly in the ocean. In contrast, during this El Niño, most material originated via productivity by terrestrial plants. Thus, wet El Niños represent an agent that switches the system from one dependent primarily on allochthonous input to a system driven to a greater extent by in situ productivity. The influence of this pulse of terrestrial productivity extends beyond the El Niño years: the persistence and slow release of plant and detrital biomass reserves may also greatly affect dynamics for years after the El Niño event has passed. We suggest that large-scale climatic events such as El Niño may be long-lasting determinants of community dynamics rather than occasional disturbance events.

Topics on Brassinosteroid Mutants (Including Brief Reports on the Twenty-Fourth Annual Plant Growth Regulator Society of America Meeting)

Topics on Brassinosteroid Mutants (Including Brief Reports on the Twenty-Fourth Annual Plant Growth Regulator Society of America Meeting)

The accumulation and storage of nitrogen by herbaceous plants

Abstract Accumulation of nitrogen (N) by plants in response to N supply outstripping demand is contrasted with storage of N, which implies that N in one tissue can be reused for the growth or maintenance of another. Storage can, therefore, occur in N‐deficient plants; accumulation can not. The consequence of accumulation and storage of N is considered, particularly in relation to the reproductive growth of annual plants, which can often use a great deal of stored N. Nitrate and proteins are the forms of N most often stored in vegetative tissues and, quantitatively, ribulose 1,5‐bisphosphate carboxylase/oxygenase is often the most important protein store. While storing nitrate will be less costly to the plant in terms of energy, protein stores offer several possible advantages. These advantages are (i) maximizing the potential for carbon assimilation, (ii) avoiding problems with the regulation of leaf turgor and (iii) allowing the reduction on nitrate to occur in the young, fully illuminated leaf.

Environment and Variation in Life History Traits of the Chuckwalla, Sauromalus Obesus

Life history attributes for the western chuckwalla, Sauromalus obesus, and environmental variables, e.g., rainfall and vegetational growth, were recorded simultaneously during a 7—yr investigation in the Colorado desert of southeastern California. The timing of rainfall was most critical to the growth of annual plants, and the standing crop of winter annuals was greatest when substantial rainfall occurred early (October—January). Chuckwallas preferred to eat winter annuals during the spring. However, broad and opportunistic feeding habits were observed, and the persistence of relatively mild winters and frequent summer rainfall enabled individuals to feed throughout most of the year. Males typically achieved reproductive maturity at 125 mm snout—vent length (SVL) and 2 yr of age. Females achieved reproductive maturity at 125 mm SVL and 2—3 yr only when optimal environmental conditions prevailed. Clutch size was highly correlated with body size, and the mean for the study period was 6.9 eggs. Mean values for other reproductive attributes were: egg mass, 8.4 g; relative clutch mass (RCM), 0.343; and expenditure per progeny (EPP), 0.053. Clutch size, egg mass, RCM, and EPP did not differ significantly among years for a given body size. Mean annual frequency of reproduction was 52%, but ranged from 0 to 95% during the study period. Mean 1st—yr survivorship was 38% but showed considerable year—to—year variability. Egg mortality had the greatest impact on 1st—yr survivorship. Mean survivorship for chuck—wallas older than 1 yr approached 75% and values for males and females were not significantly different. Adults of both sexes appeared to be considerably more susceptible to predation after achieving 165 mm SVL. Consequently, large adult individuals were never common. Annual recruitment was 20% and was largely the result of reproduction. Population densities showed nearly a twofold annual variation, ranging from 15 to 30 individuals/ha. Life table analysis showed that younger females (3—6 yr) contributed to 50% of the replacement rate; mean generation time was 8.2 yr, and the life expectancy was ≈15 yr. Year—to—year consistency of various reproductive attributes (clutch size, egg mass, and RCM), indicative of "boom or bust" iteroparity, is possibly a typical adaption for extremely long—lived lizard species. Relatively mild winters and occurrence of summer rainfall in the Colorado desert greatly promoted early maturity and frequent reproductions. In addition, summer rainfall improved the survivorship of eggs, probably by providing adequate moisture for incubation. Such conditions were responsible for relatively high densities and predation rates. However, under drier conditions maturity was delayed, reproduction less frequent, and egg survivorship much lower; such conditions are typical in the Mojave desert. The relative stability of clutch size, egg mass, and RCM, but apparent variability of age at reproductive maturity and reproductive frequency in this study, may indicate that the life history of chuckwallas evolved under a variable but predictable environmental setting.

Nutrient and particulate fluxes in a salt marsh ecosystem: Tidal exchanges and inputs by precipitation and groundwater 1

Waterborne nutrients enter Great Sippewissett Marsh through groundwater, rain, and tidal flooding. The ebb of tidal water removes nutrients. During summer, uptake by marsh biota leads to net import of nutrients. The increased export of ammonium in August may be due to leaching from senescent marsh plants. There is a net annual export of ammonium, nitrate, nitrite, dissolved organic (DON) and particulate (PN) nitrogen, particulate carbon (PC), and phosphate. Ammonium, DON, and PN are the major forms of nitrogen exported. Nutrient concentrations in coastal and marsh water are correlated, and marsh exports could contribute substantially to nutrient supplies of coastal waters.Groundwater entering the marsh provides primarily NO3‐N and DON. Nutrient inputs through precipitation consist primarily of DON, NO3‐N, and NH4‐N. Particulate materials in rain have a high C:N ratio, contributing little to enrichment of the nitrogen‐limited salt marsh. Groundwater carries over 20 times the amount of nutrients brought in by rain. The nitrogen provided by both sources is more than enough to support annual plant growth. Inputs of nitrogen by groundwater arc therefore important to the nitrogen economy of a salt marsh.About half the dissolved inorganic nitrogen brought into the marsh by groundwater is converted to and exported as PN. The marsh thus transforms the nitrogen that would have been used by primary producers into a form suitable for consumers such as shellfish. Large amounts of apparently refractory DON enter the marsh in groundwater and similar amounts are exported by tides. PC exported to coastal water is equivalent to 40% of the net annual production of Spartina alterniflora, the dominant marsh plant.

Annual Population Changes in California Quail

A population of California quail (Lophortyx californicus) in San Luis Obispo County, California, was kept under study and management from 1946 to 1962. Observations and age ratios obtained during fall hunting have indicated wide fluctuation of reproductive success, age ratios varying from 6-81 percent young. In general, years of high rainfall correlated with high reproduction; dry winters were followed by reduced breeding. The key factor in reproductive rate was the drive to keep nesting and renesting throughout the summer, resulting presumably from a physiological preconditioning whose nature and origin is unknown. Reproductive drive was shown to be independent of environmental conditions during the actual nesting season, appearing to be related more to early breeding season weather conditions that control annual plant growth and production of quail food. Since 1946, for purposes of management, I have studied the factors that control the abundance of California quail in the vicinity of my ranch in San Luis Obispo County, California (McMillan 1947). In the course of this study, various elements have been found to affect both the distribution and numbers of quail. Protective ground cover, water, food, roosting cover, predation, hunting, and land use have all been found to bear directly on quail welfare; management practices have been devised to overcome limiting factors and, insofar as possible, to increase quail abundance. However, year-to-year populations fluctuate widely and uniformly throughout the region over a wide range of habitat conditions, including some situations in which the known factors that control quail numbers have been brought under intensive management. The cause of these changes remains unknown and is an important problem in quail management. This paper presents the materials of the study that relate in particular to the observed fluctuations. My own interpretation of the data is offered for what it may be worth. The data of birds bagged, which represent the most significant material of the s udy, could not have been collected withThis content downloaded from 207.46.13.151 on Wed, 28 Sep 2016 05:04:19 UTC All use subject to http://about.jstor.org/terms CALIFORNIA QUAIL POPULATIONS * McMillan 703 out the cooperation of my many hunting associates. Though they are too numerous to mention individually, I want to express appreciation to each of them. The encouraging counsel and editorial assistance of A. S. Leopold has been the sustaining influence of the study. W. J. Francis and G. M. Christman have contributed their skill and talent in preparing the graph represented in the paper as Fig. 1. My wife, May, who typed the manuscript, provided help without which I could not have prepared this paper.