Patterns Of Biomass Accumulation Research Articles

Nitrogen Dynamics During Succession in a Desert Stream

Nitrogen dynamics of Sycamore Creek, Arizona, a lowland Sonoran Desert stream, are described by seven diel input—output budgets at different stages of postflood succession. Hydrologic inputs and outputs of nitrogen and N storage in periphyton, macroinvertebrates, and fish were measured over 24—h periods. Total nitrogen storage in this desert stream (3—9 g/m2) was lower than that in forest streams of Oregon (12 g/m2) and Quebec (22 g/m2). While >99% of nitrogen in the latter systems is in allochthonous detritus, benthic algae and autochthonous detritus comprised °90% of the total nitrogen pool in the desert stream. Up to 14% of nitrogen was in consumer organisms. Inputs of nitrogen to the stream ecosystem were dominated by dissolved nitrogen, of which 19—60% was inorganic, primarily nitrate. Particulate nitrogen in transport (4—15%of total input) was mostly autochthonous. Inputs of nitrogen exceeded outputs on most study dates. Rates of ecosystem nitrogen retention were as high as 400 mg°m2°d—1 and outputs exceeded inputs on only one study date. Retention was primarily of inorganic nitrogen and was presumed due to autotrophic assimilation. Nitrogen retention data from the seven budgets were used to evaluate the Vitousek and Reiners (1975) model that patterns of nitrogen retention during succession reflect patterns of net ecosystem production and biomass accumulation. Biomass and stored nitrogen increased asymptotically during a postflood successional sequence at a single site; nitrogen retention during this period accounted for increases in storage. Nitrogen retention among the seven study dates exhibited the predicted successional patterns of increases from early to middle successional stages, followed by late stage declines.

Response of Hordeum distichon cv. Igri (2-row) and H. hexastichon cv. Plaisant (6-row) winter barley to foliar applications of chlormequat

Two-row (cv. Igri) and six-row (cv. Plaisant) winter barley cultivars were incorporated into a field trial at Sutton Bonington (1984–1985) where the effects of chlormequat (CCC) applied at the three-leaf stage (main stem) and the onset of stem elongation were compared. CCC had no influence on lodging as the area cropped with ‘Igri’ completely lodged while no lodging occurred for the cultivar ‘Plaisant’. Neither CCC treatment nor cultivar influenced the rate, duration or pattern of biomass accumulation. CCC application in either the autumn or spring increased harvest index and thus grain yield for both genotypes. Mean grain mass linearly declined as ear population was increased by CCC application, with the number of grains per ear unchanged. A parabolic response of grain yield to the number of ears was inferred and an analysis was used to determine the optimum ear density.

Ecophysiology of Zigadenus nuttallii, a toxic spring ephemeral in a warm season grassland: effect of defoliation and fire.

Zigadenus nuttallii, a highly toxic spring ephemeral in tallgrass prairie, was studied in 1985 to ascertain: 1) several ecophysiological characteristics of the species, 2) seasonal patterns of biomass accumulation, and 3) its response to defoliation and fire. The maximum photosynthetic rate of Z. nuttallii measured in unburned prairie was 13.2 μmoles CO2 m-2 s-1 which occurred at 24-28° C and an incident quantum flux of 0.8-1.0 mmoles m-2 s-1. Maximum stomatal conductance measured was 5.4 mm s-1. Early in the season, belowground storage organs (bulbs) decreased in mass and supplied much of the energy for growth of leaves, even though CO2 uptake was possible. Buld mass did not increase until about 6 weeks after shoot emergence implying that, at this time, leaves had become a source rather than a sink for carbohydrates. The result of a single, severe defoliation event was a decrease in biomass of bulbs, leaves and reproductive structures in Z. nuttallii. Intrinsic compensatory mechanisms were not detected. In contrast, fire, which also defoliated plants, did not result in any biomass decrease at the end of the season. Improved post-fire microclimate and increased nutrient supply (extrinsic factors) may have contributed to higher photosynthetic rates and led to biomass compensation in burned prairie. These data support arguments that intrinsic compensatory mechanisms have evolved in response to chronic herbivory.

The Autecology and Production Dynamics of Eelgrass (Zostera marina L.) in Netarts Bay, Oregon

Changes in biomass, growth form and shoot net primary production in an eelgrass, Zostera marina L., bed were monitored along transects at three tidal heights in Netarts Bay, Oregon, from May 1979 through June 1981. During the growing season, April through October, the mean plastochrone interval was 16.5 d along the low intertidal transect and 11.6 d along the high intertidal transect. The mean export interval was 13.3 d along the low intertidal transect and 11.6 d along the high intertidal transect. The life span of a leaf averaged 48 d along the low intertidal transect and 36 d along the high intertidal transect. Shoot density was positively correlated with mean leaf area index (LAI) until the LAI reached 3.8 to 5.5, above which LAI was negatively correlated with density. The maximum Zostera biomass ranged from 143 (high intertidal transect) to 463 (low intertidal transect) g dry wt m−2. Maximum values of shoot net production ranged from 4.7 (high intertidal transect) to 13.6 (low intertidal transect) g dry wt m−2d−1. Zostera shoot net production was related to light and to the physical damage to the shoots associated with a rapid accumulation of Enteromorpha biomass in the bay. In addition, patterns of biomass accumulation were related to the duration of water coverage, as determined by both tidal height and local impoundments of water. At all transects, biomass sloughed was equal to at least 50% of the shoot net primary production in that area during that time period; sloughed leaves accounted for 25 to 97% of these losses. An estimate of the total annual net primary production of aboveground Zostera in the bed was 17,500 kg, dry wt (SE=3,080 kg dry wt), which was equivalent to a mean annual rate of 383 g C m−2 (SE=67 g C m−2)

Future Shock in Forest Yield Forecasting: The Need for a New Approach

The traditional method of predicting future yields of conventional forest products and/or biomass is based on an empirical bioassay of the growth potential of unmanaged stands, or of stands subject to one, or a small number of, management practices. The method employs the historical pattern of stem volume and/or forest biomass accumulation in the form of volume- or biomass-over-age curves. This type of yield predictor, which may be presented as a simple yield table or a more complex mensurational computer yield model, is widely considered to produce believable future yield predictions. However, the predictions will only be accurate if the future environmental conditions and management regimes are similar to those that pertained over the period during which the biomass accumulation on which the yield model is based occurred. This is unlikely because the continued growth of the human population and the resultant loss of forest land will require a great intensification of forest management. The significant changes in management that many believe await forestry in the not-too-distant future in many parts of the world will render such conventional predictions very questionable. In addition, human-induced changes in atmospheric chemistry may result in changes in the climatic (the "green-house gases" problem), canopy or soil conditions (the "acid rain" problem) that determine tree growth.Computer models of forest yield based solely on the simulation of the biological processes that determine tree growth do not at present offer a viable alternative. Either we do not yet know enough to build, or we do not have sufficient resources to develop and calibrate such process models at an adequate level of complexity.What is needed is a generation of hybrid yield models that combine traditional mensurational models with a simulation of those growth-regulating processes that are significantly altered by changing management practices and/or by changing atmospheric chemistry and climate. One such model is FORCYTE: the FORest nutrient Cycling and Yield Trend Evaluator. This is an ecologically-based forest management simulation model that can predict the long-term consequences of a wide variety of forest management practices for the future harvest yield, ecosystem nutrient budgets, economic efficiency and the energy benefit/cost ratio of management. It combines the believability of the traditional approach with the flexibility of ecological and biological process simulation. Present versions of the model focus on the consequences for future production and yield of changes in forest management. However, because of the structure of the model, it is capable of being modified to examine similar consequences of climatic change and alteration in atmospheric chemistry. Progress in the latter area must await clarification of the processes involved in acid rain damage to forests. FORCYTE is also capable, with minor modification, of being used in agriculture and mined land reclamation research and planning. Key words: Yield prediction, FORCYTE.

Effect of sowing time on growth, yield and water-use of rain-fed wheat in the Wimmera, Vic

Crops of wheat (Triticum aestivum cv. Olympic) were sown after a 10-month fallow at three times in both 1979 and 1980 in the Wimmera district of Victoria. Total above-ground plant material (biomass) and soil water content were measured for each crop at monthly intervals from sowing to anthesis and thereafter every 2 weeks. The duration of the phenophase, sowing to anthesis, varied from 88 to 163 days, but the maximum difference between anthesis date for the early (May) and late (August) sown crops was only 21 days. The duration of this phenophase was best described by a photothermal unit of 6846 day-degree-hours (>2�C, >6 h). The pattern of biomass accumulation varied markedly between crops, with biomass ranging from 9 to 13 t ha-1 and yield between 3 and 4 t ha-1. Total wateruse efficiency in the production of biomass to anthesis ranged from 30.5 to 19.8 kg ha-1 mm-1 and in the seasonal production of grain from 8.6 to 6.6 kg ha-' mm-'. Whilst the data include only one early sown crop, it was possible to identify an optimum balance between pre- and post-anthesis growth in crops sown in June to produce 9 t ha-1 of biomass at anthesis in early November, a yield sink of 12500 grains m-2 and in the 2 years of the experiment a grain yield of 4 t ha-1.

Above‐ and belowground emergent macrophyte production and turnover in a coastal marsh ecosystem, Georgia1

Seasonal patterns of aboveground plant mass and the depth distribution of live roots, rhizomes, and dead belowground organic matter were measured for Spartina alterniflora and Spartina cynosuroides in Georgia tidal marshes. Peak live aboveground biomass was 1.6 × higher for S. cynosuroides than for S. alterniflora. Live biomass was 2.4 × more belowground than aboveground for S. cynosuroides and 1.7 × for S. alterniflora. Rhizomes made up 76 and 87% of live belowground biomass during the year. Mirrored patterns of biomass accumulation and loss in above‐ and belowground tissues during the year suggest the importance of seasonal storage and redistribution of organic matter.Belowground production was measured with a technique that partially accounts for midseason decomposition. Total plant production was estimated to be 7,620 g dry mass·m−2·yr−’ for S. alterniflora and 7,708 for S. cynosuroides. Belowground production was roughly 1.6 × aboveground production. Turnover rates for belowground live material were 1.42 · yr−1 for S. cynosuroides and 3.22·yr−1 for S. alterniflora. The fate of root and rhizome material, including the extent to which such material enters the estuarine or nearshore food webs, is not clear.