ROOT PRODUCTION IN FOUR COMMUNITIES IN THE GREAT DISMAL SWAMP

A sequential coring approach was used to measure root biomass and production over 1 year in four different communities within the Great Dismal Swamp. A second method, an implanted bag technique, was also used to measure root production, and values were generally lower using this technique. On all sites, fine roots were the most dynamic root component. Both biomass (1,887 g/m²) and production (354–989 g m ² yr^-1) were highest on the mixed hardwood site, the least flooded site, and second highest on the cedar site, the site with the longest duration of soil saturation (1,033 g/m² and 274–366 g m^-2 yr^-1). The maple-gum (696 g/m² and 59–91 g m^-2 yr^-1) and cypress (824 g/m² and 68–308 g m^-2 yr^-1) sites had similarly low amounts of biomass and rates of production. Environmental parameters that influenced production include frequency and duration of flooding, and soil type. Peaks in belowground production were observed on the most productive sites (mixed hardwood and cedar) in summer and late fall-winter; the other two sites exhibited little seasonal variability. The least flooded stand appears to allocate a greater percentage of net primary production belowground than the more extensively flooded stands. The ratio of above- and belowground allocation appears to change in response to a flooding gradient. This has major implications for ecosystem functions as carbon allocation patterns determine the array of litter types generated (leaves vs. roots) which affect decomposition rates and nutrient availability.     

Root turnover as determinant of the cycling of C,N, and P in a dry heathland ecosystem

Root production and turnover were studied using sequential core sampling and observations in permanent minirhizotrons in the field in three dry heathland stands dominated by the evergreen dwarfshrub Calluna vulgaris and the grasses Deschampsia flexuosa and Molinia caerulea, respectively. Root biomass production, estimated by core sampling, amounted to 160 (Calluna), 180 (Deschampsia) and 1380 (Molinia) g m^-2 yr^-1, respectively. Root biomass turnover rate in Calluna (0.64 yr^-1) was lower compared with the grasses (Deschampsia: 0.96 yr^-1; Molinia 1.68yr^-1)). Root length turnover rate was 0.75–0.77 yr^-1 (Deschampsia) and 1.17–1.49 yr^-1 (Molinia), respectively. No resorption of N and P from senescing roots was observed in either species. Input of organic N into the soil due to root turnover, estimated using the core sampling data, amounted to 1.8 g N m^-2 yr^-1(^Calluna), 1.7 g N m^-2 yr^-1 (Deschampsia) and 19.7 g N m^-2 yr^-1 (Molinia), respectively. The organic P input was 0.05, 0.07 and 0.55 g P M^-2 yr^-1, respectively. Using the minirhizotron turnover estimates these values were20–22% (Deschampsia) and 11–30% (Molinia) lower.When the biomass turnover data were used, it appeared that in the Molinia stand root turnover contributed 67% to total litter production, 87% to total litter nitrogen loss and 84% to total litter phosphorus loss. For Calluna and Deschampsia these percentages were about three and two times lower, respectively.This study shows that (1) Root turnover is a key factor in ecosystem C, N, and P cycling; and that (2) The relative importance of root turnover differs between species.     

Translocation,remineralization, and turnover of nitrogen in the roots and rhizomes of Spartina alterniflora (Gramineae)

We used ¹⁵N to quantify rates of N translocation from aerial to belowground tissues, foliar leaching, and turnover and production of root and rhizome biomass in the plant-sediment system of short Spartina alterniflora areas of Great Sippewissett Marsh, Massachusetts. Decay of belowground tissues in litterbag incubations at 1- and 10-cm depths resulted in 80% remineralization of the original plant (¹⁵N-labeled) N and 20% burial after 3 years. Translocation of ¹⁵N from plant shoots in hydrologically controlled laboratory lysimeters maintained under field conditions was 38% of the aboveground pool while leaching of N was 10% from June to October. Most of the translocated N was not retranslocated to new aboveground growth in December but appeared to be either remineralized or buried in the sediment. Injection of ¹⁵N into field stands of grass showed initially high incorporation into plants followed by a continuous decline over the next 7 years yielding a gross tumover time of 1.5–1.6yr. Correcting the gross N turnover for recycling of label via translocation and uptake of remineralized label during this period, a net root and rhizome turnover time of 1.0–1.1 yr was obtained. Combining the turnover time with independent estimates of seasonal belowground biomass yielded an estimate of belowground production of 929–1,022 g C m⁻² yr⁻¹, similar to measurements by traditional biomass harvest, CO² based budgets and models for comparable areas of this marsh. Integration of the production and nitrogen balance estimates for short Spartina marsh yielded translocation, 1.4 g N m⁻² yr⁻¹, leaching, 0.4 g N m⁻² yr⁻¹, remineralization, 14.9–16.3 g N m⁻² yr⁻¹, and burial, 3.7–4.1 g N m⁻² yr⁻¹.     

Effects of fire,mowing and nitrogen addition on root characteristics in tall-grass prairie

Abstract. Root harvests and root windows were used to study the influence of fire, mowing and nitrogen additions on root lengths, biomass, and nitrogen content in tall-grass prairie. Four years of nitrogen additions (10 g m² yr^?1) increased below-ground mass by 15 % and nitrogen concentration in that mass by 77 %. In general, live roots and rhizomes exhibited greater increases in nitrogen concentrations than detrital roots and rhizomes. After four years of treatment, live roots and rhizomes immobilized an additional 1.5 to 5 g/m² of nitrogen, depending upon specific treatment, while dead roots and rhizomes immobilized an additional 3 to 3.5 g/m². Average root growth parameters, as measured with root windows, were positively correlated with above-ground peak foliage biomass; however, the only significant correlation was between average new root growth and above-ground peak foliage biomass (r = 0.73, p ≤ 0.04). Root growth and decay, as measured by annual mean values for eight root windows over a four year interval, were insensitive to climatic and treatment effects.     

Annual and seasonal changes in fine root biomass of a Quercus ilex L. forest

The biomass, production and mortality of fine roots (roots with diameter <2.5 mm) were studied in a typical Mediterranean holm oak (Quercus ilex L.) forest in NE Spain using the minirhizotron methodology. A total of 1212 roots were monitored between June of 1994 and March of 1997. Mean annual fine root biomass in the holm oak forest of Prades was 71±8 g m^–2 yr^–1. Mean annual production for the period analysed was 260+11 g m^–2 yr^–1. Mortality was similar to production, with a mean value of 253±3 g m^–2 yr^–1. Seasonal fine root biomass presented a cyclic behaviour, with higher values in autumn and winter and lower in spring and summer. Production was highest in winter, and mortality in spring. In summer, production and mortality values were the lowest for the year. Production values in autumn and spring were very similar. The vertical distribution of fine root biomass decreased with increasing depth except for the top 10–20 cm, where values were lower than immediately below. Production and mortality values were similar between 10 and 50 cm depth. In the 0–10 cm and the 50–60 cm depth intervals, both production and mortality were lower.     

黄河源园区高寒草地碳储量估算及其影响因素

高寒草地碳储量及其影响因素研究是认识青藏高原草地生态系统乃至陆地生态系统碳循环和气候变化的关键之一。利用2021年8月上旬地面调查数据与同期高分6号遥感数据建立回归关系,在反演研究区植被地上、地下生物量碳密度和0—40cm土壤层有机碳密度基础上,估算了黄河源园区高寒草地有机碳储量,并通过路径分析探讨了土壤理化性质对碳密度的影响驱动机制。结果表明：(1)2021年黄河源园区地上生物量、地下生物量、0—40cm土壤层碳密度分别为37.65g/m²、1305.28g/m²、4769.11g/m²;总碳储量为100.44Tg(1Tg=10¹²g),植被层和土壤层碳储量分别分为22.06Tg、78.38Tg,占总碳密度的21.96%、78.04%。(2)黄河源园区高寒草甸和高寒草原两种草地类型地上生物量碳密度分别为41.27g/m²、30.76g/m²;地下生物量碳密度分别为1661.41g/m²、618.74g/m²;0...     

An experimental study of old-field succession in relation to different environmental factors

From 1984 to 1986, old-field succession on sterilized sand and loam was studied under different water- and nutrient regimes. Within one month, moss and phanerogam species appeared on all experimental plots but further succession was rather varied. Salix species established quickly on loam and formed within 3 years a shrub layer up to 3 m in height. On sand, woody plant species were observed only at a high ground-water level. On loam, the well-known old-field succession from short-living therophytes to long-living phanerophytes of clearings and woodlands proceeded very quickly. In contrast, on sand, therophytes, hemicryptophytes and herbaceous chamaephytes of ruderal- and grassland communities were still dominant after three years. A high ground-water level as well as mineral fertilization had sometimes positive, sometimes negative effects on this succession. Periodic estimates of cover, made during the succession were supplemented at the end of the experiment by the measurements of phytomass and bioelement storage. The highest amount of biomass was measured on the three loamy soils where shrub layers were well developed. In comparison with data published elsewhere, the above-ground biomass of 2.2–2.8 kg dry matter m^-2 and the below-ground biomass up to 7.2 kg dry matter m^-2 were both extraordinarily high. Over the three years, the vegetation on sandy soils accumulated between 1.2 and 5.1 g N m^-2 yr^-1 and on loamy soils between 17.1 and 24.7 g N m^-2 yr^-1.     

Aspects of production and biomass of four seagrass species (Cymodoceoideae) from Papua New Guinea

Biomass and production data of the seagrasses Cymodocea serrulata (R. Brown) Aschers. and Magnus, Cymodocea rotundata Ehrenb. et Hempr. ex Aschers., Halodule uninervis (Forssk.) Aschers. and Syringodium iksoetifolium (aschers.) Dandy were collectede in monospecific stands in Bootless Inlet, Papua New Guinea. Cymodocea serrulata and Cymodocea rotundata were studied from November 1980 to November 1981. Total annual mean biomass was 354 and 201 g ADW m⁻², respectively. The largest proportion of these biomass values was contributed by the rhizomes (49 and 36%, respectively) and leaf biomass was ± 30% for both species. Halodule uninervis was studied at an intertidal and a subtidal site. The highest total annual mean biomass (600 g ADW m⁻²) was recorded at the intertidal site, of which 85% was found below ground. The largest proportion of the biomass, at both sites, was contributed by the below-ground vertical axes of the shoots. The biomass of the rhizomes was relatively low (9–12%) for Halodule uninervis. Proportionally, the largest above-ground biomass (40%) was recorded for Syringodium isoetifolium, of which the annual mean biomass was 481 g ADW m⁻².Total production (above and below ground) was 4.9 and 3.0 g ADW m⁻² day⁻¹ for Cymodocea serrulata and Cymodocea rotundata, respectively. Approximately 70% was production of leaves. Total production amounted to 6.0 and 4.0 g ADW m⁻² day⁻¹ for Halodule uninervis at the intertidal and subtidal sites, respectively. The maximum production was recorded for Syringodium isoetifolium, 60% of the 9.0 g ADW m⁻² day⁻¹ was contributed by the leaves. All species reached the maximum production during February and March, when the water temperatures were highest and water was retained above all sites, at all times. The increase of leaf production was mainly due to the increase in biomass of the mature leaves. Significant changes in the plastochrone interval of the leaves were not observed during this period.     

Typha productivity in a Texas pond: Implications for energy and nutrient dynamics in freshwater wetlands

Above-and below-ground biomass of Typha angustifolia L. was sampled monthly for 18 months from a small Texas pond. Maximum above-ground biomass was 2559±284 g AFDW (ash-free dry weight) m⁻² in 1983 and 2895±217 g AFDW m⁻² in 1984. Peak below-ground biomass for these 2 years was 2506±278 g AFDW m⁻² and 2314±226 g AFDW m^t-2, respectively. Stepwise multiple linear regression analyses revealed that mean above-ground biomass accrual was related to duration of growing season, cumulative precipitation, cumulative degree days and/or cumulative pan evaporation. The same was not true for below-ground biomass increases. Analysis of covariance revealed that the rates of above-ground biomass production were not significantly different (F test, p < 0.05) between the 1983 and 1984 growing seasons. Below-ground biomass turnover times for 1983 and 1984 were 2.47 and 1.21 years, respectively.     

Evaluating minirhizotron estimates of fine root longevity and production in the forest floor of a temperate broadleaf forest

The minirhizotron technique (MR) for in situ measurement of fine root dynamics offers the opportunity to obtain accurate and unbiased estimates of root production in perennial vegetation only if MR tubes do not affect the longevity of fine roots. Assuming fine root biomass is near steady-state, fine root production (g m^–2 yr^–1) can be estimated as the ratio of fine root biomass (g m^–2) to median fine root longevity (yr). This study evaluates the critical question of whether MR access tubes affect the longevity of fine roots, by comparing fine root survivorship obtained using MR with those from a non-intrusive in situ screen method in the forest floor horizons of a northern hardwood forest in New Hampshire, USA. Fine root survivorship was measured in 380 root screens during 1993–1997 and in six horizontal minirhizotron tubes during 1996–1997. No statistically significant difference was found between estimates of survivorship of fine roots (<1 mm dia.) at this site from MR versus from in situ screens, suggesting that MR tubes do not substantially affect fine root longevity in the forest floor of this northern hardwood forest and providing greater confidence in measurements of fine root production using the MR technique. Furthermore, the methodology for estimating fine root production from MR longevity data was evaluated by comparison of fine root longevity and production estimates made using single vs. multiple root cohorts, and using root-number, root-length, and root-mass weighted methods. Our results indicate that fine root-length longevity estimates based on multiple root cohorts throughout the year can be used to approximate fine root biomass production. Using this method, we estimated fine root longevity and production in the forest floor at this site to be 314 days (or 0.86 yr) and 303 g m^–2 yr^–1, respectively. Fine root production in this northern hardwood forest is approximately equivalent to standing biomass and was previously underestimated by root in-growth cores. We conclude that the use of MR to estimate fine root longevity and production as outlined here may result in improved estimates of fine root production in perennial vegetation.     

ORGANIC MATTER DYNAMICS IN FOUR SEASONALLY FLOODED FOREST COMMUNITIES OF THE DISMAL SWAMP

Budgets of organic matter dynamics for plant communities of the Great Dismal Swamp were developed to summarize an extensive data base, determine patterns of biomass allocation, transfer and accumulation, and make comparisons with other forested wetlands. Aboveground net primary production on the flooded sites (1,050–1,176 g m^-2 yr^-1) was significantly greater than on a rarely flooded site (831 g m^-2 yr^-1). Estimates of belowground net primary production were comparable to aboveground production on flooded sites (824–1,221 gm^-2 yr^-1). However, productivity was nearly three times greater belowground than aboveground on the rarely flooded site (2,256 g m^-2 yr^-1). Aboveground productivity in Dismal Swamp forests is relatively high compared to other forested wetlands. This is attributed to the timing and periodic nature of flood events. Fine root turnover is shown to be an important source of soil organic matter. Estimates indicate that roots contribute about 60% of the annual increment to soil organic matter. Leaflitter contributes 6–28% and wood debris contributes 5–15%. Comparisons with other forested wetlands suggest that detritus accounts for greater than half of the total organic matter (living + dead) in many wetland systems.     

BIOMASS AND PRODUCTION OF PONTEDERIA CORDATA AND POTAMOGETON EPIHYDRUS IN THREE CONNECTICUT RIVERS

Above- and below-ground biomass of the emergent Pontederia cordata and the floating-leaved Potamogeton epihydrus was measured during the growing season in three interconnected rivers in Connecticut, U.S.A. Maximum biomass of Pontederia, averaging 1,212 g m^-2 dry weight (524 g m^-2 above-ground, 688 g m^-2 below-ground), occurred 100–150 days after major spring growth began. Peak biomass of Potamogeton averaged 94 g m^-2 (81 g m^-2 above-ground, 14 g m^-2 below-ground) and was attained in 45–85 days. New growth of Pontederia in spring arose from, and was heavily subsidized by, the large biomass of living overwintered rhizomes and roots, which averaged 497 g m^-2 in early June. This new growth appeared to have been produced in only one season, but in reality it contained energy fixed the current season, plus energy carried over from previous years. Net production of Pontederia calculated for only one growing season averaged 1,049 g m^-2. Potamogeton also perennated from rhizomes, but the biomass of these organs in spring was low, averaging 11 g m^-2 in late May. Biomass of Potamogeton in summer consisted primarily of tissue produced during the current season. Rhizomes and roots comprised a much greater proportion of the plant in Pontederia than in Potamogeton. The ratio of new living below-ground/above-ground biomass of Pontederia rose from zero in spring to an average of 1.71 in autumn. For Potamogeton, the below-ground/above-ground ratio averaged 0.37 in late spring, 0.20 in midsummer, and 0.41 in autumn. The overwintered below-ground biomass of Pontederia alive in spring was 42–79% of the new living below-ground biomass the previous autumn. Net photosynthetic efficiency during the period between initiation of major growth in spring and attainment of peak biomass averaged 1.3% for Pontederia and 0.3% for Potamogeton.     

A Quantitative Food Web Model for the Macroinvertebrate Community of a Northern German Lowland Stream

Trophic interactions and cycling of organic carbon within the macroinvertebrate community of a Northern German lowland stream were analyzed based on a compartment model. The network model describes the structure of the food web quantifying biomass, production, and consumption of their elements, of the entire system and between trophic levels. System primary production is 153.7 g C m⁻² yr⁻¹ and invertebrate production 53.3 g C m⁻² yr⁻¹. Invertebrate consumption amounts to 702.6 g C m⁻² yr⁻¹. Main flows are identified between trophic level 1 and 2 and are connected with highly productive compartments. ‘Anodonta and Pseudanodonta’ and Dreissena polymorpha show the highest consumption of all groups with 269.9 g C m⁻² yr⁻¹ and 114.1 g C m⁻² yr⁻¹, respectively. System consumption is highest on the import from the upstream lake with 532.5 g C m⁻² yr⁻¹, sediment detritus with 135.5 g C m⁻² yr⁻¹, and primary producers with 25.7 g C m⁻² yr⁻¹. The lowest predation pressure is observed for Bivalvia with an ecotrophic efficiency of <10% and highest for Chironomidae with 91%. Approximately 20% of organic matter entering the detritus pool are recycled to the living groups of the system. Transfer efficiencies between discrete trophic levels are generally low except for transfer of detrital material between level I and II.     

Fine Root Production and Turnover in a Norway Spruce Stand in Northern Sweden: Effects of Nitrogen and Water Manipulation

Fine root length production, biomass production, and turnover in forest floor and mineral soil (0–30 cm) layers were studied in relation to irrigated (I) and irrigated-fertilized (IL) treatments in a Norway spruce stand in northern Sweden over a 2-year period. Fine roots (<1 mm) of both spruce and understory vegetation were studied. Minirhizotrons were used to estimate fine root length production and turnover, and soil cores were used to estimate standing biomass. Turnover was estimated as both the inverse of root longevity (RTL) and the ratio of annual root length production to observed root length (RTR). RTR values of spruce roots in the forest floor in I and IL plots were 0.6 and 0.5 y⁻¹, respectively, whereas the corresponding values for RTL were 0.8 and 0.9 y⁻¹. In mineral soil, corresponding values for I, IL, and control (C) plots were 1.2, 1.2, and 0.9 y⁻¹ (RTR) and 0.9, 1.1, and 1 y⁻¹ (RTL). RTR and RTL values of understory vegetation roots were 1 and 1.1 y⁻¹, respectively. Spruce root length production in both the forest floor and the mineral soil in I plots was higher than in IL plots. The IL-treated plots gave the highest estimates of spruce fine root biomass production in the forest floor, but, for the mineral soil, the estimates obtained for the I plots were the highest. The understory vegetation fine root production in the I and IL plots was similar for both the forest floor and the mineral soil and higher (for both layers) than in C plots. Nitrogen (N) turnover in the forest floor and mineral soil layers (summed) via spruce roots in IL, I, and C plots amounted to 2.4, 2.1, and 1.3 g N m⁻² y⁻¹, and the corresponding values for field vegetation roots were 0.6, 0.5, and 0.3 g N m⁻² y⁻¹. It was concluded that fertilization increases standing root biomass, root production, and N turnover of spruce roots in both the forest floor and mineral soil. Data on understory vegetation roots are required for estimating carbon budgets in model studies.     

Belowground structure and production in a Mediterranean sand dune shrub community

Belowground structure and annual production in an open Mediterranean scrub were studied on a sandy substrate which had not been harvested or exposed to fire during the last 30–40 years. Estimated belowground biomass (1328 ± 93.4 g m^-2) and production (548 ± 246.9 g m^-2 yr^-1) were lower than in other Mediterranean scrubs. However, the energy investment in belowground structures was high (root biomass/ shoot biomass = 2.7; annual belowground production/ annual aboveground production = 7.1), which is associated with a high density of fine roots in the top soil (the average distance between the fine roots = 0.76 cm). A very simple model based on nutrient diffusion was considered to analyse the resource constrains of the community. The results underline the importance of nutrients (and more specifically phosphorus) rather than water, as possible determinants of the structure and dynamics of the root system, as well as for the primary production of the community during the vegetative period.     

Shoot growth, radiation interception and dry matter production and partitioning during the establishment phase of Miscanthus sinensis'Giganteus' grown at two densities in the UK

Photosynthetic area index (PAI), radiation interception (I) and dry matter partitioning between shoots and roots were measured for Miscanthus sinensis‘Giganteus' grown from micro-propagated transplants on a fertile peaty loam soil in eastern England. In the establishment year, Miscanthus plants produced 35 and 70 shoots plant^-1 at densities of 4.0 and 1.8 plants m^-2 respectively. At the higher density, there were 140 shoots m^-2 with the largest reaching a height of 1.8 m; these canopies attained a maximum PAI of 5.45, intercepting 94% of incident radiation. Leaf lamina contributed c. 90% of total photosynthetic area with stems contributing the remainder. At the lower density, maximum PAI and I values were 2.88 and 86% respectively. PAI was related to I by calculating attenuation coefficients (k); these indicated that Miscanthus canopies were more effective at intercepting radiation per unit PAI at the lower density (k= -0.31) compared with the higher density (k= -0.20). Radiation interception was related to dry matter accumulated by calculating conversion efficiencies (e). At 4 plants m^-2, × for shoot dry matter production was 1.17g MJ^-1. Miscanthus partitioned a relatively large amount of total dry matter into below-ground biomass. By plant senescence, c. 30% of total dry matter had been partitioned into root and rhizome; rhizome biomass contributed 80% of below-ground dry matter, × increased to 1.62 g MJ^-1 when calculated on a total dry matter basis (shoot + root + rhizome). Total dry matter production was increased 68% by a 2.2-fold increase in plant density.     

Nitrogen availability and uptake by grassland in mesocosms at two water levels and two water qualities

We studied the effect of water table (-5 or -30 cm) and water type (rain- or groundwater) on the above- and below-ground phytomass production, species composition and nitrogen uptake of grassland.Nitrogen mineralization, nitrification, methane production, redox potential and pH at different depths in the profile were measured and used to monitor gradual changes in variables influencing phytomass production.The rise in the water level lowered the nitrogen uptake in the above-ground phytomass from 14.1 to 11.4 g N per m², but the DM production did not decrease and varied from 566 to 690 g per m². The total root mass increased from 82 to 363 g DM per m², with the proportion in the 5 to 10 cm layer increasing the most from 13 to 24%.The high water level lowered the potential N mineralization in the upper 5 cm of the soil from 16.1 to 4.3 g N per m² and in the deeper 5 to 30 cm layer from 12.6 to 9.4 g N per m² respectively, so the importance of the deeper layer as a source of N increased. The total amount of mineral N that accumulated in the 40 cm deep soil cores decreased from 31.3 to 15.5 g N per m². The above-ground vegetation took up 71 to 76% of this amount in the high water level treatment and only 37 to 57% under drier conditions.Redox potential and methane production indicated anaerobic conditions below 5 cm in both level treatments and in the top 5 cm of the high water level treatment. But some nitrification was measured there also, thus aerobic and anaerobic conditions occurred together. The low N mineralization was attributed to low soil respiration.Raising the water level brought about an increase in the above ground biomass of Glyceria fluitans and an increase in root mass, especially deeper in the soil. Both are responsible for the relatively greater fraction of nitrogen that was taken up from the soil, although less N was available. The nitrification indicates that oxygen is transported by the root system to soil microsites and partly compensates for the anaerobic conditions caused by water saturation.The calcareous groundwater raised the pH in the upper soil layer from 5.3 to 5.8 but no effect on N mineralization was measured.     

Growth, secondary production and gonad development of two co-existing amphioxus species (Branchiostoma belcheri and B. malayanum) in subtropical Hong Kong

The present study investigated the growth, secondary production and gonad development of two co-existing amphioxus species Branchiostoma belcheri and B. malayanum in subtropical Hong Kong from June 2005 to June 2006. Based on the modal progression analysis, amphioxus populations were decomposed into separate cohorts. The von Bertalanffy growth models were also estimated according to the size incremental data. From the growth models, the size ranges of one, two and three-year-old B. belcheri were estimated to be 5-28 mm, 28-38 mm and 38-45 mm BL, respectively; while the one and two-year-old B. malayanum were estimated to be 7-30 mm and 30-35 mm BL, respectively. The secondary production was calculated at 1.15 g m^− 2 yr^− 1 DW or 0.63 g m^− 2 yr^− 1 AFDW for B. belcheri with density 424 ind m^− 2, and 0.51 g m^− 2 yr^− 1 DW or 0.40 g m^− 2 yr^− 1 AFDW for B. malayanum with density 121 ind m^− 2. The production to biomass ratio (P/B) was 1.13 for B. belcheri and 0.98 for B. malayanum. Changes in the gonad length index indicated that B. belcheri spawned mainly in June and July, while B. malayanum mainly in April and August. As compared with B. belcheri, B. malayanum was characterized by rapid growth, shorter life span, early maturity and lower population density. Such differences in population dynamics may allow both species to share a similar habitat and co-exist in subtropical waters of Hong Kong.     

Growth characteristics of aquatic macrophytes cultured in nutrient-enriched water: II. Azolla,Duckweed, and Salvinia

Seasonal growth characteristics and biomass yield potential of 4 small-leaf, floating, aquatic macrophytes cultured in nutrient nonlimiting conditions were evaluated for central Florida’s climatic conditions. Biomass yields were found to be 10.6, 11.3, 16.1, and 32.1 t (dry wt) har^?1 yr^?1, respectively, for azolla (Azolla caroliniana), giant duckweed (Spirodela polyrhiza), common duckweed (Lemna minor), and salvinia (Salvinia rotundifolia). Operational plant density was in the range of 10–80 g dry wt m^?2 for azolla, 10–88 g dry wt m^?2 for giant duckweed, 10–120 g dry wt m^?2 for common duckweed, and 35–240 g dry wt m^?2 for salvinia. Specific growth rate (% increase per day) was maximum at low plant densities and decreased as the plant density increased. Results suggest that small-leaf, floating plants may not be suitable in monoculture biomass production systems because of low biomass yields, but they may be suitable for inclusion in poly culture systems with larger aquatic plants. The high N content (crude protein = 20–33%) of small-leaf,floating plants suggests the use of biomass as animal feed.     

Influence of floristic composition on the net primary production and dry matter turnover in a tropical grassland

Plant biomass, net primary productivity and dry matter turnover were studied in a grassland situated in a tropical monsoonal climate at Kurukshetra, India (29°58′N, 76°51′E). Based on differences in vegetation in response to microrelief, three stands were distinguished on the study site. The stand I was dominated by Sesbania bispinosa, stand II represented mixed grasses and stand III was dominated by Desmostachya bipinnata. Floristic composition of the three stands revealed the greatest number of species on stand II (75). The study of life form classes indicated a thero-cryptophytic flora. The biomass of live shoots in all the three stands attained a maximum value in September (424–1921 g m^-2) and below ground plant biomass in November (749–1868 g m^-2). The annual above ground net primary production was greatest on stand I (2143 g m^-2) and lowest on stand II (617 g m^-2). The rate of production was highest during the rainy season (15.34 to 3.18 g m^-2 day^-2). Below ground net production ranged from 1592 to 785 g m^-2 y^-2 and the rates were high in winter and summer seasons. Total annual net primary production was estimated to be 3141, 1403, 2493 and 2134 g m^-2 on stands I, II, III and on the grassland as a whole, respectively. The turnover of total plant biomass plus below ground biomass indicated almost a complete replacement of phytomass within the year. The system transfer functions showed greater transfer of material from total net primary production to the shoot compartment during rainy season and to the root compartment during winter and summer seasons.