Spoil characteristics and vegetation development of an age series of mine spoils in a dry tropical environment

A series of coal mine spoils (5, 10, 12, 16 and 20-yr old) in a dry tropical environment was sampled to assess the changes with time in spoil characteristics, species composition and plant biomass. Coarse fragments (>2 mm) decreased with age of mine spoil while the proportion of 0.2–0.1 mm particles increased. Total soil N, mineral N, NaHCO₃-extractable Pi, and exchangeable K increased with age of mine spoil and these parameters were lower in mine spoils than native forest soil even after 20 years of succession. Exchangeable Na decreased with age of mine spoil and in 20-yr old spoil it was higher than native forest soil. Plant community composition changed with age. Only a few species participated in community formation. Species richness increased with age, while evenness and species diversity declined from 5-yr old to 16-yr old community with an increase in the 20-yr old community. A reverse trend occurred for concentration of dominance. Area-weighted shoot and root biomass of other species increased with the age of the mine spoil while that of Xanthium strumarium patches declined with age. Data collected on spoil features, microbial C, N and P, and shoot and root biomass when subjected to Discriminant Analysis indicated a continued profound effect of age. 10 and 12-yr old mine spoils were closer to each other, and 5 and 20-yr old spoils were farthest apart.     

Changes in the canopy structure of the Mediterranean shrub Lavandula stoechas after disturbance

Abstract. This study attempts to show the dynamics of the canopy structure of the Mediterranean pioneer shrub Lavandula stoechas after man-made perturbation (i.e. grazing). The development of the vertical structure of the shrub was studied by harvesting the canopy of plants of 2–6 yr old in horizontal layers. The supportive biomass of the canopy was concentrated near the base at all ages. Leaf biomass was evenly distributed all over the vertical profile in 2- and 3-yr old plants. In 4-yr old plants it presented a maximum near the top of the canopy. For 5-yr old plants a structural transition started with leaf profiles showing a bimodal distribution. Leaf biomass predominated near the base in 6-yr old plants, suggesting that the transition was completed. Three canopy stages in the growth processes of the plant were recognized after the first year of growth: in the first one (from 2 to 3 yr old) both leaf and supportive biomass increased; in the second one (from 3 to 4 yr) leaf biomass remained stable and there was an increase in supportive biomass until the plants reached a ‘mature stage’, in 4-yr old plants; finally, in 5- and 6-yr old plants there was a decrease both in leaf and supportive biomass and plant structure showed evidence of senescence. Early transitions from seedling to 1-yr old plant and from this to 2- to 3-yr old plants were less obvious. The leaf/supportive biomass ratio always decreased with plant age, from 1.88 in seedlings to 0.01 in 6-yr old plants. Biomass density followed the pattern of supportive biomass, with an increase from 1.7 g/dm³ (2-yr old plants) to 2.4 g/dm³ (4-yr old plants). Thereafter, biomass density decreased to 0.6 g/dm³ (6-yr old plants).     

Biomass and production of fine and coarse roots during regrowth of a disturbed subtropical humid forest in north-east India

Seasonal variation and depthwise distribution of dry matter in roots of different diameter classes and their annual production were studied using sequential core sampling. The investigations were carried out in three stands of a subtropical humid forest of north-east India representing different stages of regrowth after tree cutting. The mean annual standing crop of fine (<2 mm in diameter) and coarse (2–15 mm diameter) roots increased gradually from 5.4 Mg ha^-1 and 0.7 Mg ha^-1 in 7-yr old regrowth to 9.4 Mg ha^-1 and 2.8 Mg ha^-1 in 16-yr old regrowth, respectively. The contribution of fine roots to the total root mass declined from 88% in 7-yr old regrowth to 77% in both 13 and 16-yr old regrowths, while that of coarse roots increased from 12 to 23%. A major portion of fine roots (59–62%) was present in 0–10 cm soil layer, but the coarse roots were concentrated in 10–20 cm soil depth (38–48%). In all the three stands, biomass of both fine and coarse roots followed a unimodal growth curve by showing a gradual increase from spring/pre-rainy season to autumn/post-rainy season. Biomass to necromass ratio increased from 2.5 in the 7-yr old to 3.2 in the 16-yr old stand. The annual fine root production increased from 5.9 Mg ha^-1 to 7.7 Mg ha^-1 and total root production from 7.6 Mg ha^-1 to 14.7 Mg ha^-1 from 7-yr to 16-yr old regrowth.     

模拟增温对青藏高原高寒草甸根系生物量的影响

在青藏高原高寒草甸布设模拟增温实验样地,采用土钻法于2012—2013年植被生长季获取5个土层的根系生物量,探讨增温处理下根系生物量在生长季不同月份、不同土壤深度的变化趋势及其与相应土层土壤水分、温度的关系。结果表明:(1)根系生物量在2012年随月份呈增加趋势,其中7—9月较大,其平均值在对照、增温处理下分别为3810.88 g/m~2和4468.08 g/m~2;在2013年随月份呈减小趋势,其中5—6月较大,其平均值在对照、增温处理下分别为4175.39 g/m~2和4141.6 g/m~2。增温处理下的总根系生物量高出对照处理293.97 g/m~2,而各月份总根系生物量在处理间的差值均未达到显著水平。表明在增温处理下根系生物量略有增加,但在生长季不同月份其增加的程度不同,致使年际间的增幅出现差异。(2)根系生物量主要分布在0—10 cm深度,所占百分比为50.61%。在增温处理下,0—10 cm深度的根系生物量减少,减幅为8.38%;10—50 cm深度的根系生物量增加,增幅为2.1%。相对于对照处理,增温处理下0—30 cm深度的根系生物量向深层增加,30—50 cm深度的根系生物量增加趋势略有减缓。可见,在增温处理下根系生物量的增幅趋向于土壤深层。(3)根系生物量与土壤水分呈极显著的递减关系,在增温处理下线性关系减弱;与土壤温度呈极显著的递增关系,在增温处理下线性关系增强。表明土壤水分、温度都可极显著影响根系生物量,但在增温处理下土壤温度对根系生物量的影响较土壤水分更为敏感而迅速。     

地质封存CO2泄漏对玉米根系形态的影响

碳捕集与封存（Carbon Capture and Storage,CCS）是应对全球气候变化、实现煤炭清洁利用的有效手段之一,但是地质封存的CO₂存在泄漏的风险,可能对农田生态系统产生重大威胁,影响我国粮食安全。根系生长是地上部和地下部相互作用、相互促进的统一过程,其形态特征对作物生产力有显著影响,但CCS泄漏对植物根系的影响评估尚不多见。本文以玉米为研究对象,采用盆栽底部通入CO₂的方法模拟不同CO₂泄漏情景,研究CK（0 g m^-2 d^-1）和G1000（1000 g m^-2 d^-1）和G2000（2000 g m^-2 d^-1）三种泄漏情景下CO₂对玉米根系形态的影响。结果表明：CO₂泄漏对玉米根系形态有明显的影响,随着泄漏量的增大总根长从40290.81 cm减少至21448.18 cm,减少46.77%,其中细根大幅减少;CO₂泄漏造成玉米明显减产,最大减产率达26.64%;玉米的地上部生物量较地下部生物量对CO₂泄漏更加敏感。综合来看,随着CO₂泄漏量增大,对玉米根的生长、地上部生物量、地下部生物量以及产量有显著的抑制作用。作物根系形态对封存CO₂泄漏的响应可为CCS泄漏监测和生态修复提供系统科学依据。     

Vertical distribution and seasonal changes of fine and coarse root mass in Pinus kesiya Royle Ex.Gordon forest of three different ages

Seasonal changes and vertical distribution of fine (< 2 mm diameter) and coarse (2-10 mm diameter) root mass of Pinus kesiya and fine root and rhizome mass of herbaceous species, and root production were studied in the 6-, 15- and 23-year old Pinus kesiya forest stands at Shillong, in the Meghalaya state of north-east India. Maximum fine and coarse root mass of P. kesiya, and fine root and rhizome mass of the ground vegetation were recorded during the rainy season. The contribution of the tree fine roots in 0-10 cm soil layer declined from 51% in the 6-year old stand to about 33% in the older stands. The major proportion (63-88%) of herbaceous fine root and rhizome mass was concentrated in this soil layer in all the three stands. The majority (36-57%) of tree coarse roots were present in the 10-20 cm layer in all the stands. The biomass and necromass values in the case of fine roots were more or less equal in a given stand, but the coarse roots had 5 to 9 times more live than the dead mass. The proportion of herbaceous fine root mass to the total fine root mass declined from 54% in the 6-year old stand to 30-32% in the 15- and 23-year old stands. The mean total fine root mass (pine + herbaceous species) decreased from 417 g m^–2 in the 6-year old stand to 302 in 15-year and 322 g m^–2 in the 23-year old stand. Annual fine root production showed a marked decrease from 1055 g m^–2 in the 6-year old stand to 743 g m^–2 in the 23-year old stand, but coarse root production increased from 169 g m^–2 in the 6-year to 466 g m^–2  in the 23-year old stand; the total root production thus remained approximately constant.     

Seasonal changes of fine root density in the Southern Californian chaparral

Summary Fine root extractions from soil cores of a south facing slope in the Southern Californian chaparral were used to study the dynamics of feeder root growth in a summer-dry area. The studies were concentrated on the root systems of Adenostoma fasciculatum, Arctostaphylos glauca, Ceanothus greggii, and Rhus ovata. The total fine root biomass of Adenostoma fasciculatum increased from 0.6 g dm^-3 in early spring to 3.6 g dm^-3 in late summer. Considering the specific soil conditions at this site and earlier gained information on fine root distribution with depth, the value of 3.6 g dm^-3 converts to 1.58 kg m^-2 of ground shaded by the shrub canopy. The observed seasonal biomass increase is mainly due to the accumulation of dead root material in the soil when low soil moisture contents presumably inhibited decomposition processes. The total length of living fine roots also increased during the season, e.g. from 0.8 m dm^-3 to more than 5 m dm^-3 (0.35 km m^-2 to 2.2 km m^-2) in A. fasciculatum. Unusual summer rains in the research year stimulated vigorous fine root growth at a time when the normally low soil moisture would prohibit further fine root growth. The average fine root diameters and total lengths of fine roots beneath one square meter of ground surface allowed an estimate of root area indices (RAI) analogous to the leaf area indices (LAI). The data provide evidence for a significant fine root turnover in the chaparral.     

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract

Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m^?2, and that of spruce and pine 297 g m^?2 and 277 g m^?2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.     

The Biogeochemistry of Carbon at Hubbard Brook

The biogeochemical behavior of carbon in the forested watersheds of the Hubbard Brook Experimental Forest (HBEF) was analyzed in long-term studies. The largest pools of C in the reference watershed (W6) reside in mineral soil organic matter (43% of total ecosystem C) and living biomass (40.5%), with the remainder in surface detritus (14.5%). Repeated sampling indicated that none of these pools was changing significantly in the late-1990s, although high spatial variability precluded the detection of small changes in the soil organic matter pools, which are large; hence, net ecosystem productivity (NEP) in this 2nd growth forest was near zero (± about 20 g C/m²-yr) and probably similar in magnitude to fluvial export of organic C. Aboveground net primary productivity (ANPP) of the forest declined by 24% between the late-1950s (462 g C/m²-yr) and the late-1990s (354 g C/m²-yr), illustrating age-related decline in forest NPP, effects of multiple stresses and unusual tree mortality, or both. Application of the simulation model PnET-II predicted 14% higher ANPP than was observed for 1996–1997, probably reflecting some unknown stresses. Fine litterfall flux (171 g C/m²-yr) has not changed much since the late-1960s. Because of high annual variation, C flux in woody litterfall (including tree mortality) was not tightly constrained but averaged about 90 g C/m²-yr. Carbon flux to soil organic matter in root turnover (128 g C/m²-yr) was only about half as large as aboveground detritus. Balancing the soil C budget requires that large amounts of C (80 g C/m²-yr) were transported from roots to rhizosphere carbon flux. Total soil respiration (TSR) ranged from 540 to 800 g C/m²-yr across eight stands and decreased with increasing elevation within the northern hardwood forest near W6. The watershed-wide TSR was estimated as 660 g C/m²-yr. Empirical measurements indicated that 58% of TSR occurred in the surface organic horizons and that root respiration comprised about 40% of TSR, most of the rest being microbial. Carbon flux directly associated with other heterotrophs in the HBEF was minor; for example, we estimated respiration of soil microarthropods, rodents, birds and moose at about 3, 5, 1 and 0.8 g C/m²-yr, respectively, or in total less than 2% of NPP. Hence, the effects of other heterotrophs on C flux were primarily indirect, with the exception of occasional irruptions of folivorous insects. Hydrologic fluxes of C were significant in the watershed C budget, especially in comparison with NEP. Although atmospheric inputs (1.7 g C/m²-yr) and streamflow outputs (2.7 g C/m²-yr) were small, larger quantities of C were transported within the ecosystem and a more substantial fraction of dissolved C was transported from the soil as inorganic C and evaded from the stream as CO₂ (4.0 g C/m²-yr). Carbon pools and fluxes change rapidly in response to catastrophic disturbances such as forest harvest or major windthrow events. These changes are dominated by living vegetation and dead wood pools, including roots. If biomass removal does not accompany large-scale disturbance, the ecosystem is a large net source of C to the atmosphere (500–1200 g C/m²-yr) for about a decade following disturbance and becomes a net sink about 15–20 years after disturbance; it remains a net sink of about 200–300 g C/m²-yr for about 40 years before rapidly approaching steady state. Shifts in NPP and NEP associated with common small-scale or diffuse forest disturbances (e.g., forest declines, pathogen irruptions, ice storms) are brief and much less dramatic. Spatial and temporal patterns in C pools and fluxes in the mature forest at the HBEF reflect variation in environmental factors. Temperature and growing-season length undoubtedly constrain C fluxes at the HBEF; however, temperature effects on leaf respiration may largely offset the effects of growing season length on photosynthesis. Occasional severe droughts also affect C flux by reducing both photosynthesis and soil respiration. In younger stands nutrient availability strongly limits NPP, but the role of soil nutrient availability in limiting C flux in the mature forest is not known. A portion of the elevational variation of ANPP within the HBEF probably is associated with soil resource limitation; moreover, sites on more fertile soils exhibit 20–25% higher biomass and ANPP than the forest-wide average. Several prominent biotic influences on C pools and fluxes also are clear. Biomass and NPP of both the young and mature forest depend upon tree species composition as well as environment. Similarly, litter decay differs among tree species and forest types, and forest floor C accumulation is twice as great in the spruce–fir–birch forests at higher elevations than in the northern hardwood forests, partly because of inherently slow litter decay and partly because of cold temperatures. This contributes to spatial patterns in soil solution and streamwater dissolved organic carbon across the Hubbard Brook Valley. Wood decay varies markedly both among species and within species because of biochemical differences and probably differences in the decay fungi colonizing wood. Although C biogeochemistry at the HBEF is representative of mountainous terrain in the region, other sites will depart from the patterns described at the HBEF, due to differences in site history, especially agricultural use and fires during earlier logging periods. Our understanding of the C cycle in northern hardwood forests is most limited in the area of soil pool size changes, woody litter deposition and rhizosphere C flux processes.     

A TEN-YEAR RECORD OF ABOVEGROUND BIOMASS IN A KANSAS TALLGRASS PRAIRIE: EFFECTS OF FIRE AND TOPOGRAPHIC POSITION

Measurements of mid-season live and dead aboveground biomass are reported for a 10-yr period (1975–84) in a northeast Kansas tallgrass prairie. Study sites included shallow, rocky upland and deep, non-rocky lowland soils in annually burned (April) and unburned watersheds. Lowland sites had significantly greater live biomass than upland sites for both burned and unburned prairie for the 10-yr period. Moreover, live biomass was greater on burned than unburned lowland sites, but was not significantly increased by fire on the upland sites. Averaged across upland and lowland sites, mid-season live biomass was 422 g m^–2 on annually burned and 364 g m^–2 on unburned sites for the 10-yr period. Each site had its lowest live biomass value during the severe drought year of 1980 (range = 185–299 g m^–2). During the study period, live biomass was most strongly correlated with seasonal pan water evaporation (r = –0.45 to –0.82), whereas dead biomass was correlated with the previous yr's precipitation (r = 0.61 and 0.90 for upland and lowland sites, respectively). When aboveground biomass was sampled throughout the 1984 season and separated into several components, biomass of the graminoids was 40% lower, whereas that of forbs and woody plants was 200–300% greater in the unburned than in the annually burned site.     

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.     

Size and Structure of Fine Root Systems in Old-growth and Secondary Tropical Montane Forests (Costa Rica)

The fine root systems of three tropical montane forests differing in age and history were investigated in the Cordillera Talamanca, Costa Rica. We analyzed abundance, vertical distribution, and morphology of fine roots in an early successional forest (10–15 years old, ESF), a mid‐successional forest (40 years old, MSP), and a nearby undisturbed old‐growth forest (OGF), and related the root data to soil morphological and chemical parameters. The OGF stand contained a 19 cm deep organic layer on the forest floor (i.e., 530 mol C/m²), which was two and five times thicker than that of the MSF (10 cm) and ESF stands (4 cm), respectively. There was a corresponding decrease in fine root biomass in this horizon from 1128 g dry matter/m² in the old‐growth forest to 337 (MSF) and 31 g/m² (ESF) in the secondary forests, although the stands had similar leaf areas. The organic layer was a preferred substrate for fine root growth in the old‐growth forest as indicated by more than four times higher fine root densities (root mass per soil volume) than in the mineral topsoil (0–10 cm); in the two secondary forests, root densities in the organic layer were equal to or lower than in the mineral soil. Specific fine root surface areas and specific root tip abundance (tips per unit root dry mass) were significantly greater in the roots of the ESF than the MSF and OGF stands. Most roots of the ESF trees (8 abundant species) were infected by VA mycorrhizal fungi; ectomycorrhizal species (Quercus copeyemis and Q. costaricensis) were dominant in the MSF and OGF stands. Replacement of tropical montane oak forest by secondary forest in Costa Rica has resulted in (1) a large reduction of tree fine root biomass; (2) a substantial decrease in depth of the organic layer (and thus in preferred rooting space); and (3) a great loss of soil carbon and nutrients. Whether old–growth Quercus forests maintain a very high fine root biomass because their ectomycorrhizal rootlets are less effective in nutrient absorption than those of VA mycorrhizal secondary forests, or if their nutrient demand is much higher than that of secondary forests (despite a similar leaf area and leaf mass production), remains unclear.     

Influence of a developing tree canopy on the yield of Pennisetum pedicellatum sown on a mine spoil

Abstract. Shoot and root biomass yield of a sown grass, Pennisetum pedicellatum, were measured at below-canopy, canopy edge and open locations in young monoculture stands of eight tree species planted on a coalmine spoil. Incident light as percentage of full sunlight decreased from open to canopy edge to below-canopy locations. The shoot and root weights of Pennisetum in different tree stands for each of the three locations were significantly different and were significantly related to each other, and to percentage sunlight across all tree species plots and locations. The gradient of incident light was the principal factor governing the gradient of grass biomass under developing canopies of tree plantations on the mine spoil.     

毛竹种群向针阔林扩张的根系形态可塑性

为了弄清毛竹(Phyllostachys edulis)向针阔林扩张过程中根系的形态可塑性反应,在浙江天目山自然保护区毛竹向针阔林扩张的典型过渡地带,连续区域上设置毛竹纯林、针阔-毛竹混交林(以下简称过渡林)、针阔林3种样地。用根钻法采集样地毛竹根系、针阔树根系并比对其生物量密度、细根比根长、相邻同级侧根节点距等形态特征参数变化。结果表明:随着毛竹的扩张程度增加,林内根系生物量密度增加;且与针阔树竞争过程中毛竹将更多的根系放置于表层;同时在水平方向上随离样株距离的增加未出现明显变化,而针阔树根系则随离样木距离的增加而逐渐减少;毛竹根系比根长明显增加,平均增幅15%;一、二级侧根节点距则均有所下降,毛竹侧根数量增多。这些结果表明毛竹种群可通过根系生物量密度、细根比根长、相邻同级侧根节点距等形态可塑性方式实现向周边森林扩张。     

岩溶地区不同石漠化程度下草地细根对土壤养分的贡献

细根分解和周转是土壤有机质和养分的重要来源。为探明不同石漠化程度天然草地细根对土壤养分的贡献,于2017年3月至次年1月,采用土柱法和分解袋法,研究不同石漠化程度下天然草地的细根生物量、分解和养分释放动态及对石漠化的响应。结果表明:3种不同石漠化程度下草地的细根生物量随季节均呈现先增加后降低的趋势,随石漠化程度的加剧均呈现逐渐降低的趋势,潜在、中度和强度石漠化草地的细根生物量分别为3355.65、2944.02 g/m~2和1806.80 g/m~2。细根分解速率呈现先快后慢的趋势,分解300天后的残留率均低于50%。细根有机碳、全氮、全磷和全钾的释放过程具有显著不同,释放模式最终均表现为"释放",潜在、中度和强度石漠化草地细根的有机碳、全氮、全磷、全钾的年归还量分别为32.46—161.08、0.24—3.88、0.08—0.32、0.15—2.78 g/m~2。随石漠化程度的加剧,细根生物量和分解率呈现逐渐降低趋势,土壤有机碳、全氮归还量呈现逐渐增加趋势。     

Contribution of Root Respiration to Total Soil Respiration in a Leymus chinensis （Trin.） Tzvel, Grassland of Northeast China

The loss of carbon through root respiration Is an Important component of grassland carbon budgets. However, few data are available concerning the contribution of root respiration to total soil respiration in grasslands in China. We Investigated seasonal variations of soil respiration rate, root blomaaa, microbial blomaaa C and organic C content of the soil In a semi-arid Leymus chinensis （Trin.） Tzvel. grassland of northeast China during the 2002 growing season （from May to September）. The linear regression relationship between soil respiration rate and root blomaaa was used to determine the contribution of root respiration to total soil respiration. Soil respiration rate ranged from 2.5 to 11.9 g C/m^2 per d with the maximum in late June and minimum In September. The microbial blomaaa C and organic C content of the soil ranged from 0.3 to 1.5 g C/m^2 and from 29 to 34 g C/kg respectively. Root blomaaa had two peaks, In early June （1.80 kg/m^2） and mid-August （1.73 kg/m^2）. Root respiration rate peaked In mid-August （6.26 g C/m^2 per d）, whereas microbial respiration rate peaked In late June （7.43 g C/m^2 per d）. We estimated that the contribution of root respiration to total soil respiration during the growing season ranged from 38% to 76%.     

Differential recovery of above‐ and below‐ground rich fen vegetation following fertilization

Abstract. For seven years we studied the recovery of vegetation in a Belgian P limited rich fen (Caricion davallianae), which had been fertilized with nitrogen (200 g.m^?2) and phosphorus (50 g.m^?2) in 1992. The vegetation in this fen has low above‐ground biomass production (< 100 g m^?2) due to the strong P limitation. Above‐ground biomass was harvested from 1992 to 1998 and P and N concentrations measured. In 1998, below‐ground biomass was also harvested. The response to fertilization differed markedly between below‐ and above‐ground compartments. Above‐ground, P was the single most important factor that continued to stimulate growth 7 yr after fertilization. Below‐ground, N tended to decrease live root biomass and increase dead root biomass and seemed to have a toxic effect on the roots. In the combined NP treatment the stimulating effect of P (an increase of live root biomass) was countered by N. The 1998 soil analysis showed no difference in soil P in the plots. Thus, Fe hydroxides are not capable of retaining P in competition with fen vegetation uptake. However, higher capture of P in root Fe coatings from N plots may partially explain this negative N effect. The results suggest that N root toxicity will be amplified in strongly P limited habitats but that its persistence will be less influenced by P availability. This mechanism may be a competitive advantage for N₂ fixing species that grow in strongly P limited wetlands.     

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.     

Organic matter distribution and fluxes within a holm oak (Quercus ilex L.) stand in the Etna volcano

Located at 1100 m above sea level, on the western site of the Etna volcano, the ecophysiology of the Mount Minardo holm oak coppice has been investigated for more then twenty years. In this stand, now 31 years old, the above ground biomass amounts to 15000 g m^-2 of organic material, including leaves and perennial woody material. During these 31 years, the mean annual production has been around 775 g m^-2. The yearly mean litterfall amounts to 310 g m^-2, including 200 g m^-2 of leaves, mostly two years old. The soil surface is covered by a litter layer amounting to 3150 g m^-2. Each year, following Jenny's decomposition rate and field measurements, 290 g m^-2 of the litter turns into CO₂, or becomes incorporated in the soil organic matter.     

Primary production and biomass on a Dutch salt marsh: emphasis on the below-ground component

The primary production and below-ground biomass of angiosperms were measured in four almost monospecific vegetation stands situated on a salt marsh along the Oosterschelde estuary, The Netherlands. Maximum below-ground biomass values found for Spartina anglica, Elymus pycnanthus, Halimione portulacoides and Triglochin maritima, were very high relative to values reported from other European salt marshes: 12 586, 9 717, 17 737 and 16 121 g m^-2 respectively. These relatively high values may be due to the fineness of the sieve used, compared to other studies. The actual values are likely to be even higher because the sample treatment has probably caused loss of fine root material. Below-ground production estimates, based on the difference between maximum and minimum biomass, yielded: 6 044 g m^-2 yr^-1 for Spartina, 4 421 g m^-2 yr^-1 for Elymus, 7 799 g m^-2 yr^-1 for Halimione and 3 475 g m^-2 yr^-1 for Triglochin. This high production is mainly concentrated in the deeper layers of the root environment (20–60 cm). Although these production figures are considerably higher than those generally reported for comparable species or vegetation types in Europe, statistical evidence suggests that, for the first three species, they are real values rather than figures caused by random fluctuations.