Structure and Function of Oak Forests in Central Himalaya. I. Dry Matter Dynamics

The present study deals with structure and functioning of threeareas of Himalayan oak forest. Low- and mid-altitude oaks, namelyQuercus leucotrichophora, and Quercus floribunda, form predominantevergreen forests in Central and Western Himalaya. The totaltree basal cover ranged between 33·89 m² ha^–1 (Q.floribunda site) to 36·83 m² ha^–1 (Q. leucotrichophorasite). The density ranged between 570 and 760 individuals ha^–1.Allometric equations relating biomass of different tree componentsto GBH (girth at breast height) were significant with the exceptionof leaf biomass in Q. leucotrichophora and Rhododendron arboreum.Total vegetation biomass (29·40–467·0 tha^–1) was distributed as 377·1 t ha^–1 intrees, 5·40 t ha^–1 in shrubs and 1·23 tha^–1 in herbs. Total forest floor biomass ranged between4·6 and 6·2 t ha^–1. Of the total annuallitter fall (4·7–4·8 t ha^–1), 77·5% was contributed by leaf litter, 17·8 % by wood litterand 4·7 % by miscellaneous litter. Turnover rate of treelitter varied from 0·66 to 0·70. Net primary productionof total vegetation ranged between 15·9 and 20·6t ha^–1 yr^–1, of which the contribution of trees,shrubs and herbs was 81·2 %, 8·6 % and 10·2%, respectively. A compartment model of dry matter on the basisof mean data across sites was developed to show dry matter storageand flow of dry matter within the system. Quercus leucotrichophora forest, Q. floribunda forest, Q. lanuginosa forest, biomass, litter fall, net primary production, compartmental transfer     

Structure and Function of an Age Series of Eucalypt Plantations in Central Himalaya. I. Dry Matter Dynamics

The biomass and net primary productivity (NPP) of 2- to 8-year-oldplantations of Eucalyptus tereticornis Sm. (= E. hybrid) growingin the tarai (a level area of superabundant water) region ofCentral Himalaya were estimated. Allometric equations for allthe above-ground and below-ground components of trees and shrubswere developed for each stand. Understorey, forest floor biomassand litter fall were also estimated from stands. Shrubs appearedfirst at 5-year-old plantation. The biomass of vegetation, forestfloor littermass, tree litter fall and net primary productivity(NPP) of trees and shrubs increased with the increase in plantationage, whereas herb biomass and NPP significantly (P < 0·01)decreased with the increase in plantation age. The total plantationbiomass increased from 7·7 t ha^–1 in the 2-year-oldto 126·7 t ha^–1 in the 8-year-old plantation andNPP from 8·6 t ha^–1 year^–1 in the 2-year-oldto 23·4 t ha^–1 year^–1 in the 8-year-old plantation.The biomass accumulation ratio ranged from 0·81 to 5·93. Eucalyptus tereticornis Sm, plantation, biomass, forest floor, litter fall, net primary productivity, biomass accumulation ratio     

Structure and Function of an Age Series of Poplar Plantations in Central Himalaya: I Dry Matter Dynamics

The biomass and net primary productivity (NPP) of 5- to 8-year-oldpoplar (Populus deltoides Marsh, Clone D₁₂₁) plantations growingin the Tarai belt (low-lying plains with high water table adjacentto foothills of central Himalaya) were estimated. Allometricequations for all the above-ground and below-ground componentsof trees and shrubs were developed for each stand. Understorey,forest floor biomass, and litter fall were also estimated fromstands. The biomass of plantation, forest floor litter mass,tree litter fall and net primary productivity (NPP) of treesand shrubs increased with increase in plantation age, whereasherb biomass and NPP significantly (P < 0·01) decreasedwith increasing plantation age. The total plantation biomassincreased from 84·0 in the 5-year-old to 170·0t ha^-1 in the 8-year-old plantation and NPP from 16·8t ha^-1 year^-1 in the 5- and 6-year-old to 21·8 t ha^-1year^-1 in the 8-year-old plantation. The biomass accumulationratio (biomass: net production, BAR) for different tree componentsincreased with the age of plantation increase. The BAR ratioranged from 4·9 in the 5-year-old to 7·7 in the8-year-old plantation.Copyright 1995, 1999 Academic Press Populus deltoides plantations (Clone D₁₂₁), biomass, dry matter turnover, net primary productivity, Tarai belt of Central Himalaya     

Structure and Function of High Altitude Forests of Central Himalaya I. Dry Matter Dynamics

The present study deals with the structure and functioning ofthree different forest communities, viz., horse chestnut, silverfir and kharsu oak forests, in a high altitude region of CentralHimalaya. The tree density and total basal cover of horse chestnutforest was 280 and 76, silver fir forest 355 and 106, and kharsuoak forest 480 trees ha^-1 and 73 m² ha^-1, respectively. Allometricequations relating biomass of different tree components to cbh(circumference at breast height) were significant. Total vegetationbiomass was 505 t ha^-1 in horse chestnut, 566 t ha^-1 in silverfir and 593 t ha^-1 in kharsu oak forests, of which maximum contributionwas by tree layer followed by shrub, herb, sapling and seedlinglayers. The forest floor litter biomass was 2·1, 4·7and 4·2 t ha^-1 in horse chestnut, silver fir and kharsuoak forests, respectively. The total litter fall was 7·3,6·7 and 9·4 t ha^-1 year^-1, of which leaf littercontributed 48, 39 and 64% in horse chestnut, silver fir andkharsu oak forests, respectively. Turnover rate of tree litterwas 0·80 in horse chestnut, 0·61 in silver firand 0·71 in kharsu oak forests. Net primary productionof total vegetation was 19·6, 18·9 and 24·9t ha^-1 year-1, of which tree layer contributed maximum proportionfollowed by herb, shrub, sapling and seedling layers. To showdry matter storage and flow of dry matter within the system,compartment models were developed for all forests.Copyright1995, 1999 Academic Press Total basal cover, biomass, productivity, Quercus, Aesculus, Abies, high altitude, litter, compartmental transfer     

Nutrient Movement in Litter Fall and Precipitation Components for Central Himalayan Forests

The annual total litter fall in six Central Himalayan forestsranged from 2.1 to 3.8 t C ha^–1, of which 54 to 82 percent was leaf litter, 9–20 per cent wood litter and 6–14per cent other litter. In all forests the order of relativeabundance of nutrients (kg ha^-1 year^-1) in litter fall was Ca(50.8–91.6) > N (47.7–72.2) > K (22.8–37.1)> P (4.1–6.4). Leaf litter accounted for 63–95per cent of the total nutrients returned through litter fall. In these forests throughfall ranged from 71.3 to 81.4 per cent,stemflow from 0.50 to 2.16 per cent and canopy interceptionfrom 17.7 to 28.2 per cent of the gross rainfall. In the incidentrainfall the concentration and annual input of Ca was the greatestand of P the least. Canopy precipitation was richer in all nutrientscompared to incident rainfall. Net gain of nutrients from thecanopy ranged from 0.16 kg ha^-1 year^-1, for P, to 17.77 kg ha^-1year^-1 for K. Leaching was greatest for K and least for N. Ofthe total quantity of nutrients returned to the soil, 11 to46 per cent was accounted for by precipitation components. Thusprecipitation inputs play a significant role in nutrient cyclingof these forests. Himalaya, forest, litter fall, precipitation components, nutrients     

Structure and Function of Oak Forests in Central Himalaya. II. Nutrient Dynamics

This paper elucidates nutrient dynamics in oak forests previouslyinvestigated for dry matter dynamics. The nutrient concentrationsin different life forms were of the order: herb > shrub >tree, whereas the standing state of nutrients were of the order:tree > shrub > herb. Soil, litter and vegetation, respectively,accounted for 32·4–98·0 %; 0·3–3·5%, and 10·2–66·6 % of the total nutrientsin the system. Considerable reductions (8·5–41·7%)in concentrations of nutrients in leaves occurred during senescence.The uptake of nutrients by vegetation, and also by differentcomponents with and without adjustment for internal recycling,has been calculated separately. Annual transfer of litter (above+ below ground) to the soil by vegetation was 115·9–187N, 7·5–15·6 P, 122·7–195·1Ca, 36·1–48·8 K and 2·88–5·16Na kg ha^–1 yr^–1. Turnover rate and turnover timefor different nutrients ranged between 0·66–0·84yr^–1 and 1·19–1·56 yr^–1, respectively.Compartment models for nutrient dynamics have been developedto represent the distribution of nutrient contents and net annualfluxes within the system. Quercus leucotrichophora forest, Q.floribunda forest, Q. lanuginosa forest, Nutrient concentration, standing state, uptake, internal cycling, turnover     

Species Structure, Dry Matter Dynamics and Carbon Flux of a Dry Tropical Forest in India

Species composition, plant biomass and net primary productivitywere studied on three sites of a dry tropical forest The forestwas characterized by small structure with 38–10.4 m2 ha^–1tree and 3 1–7 8 m² ha^–1 shrub basal cover Speciesdiversity was highest for the mid-slope site while the concentrationof dominance was greatest for the hill-top stand The beta diversitywas 3 1 Total standing crop of vegetation averaged 66 98 t ha^–1with 46 70 t ha^–1 in the tree layer, 13.97 t ha^–1in the shrub layer, 0.35 t ha^–1 in the herb layer, 2 83t ha^–1 in the litter layer and 3 13 t ha^–1 in fineroots Of the total annual litterfall (4 88–6.71 t ha^–1),69% was accounted for by leaves and 31% by non-leaf matter Netprimary production (NPP) ranged between 11 3 and 19 2 t ha^–1year^–1, to which the contributions of trees, shrubs andherbs averaged 72, 22 and 6%, respectively Contribution of rootsto NPP was substantial and ranged from 2 9 to 5 3 t ha^–1year^–1 A total of 83% of vegetation carbon was storedin the above-ground plant parts while the above-ground NPP wasresponsible for 72% of the total carbon input into the systemThe contribution of foliage, herbaceous vegetation and fineroots to carbon turnover was disproportionately larger comparedto their share in the total standing crop Carbon budgeting indicatedthat the forest was an accumulating system, over at least theshort term Dry tropical forest, biomass, litterfall, net primary production, carbon budget, carbon flux     

Structure and Function of an Age Series of Poplar Plantations in Central Himalaya. II Nutrient Dynamics

This paper elucidates nutrient dynamics in 5- to 8-year-oldpoplar (Populus deltoides) clone D₁₂₁ plantations previouslyinvestigated for dry matter dynamics. The nutrient concentrationin different layers of the vegetation were in the order: tree> shrub > herb, whereas the standing state of nutrientswere in the order: tree > herb > shrub. Soil, litter andvegetation, respectively, accounted for 80-89, 2-3 and 9-16%of the total nutrients in the system. Considerable reductions(trees 42-54, shrubs 31-37 and herbs 15-23%) in concentrationof nutrients in leaves occurred during senescence. The uptakeof nutrients by the vegetation and also by the different components,with and without adjustment for internal recycling, has beencalculated separately. Annual transfer of litter nutrient tothe soil by vegetation was 113·7-137·6 N, 11·6-14·6P and 80·1-83·2 K kg ha^-1 year^-1. Turnover rateand time for different nutrients ranged between 0·72-0·89year^-1 and 1·12-1·39 years, respectively. Thehigh turnover rate of litter on the forest floor indicates thegreater productivity of the stands, which was due to the higherdry matter dynamics and nutrient release for the growing vegetation.The nutrient use efficiency in poplar plantations ranged from159-175 for N, 1405-1569 for P and 295-332 for K. Compared withEucalyptus, there was a higher proportion of nutrient retranslocationin poplars largely because of higher tissue nutrient concentrations;this indicates lower nutrient use efficiency as compared tothe eucalypt plantation. Compartment models for nutrient dynamicshave been developed to represent the distribution of nutrientpools and net annual fluxes within the system.Copyright 1995,1999 Academic Press Populus deltoides plantations (Clone D₁₂₁), nutrient retranslocation, net nutrient uptake, nutrient use efficiency, nutrient cycling, nutrient pool, nutrient fluxes     

Nutrient Cycling in a New South Wales Subtropical Rainforest: Organic Matter and Phosphorus

Biomass and phosphorus distribution and accumulation rates wereestimated for an undisturbed subtropical rainforest in northernNew South Wales. The accumulation rates were estimated overa 16-year period. It is estimated that the steady-state above-groundbiomass for this forest is 35.0 tonne ha^–1. Most of theannual biomass production was replacing litterfall and mortality.The above-ground forest contained 52 kg P ha^–1 with agross annual accumulation of about 0.4 kg P ha^–1/yr^–1.The forest understorey and forest floor contained 4.7 kg P ha^–1and 7.9 kg P ha^–1, respectively. The annual uptake wasapprox. 4 kg P ha^–1 yr^–1. The phosphorus utilizationof this stand was compared with that of a Eucalyptus grandisplantation Sub-tropical rainforest, biomass accumulation, phosphorus cycling     

Biomass, Productivity and Energetics in Himalayan Alder Plantations

Biomass, net primary production and energy fixation in an agesequence of Himalayan alder (Alnus nepalensis D. Don) plantationswere estimated in the Kalimpong forest division of the easternHimalayas. Biomass in the plantations ranged from 106 t ha^–1(7-year stand) to 606 t ha^–1 (56-year stand) demonstratingthe potential of the alder for accumulating large biomass. Netprimary production and net energy fixation rates of the plantationswere reduced by nearly half in the 7-year stand (25 t ha^–1year^–1; 421 x 10⁶ kJ ha^–1 year^–1) comparedwith the 56-year stand (13 t ha^–1 year^–1; 215 x10⁶ kJ ha^–1 year^–1). Compartmental models of energystorage and flow rates were developed for the 7-year and 56-yearstands. The production efficiency, energy conversion efficiencyand energy efficiency in N₂ fixation have inverse relationshipswith plantation age. These efficiencies, when treated with eachother, showed significant exponential functions. Alnus nepalensis D. Don, Himalayan alder, plantation age, biomass, net primary production, energy flow, efficiencies     

Nitrogen Economy of Post-fire Stands of Shrub Legumes in Jarrah (Eucalyptus marginata Donn ex Sm.) Forest of S.W. Australia

Hansen, A. P., Pate, J. S., Hansen, A. and Bell, D. T. 1987.Nitrogen economy of post-fire stands of shrub legumes in jarrah(Eucalyptus marginata Donn ex Sm.) forest of S.W. Australia.—J.exp. Bot. 38: 26–41. Growth, demography and N economy of 1–6-year-old standsof Acacia pulchella, A. alata, A. extensa and Bossiaea aquifoliumwere examined using population sampling to assess annual incrementsof N as living biomass, and returns of N as litter, seed anddead plants. Dependence on nitrogen fixation was assessed fromseasonal profiles of acetylene reduction, employing data fromprevious calibrations to convert C₂H₂ reduced to N₂ fixed. After2 years of slow growth and minimal reproduction all speciesgrew rapidly to achieve maximum or near maximum size and seedproduction. Intense self-thinning of stands occurred in thesecond and third years, especially in the highly dense standsof the smallest species, A. alata. Annual turnover in standsranged from 0?3 to 127 kg N ha^–1 year^–1, dependingon species current age and density of a stand. Returns of Nas litter and shed seed comprised small proportions of the annualbudgets, but returns due to plant death equalled or exceededincrements of living biomass in years when stands were thinningrapidly. Proportional dependencies of the species on fixed N₂were relatively high (13–61%) in first year seedlings,and then declined markedly to 1?1–3?4percnt; in the second,0?3–1?6% in the third, and, with one exception, to wellbelow 1% in the fourth and sixth year stands. Mean annual ratesof N₂ fixation over the 6-year post-fire period were 1?6 kgN ha^–1 year^–1 for A. alata, 0–49 for A. pulchella,0?19 for B. aquifolium and 0-10 for A. extensa Key words: Shrub legumes, post-fire N economy     

The Carbon Economy of Rubus chamaemorus L. II. Respiration

Respiratory activity and seasonal changes in carbohydrate contentof the storage organs of Rubus chamaemorus L. have been investigated.Leaf dark respiration rate increases in a non-linear mannerfrom 0·7 mg CO₂ evolved dm^–2 h^–1 at 0 °Cto 4·6 rng CO₂ evolved dm^–2 hh^–1 at 30 °C.Root and rhizome respiration rates increase from 1 µ1O₂ uptake g^–1 fresh weight h^–1 at 0.7 ° C to10 µ10, uptake g^–1 f. wt h^–1 at 20 °C.Rhizome carbohydrate reserves decline from a September peakof 33 per cent alcohol insoluble d. wt to 16 per cent in May. The circumpolar distribution of R. chamaemorus is discussedin relation to the evidence presented here and in the precedingpaper of the series.     

Determination of a Critical Nitrogen Dilution Curve for Winter Wheat Crops

A set of N-fertilization field experiments was used to determinethe 'critical nitrogen concentration', i.e, the minimal concentrationof total N in shoots that produced the maximum aerial dry matter,at a given time and field situation. A unique 'critical nitrogendilution curve' was obtained by plotting these concentrationsN_ct (% DM) vs. accumulated shoot biomass DM (t ha^-1). It couldbe described by the equation: N_ct = 5·35DM^-0·442 when shoot biomass was between 1·55 and 12 t ha^-1. Anexcellent fit was obtained between model and data (r² = 0·98,15 d.f.). A very close relationship was found using reducedN instead of total N, because the nitrate concentrations inshoots corresponding to critical points were small. The criticalcurve was rather close to those reported by Greenwood et al.(1990) for C₃ plants. However, this equation did not apply whenshoot biomass was less than 1·55 t ha^-1. In this case,the critical N concentration was independent of shoot biomass:the constant critical value N_ct = 4·4% is suggested forreduced-N. The model was validated in all the experimental situations,in spite of large differences in growth rate, cultivar, soiland climatic conditions; shoot biomass varying from 0·2to 14 t ha^-1. Plant N concentration was found to vary by a factor of fourat a given shoot biomass level. In the heavily fertilized treatments,shoot N concentration could be 60% higher than the criticalconcentration. Most (on average 80%) of the extra N accumulatedwas in the form of reduced N. The proportion of nitrate to totalN in shoot mainly depended on the crop stage of development.It was independent of the nitrogen nutrition level.Copyright1994, 1999 Academic Press Winter wheat, Triticum aestivum, arable crops, plant N concentration, aerial biomass, critical nitrogen, dilution curve, fertilization, reduced N, nitrate     

Azetidine-2-carboxylic Acid and Lily Pollen Tube Elongation

Azetidine-2-carboxylic acid (AZC), which occurs naturally inLiliaceous plants, is reported to be a proline (pro) analoguePlant cell walls contain ‘extensin’, which is richin hydroxyproline (hyp). Peptidyl hyp arises through hydroxylationof peptidyl pro followed by glycosylation (arabinose attachment)of hyp Because AZC replaces peptidyl prolyl residues, it maybe a useful tool for evaluating the significance of hyp-o-arabinoselinkages in cell elongation. Therefore, we determined the effectof AZC on [¹⁴C]pro uptake, incorporation and conversion to wall-bound[¹⁴C]hyp in relation to elongation of lily pollen tubes whosewalls consist, in part, of hyp-containing glycopeptides TheAZC suppressed pollen germination 9–42 per cent (1–10mM) and subsequent tube elongation 40–54 per cent (0·1–1mM without affecting respiration In contrast, similar hyp concentrationswere without effect on tube elongation Whereas uptake of [¹⁴C]prowas 16·5–6·2 per cent of the control at0·1–1 mM AZC, [¹⁴C]leucine uptake was 85–25per cent of the control. Light microscope radioautography revealedfewer silver grains over tubes elongated in 0·1–1mM AZC than in its absence. Incorporation of [¹⁴C]pro into tnchloroaceticacid (TCA)-precipitable cytoplasm was reduced by only 10 percent at 0·01–1 mM but 43 per cent at 10 mM AZCGel filtration of cytoplasm from pollen germinated without AZCbut with [¹⁴C]pro resulted in labelled void volume (V) and threeretarded peaks (RI–III) Incorporation into V and RI wasinhibited at both 0·01 and 1 mM AZC These AZC concentrationsreduced conversion of [¹⁴C]pro to wall-bound hyp by 20 percent However, total incorporation of [¹⁴C]pro into salt-water-purifiedwall fractions was suppressed 47–53 per cent (0·1–1mM AZC). Lilium longiflorum, lily, hydroxyproline, proline, azetidine-2-carboxylic acid, pollen, pollen tube elongation     

The Structure and Function of Pine Forest in Central Himalaya. II Nutrient Dynamics

This paper elucidates nutrient dynamics in a pine forest, previouslyinvestigated for dry matter dynamics. The nutrient concentrationsin different life forms were of the order: herb > shrub >tree whereas the standing state of nutrients were of the order:tree > shrub > herb. Soil, litter and vegetation respectivelyaccounted for 38·1–82·2, 2·4–3·7and 15·4–58·2 per cent of the total nutrientsin the system. Considerable reductions (52–69 per cent)in concentrations of nutrient in needles occurred during senescence.The uptake of nutrients by vegetation, and also by differentcomponents with and without adjustment for internal recycling,has been calculated separately. Annual transfer of litter tothe soil by vegetation was 76·21 N, 6·25 P, 57·24Ca, 14·22 Mg, 19·92 K and 1·92 kg ha^–1Na. Turnover rate and turnover time for different nutrientsranged between 0·40–0·64 and 1·56–2·50year, respectively. Compartment models for nutrient dynamicshave been developed to represent the distribution of nutrientcontents and net annual fluxes within the system. Nutrient concentration, standing state, uptake, internal recycling, nutrient return, turnover, nutrient cycling     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). II. Canopy Structure and Growth

The growth of lucerne var. Europe was examined in the fieldduring 1976. The annual dry matter production of unirrigatedlucerne during 1976, with no nitrogen fertilizer application,was 82.5 per cent greater than unirrigated S.24 perennial ryegrass,with a nitrogen application of 384 kg ha^–1. The mean aboveground growth rate of lucerne was 7.3 g DM m^–2 day^–1between March and early June, of which stem material contributeda maximum of 76.5 per cent. Significant losses of leaves andstems occurred from the end of April, indicating a loss of potentialforage material. Nitrogen analyses of the above ground crop suggested that in56 days lucerne yielded 10.7 per cent more nitrogen than didS.24 annually with a nitrogen fertilizer addition of 280 kgha^–1. Between 13 and 57 per cent of the daily photosynthate is translocatedbelow ground. Medicago sativaL, lucerne, dry matter production, canopy structure, nitrogen analyses     

Estimates of biomass and primary productivity in a high-altitude maple forest of the west central Himalayas

The paper describes the biomass and productivity of maple (Acer cappadocicum) forest occurring at an altitude of 2,750 m in the west central Himalayas. Total vegetation biomass was 308.3 t ha⁻¹, of which the tree layer contributed the most, followed by herbs and shrubs. The seasonal forest-floor litter mass varied between 5.4 t ha⁻¹ (in rainy season) and 6.6 t ha⁻¹ (in winter season). The annual litter fall was 6.2 t ha⁻¹, of which leaf litter contributed the largest part (59% of the total litter fall). Net primary productivity of total vegetation was 19.5 t ha⁻¹ year⁻¹. The production efficiency of leaves (net primary productivity/leaf mass) was markedly higher (2.9 g g⁻¹ foliage mass year⁻¹) than those of the low-altitude forests of the region.     

The Effects of Elevated Atmospheric Carbon Dioxide and Water Stress on Ligth Interception, Dry Matter Production and Yield in Stands of Groundnut (Arachis hypogaea L.

Stands of groundnut (Arachis hypogaea L.), a C₃ legume, weregrown in controlled-environment glasshouses at 28 °C (±5°C)under two levels of atmospheric CO₂ (350 ppmv or 700 ppmv) andtwo levels of soil moisture (irrigated weekly or no water from35 d after sowing). Elevated CO₂ increased the maximum rate of net photosynthesisby up to 40%, with an increase in conversion coefficient forintercepted radiation of 30% (from 1–66 to 2–16g MJ^–1) in well-irrigated conditions, and 94% (from 0–64to 1·24 g MJ^–1) on a drying soil profile. In plantswell supplied with water, elevated CO₂ increased dry matteraccumulation by 16% (from 13·79 to 16·03 t ^–1) and pod yield by 25% (from 2·7 to 3·4t ha^–1).However, the harvest index (total poddry weight/above-grounddry weight) was unaffected by CO₂ treatment. The beneficial effects of elevated CO₂ were enhanced under severewater stress, dry matter production increased by 112% (from4·13 to 8·87 t ha^–1) and a pod yield of1·34t ha^–1 was obtained in elevated CO₂, whereascomparable plotsat 350 ppmv CO₂ only yielded 0·22 t ha^-1.There was a corresponding decrease in harvest index from 0·15to 0·05. Following the withholding of irrigation, plants growing on astored soil water profile in elevated CO₂ could maintain significantlyless negative leaf water potentials (P<0·01) for theremainder of the season than comparable plants grown in ambientCO₂, allowing prolonged plant activity during drought. In plants which were well supplied with water, allocation ofdry matter between leaves, stems, roots, and pods was similarin both CO₂ treatments. On a drying soil profile, allocationin plants grown in 350 ppmv CO₂ changed in favour of root developmentfar earlier in the season than plants grown at 700 ppmv CO₂,indicating that severe waterstress was reached earlier at 350ppmv CO₂. The primary effects of elevated CO₂ on growth and yield of groundnutstands weremediated by an increase in the conversion coefficientfor intercepted radiation and the prolonged maintenance of higherleaf water potentials during increasing drought stress. Key words: Arachis hypogaea, elevated CO₂, water stress, dry matter production     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: III. POST-ANTHESIS KINETICS OF NET NITRATE UPTAKE AND THE ROLE OF THE RELATIVE ROOT SIZE IN DETERMINING THE CAPACITY FOR NITRATE ACQUISITION

Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the ‘HN’ culture the relative rate of nitrate-Naddition (RA) was 0·08 d^–1 until day 48 and thendecreased stepwise to, finally, 0·005 d^–1 duringgrain-filling; the ‘LN’ culture received 45% ofthe nitrogen added in HN; the ‘CN’ culture was maintainedat RA 0·0375 d^–1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m^–3external nitrate. V_max (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative V_max (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·3–2·3d^–1 during vegetative growth to 0·1–0·7d^–1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m^–3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative V_max can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative V_max and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, V_max     

Nutrient Cycling in an Age Sequence of Western Washington Douglas-fir Stands

The cycling of nitrogen, phosphorus, calcium, magnesium andpotassium in a series of western Washington Douglas-fir [Pseudotsugamenziesii (Mirb.) Franco] stands ranging in age from 9 to 95years has been described. The stands were of relatively lowproductivity being limited by low nitrogen. The content of nitrogen,phosphorus, magnesium and potassium in tree foliage all tendedto stabilize at about 40 years whereas calcium continued toincrease. The content of all nutrients in the wood continuedto increase with stand age. Nitrogen in the forest floor accumulatedconstantly at about 5.7 kg ha^–1 year^–1 and thistogether with the above-ground tree accumulation meant about10.5 kg ha^–1 year^–1 nitrogen was immobilized. Calciumalso increased with time in the forest floor with age whereasthe other nutrients were fairly constant after about 30 years.Understorey nutrient content reached a peak at about 20 years,while understorey litter-fall was significant throughout theage sequence. Internal redistribution, especially of nitrogen,represented an increasingly greater proportion of stand requirementwith increasing stand maturity. Pseudotsuga menziesti (Mirb.) Franco, Douglas-fir, biomass, litter-fall, nutrient content, nutrient cycling