Peak Leaf Research Articles

CONTRIBUTION OF STREAM DETRIVORES, FUNGI, AND BACTERIA TO LEAF BREAKDOWN BASED ON BIOMASS ESTIMATES

Linking species and ecosystems is currently one of the great challenges in ecology. To this end, we assess here the contributions of bacteria, fungi, and detritivorous invertebrates (shredders) to leaf litter breakdown, a key ecosystem-level process. We enclosed alder (Alnus glutinosa) and willow (Salix fragilis) leaves in coarse-mesh bags (5 g dry mass), placed them in a stream during peak leaf fall, and retrieved them periodically to determine leaf mass remaining and the biomass of leaf-associated organisms. Shredder biomass was derived from numbers and length–mass relationships, bacterial numbers and biomass were determined by epifluorescence microscopy, and fungal biomass was measured as ergosterol. In addition, conidial production of aquatic hyphomycetes was determined. Leaves decomposed rapidly with exponential breakdown coefficients k of 0.035 d−1 (alder) and 0.027 d−1 (willow). Leaves were also quickly colonized within the first 4 wk of decomposition, when shredder biomass reached 263 and 141 mg dry mass/litter bag, respectively. Maximum bacterial numbers (5.6 and 4.8 × 1010 g−1 detrital dry mass) were attained after 8 wk and corresponded to a biomass of 3.6 (alder) and 3.1 (willow) mg dry mass/g, <5% of the maximum fungal biomass (77 and 70 mg dry mass/g, respectively). Aquatic hyphomycetes released up to 2.7 and 1.4 × 106 conidia·g−1·d−1, equivalent to a daily conidial production of 9.4 and 2.9 mg dry mass/g on alder and willow, respectively. Calculations based on the measured decomposer biomass and conidial production, published microbial growth efficiencies, turnover times, and shredder feeding rates indicate that shredders accounted for the largest portion of overall leaf mass loss (64% and 51% on alder and willow leaves, respectively), fungi contributed at least 15% and 18%, and bacterial contribution also was estimated to be substantial (7% and 9%). Analyses of elemental flows from allochthonous leaf litter thus clearly require a quantitative consideration of the complex decomposer consortium responsible for leaf decomposition.

Phenology, litterfall and nutrient resorption in Avicennia marina (Forssk.) Vierh in Gazi Bay, Kenya

The phenology and litterfall of the mangrove Avicennia marina were monitored from August 1993 to November 1994 in Gazi Bay, Kenya. Phenological trends in the emergence and fall of leaves were monitored at regular intervals from 200 tagged terminal shoots distributed over 34 different trees randomly selected within three sites in a monospecific stunted A. marina stand. Litterfall data were collected using 23 litter traps randomly distributed in the same stand. The results showed a marked seasonality in leaf emergence in A. marina with a peak of 1.61±0.34 leaves per leaves present day–1 during the rainy season. Most litterfall was recorded at the beginning of the dry season. Average total litterfall amounted to 6.2±4.7 ton ha–1 year–1 with leaves contributing up to 83% of the total. Peak leaf emergence preceded peak leaf fall by approximately 1 month. Trees produced most new leaves when there were optimal conditions of runoff (nutrients), low evapotranspiration and reduced salinity during the rainy season. The average leaf longevity observed in the present study was approximately 11 months (1.1 turnover per year). Analysis of leaves of different physiological ages showed a nutrient resorption in the A. marina stand of 68% for N and 61% for P. Chloride content did not change with the ageing of leaves.

Effects of ontogeny and soil nutrient supply on production, allocation, and leaf area efficiency in loblolly and slash pine stands

The effects of ontogeny and soil nutrient supply on aboveground biomass accumulation, allocation, and stemwood growth efficiency of loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliottii) were investigated in north-central Florida over 16 years using a 2 × 2 × 2 factorial experiment (species, fertilization, weed control). Aboveground biomass growth responses to the combined fertilizer and weed control treatments (FW) averaged ~2- and 2.8-fold for slash and loblolly pine, respectively. In the same treatment, annual needlefall (NF) production for slash pine approached a "steady state" of 6 Mg·ha-1 at ages 8-14 years, while loblolly pine NF production peaked at 7 Mg·ha-1 at age 10 years, and then declined 17% following curtailment of the fertilizer treatment. Periodic stemwood biomass increment (PAI) for the FW treatment for both species culminated at about 15 Mg·ha-1·year-1 at age 8 years and then declined rapidly (~275%) to &lt;4 Mg·ha-1·year-1 at 15 years; reductions for the untreated control were considerably slower. The progressive decline in PAI following peak leaf area development was closely associated with a decrease in stemwood production per unit leaf area (growth efficiency). A unit increase in leaf area index in the 7- to 9-year-old stands produced about 3.0 and 3.1 times more stemwood biomass per year than in the 14- to 16-year-old stands for loblolly and slash pine, respectively.

Phenology of Tree Species in Bolivian Dry Forests

ABSTRACTPhenological characteristics of 453 individuals representing 39 tree species were investigated in two dry forests of the Lomerío region, Department of Santa Cruz, Bolivia. The leaf, flower, and fruit production of canopy and sub–canopy forest tree species were recorded monthly over a two–year period. Most canopy species lost their leaves during the dry season, whereas nearly all sub–canopy species retained their leaves. Peak leaf fall for canopy trees coincided with the peak of the dry season in July and August. Flushing of new leaves was complete by November in the early rainy season. Flowering and fruiting were bimodal, with a major peak occurring at the end of the dry season (August–October) and a minor peak during the rainy season (January). Fruit development was sufficiently long in this forest that fruiting peaks actually tended to precede flowering peaks by one month. A scarcity of fruit was observed in May, corresponding to the end of the rainy season. With the exception of figs (Ficus), most species had fairly synchronous fruit production. Most canopy trees had small, wind dispersed seeds or fruits that matured during the latter part of the dry season, whereas many sub–canopy tree species produced larger animal– or gravity–dispersed fruits that matured during the peak of the rainy season. Most species produced fruit annually. Lomerio received less rainfall than other tropical dry forests in which phenological studies have been conducted, but rainfall can be plentiful during the dry season in association with the passage of Antarctic cold fronts. Still, phenological patterns in Bolivian dry forests appear to be similar to those of other Neotropical dry forests.

Phenology of Tree Species in Bolivian Dry Forests1

Phenological characteristics of 453 individuals representing 39 tree species were investigated in two dry forests of the Lomerío region, Department of Santa Cruz, Bolivia. The leaf, flower, and fruit production of canopy and sub-canopy forest tree species were recorded monthly over a two-year period. Most canopy species lost their leaves during the dry season, whereas nearly all sub-canopy species retained their leaves. Peak leaf fall for canopy trees coincided with the peak of the dry season in July and August. Flushing of new leaves was complete by November in the early rainy season. Flowering and fruiting were bimodal, with a major peak occurring at the end of the dry season (August–October) and a minor peak during the rainy season (January). Fruit development was sufficiently long in this forest that fruiting peaks actually tended to precede flowering peaks by one month. A scarcity of fruit was observed in May, corresponding to the end of the rainy season. With the exception of figs (Ficus), most species had fairly synchronous fruit production. Most canopy trees had small, wind dispersed seeds or fruits that matured during the latter part of the dry season, whereas many sub-canopy tree species produced larger animal- or gravity-dispersed fruits that matured during the peak of the rainy season. Most species produced fruit annually. Lomerío received less rainfall than other tropical dry forests in which phenological studies have been conducted, but rainfall can be plentiful during the dry season in association with the passage of Antarctic cold fronts. Still, phenological patterns in Bolivian dry forests appear to be similar to those of other Neotropical dry forests.

Leaf area dynamics in Liquidambar styraciflua saplings: responses to nitrogen fertilization

Total leaf production, vertical foliage profiles, and the timing of leaf production and loss were compared in fertilized and unfertilized 3-year-old sweetgum (Liquidambar styraciflua L.) saplings. Nitrogen (N) fertilization increased total leaf area and mass through increased leaf size rather than changes in leaf number or specific leaf mass. Both the vertical and temporal distribution of foliage shifted in response to N. Fertilization increased leaf area primarily in the mid- to upper crown. The midheight of the tree crowns shifted upward throughout the season as leaf abscission occurred from the base to the top of the tree and acropetally along the branches. Peak leaf display occurred in July regardless of N supply. However, fertilized trees had twice the leaf area of the unfertilized trees by early autumn. Leaf area production and loss were modeled separately as a function of fertilization and crown height and the equations combined to model temporal changes in leaf area display.

Leaf Area and Above- and Belowground Growth Responses of Loblolly Pine to Nutrient and Water Additions

Abstract A 2 x 2 nutrient and water factorial experiment with four replications was installed in an 8-yr-old stand of loblolly pine (Pinus taeda L.) growing on an infertile, excessively drained sandy site in Scotland County, North Carolina. After the fourth year of treatment, estimated stem volume increment, total biomass production, and peak leaf area index (LAI) increased 152%, 99%, and 101%, respectively, with fertilization and 25%, 23%, 16%, respectively, with irrigation. Stem volume growth efficiency (growth per unit LAI) increased 21% with fertilization, 9% with irrigation, and 30% with both fertilization and irrigation. Total biomass production efficiency increased 91% with fertilization, 29% with irrigation, and 120% with both fertilization and irrigation. The observed increase in stem volume growth efficiency may have been due, in part, to changes in biomass partitioning. However, altered partitioning patterns alone did not explain the observed increase in total biomass production efficiency. We hypothesized that the change in total biomass production efficiency may have been a result of greater allocation to foliage (photosynthesizing tissue) and less allocation to fine roots (a high maintenance respiration tissue) under fertilization and irrigation treatments. For. Sci. 44(2):317-328.

１９９６一斉開花年におけるキナバル山丘陵・山地林のリター動態

We investigated the litter-fall) dynamics in rain forests in a matrix of two altitudes (approximately 800 and 2000 m) and two geological substrates (sedimentary versus ultrabasic rocks) on Mount Kinabalu, Borneo, during the 1996 masting year. The two forests at 800 m were hill rain forests, and those at 2000 m were lower montane rain forests. Litter was collected at 2-week intervals with 20 litter traps in each forest for 10 months. Significant variations were observed among the dates of collection for the leaf litter fraction in all forests (P0.05). A distinctly dry spell with depressed (3-4 °C colder) minimum air temperatures appeared in March throughout the slope, which preceded the peak of leaf litter- fall. However, the peak leaf litter appeared one month later in the wettest montane forest on sedimentary rock than in the other forests, suggesting that the response to a trigger factor might be a function of moisture. We suggested that aridity might cause the seasonality of leaf litter-fall. However, we could not find a single proximate cause for flower/fruit dynamics during the masting year.

Effect of Seasonal Water Availability on Phenology and the Annual Shoot Carbohydrate Cycle of Tropical Forest Shrubs

Summary 1. The effect of seasonal water availability on phenology and shoot total non-structural carbohydrate (TNC) of three Psychotria species was investigated by irrigating two large plots of mature tropical forest in Panama during the dry season for five consecutive years. This study reports results for the fifth and final year of irrigation. 2. Irrigation did not affect total production of leaves, inflorescences or infructescenes but did advance the timing of leaf production in all Psychotria, and advanced the timing of inflorescence production in l? furcata and P. marginata and infructescence production in P. furcata. Irrigation also reduced shoot TNC levels. 3. Shoot TNC levels in all three species of Psychotria showed similar depressions at the end of the dry season and maximum levels near the end of the wet season. Depletion of shoot TNC occurred just before or during peak leaf production but did not coincide with production of inflorescences or infructescences. Therefore, we hypothesize that shoot TNC supported part of the cost of new leaf production but production of inflorescences and infructescences was most likely supported by current photosynthate. 4. Tropical plants generally show less seasonal variation in TNC than plants from more variable climates but stored carbon still plays an important role in the growth of Psychotria, although its direct role in reproduction appears limited.

Spectral response of two diverse pigeonpea (Cajanus cajan L.) cultivars

Spectral-plant parametric functional relations of two widely cultivated and diverse pigeonpea cultivars (GT-100 and BDN-2) revealed a decline in red radiance values from 10 weeks after sowing (WAS) onwards in both the cultivars and an increase in red radiance at 16 WAS associated with leaf senescence. Increased IR radiance was noticed at peak leaf area indices. IR/R ratio attained peak values by 16 WAS and higher IR/R ratio in GT-100 was associated with high LAI. ND attained a value of 0.87 in GT-100 and 0.84 in BDN-2 during first flowering stage. IR/R ratio and ND values were positively and red radiance values negatively correlated with LAI and dry matter. Based on coefficient of determination values, the regression models between plant parameters and ND for GT-100 and IR/R ratio for BDN-2 were suggested for estimating pigeonpea development.

Performance of the LAI-2000 plant canopy analyzer in estimating leaf area index of some Scots pine stands

The LAI-2000 plant canopy analyzer (Li-Cor, Inc., Lincoln, NE) was tested at six experimental plots of Scots pine (Pinus sylvestris L.) in central Sweden at peak leaf area in August and after litterfall in October 1990. An independent estimate of leaf area index for August 1990 was obtained based on an empirically derived regression of needle area on stem sapwood area, and the decrease in leaf area between the two measurements was estimated from measurements of litterfall. A strong linear relationship was found between estimates by the LAI-2000 (L(Li-Cor)) and the indirect estimates of leaf area index (taken as half of total surface area) (L). The finding that L(Li-Cor) was considerably smaller than L was explained theoretically. It was shown that if shoots, instead of individual needles, are randomly distributed in the canopy, L(Li-Cor) corresponds to L multiplied by a factor (beta) characterizing the mutual shading of needles on the shoot. The shading factor, beta, was equal to the ratio of spherically projected shoot area to spherically projected needle area, where the spherically projected area is defined as the average projection (silhouette) area taken over all directions in space. The quantity betaL was defined as the shoot silhouette area index (SSAI), and an equation for the relationship between SSAI and the mean silhouette to total area ratio (mean STAR) of shoots was derived. Measured values of mean STAR for Scots pine indicated that L(Li-Cor) corresponds to SSAI rather than L. However, the decrease in leaf area index due to litterfall occurring between August and October was only partly detected by the LAI-2000, possibly because SSAI did not change to the same degree as L, i.e., there was an increase in the factor beta. This hypothesis is supported by data showing a large increase in mean STAR with shoot age.

Aerodynamic and canopy resistance of short-rotation forest in relation to leaf area index and climate

The aerodynamic and canopy resistances of a willow short-rotation stand were estimated during the course of a growing season on the basis of micrometeorological measurements. The normalized roughness length (z0/h) decreased from about 0.10 at a leaf area index of one to 0.05 at a leaf area index of seven. This implies that the aerodynamic resistance at peak leaf area index is more than twice the value at zero leaf area index, all other variables unchanged. The canopy resistance depended strongly on air water concentration deficit and on leaf area index. The Lohammar equation showed good agreement between estimated and “measured” canopy resistances over the whole course of leaf development. The stand was well-coupled to the atmosphere only for very small values of leaf area indices, less than one, and it was practically de-coupled for leaf area indices above two. From the point of view of factors controlling evaporation, this type of stand acts as a traditional forest at the beginning and end of the season and as an agricultural crop in the middle of the season.

Effects of CO_2 and Temperature on Growth and Resource Use of Co‐Occurring C_3 and C_4 Annuals

We examined how CO2 concentrations and temperature interacted to affect growth, resource acquisition, and resource allocation of two annual plants that were supplied with a single pulse of nutrients. Physiological and growth measurements were made on individuals of Abutilon theophrasti (C3) and Amaranthus retroflexus (C4) grown in environments with atmospheric CO2 levels of 400 or 700 @mL/L and with light/dark temperatures of 28°/22° or 38°/31°C. Elevated CO2 and temperature treatments had significant independent and interactive effects on plant growth, resource allocation, and resource acquisition (i.e., photosynthesis and nitrogen uptake), and the strength and direction of these affects were often dependent on plant species. For example, final biomass of Amaranthus was enhanced by elevated CO2 at 28° but was depressed at 38°. For Abutilon, elevated CO2 increased initial plant relative growth rates at 28° but not at 38°, and had no significant effects on final biomass at either temperature. These results are interpreted in light of the interactive effects of CO2 and temperature on the rates of net leaf area production and loss, and on net whole—plant nitrogen retention. At 28°, elevated CO2 stimulated the initial production of leaf area in both species, which led to an initial stimulation of biomass accumulation at the higher CO2 level. However, in elevated CO2 at 28°, the rate of net leaf area loss for Abutilon increased while that of Amaranthus decreased. Furthermore, high CO2 apparently enhanced the ability of Amaranthus to retain nitrogen at this temperature, which may have helped to enhance photosynthesis, whereas nitrogen retention was unaffected in Abutilon. Thus, at 28°, final biomass of Abutilon was not simulated in a high CO2 environment whereas the final biomass of Amaranthus was. At 38°, Abutilon had slightly reduced peak leaf areas under elevated CO2 in comparison to ambient CO2 grown plants, but increased rates of photosynthesis per unit leaf area early in the experiment apparently compensated for reduced leaf area. For Amaranthus at 38°, peak leaf area production was not affected by CO2 treatment, but the rate of net leaf area loss hastened under elevated CO2 conditions and was accompanied by substantial reductions of whole—plant nitrogen content and leaf photosynthesis. This may have led to the reduced biomass accumulation of high CO2 grown plants that we observed during the last 30 d of growth. Plants of both species grown in elevated CO2 exhibited reduced tissue—specific rates of nitrogen absorption, increased plant photosynthetic rate per unit of conductance, and increased initial allocation of biomass to roots, irrespective of temperature. Plants of both species grown under an elevated temperature regime had substantially decreased reproductive allocation, increased allocation to stem biomass, and increased plant water flux at both CO2 treatments. The age of plants also affected our interpretations of plant responses to CO2 and temperature treatments. For example, significant effects of CO2 treatment on the growth of Abutilon were evident early, prior to the initiation of flowering, when nitrogen availability would have been highest and pot space would not have been limited. Nevertheless, the opposite was true for Amaranthus, in which significant effects of CO2 treatment on plant growth were not detectable until the final 30 d of the experiment. Elevated CO2 interacted with temperature to affect plant productivity in different ways than would have been predicted from plant responses to elevated CO2 alone. Furthermore, a majority of the interactive effects of CO2 concentration and temperature on plant growth could be interpreted in light of their effects on the rates of net leaf area production and loss, nitrogen retention, and, to a lesser degree, photosynthesis and resource partitioning.

Response of Seed Carrot to Various Water Regimes. I. Vegetative Growth and Plant Water Relations

The influence of irrigation frequency and the severity and rate of development of soil water deficits on the vegetative growth and water status of carrots (Daucus carota L. var. sativa DC.) grown for seed were investigated in a fine sandy loam soil. Beginning with the period of rapid development of primary umbels, various irrigation frequencies [daily vs. intervals corresponding to 30 mm of accumulated crop evapotranspiration (ETc)] were investigated at irrigation rates ranging from 40% to 120% of estimated ETC. The magnitude and rate of development of soil water deficits markedly influenced carrot responses to developing water deficits. Stomata] conductance and leaf water potential (LWP) measurements exhibited some potential for use in irrigation scheduling and were the most sensitive and consistent indicators of plant water status. Under low-frequency continuous-deficit irrigation, a combination of moderate reductions in stomatal conductance and major reductions in peak leaf area and late-season maintenance of viable leaf area occurred. These responses were effective water-conserving mechanisms, allowing growth at a reduced rate and continued development of viable seed. In contrast, rapid development of soil water deficits resulted in nearly complete stomatal closure, cessation of growth, and rapid reductions in leaf area.

Canopy Density and Microclimate Effects on the Development of Aerial Stem Rot of Potatoes

(...) Plant density had no significant effect on epiphytic population size of soft rot erwinias, although some seasonal trends were noted. Populations of the epiphytes were not detected early in the season, but increased to peaks at mid- or late-season and generally declined by the end of the season. Average duration of leaf wetness was proportional to the leaf area index and periods of leaf wetness were of a longer duration in dense than in sparse plantings. Peak leaf area index values and longest periods of leaf wetness preceded extensive symptom development by 2 wk for all plant densities

Phenology of the shrub strata of successional sub-tropical humid forests of north-eastern India

The phenology of 70 shrub species occurring in 5-, 25- and 60-yr old forest fallows, developed after slash and burn agriculture in north-eastern India, was studied. The early successional shrubs were largely deciduous with predominant leaf fall during the dry winter, while late successional shrubs were evergreen and with a less pronounced leaf fall pattern; the species in the 25-yr old fallow were largely of the leaf-exchanging-evergreen type. Peak leaf production, flowering and fruiting are delayed by one month in the 60-yr old fallow. The phenological separation of the growth types in the three fallows is discussed and related to possible micro-environmental differences.

Leaf‐pack dynamics in a southern African mountain stream

SUMMARY 1. The occurrence, composition and invertebrate fauna of naturally‐occurring leaf packs were studied over 24 months in Langrivier, a second‐order mountain stream in the south‐western Cape, South Africa. Langrivier is shallow and fast‐flowing and stores very low levels of allochthonous detritus, although natural leaf packs form an obvious part of the energy base in the stream throughout the year.2. The occurrence and size of the packs were influenced mainly by stream discharge and by the timing and character of leaf fall from riparian trees. Packs were smallest (minimum dry mass 17 g, minimum volume 1.7–10−5 m3) in winter when discharge was high, and largest (maximum dry mass 191 g, maximum volume 4.2–10−3 m3) in spring when discharge decreased and leaf fall from the evergreen riparian trees began. Through the year the packs covered a mean 0.41 % of the stream bed and had a mean abundance of 0.46 packs m−2 of stream bed. They were ephemeral, lasting on average &lt;1.7 months and yet accounted for 29% of the stored detritus in the system. Wood was the dominant component of packs, and leaves at ali stages of decomposition were present throughout the year.3. The ratio of numbers of invertebrates in packs: numbers of individuals in the benthos was very low (0.002–0.030), presumably because of the rarity and small size of the packs. Nevertheless, the density of invertebrates per unit area covered by leaf packs was consistently much higher than the density in an equivalent area of the benthos, except during peak leaf fall (October to December).4. Experiments were undertaken with artificial leaf packs in order to determine the extent to which these simulated natural packs. Although both natural and artificial leaf packs contained a high proportion of Plecoptera (46% and 29% respectively), the natural packs contained high numbers of simuliid larvae (33% of total), whereas artificial packs had a high percentage of chironomid larvae (62%), Several other taxa regularly occurred in both types of pack but in very low numbers. In addition,

Kinetics and mechanisms of dissolved organic carbon retention in a headwater stream

Freeze-dried aqueous extracts of autumn-shed maple leaves, birch leaves, and spruce needles were added to a third-order reach of Bear Brook, New Hampshire at concentrations similar to those predicted to occur during peak leaf fall. Leachate from each species was rapidly removed from solution. With initial concentrations of added leachate of approximately 5 mgl−1, dissolved organics (DOC) uptake ranged from 73 to 130 mg m−2 h−1 for the first five hours of travel downstream from the point of addition. There was no preferential removal of DOC of low molecular weight, or of monomeric carbohydrates relative to phenolics or unidentified DOC. Stream sediments and organic debris rapidly removed DOC from solution in laboratory experiments. No significant flocculation or microbial assimilation of sugar maple leachate occurred in stream water alone. Stream sediments showed small increases in respiration with addition of leaf leachate, but no increase in respiration occurred upon addition of leachate to organic debris. Abiotic adsorption due to the high concentrations of exchangeable iron and aluminium in stream sediments may be responsible for much of the rapid removal of leaf leachate observed in field experiments. Abiotic processes appear to retain DOC within the stream, thereby allowing subsequent metabolism of dissolved organic carbon by stream microflora.

The Effect of Sand Deposits on the Growth and Morphology of Ammophila Breviligulata

(1) The effects of sand deposition on the growth and morphology of Ammophila breviligulata were studied in the field. (2) Both belowand above-ground biomass increased as depth of sand-burial increased. On stable dunes compared with mobile ones, a greater below-ground biomass was supported by a relatively smaller above-ground biomass. (3) Leaf area was directly related to sand burial. Peak leaf area of 23.5 cm2 g-1 fresh weight occurred with 22 cm of sand burial. Plant height increased exponentially with increased sand burial and reached a maximum of 64.5 cm with 59 cm of sand. (4) The number of buds per tiller, the number of rhizomes per plant, the internode length on vertical rhizomes, and the number of horizontal rhizomes, all increased with increased sand burial. (5) The concentration of chlorophyll in leaves increased exponentially with increased burial. Maximum total chlorophyll (2-3 mg g-1 fresh weight) was found in plants buried to a depth of 23 cm. (6) Most increases in plant cover were found where sand accumulated, while most of the decreases were on stable sites. A multiple regression, in part based on sand burial, accounted for 57% of the variance associated with changes in cover.

Effects of date of planting on plant emergence, leaf growth, and yield in contrasting potato varieties

SUMMARYFive experiments which studied the effects of a wide range of dates of planting on contrasting potato varieties in Pembrokeshire are reported. In three experiments (1976–7) four early varieties (Home Guard, Arran Comet, Irish Peace and Ulster Sceptre) were sprouted from the end of dormancy and compared at four dates of planting, which began as soon as soil conditions allowed (February in 1975 and 1976 and March in 1977). In these experiments all early-emerging treatments were damaged by frost and in 1975 and 1976 date of planting had little effect on leaf area index or yield. In 1977 planting in late April delayed and increased peak leaf area index but reduced yields throughout harvesting. In all experiments the emergence of varieties was affected by date of planting. The varieties with the longest sprouts emerged first only from the earliest plantings; at late plantings all varieties emerged together, which suggests that rate of post-planting sprout elongation decreased in this old seed as planting was delayed despite increasing soil temperatures. The implications for testing of early varieties are discussed.In two further experiments two early varieties (Home Guard in both years and Red Craigs Royal and Arran Comet in 1 year) were compared with three maincrop varieties (Désirée, Maris Piper, Stormont Enterprise) using seed which did not begin to sprout until January at dates of planting beginning in March. Sprout length was again poorly related to earliness of emergence. Delaying planting delayed and increased peak leaf area index in all varieties but only increased yields in the early varieties which had the smallest leaf areas. In maincrop varieties date of planting had little effect on final yields. In these years there were long periods without rain and in 1976 yields were limited by the amount of water available from the soil, for as each treatment exhausted this supply bulking ceased.