Higher Light Interception Research Articles

Restoration of floral diversity through plantations on abandoned agricultural land

Plantations have been claimed to be "monocultures", or "biological deserts". We investigated these claims in the context of a long-term study on plant diversity within plantations with different indigenous tree species, spacings, and soil types that were compared with 410 native stands. Soil type had no influence on plantation species diversity or abundance, and wider spacing resulted in higher richness, lower woody plant abundance, slightly higher cover of herbaceous plants, and large increases in cryptogam cover. We also found a canopy species × spacing interaction effect, where the impact of increased spacing on understory vegetation was more pronounced in spruce than in pine plantations. The dynamic community interactions among species of feathermoss appear to be in response to the physical impediment from varying amounts of needle rain from the different tree species. High light interception and needle fall were negatively correlated with understory plant diversity, as was lack of structural diversity. This study indicates that through afforestation efforts agricultural lands can be restored to productive forests that can harbour nearly one-half of the plant species found in equivalent natural forests within the same geographic region in as little as 50 years. We recommend applying afforestation using indigenous conifer species as a first step towards rehabilitating conifer forests that have been converted to agriculture and subsequently abandoned.

Canopy growth and biomass partitioning to yield in short-season lentil

Lentil (Lens culinaris L.) cultivars in the large green market class in Western Canada have late-season bushy growth, low harvest index (HI), and lodge readily. The aim of this study was to compare a range of genotypes for canopy traits such as rapid growth, light interception, HI, lodging, and yield. Four stiff-stem unadapted genotypes varying in leaf size and canopy openness were compared with two large green market class and other locally adapted cultivars at three population densities in the field in 2001 and 2002. Canopy measurements included biomass and light interception at weekly intervals, lodging score, end of season HI and yield. Adapted cultivars had high biomass (525 to 700 g m-2), high seed yield (96 to 130 g m-2), high maximum light interception (61 to 80%), high final branch number (17 to 19), and greatest overall plant height (0.3 to 0.44 m), but large green cultivars were prone to lodging. Unadapted genotypes produced less biomass and lodged the least. Genotypes that accumulated most above-ground biomass yielded the highest, grew the tallest, branched the most, but lodged the most. Unadapted genotypes FLIP 2000-7L (tallest, highest yielding of the unadapted types) and FLIP 96-7L (most lodging resistant (2001) and most brittle stemmed (2002) were promising parents for improving lodging resistance, on the basis of lodging resistance and yield or stem stiffness, respectively. CDC Milestone had the best canopy characteristics of moderate biomass and high harvest index for Western Canada. Key words: Lentil, Lens culinaris, biomass, harvest index, yield, lodging

Partial rootzone drying: effects on growth and fruit quality of field-grown grapevines (Vitis vinifera).

A study to assess the effects of the Partial Rootzone Drying (PRD) irrigation strategy in comparison to other irrigation systems was carried out in southern Portugal in two field-grown grapevines varieties, Moscatel and Castelão. We addressed the question of whether by regulating growth and plant water use, the PRD system would enable an equilibrated vegetative development, leading to a favourable capture of solar radiation for photoassimilate production and, at the same time to provide an optimum environment for fruit maturation. Three irrigation schemes were applied in addition to the non-irrigated (NI) vines: partial root drying (PRD), 50% of crop evapotranspiration (ETc), supplied to only one side of the root system while the other one was allowed to dry, alternating sides every 15 days; deficit irrigated (DI), 50% ETc supplied, half to each side of the root system and full irrigated (FI, 100% ETc). During the whole season FI plants of both varieties exhibited a high leaf predawn water potential (ψpd , ca-0.2MPa) while a progressive decline was observed in NI plants, reaching ψpd values near -0.7 MPa at the end of August. PRD and DI presented intermediate values. PRD vines exhibited a stronger control over vegetative growth as compared with DI and FI plants. This was expressed by lower values of total leaf area at harvest, leaf layer number, canopy wideness and water shoots number, allowing a higher light interception at the cluster zone that induced an improvement in some berry quality characteristics. Watering had no significant effects on sugar accumulation in the berries but led to a favourable increase in the must titratable acidity, mainly in Castelão. Whereas in DI and FI treatments berry skin anthocyanins and phenols content were always lower than in NI, in PRD there was either no reduction or the reduction was much lower than in the other irrigation treatments. Water use efficiency (WUE) was increased by about 80% in PRD and DI when compared with FI, as a result of almost similar yields in the three treatments. Yield gains of irrigated plants in relation to NI were modest, explained by the rainy spring in both years.

Early Performance of 'Conference' Pear on Four Training Systems

To determine how different training systems affected early growth and fruiting (first 5 years), `Conference' pear (Pyrus communis L.) trees on Quince A (Cydonia oblonga L.) rootstock were trained to angled trellis, slender spindle, vertical axe, or Y-trellis. The trees of the Y-trellis had the greatest spread after 5 years, and the vertical axe and slender spindle trees were the tallest. The Y-trellis trees had the highest light interception and had significantly higher yields in 1997 than the other training systems. Average fruit weight was inversely related to crop load.

Managing forests for wood yield and carbon storage: a theoretical study.

Which forest management regimes best achieve the dual objectives of high sustained timber yield and high carbon storage, including the carbon stored in soil and wood products? A mechanistic forest ecosystem simulator, which couples carbon, nitrogen and water (Edinburgh Forest Model), was calibrated to mimic the growth of a pine plantation in a Scottish climate. The model was then run to equilibrium (1) as an undisturbed forest, (2) removing 2.5, 10, 20 or 40% of the woody biomass each year (3) removing 50% of the woody biomass every 20 years, and (4) clear-felling and replanting every 60 years as in conventional plantations in this climate. More carbon was stored in the undisturbed forest (35.2 kg C m(-2)) than in any regime in which wood was harvested. Plantation management gave moderate carbon storage (14.3 kg C m(-2)) and timber yield (15.6 m(3) ha(-1) year(-1)). Notably, annual removal of 10 or 20% of woody biomass per year gave both a high timber yield (25 m(3) ha(-1) year(-1)) and high carbon storage (20 to 24 kg C m(-2)). The efficiency of the latter regimes could be attributed (in the model) to high light interception and net primary productivity, but less evapotranspiration and summer water stress than in the undisturbed forest, high litter input to the soil giving high soil carbon and N(2) fixation, low maintenance respiration and low N leaching owing to soil mineral pool depletion. We conclude that there is no simple inverse relationship between the amount of timber harvested from a forest and the amount of carbon stored. Management regimes that maintain a continuous canopy cover and mimic, to some extent, regular natural forest disturbance are likely to achieve the best combination of high wood yield and carbon storage.

Modeling the effect of physiological responses to green pruning on net biomass production of Eucalyptus nitens.

Green pruning of Eucalyptus nitens (Deane and Maiden) Maiden increases instantaneous rates of light-saturated CO(2) assimilation (A), and changes patterns of total leaf area and foliage distribution. We investigated the importance of such changes on the rate of recovery of growth following pruning. A simple process-based model was developed to estimate daily net biomass production (G(d)) of three-year-old plantation-grown trees over a 20-month period. The trees had been pruned by removal of 0, 50 or 70% of the length of green crown, equivalent to removal of 0, 55 or 88% of leaf area, respectively, when the plantation verged on canopy closure. Total G(d) was reduced by only 20% immediately following the 50%-pruning treatment, as a result of both the high leaf dark respiration and low A in the portion of the crown removed compared to the top of the crown. Pruning at the time of canopy closure preempted a natural and rapid decline in G(d) of the lower crown. Although leaf area index (L) was approximately 6.0 at the time of pruning, high light interception (95%) occurred with an L of 4.0. The 50%-pruning treatment reduced L to 3.5, but the physiological responses to pruning were sufficient to compensate fully for the reduction in intercepted radiation within 110 days of pruning. The 70%-pruning treatment reduced L to 1.9, and reduced G(d) by 77%, reflecting the removal of branches with high A in the mid and upper crown. Physiological responses to the 70%-pruning treatment were insufficient to increase G(d) to the value of unpruned trees during the study. Model sensitivity analysis showed that increases in A following pruning increased G(d) by 20 and 25% in the 50- and 70%-pruned trees, respectively, 20 months after pruning. Changes in leaf area/foliage distribution had a greater effect on G(d) of 50%-pruned trees (47% increase) than did changes in A. However, the reduction in photosynthetic potential associated with the 70%-pruning treatment resulted in only small changes in leaf area/foliage distribution, which consequently had little effect on G(d). The effects of physiological processes occurring within the crown and in response to green pruning on G(d) are discussed with respect to pruning of plantations.

Environmental control of potential yield of sunflower in the subtropics

A simple framework was used to analyse the determinants of potential yield of sunflower (Helianthus annuus L.) in a subtropical environment. The aim was to investigate the stability of the determinants crop duration, canopy light interception, radiation use efficiency (RUE), and harvest index (HI) at 2 sowing times and with 3 genotypes differing in crop maturity and stature. Crop growth, phenology, light interception, yield, prevailing temperature, and radiation were recorded and measured throughout the crop cycle. Significant differences in grain yield were found between the 2 sowings, but not among genotypes within each sowing. Mean yields (0% moisture) were 6·02 and 2·17 t/ha for the first sowing, on 13 September (S1), and the second sowing, on 5 March (S2), respectively. Exceptionally high yields in S1 were due to high biomass assimilation associated with the high radiation environment, high light interception owing to a greater leaf area index, and high RUE (1·47–1·62 g/MJ) across genotypes. It is proposed that the high RUE was caused by high levels of available nitrogen maintained during crop growth by frequent applications of fertiliser and sewage effluent as irrigation. In addition to differences in the radiation environment, the assimilate partitioned to grain was reduced in S2 associated with a reduction in the duration of grain-filling. Harvest index was 0·40 in S1 and 0·25 in S2. It is hypothesised that low minimum temperatures experienced in S2 reduced assimilate production and partitioning, causing premature maturation.

Growth of Lettuce, Onion, and Red Beet. 1. Growth Analysis, Light Interception, and Radiation Use Efficiency

A field experiment was carried out to analyse the growth of lettuce, onion and red beet in terms of: ( a) canopy architecture, radiation interception and absorption; ( b) efficiency of conversion of absorbed radiation into biomass; and ( c) dry matter partitioning. Growth analysis, total solar radiation interception, PAR interception and absorption by the crop canopy, ground cover, maintenance respiration of onion bulbs and red beet storage roots were measured. Models for different leaf angle distribution and ground cover were used to simulate light transmission by the crop canopy. The three crops are shown to have contrasting growth patterns from both a morphological and a physiological point of view. Lettuce showed very high light interception and growth after the early growth stages but, throughout the growth cycle, this leafy crop showed the lowest radiation use efficiency due to the respirational cost of the high leaf area. Onion showed a lower early relative growth rate than lettuce and red beet. This was due partly to the low light interception per unit leaf area in the later stages of growth and partly to the low initial radiation use efficiency compared with the other two crops. On the other hand, thanks to more uniform distribution of the radiation inside the canopy, to the earlier termination of leaf development and to the very low level of bulb respiration, onion showed high radiation use efficiency and was able to produce a large amount of dry matter. Red beet leaf posture and canopy structure resulted in high light interception and absorption. Its radiation use efficiency was lower than that of onion, partly perhaps because of the more adverse distribution of the intercepted radiation fluxes within the canopy and partly because of the high respiration cost of a continuous dry-matter allocation to the leaves. However, this crop can accumulate a very large amount of dry matter as leaf blade development and storage root growth can both continue almost indefinitely, providing continuously available sinks. Ground cover gave a good estimate of the PAR interception only at low values of light interception but, in general, it underestimated PAR interception in all three crops. Ratios between attenuation coefficients established by considering PAR or total solar radiation and LAI or ground cover were calculated.

Potential for increasing early vigour and total biomass in spring wheat. II. Characteristics associated with early vigour

Increased early growth and total dry matter production have been suggested as useful traits to improve yield in Mediterranean-type environments. In Part I, genotypic variation for early growth and total dry matter production was identified among cultivars and some introduced lines. In this part, characteristics associated with early vigour in five of these introduced lines and ten Australian cultivars were examined in a field study at Wongan Hills in Western Australia. Differences in dry matter production were observed at all sampling times during the season, with three of the introduced lines (CEP 8058, Kansu No. 32 and V979-28) having consistently higher dry matter production than the standard cultivars during the early growth period. Those genotypes with a higher dry matter production at 54 days after sowing had higher relative growth rates and green area indices than those with low dry matter production. Both genotypes with large leaves on few tillers and genotypes with small leaves on many tillers had higher green area indices and higher dry matter production. While high dry matter production was associated with a large degree of ground cover and high light interception, it was not associated with the earlier commencement of reproductive development. Incorporation of early vigour and high dry matter production into locally adapted cultivars is required to demonstrate its benefit in these environments.

Growth and grain-yield of contrasting barley cultivars under different plant densities

The effect of planting density on dry-matter growth and grain-yield of contrasting cultivars of barley was examined over three years. The particular objective was to examine whether high-density planting or the use of vigorous cultivars would be disadvantageous in areas where frequent rainfall during early growth is followed by prolonged drought up to maturity.Pre-heading growth varied greatly among cultivars and densities; this variation was partly related to the number of tillers, with two-row cultivars and high densities having more tillers per unit area than six-rows and low densities respectively. The relationship between tiller number and canopy light interception, however, varied among cultivars. A detailed study of two contrasting cultivars showed that the cultivar which had the highest light interception per unit leaf area also had the highest dry-matter production. The result indicates the importance of radiation interception in pre-heading stages with incomplete ground cover.High densities promoted phenological development, with flag-leaf exsertion and heading occurring 6–7 days earlier in the high density (120 plants m−2) than in the low (36 plants m−2). No significant effect of density on grain-yield was observed in one season where water stress developed in the early-grain-filling period. Cultivars which headed earlier tended to escape water stress and produced higher grain-yield. Post-heading growth of late-heading cultivars was low, but this was partially compensated for by the apparent use of pre-heading assimilates.When there was frequent rain during the early stages of growth, water use was not affected by density and cultivar despite a large variation in total dry-matter production among treatments. In another season where favourable weather conditions were maintained throughout growth, yield response to plant density varied among cultivars. In one six-row cultivar with a limited ability to produce tillers, grain-yield increased with increase in density up to the highest of 150 plants m−2. In other cultivars, there was no consistent effect of plant density on grain-yield.It is concluded that grain-yield will not be reduced by the use of high plant density or vigorous cultivars which promote biomass production during early stages of growth, if rainfall is frequent at that time.

Ecophysiological consequences of non-random leaf orientation in the prairie compass plant, Silphium laciniatum.

The prairie compass plant (Silphium laciniatum L.) has vertical leaves that are characteristically oriented in a north-south plane (i.e., the flat surfaces of the lamina face east and west). We explored the consequences of this orientation by determining basic photosynthetic and water use characteristics in response to environmental factors and by determining total daily photosynthesis and water use of leaves held in different orientations. Average maximum CO2 exchange rate (CER) of leaves near Ames, IA was constant at 22 micromol m-2 s-1 from May through August and then declined. CER did not exhibit a distinct lightsaturation point. CER at photon flux densities near full sunlight was constant from 22 to 35°C leaf temperature but declined at higher temperatures. However, leaf temperatures rarely exceed 35°C during the growing season. There was no change in the pattern of response of CER to temperature over the growing season. We constrained leaves to face east-west (EW,=natural), to face north-south (NS), or to be horizontal (HOR) on eight days in 1986-1988. EW leaves had the highest light interception, leaf temperatures, CER, and transpiration early and late in the day, whereas HOR leaves had the highest values in the middle of the day. Integrations of CER and transpiration over the eight daytime periods showed EW and HOR leaves to have equivalent carbon gain, higher than that of NS leaves. HOR leaves had the highest daily transpiration. Daily water use efficiency (WUE, carbon gained/water lost) was always highest in EW leaves, with the HOR leaves having 16% lower WUE and NS leaves having 33% lower WUE. The natural orientation of compass plant leaves results in equivalent or higher carbon gain and in increased WUE when compared to leaves with other possible orientations; this is likely to have a selective advantage in a prairie environment.

Apples on the Lincoln Canopy—Mechanized Management

Abstract The Lincoln canopy method of training apple trees originated at the New Zealand Agricultural Engineering Institute during a program to mechanize the production of fresh-market-grade fruit. Work began in 1970. The shallow formalized tree form that results and the easy access that it offers from below and above have simplified the imposition of mechanized processes for spraying, pruning, and harvesting. This form, and a tree density of ≈ 1000/ha, a continuous canopy width of 3 m, and the ease with which branches can be developed and positioned to produce a full canopy all contribute to high light interception and a high yield potential.

Conversaziones, 1972

CONVERSAZIONES were held this year on 4 May and 29 June. At thefirst conversazione twenty-four exhibits and a film were shown. Dr J. E. Jackson, Mr A. P. Preston and Mr J. W. Palmer of the East Mailing Research Station, Kent, arranged an exhibit on radiation reception and orchard design. Good orchard design involves maximizing light interception and hence potential yield and minimizing the proportion of the orchard canopy which is severely shaded and thus cannot produce good quality fruits but still adds to management costs. Conventional orchards attain high light interception very slowly. Mature, large hemispherical trees give excess within-tree shade which, as shown also by shading experiments, reduces fruit initiation, retention, size, dry matter content and colour. Computer model and orchard studies of light interception and distribution suggest that triangular section hedgerows or shallow horizontal cropping canopies are preferable. Control of individual tree size is critically important. Currently evolving hedgerow systems depend on dwarfing East Mailing root-stocks and possible future bed systems may be based on the new very dwarfing Mailing 27 stock.