Nutrient content in Quercus ilex canopies: Seasonal and spatial variation within a catchment

Spatial and temporal changes in canopy nutrient content were studied in 1988 and 1989 in a Mediterranean Quercus ilex ssp. ilex L. forest in north-eastern Spain. Sampling was conducted in parallel at two sites which represent endpoints along a slope gradient within a small catchment (ridge top at 975 m and valley bottom at 700 m). Deeper soils resulted in significantly higher N and P concentrations, and N content on a leaf area basis at the valley bottom site. In contrast, K concentration in leaves was significantly higher at the ridge top site, where soil K concentration was also higher. At both sites, N and P content on a leaf area basis was highest at the top of the canopy, where leaf area is highest. N resorption efficiency decreased from top to bottom of the canopy. Results suggested a minor role of shaded leaves as nutrient storage sites. Lower P resorption efficiency was found at the ridge top site. Seasonal changes of P and N concentration on a leaf area basis suggest P replenishment, and to a lesser degree N, during periods of lower growth activity due to low temperatures, but coinciding with higher water availability (autumn-early spring period). Thus, N and P resorption from the remaining foliage in the canopy took place, and to a larger degree at the valley bottom site, coinciding with a slightly higher leaf area index and productivity at this site.     

Forest growth along a rainfall gradient in Hawaii: Acacia koa stand structure,productivity, foliar nutrients,and water- and nutrient-use efficiencies

We tested whether variation in growth of native koa (Acacia koa) forest along a rainfall gradient was attributable to differences in leaf area index (LAI) or to differences in physiological performance per unit of leaf area. Koa stands were studied on western Kauai prior to Hurricane Iniki, and ranged from 500 to 1130 m elevation and from 850 to 1800 mm annual precipitation. Koa stands along the gradient had basal area ranging from 8 to 42 m²/ha, LAI ranging from 1.4 to 5.4, and wood increment ranging from 0.7 to 7.1 tonnes/ha/year. N, P, and K contents by weight of sun leaves (phyllodes) were negatively correlated with specific leaf mass (SLM, g m^-2) across sites; on a leaf area basis, N increased whereas P and K decreased with SLM. LAI, aboveground woody biomass increment, and production per unit leaf area (E) increased as phyllode ¹³C became more negative. The ¹³C data suggested that intrinsic water-use efficiency (ratio of assimilation to conductance) increased as water availability decreased. In five of the six sites, phyllode P contents increased as LAI increased, but biomass increment and E were not correlated with phyllode nutrient contents, suggesting that productivity was limited more by water than by nutrient availability. Because vapor pressure deficits increased with decreasing elevation, actual water-use efficiency (ratio of assimilation to transpiration) was lower at drier, low-elevation sites. There was a trade-off between intrinsic water-use efficiency and production per unit of canopy N or P across the gradient. In summary, koa responds to water limitation both by reducing stand LAI and by adjusting gas exchange, which results in increased intrinsic water-use efficiency but decreased E.     

Impact of nitrogen allocation on growth and photosynthesis of Miscanthus (Miscanthus × giganteus)

Nitrogen (N) addition typically increases overall plant growth, but the nature of this response depends upon patterns of plant nitrogen allocation that vary throughout the growing season and depend upon canopy position. In this study seasonal variations in leaf traits were investigated across a canopy profile in Miscanthus (Miscanthus × giganteus) under two N treatments (0 and 224 kg ha^?1) to determine whether the growth response of Miscanthus to N fertilization was related to the response of photosynthetic capacity and nitrogen allocation. Miscanthus yielded 24.1 Mg ha^?1 in fertilized plots, a 40% increase compared to control plots. Photosynthetic properties, such as net photosynthesis (A), maximum rate of rubisco carboxylation (V_cmax), stomatal conductance (g_s) and PSII efficiency (F_v'/F_m'), all decreased significantly from the top of the canopy to the bottom, but were not affected by N fertilization. N fertilization increased specific leaf area (SLA) and leaf area index (LAI). Leaf N concentration in different canopy layers was increased by N fertilization and the distribution of N concentration within canopy followed irradiance gradients. These results show that the positive effect of N fertilization on the yield of Miscanthus was unrelated to changes in photosynthetic rates but was achieved mainly by increased canopy leaf area. Vertical measurements through the canopy demonstrated that Miscanthus adapted to the light environment by adjusting leaf morphological and biochemical properties independent of nitrogen treatments. GPP estimated using big leaf and multilayer models varied considerably, suggesting a multilayer model in which V_cmax changes both through time and canopy layer could be adopted into agricultural models to more accurately predict biomass production in biomass crop ecosystems.     

Canopy structure in savannas along a moisture gradient on Kalahari sands

Measurements of tree canopy architecture were made at six savanna sites on deep, sandy soils, along a gradient of increasing aridity. There was substantial variation in the leaf area estimated within each site, using the same sample frame, but different measurement techniques. The trends in canopy properties in relation to the aridity gradient were consistent, regardless of the technique used for estimating the properties. The effective plant area index for the tree canopy (the sum of the stem area index and the leaf area index (LAI)) declined from around 2 to around 0.8 m² m^?2 over a gradient of mean annual rainfall from 1000 to 350 mm. Stems contributed 2–5% of the tree canopy plant area index. Since the tree canopy cover decreased from 50% to 20% over this aridity range, the leaf area index within the area covered by tree canopies remained fairly constant at 3–4 m² m^?2. Tree leaves tended from a horizontal orientation to a more random orientation as the aridity increased. On the same gradient, the leaf minor axis dimension decreased from around 30 mm to around 3 mm, and the mean specific leaf area decreased from 14 to 5 m² kgha^?1. There was good agreement between LAI observed in the field using a line ceptometer and the LAI inferred by the MODIS sensor on the Terra satellite platform, 2 months later in the same season.     

Leaf litterfall,leaf area index,and radiation transmittance in cypress wetlands and slash pine plantations in north-central Florida

The seasonal dynamics of leaf litterfall and leaf area index (LAI, all-sided basis), light penetration and the vertical distribution of surface area index, and the feasibility of estimating LAI from radiation transmittance were studied from April 1993 to March 1994 in the canopies of three cypress (Taxodium ascendens) wetlands and their surrounding slash pine (Pinus elliottii) uplands in Florida flatwoods. Annual leaf litterfall ranged from 324 to 359 g m^–2 in the wetlands, which was very close to the average for 11 sites throughout Florida of 340±26 g m^–2. The seasonal pattern of the normalized LAI obtained for the dominant tree species in the ecosystems could be used to construct the seasonal dynamics of LAI at the ecosystem scale. The vertical distribution of surface area index in the wetlands was significantly different from that in the surrounding pine uplands. The maximum LAI of cypress wetlands in this area was about 8 m² m^–2, which was higher than the maximum of slash pine plantations of 6 m² m^–2. Cypress leaves were strongly erectophile in space. Results showed that the LAI-2000 canopy analyzer could generally be used to estimate forest LAI, whether the forest canopy was closed or not, if an overall clumping index of 2.00 was applied. However, as LAI decreased, the relative error contained in the radiation-based LAI estimates increased. This indicated that foliage clumping at the stand scale was more important than that at the tree or branch scale.     

Preliminary results of a fertilization-irrigation experiment in a Quercus ilex L. forest in relation to leaves and twigs characteristics

A multifactorial ANOVA experiment was designed for a Quercus ilex forest in the Prades mountains in Tarragona (NE Spain). The purpose of this study was to clarify the relative importance of water, nitrogen and phosphorus as factors controlling primary production.Eight plots comprising all possible combinations of the three factors (including a control) were laid out in three replicate blocks. Fertilizers were applied to the appropriate treatments in March 1989 with a dosage of 125 kg of P/ha and 250 kg N/ha. Irrigation was applied with a rate of 20 mm per week during the warm season.To evaluate the effects on canopy structure we measured specific leaf weight (mg/cm²), average leaf weight (mg), average twig height and average twig length. These variables were selected as they are the most likely to manifest changes over short time periods following changes in environmental conditions.The values of these parameters before initial treatments (autumn 1988) and after treatments (summer 1990) were analyzed. The results obtained show that water and nitrogen have a greater effect than phosphorus on tree canopy structure, at least during initial development.     

Airborne LiDAR technique for estimating biomass components of maize: A case study in Zhangye City,Northwest China

Crop biomass is an important ecological indicator of growth, light use efficiency, and carbon stocks in agro-ecosystems. Light detection and ranging (LiDAR) or laser scanning has been widely used to estimate forest structural parameters and biomass. However, LiDAR is rarely used to estimate crop parameters because the short, dense canopies of crops limit the accuracy of the results. The objective of this study is to explore the potential of airborne LiDAR data in estimating biomass components of maize, namely aboveground biomass (AGB) and belowground biomass (BGB). Five biomass-related factors were measured during the entire growing season of maize. The field-measured canopy height and leaf area index (LAI) were identified as the factors that most directly affect biomass components through Pearson's correlation analysis and structural equation modeling (SEM). Field-based estimation models were proposed to estimate maize biomass components during the tasseling stage. Subsequently, the maize height and LAI over the entire study area were derived from LiDAR data and were used as input for the estimation models to map the spatial pattern of the biomass components. The results showed that the LiDAR-estimated biomass was comparable to the field-measured biomass, with root mean squared errors (RMSE) of 288.51 g/m² (AGB), and 75.81 g/m² (BGB). In conclusion, airborne LiDAR has great potential for estimating canopy height, LAI, and biomass components of maize during the peak growing season.     

Drought effects on canopy properties and productivity in thinned and unthinned Turkey oak stands

ABSTRACT

Drought responses, leaf area index (LAI), leaf characteristics and light extinction coefficient (k) were analysed in thinned and unthinned Turkey oak (Quercus cerris L.) stands at two sites: Valsavignone, in the Apennines, with a mild climate, and Caselli, near the Tyrrhenian coast, with a longer and more accentuated dry period in the summer. Turkey oak showed a good adaptability to drought due to a series of modifications in leaf characteristics, canopy properties and biomass allocation such as leaf area reduction, increased leaf thickness, smaller number of leaves and, at stand level, lower LAI, leaf biomass and LWR values and higher light extinction coefficients. In spite of the better environmental conditions and the higher LAI values, productivity was lower in the wet site. The differences in Turkey oak canopy properties, light extinction coefficients, LAI and their relations with drought and productivity are discussed.     

南方红壤侵蚀区芒萁叶片对微地形的响应

植物功能性状可以反映植物应对环境变化的响应策略。该文以芒萁为研究对象,主要采用单因素方差分析和冗余分析,比较了3种微地形(沟脊、沟壁、沟底)中环境因子和芒萁叶片功能性状的差异,分析了芒萁对浅沟微地形的响应及其适应策略。结果表明:(1)芒萁叶片功能性状的总体变异程度在0.05～0.47之间,叶厚和叶面积均表现为沟底>沟壁>沟脊(P<0.05),沟壁的叶氮含量显著高于沟脊和沟底,沟脊的叶磷含量显著低于沟壁和沟底,比叶面积和叶碳含量在3种微地形间均无显著差异。(2)沟脊的芒萁通过减小叶面积来降低水分散失进行自我保护,沟壁的芒萁通过增加叶氮含量来提高叶片光合速率而促进生长,沟底的芒萁通过增大叶面积来提高光捕获能力而促进生长。综上结果认为,土壤养分和温湿条件的差异,促使芒萁通过调节营养物质含量和改变叶片形态以更好地适应环境。     

Variation of specific leaf area and upscaling to leaf area index in mature Scots pine

Reliable and objective estimations of specific leaf area (SLA) and leaf area index (LAI) are essential for accurate estimates of the canopy carbon gain of trees. The variation in SLA with needle age and position in the crown was investigated for a 73-year-old Scots pine (Pinus sylvestris L.) stand in the Belgian Campine region. Allometric equations describing the projected needle area of the entire crown were developed, and used to estimate stand needle area. SLA (cm² g⁻¹) as significantly influenced by the position in the crown and by needle age (current-year versus 1-year-old needles). SLA increased significantly from the top to the bottom of the crown, and was significantly higher near the interior of the crown as compared to the crown edge. SLA of current-year needles was significantly higher than that of 1-year-old needles. Allometric relationships of projected needle area with different tree characteristics showed that stem diameter at breast height (DBH), tree height and crown depth were reliable predictors of projected needle area at the tree level. The allometric relationships between DBH and projected needle area at the tree level were used to predict stand-level needle area and estimate LAI. The LAI was 1.06 (m² m⁻²) for current-year needles and 0.47 for 1-year-old needles, yielding a total stand LAI of 1.53.     

Root growth and nitrogen uptake in sycamore (Acer pseudoplantanus L.) seedlings in relation to nitrogen supply

Acer pseudoplatanus L. trees were grown in sand culture for 2 years and, in 1988, supplied with either 1.0 mol N m^-3 (low N) or 6.0 mol N m^-3 (high N) to precondition their growth. In 1989, the same trees received either high or low nitrogen, producing four treatments; High N in 1988/High N in 1989; High N in 1988/Low N in 1989; Low N in 1988/Low N in 1989; and Low N in 1988/High N in 1989. Plant growth was affected by N supply in both years. In 1989 the Low N/High N treated trees had the same overall mass, leaf mass and stem girth as the High N/High N treatment. Early spring growth of foliage and roots was conditional on nitrogen supplied in the previous season. Later, the rapid increases in leaf, stem and root growth under high N was through root uptake. Internal partitioning of growth was affected, with the Low N/High N treatment producing more new leaves on axillary shoots, and more new white roots on existing structures, than the Low N/Low N treatment. Despite effects of the N preconditioning on the structure of both canopy and root system, nitrogen uptake was solely dependent on the current nitrogen supply.     

Dynamics of leaf minerals,bdleaf area,and biomass from hardwoods intensively grown on a peat bog

Summary Water willow and grey alder were grown on a raised sphagnum bog in central Sweden. The stands were intensively treated by daily irrigation and fertilization during the growing period in order to improve site fertility. After a 2-year establishment period high production rates were achieved in willow stands, 0.8 kg stem dry weight m^–2 year^–1 on current plus one (C+1) year old shoots. In these stands the canopy was closed with a leaf area index (LAI) that peaked at approximately 7. The canopy in the alder stand did not close during the initial 3 years of growth and the measured production rate was relatively low, at approximately 0.4 kg dry weight m^–2 year ^–1 in the last year. The leaf nitrogen content was 3%–4% of dry weight during the summer and the other studied mineral elements were in almost optimal proportion to nitrogen. This was considered to be an effect of the intensive fertilization regime. Above-ground production close to maximum yield was attained in the prevailing conditions of soil, climate and biomass partitioning.     

Rates of apparent photosynthesis,respiration and dry matter accumulation in maize canopies

The rates of canopy apparent photosynthesis (P_C) and canopy respiration (R_c) were studied during vegetation season in two erectophile and two planophile hybrids of maize (Zea mays L.) grown at two canopy densities [7.5 plants m^-2 (HD) and 4.5 plants m^-2 (LD)]. Large differences in P_C, R_c, R_C/P_C, leaf area index (LAI), dry matter accumulation and grain yield were found among hybrids and plant densities. Variations in P_C and R_C were associated mainly with changes in LAI. There was also found change in P_C per unit LAI with time. The average R_C/P_C was 28.9 % for all treatments throughout the vegetation season. P_C and R_C per unit dry matter were higher in LD than in HD and decreased throughout the measurement period. The HD stand had higher P_C and yield in hybrids with erectophile foliage, whereas LD stand had higher P_C after male tetrad and got higher yield in hybrids with planophile foliage. Only R_C in hybrids of the two foliage types was higher under HD than under LD throughout the vegetation period.     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

Do the energy fluxes and surface conductance of boreal coniferous forests in Europe scale with leaf area?

Earth observing systems are now routinely used to infer leaf area index (LAI) given its significance in spatial aggregation of land surface fluxes. Whether LAI is an appropriate scaling parameter for daytime growing season energy budget, surface conductance (G_s), water‐ and light‐use efficiency and surface–atmosphere coupling of European boreal coniferous forests was explored using eddy‐covariance (EC) energy and CO₂ fluxes. The observed scaling relations were then explained using a biophysical multilayer soil–vegetation–atmosphere transfer model as well as by a bulk G_s representation. The LAI variations significantly alter radiation regime, within‐canopy microclimate, sink/source distributions of CO₂, H₂O and heat, and forest floor fluxes. The contribution of forest floor to ecosystem‐scale energy exchange is shown to decrease asymptotically with increased LAI, as expected. Compared with other energy budget components, dry‐canopy evapotranspiration (ET) was reasonably ‘conservative’ over the studied LAI range 0.5–7.0 m² m^?2. Both ET and G_s experienced a minimum in the LAI range 1–2 m² m^?2 caused by opposing nonproportional response of stomatally controlled transpiration and ‘free’ forest floor evaporation to changes in canopy density. The young forests had strongest coupling with the atmosphere while stomatal control of energy partitioning was strongest in relatively sparse (LAI ~2 m² m^?2) pine stands growing on mineral soils. The data analysis and model results suggest that LAI may be an effective scaling parameter for net radiation and its partitioning but only in sparse stands (LAI <3 m² m^?2). This finding emphasizes the significance of stand‐replacing disturbances on the controls of surface energy exchange. In denser forests, any LAI dependency varies with physiological traits such as light‐saturated water‐use efficiency. The results suggest that incorporating species traits and site conditions are necessary when LAI is used in upscaling energy exchanges of boreal coniferous forests.     

Seasonal dynamics of <Emphasis Type="Italic">Zostera noltii</Emphasis> Hornem. in two Mediterranean lagoons

The density, biomass and shoot morphology of two populations of Zostera noltii were monitored from January 1998 to July 1999 at two shallow Mediterranean lagoons of Biguglia and Urbino, which differ in hydro-morphological conditions and nutrient loading. Monitoring included the principal biological and foliar parameters (shoot density, aboveground and belowground biomass, length, width and number of leaves, LAI and coefficient A: percentage of leaves having lost their apex), the organic matter contents of the sediment and the environmental conditions (salinity, turbidity, temperature, nutrient concentrations and dissolved oxygen levels). The two populations of Z. noltii displayed seasonal changes in density (1600–19600 m²), aboveground biomass (11–153 g. DW. m⁻²), leaf length (33–255 mm), and leaf width (0.9–1.8 mm). Temperature and turbidity were significant environmental factors influencing the temporal changes observed in the Z. noltii meadows studied. Conversely, the belowground biomass, the number of leaves per shoot and the LAI did not undergo any seasonal changes. In the Biguglia lagoon, the functioning dynamics of the Z. noltii seagrass beds are determined by the catchment area and the inputs of nutrients derived from it, whereas in the Urbino lagoon the dynamics of the Z. noltiibeds depend on low levels of water turbidity.     

Seasonal changes in canopy photosynthesis and foliage respiration in a Rhizophora stylosa stand at the northern limit of its natural distribution

Gross photosynthesis and respiration rates of leaves at different canopy heights in a Rhizophora stylosa Griff. stand were measured monthly over 1 year at Manko Wetland, Okinawa Island, Japan, which is the northern limit of its distribution. The light-saturated net photosynthesis rate for the leaves at the top of the canopy showed a maximum value of 17 μmol CO₂ m⁻² s⁻¹ in warm season and a minimum value of 6 μmol CO₂ m⁻² s⁻¹ in cold season. The light-saturated gross photosynthesis and dark respiration rates of the leaves existing at the top of the canopy were 2−7 times and 3–16 times, respectively, those of leaves at the bottom of the canopy throughout the year. The light compensation point of leaves showed maximum and minimum peaks in warm season and cold season, respectively. The annual canopy gross photosynthesis, foliage respiration, and surplus production were estimated as 117, 49, and 68 t CO₂ ha⁻¹ year⁻¹, respectively. The energy efficiency of the annual canopy gross photosynthesis was 2.5%. The gross primary production GPP fell near the regression curve of GPP on the product of leaf area index and warmth index, the regression curve which was established for forests in the Western Pacific with humid climates.     

Above-ground biomass structure of a Chusquea tessellata bamboo páramo,Chingaza National Park,Cordillera Oriental,Colombia

The present study was carried out in the bamboo (Chusquea tessellata) páramo of Parque Natural Nacional de Chingaza, Eastern Cordillera, Colombia from December 1987 to April 1988. Above-ground biomass structure of bamboo páramo was quantified in 16 plots. These data are compared with previous results on above-ground biomass structure of bunch-grass (Calamagrostis spp.) páramos.The total (non-living and living) above-ground biomass of a Chusquea tessellata bamboo páramo was low (2,625 g DW · m^–2) compared to bunch-grass páramo. Nevertheless, higher values of standing living biomass and litter are found in the bamboo páramo due to the leaf shed of the bamboo. The thick litter layer may inhibit germination and growth of nearby plants.Maximum biomass is found near the ground surface. Cumulative LAI (In transformed) and height in the bamboo vegetation are related parabolically for Chusquea tessellata and linearly for bunch-grass due to differences in leaf distribution. The mean bifacial LAI of living Chusquea tessellata leaves is 2.2 m² · m^–2, whereas it is 2.5 m² · m^-2 for all Poaceae.     

Nutrient content and seasonal fluctuations in the leaf component of coark-oak (Quercus suber L.) litterfall

Nutrient content and seasonality of the leaf component in cork-oak litterfal were studied over a two year period in two cork-oak forest sites differing in biomass and edaphic condition in the north-eastern Iberian peninsula. Fallen senescent leaves compared to young leaves showed higher non-mobile nutrient concentrations and lower mobile nutrient concentrations, specially P, N, K, and Mg. At both sites, seasonal fluctuations affected both leaf production and leaf mineral content. The maximum leaf fall period correspond to the start of the vegetative growth and to the lowest N and P concentration in the falling leaves. The opposite was true for the winter, when litterfal was minimal and N and P content in falling leaves was at a maximum.The comparison between falling leaves and canopy leaves suggests that the analysis of fallen leaves can be a useful measure of N and P nutrition in cork-oak. We found site dependent differences in nutrient content and nutrient remobilization. In comparison with Q. ilex, although litter production was in the same range, nutrient retranslocation was greater for Q. suber.     

Topographical pattern of the forest vegetation on a river basin in a warm-temperate hilly region,central Japan

The relationship between tree distribution and topography was examined in a small river basin (3.4 ha) comprising a complex mosaic of topographical units at 10² to 10³ m² order, each of which had a shallow valley bordered by small ridges or breaks of slopes. Twenty-five major woody species were divided into two groups (groups A and B) based on a cluster analysis using the distribution data in the basin. Group A, which mainly consisted of early-successional species, was distributed around the valley sites of the topographical units, while group B, which mainly consisted of late-successional species, was distributed around the ridge sites of the topographical units. This vegetation pattern coincided with erosional condition in the basin. That is, the valley sites were eroded more actively than the ridge sites, as soil depth tended to be thin in the valley sites and thick in the ridge sites, and because large (canopy) trees were restricted in the ridge sites. There was no tendency that group B was replacing group A, and hence it was suggested that repeated disturbance by slope failures or small-scale shallow landslides have prevented compositional change from the early-successional (group A) to the late-successional (group B) species by preventing the invasion of the latter into valley sites.