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.     

Changes in foliage distribution with relative irradiance and tree size: Differences between the saplings ofAcer platanoides andQuercus robur

Dependencies of foliage arrangement and structure on relative irradiance and total height (TH) were studied in saplings ofAcer platanoides andQuercus robur. The distribution of relative foliar area and dry weight (leaf area and weight in a crown layer per total tree leaf area and weight, respectively) were examined with respect to relative height (RH, height in the crown per TH) and characterized by the Weibull function. The distributions of relative area and weight were nearly identical, and the differences between them were attributable to a systematic decline in leaf dry weight per area with increasing crown depth. Foliage distribution was similarly altered by tree size in both species; RH at foliage maximum was lower and relative canopy size (RCS, length of live crown per TH) greater in taller trees. However, the distribution was more uniform inA. platanoides than inQ. robur. Apart from the size effects, relative irradiance also influenced canopy structure; RCS increased inQ. platanoides and decreased inQ. robur with increasing irradiance. As crown architecture was modified by irradiance, foliage distribution was shifted upwards with decreasing irradiance inA. platanoides, but it was independent of irradiance inQ. robur. Higher foliage maximum at lower irradiance in more shade-tolerantA. platanoides is likely to contribute towards more efficient foliar display for light interception and increase the competitive ability of this species in light-limited environments. Consequently, these differences in crown architecture and foliage distribution may partly explain the superior behavior ofA. platanoides in understory.     

Leaf dynamics and insect herbivory in a Eucalyptus camaldulensis forest under moisture stress

Abstract The influence of soil moisture content on leaf dynamics and insect herbivory was examined between September 1991 and March 1992 in a river red gum (Eucalyptus camaldulensis) forest in southern central New South Wales. Long-term observations of leaves were made in trees standing either within intermittently flooded waterways or at an average of 37. 5m from the edge of the waterways. The mean soil moisture content was significantly (P≤0.05) greater in the waterways than in the non-flooded areas. Trees in the higher soil moisture regime produced significantly larger basal area increments and increased canopy leaf area. This increase in canopy leaf area was achieved, in part, through a significant increase in leaf longevity and mean leaf size. Although a greater number of leaves was initiated and abscissed per shoot from the non-flooded trees, more leaves were collected from litter traps beneath the denser canopies of the flooded trees. Consumption of foliage by insects on the trees subjected to flooding compared to the non-flooded trees was not significantly different. However, the relative impact of insect herbivory was significantly greater on the non-flooded trees. Leaf chewing was the most common form of damage by insects, particularly Chryso-melidae and Curculionidae. No species was present in outbreak during this study. Leaf survival decreased as the per cent area eaten per leaf increased. In addition, irrespective of the level of herbivory, leaf abscission tended to be higher in E. camaldulensis under moisture deficit. The influence of soil moisture content on the balance between river red gum growth and insect herbivory is discussed.     

Predicting responses of photosynthesis and root fraction to elevated [CO2]a: interactions among carbon,nitrogen, and growth*

At elevated atmospheric CO₂ concentrations ([CO₂]_a), photosynthetic capacity (A_max) and root fraction (η_R, the ratio of root to plant dry mass) increased in some studies and decreased in others. Here, we have explored possible causes of this, focusing on the relative magnitudes of the effects of elevated [CO₂]_a on specific leaf (n_m) and plant (n_p) nitrogen concentrations, leaf mass per unit area (h), and plant nitrogen productivity (α). In our survey of 39 studies with 35 species, we found that elevated [CO₂]_a led to decreased n_m and n_p in all the studies and to increased h and α in most of the studies. The magnitudes of these changes varied with species and with experimental conditions. Based on a model that integrated [CO₂]_a-induced changes in leaf nitrogen into a biochemically based model of leaf photosynthesis, we predicted that, to a first approximation, photosynthesis will be upregulated (A_max will increase) when growth at increased [CO₂]_a leads to increases in h that are larger than decreases in n_m. Photosynthesis will be downregulated (A_max will decrease) when increases in h are smaller than decreases in n_m. The model suggests that photosynthetic capacity increases at elevated [CO₂]_a only when additional leaf mesophyll more than compensates the effects of nitrogen dilution. We considered two kinds of regulatory paradigms that could lead to varying responses of η_R to elevated [CO₂]_a, and compared the predictions of each with the data. A simple static model based on the functional balance concept predicts that η_R should increase when neither n_p nor h is very responsive to elevated [CO₂]_a. The quantitative and qualitative agreement of the predictions with data from the literature, however, is poor. A model that predicts η_R from the relative sensitivities of photosynthesis and relative growth rate to elevated [CO₂]_a corresponds much more closely to the observations. In general, root fraction increases if the response of photosynthesis to [CO₂]_a is greater than that of relative growth rate.     

Nucleotide sequence and expression of a ripening and water stress-related cDNA from tomato with homology to the MIP class of membrane channel proteins

The nucleotide sequence and derived amino acid sequence were determined for a full-length version of the tomato cDNA clone, pTOM75, the mRNA for which has previously been shown to accumulate in roots, ripening fruit and senescing leaves. Computer analysis of the predicted protein product, which we have named tomato ripening-associated membrane protein (TRAMP) indicates strong homology to known transmembrane channel proteins from other organisms. Northern analysis showed that this gene was induced by waterstress and that this induction was unaffected in an ABA-deficient genetic back-ground.     

Genotypic variation in the responsiveness to GA3 within tall (rht1) and semi-dwarf (Rht1) spring wheat

The effect of GA₃ on coleoptile-and first leaf elongation of tall (rht1) and semi-dwarf (Rht1) nearly-isogenic genotypes, within each of 25 random F₉ wheat families, was determined on seedlings grown in a growth room at 18 °C. Conspicuous and very significant inter-family variation in the response of the first leaf to GA₃ application was found in both the rht1 and Rht1 genotypes. The magnitudes of the response of the different families within genotypes to GA₃ were not related to the leaf length of their untreated seedlings. It is suggested that, under given environmental conditions, background genotypic effects, inducing inter-family variation in responsiveness to GA₃, regulate the elongation growth up to the limits set by the Rht alleles.     

Leaf and twig anatomy of the Pterostemonaceae (Engl.) Small: ecological and systematic features

An anatomical investigation of the leaves and twigs of Pterostemonaceae (Engl.), a monogeneric family of two species, has been made. The following anatomical characters in the leaf are of particular interest: glandular hairs, hydathodes on the marginal dentations and secretory substances in the glands and palisade cells. Characters of interest in the twig xylem include: vessel lumina of very small tangential diameter and with simple perforation plates; fibriform vessels with scalariform plates having one to six bars and also plates with perforations in irregular patterns.     

Comparative anatomy and systematics of woody Saxifragaceae. Aphanopetalum Endl.

The floral and vegetative anatomy of the small Australian genus Aphanopetalum were studied. Wood is described for the first time and is characterized by predominantly solitary pores, scalariform vessel element perforation plates with low bar numbers, imperforate tracheary elements with distinctly bordered pits, sparse axial parenchyma, and a combination of homocellular and heterocellular rayS. Starch occurs in both axial and ray parenchyma of the wood. Stems possess unilacunar, one-trace nodes and the uncommon feature of an endodermis with well-defined Casparian stripS. Leaves have anomocytic stomata, a bifacial mesophyll and semicraspedodromous venation or a combination of semicraspedodromous and brochidodromous venation. The tetramerous flowers are apetalous or have minute petals. The compound, half-inferior gynoecium consists of essentially totally united carpels. The pattern of floral vascularization resembles different Saxifragaceae sensu lalo in that the compound sepal-plane and petal-plane traces give rise to staman bundles as well as sepal, petal, and carpel wall venation in their respective planes. The ventral ovarian bundles are fused into a single ventral complex that subdivides at the top of the ovary to form ventral bundles and to supply the one ovule in each locule. Vegetative and floral features provide compelling evidence to suggest that Aphanopetalum has its nearest relatives among the Saxifragaceae sensu lato rather than Cunoniaceae. The genus is probably best treated as forming its own subfamily (or family) among the saxifragaean alliance.     

Enhancement of extractable ethylene at light/dark transition in primary leaves of paclobutrazol-treated Phaseolus vulgaris seedlings

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol], a triazole growth retardant, increased the 1-aminocyclopropane-1-carboxylic acid (ACC) level and resulted in reduced ethylene production, estimated as ethylene release in a closed system or by vacuum-extraction, in the primary leaves of Phaseolus vulgaris L. cv. Juliska seedlings exposed to light. At the light/dark transition, a definite enhancement of the endogenous ethylene level was observed by vacuum-extraction of primary leaves of treated plants and the ethylene deficiency of retardant-treated leaves ceased. The concentration of ACC after the light/dark transition followed the pattern for ethylene, and the increase in ACC content was paralleled by a decrease in malonyl-ACC.
It is concluded that the internal level of ethylene is not necessarily lower in the primary leaves of paclobutrazol-treated bean plants, but under special environmental conditions in vivo it may reach that of the control.     

Growth analysis of UV-B-irradiated cucumber seedlings as influenced by photosynthetic photon flux source and cultivar

A growth analysis was made of ultraviolet-B (UV-B)-sensitive (Poinsett) and insensitive (Ashley) cultivars of Cucuumis satives L. grown in growth chambers at 600 μmol m⁻² s⁻¹ of photosynthetic photon flux (PPF) provided by red- and far-red-deficient metal halide (MH) or blue- and UV-A-deficient high pressure sodium/deluxe f HPS/DX) lamps. Plants were irradiated 6 h daiiy with 0.2 f-UV-B) or 18.2 C+UV-B) kJ m⁻² day⁻¹ of biologically effective UV-B for 8 or 15 days from time of seeding. In general, plants given supplemental UV-B for 15 days showed lower leaf area ratio (LARs, and higher specific leaf mass (SLM) mean relative growth rate (MRGR) and net assimilation rate (NAR) than that of control plants, but they showed no difference in leaf mass ratio (LMR), Plants grown under HPS/DX lamps vs MH lamps showed higher SLM and NAR. lower LAR and LMR. hut no difference in MRGR. LMR was the only growth parameter affected by cultivar: at 15 days, it was slightly greater in Poinsett than in Ashley. There were no interactive effects of UV-B. PPF source or cultivar on any of the growth parameters determined, indicating that the choice of either HPS/DX or MH lamps should not affect growth response to UV-B radiation. This was true even though leaves of UV-B-irradiated plants grown under HPS/DX lamps have been shown to have greater chlorosis than those grown under MH lamps.