Leaf Tissue Density Research Articles

The Importance of Tissue Density for Growth and Life Span of Leaves and Roots: A Comparison of Five Ecologically Contrasting Grasses

Under nutrient-poor conditions initially fast-growing species will in the long term be competitively inferior to slow-growing species. Here, we ask whether this phenomenon can be explained by constraints caused by tissue density. The hypothesis is that low tissue density is necessary for fast growth but has as a consequence short organ life span. This leads to a rapid loss of nutrients that cannot be sustained under nutrient-poor conditions. Biomass accumulation, turnover rate of leaves and roots, and tissue density were studied for five ecologically contrasting grass species. Plants were grown in a garden experiment over two growing seasons on sand with a low nutrient supply level. Species that were characteristic of nutrient-rich sites had a low leaf and root tissue density and were larger after one growing season than species of nutrient-poor sites. However, after two growing seasons the species of nutrient-poor sites were larger. These species had a high tissue density. Life span of both leaves and roots was also correlated with tissue density. Species with low tissue density had a faster turnover of leaves and roots. It is concluded that tissue structure is an inherent constraint that prevents simultaneous maximization of both nutrient acquisition and nutrient conservation. The short life span of fast-growing organs explains the long-term disadvantage of a high growth rate for plants in low nutrient conditions.

Different susceptibility of runner bean plants to excess copper as a function of the growth stages of primary leaves

Summary Runner bean plants (Phaseolus coccineus L., cv. Piekny Jaś) grown hydroponically in Knop solution were treated with excess Cu (20mgL−1 in the form of CuSO4 · 5H2O) at three different growth stages of primary leaves, and after 3–12 days of Cu action, respectively, their growth parameters and plastid pigment content were investigated. Moreover, photosynthetic O2 evolution of chloroplasts isolated from plants treated with excess Cu at the different growth stages 10 days after the treatment was compared. The plants treated with Cu at the intensive leaf growth stage were characterized by fast and strong growth (measured as leaf area), a fresh weight decrease and a simultaneously increased chlorophyll content in comparison with the control, indicating some inhibition of elongation processes. Relatively smaller changes in growth parameters that were correlated with some modifications of the specific leaf area (calculated per fresh weight), leaf density and pigment composition were observed in the plants treated with Cu at an intermediate growth stage. However, at a longer exposure to Cu there occurred a tendency of Chl a/b and Chl/Car ratios to decrease. These changes, depending on the time of Cu action, were much more distinct in the plants treated with Cu at the stationary growth stage of primary leaves. A simultaneous decrease in leaf tissue density and enhanced specific leaf area, which contributes to an enlarged area for water loss, correlated with chlorophyll content reduction, indicated that a leaf senescence increase was presumably a consequence of water deficiency. In the plants treated with Cu at this stage of leaf growth, photosynthetic O2 evolution decreased significantly.

Light Acclimation in Citrus Leaves. I. Changes in Physical Characteristics, Chlorophyll, and Nitrogen Content

Abstract ‘Duncan’ grapefruit (C. paradisi Macf.) and ‘Pineapple’ sweet orange (Citrus sinensis L.) seedlings were grown in full sunlight, 50% and 90% shade; maximum photosynthetic photon flux densities (PPFD) of 2300, 1100 and 200 μmol s−1m−2, respectively. In fully expanded matured (hardened) leaves, leaf thickness, specific leaf weight (SLW), tissue density, and nitrogen content were highest in full sun leaves and lowest in 90% shade leaves. Leaf chlorophyll content was highest in 90% shade leaves. Half of the seedlings which were grown in full sunlight were transferred into 50% shade to simulate normal canopy development; half of the seedlings from 50% and 90% shade were moved into full sunlight to simulate changes that occur after hedging. Specific leaf weight and tissue density changed in the same direction as PPFD. Leaf nitrogen content decreased temporarily when leaves were exposed to new PPFD conditions regardless of the PPFD levels. Total leaf chlorophyll content initially decreased when seedlings were transferred into full sunlight but began to increase after 4–6 weeks. Chlorophyll content increased in seedlings transferred from full sun to 50% shade. Percentage of air space within leaf tissues did not change during acclimation to new PPFD levels. Changes in leaf anatomy, physical characteristics, and chemical components are mechanisms that enable citrus leaves to acclimate to a wide range of changing light environments, even after leaves are fully mature.