Changes in leaf lifespan, nitrogen resorption, and mean residence time of leaf nitrogen along a soil fertility gradient in an evergreen oak tree.

The ability of plants to retain nitrogen (N) for a long period of time is critical to their N use efficiency, growth, and fitness, particularly in infertile environments. The mean residence time of leaf N (MRT) and its two determinants, leaf lifespan and N resorption efficiency (r, the fraction of the total leaf N pool that is resorbed during leaf senescence), have been hypothesized to increase plastically with decreasing soil N fertility but this remains to be fully tested. To avoid confusion by random changes in these characteristics in a relatively narrow N fertility range, MRT, leaf lifespan, and N resorption efficiency were measured in Quercus glauca over a broad N fertility range.

Effect of symbiotic N fixation on leaf protein contents, protein degradation and nitrogen resorption during leaf senescence in temperate deciduous woody species.

Nitrogen (N) resorption from senescing leaves enables plants to reuse N, making them less dependent on current N uptake from the environment, leading to higher fitness, particularly under low N supply. Species that form a symbiotic association with N-fixing bacteria have not evolved proficient N resorption, i.e.

Supra-optimal leaf area index of a temperate liana Pueraria lobata for competition with Solidago altissima at the expense of canopy photosynthesis.

Leaf area index (LAI) measured for the actual plant canopy is higher than the LAI that maximizes canopy photosynthesis (referred to as optimal LAI) because each individual can increase its light interception by unilaterally producing more leaf area. The LAI of an invasive woody vine Pueraria lobata (kudzu) is one of the highest among plant species, sometimes attaining nearly 10 m2 m-2. The high LAI casts heavy shade over neighboring plants, making their survival difficult.

Leaf productivity and persistence have been improved during soybean (Glycine max) domestication and evolution.

Artificial and natural selection improved the leaf photosynthetic rate of soybean (Glycine max (L.) Merr. subsp.

Species-specific nitrogen resorption proficiency in legumes and nonlegumes.

Nitrogen (N) resorption from senescing leaves enables plants to reuse N, thereby making them less dependent on current N uptake from the environment. Therefore, N resorption is important for survival and fitness, particularly for plants growing under low N supply. We studied N resorption from senescing leaves of 25 legumes and 25 nonlegumes in a temperate region of Japan to test the hypothesis that high N resorption has not evolved in legumes that fix atmospheric N.

Leaf shedding increases the photosynthetic rate of the canopy in N2-fixing and non-N2-fixing woody species.

It has long been hypothesized that timing of leaf shedding is critical for plant fitness but there is little experimental evidence to support the hypothesis. According to an optimality theory, shedding of old leaves increases canopy photosynthesis despite some nitrogen (N) being lost as litterfall, when the ratio of daily photosynthesis to leaf N (N-use efficiency, ε) in old leaves, expressed as a fraction of ε in new leaves, becomes lower than the fraction of leaf N that is resorbed before shedding (RN). This was shown to be true for N-poor plants but not for N-rich plants in a pot experiment; however, the use of planting pots imposes a variety of physical, chemical and biological constraints that could change the experimental results.

Crossover from localized to itinerant states in hydrocarbon Mott insulators.

Crossover from an itinerant state to an isolated electronic state in electron-doped polycyclic aromatic hydrocarbon (PAH) was studied for the two smallest zigzag-type molecules of naphthalene (NN) and anthracene (AN) by focusing on their 1 : 1 stoichiometry, A(NN) and A(AN), with alkali metals (A = K and Rb). The competition between on-site Coulombic repulsion energy (U) and bandwidth (W) was argued in terms of their magnetic and electrical properties upon lattice expansion, when A varies from K, with a smaller ionic radius, to Rb, with a larger ionic radius. The temperature-dependence of magnetic susceptibility shows a pronounced hump associated with antiferromagnetic (AFM) interactions for Rb(NN), being similar to those of K(NN) and K(AN) in the earlier report.

Inconsistent intraspecific pattern in leaf life span along nitrogen-supply gradient.

Premise Of The Study: Leaf life span (LLS) has long been hypothesized to plastically increase with decreasing nitrogen (N) supply from soil to maximize N retention, carbon assimilation, and fitness; however, accumulating evidence shows no consistent trend. The apparent inconsistencies are explained by a recent model that assumes LLS has a hump-shaped quadratic response to the N-supply gradient. The available evidence mostly originates from comparisons of LLS at only two levels of N availability, and the hypothesis remains unanswered.

A meta-analysis of leaf nitrogen distribution within plant canopies.

Background And Aims: Leaf nitrogen distribution in the plant canopy is an important determinant for canopy photosynthesis. Although the gradient of leaf nitrogen is formed along light gradients in the canopy, its quantitative variations among species and environmental responses remain unknown. Here, we conducted a global meta-analysis of leaf nitrogen distribution in plant canopies.

Changes in leaf area, nitrogen content and canopy photosynthesis in soybean exposed to an ozone concentration gradient.

Influences of ozone (O3) on light-saturated rates of photosynthesis in crop leaves have been well documented. To increase our understanding of O3 effects on individual- or stand level productivity, a mechanistic understanding of factors determining canopy photosynthesis is necessary. We used a canopy model to scale photosynthesis from leaf to canopy, and analyzed the importance of canopy structural and leaf ecophysiological characteristics in determining canopy photosynthesis in soybean stands exposed to 9 concentrations of [O3] (37-116 ppb; 9-h mean).

Leaf dynamics in growth and reproduction of Xanthium canadense as influenced by stand density.

Background And Aims: Leaf longevity is controlled by the light gradient in the canopy and also by the nitrogen (N) sink strength in the plant. Stand density may influence leaf dynamics through its effects on light gradient and on plant growth and reproduction. This study tests the hypothesis that the control by the light gradient is manifested more in the vegetative period, whereas the opposite is true when the plant becomes reproductive and develops a strong N sink.

Seasonal change in light partitioning among coexisting species of different functional groups along elevation gradient in subalpine moorlands.

Species niches are expected to differ between different functional groups and between species with different functional traits. However, it is still unclear how functional traits contribute to niche separation between species coexisting in a community and between sites along environmental gradients. We studied seasonal changes in light partitioning among coexisting species belonging to different functional groups in moorland plant communities at different altitudes.

Mean residence time of leaf number, area, mass, and nitrogen in canopy photosynthesis.

Mean residence time (MRT) of plant nitrogen (N), which is an indicator of the expected length of time N newly taken up is retained before being lost, is an important component in plant nitrogen use. Here we extend the concept MRT to cover such variables as leaf number, leaf area, leaf dry mass, and nitrogen in the canopy. MRT was calculated from leaf duration (i.

Demand and supply of N in seed production of soybean (Glycine max) at different N fertilization levels after flowering.

Nitrogen (N) has been suggested as a determinant of seed production especially in species with high seed N content. Assuming that seed yield was determined as the balance between N demand and supply for seed production, we studied the effect of N fertilization after flowering on soybean (Glycine max L. Merr.

Effects of elevated CO2 concentration on seed production in C3 annual plants.

The response of seed production to CO(2) concentration ([CO(2)]) is known to vary considerably among C(3) annual species. Here we analyse the interspecific variation in CO(2) responses of seed production per plant with particular attention to nitrogen use. Provided that seed production is limited by nitrogen availability, an increase in seed mass per plant results from increase in seed nitrogen per plant and/or from decrease in seed nitrogen concentration ([N]).

Light interception in species with different functional groups coexisting in moorland plant communities.

Competition for light is one of the most essential mechanisms affecting species composition. It has been suggested that similar light acquisition efficiency (Φ(mass), absorbed photon flux per unit aboveground mass) may contribute to species coexistence in multi-species communities. On the other hand, it is known that traits related with light acquisition vary among functional groups.

Reproductive yield of individuals competing for light in a dense stand of an annual, Xanthium canadense.

In a dense stand, individuals compete with each other for resources, especially for light. Light availability decreases with increasing depth in the canopy, thus light competition becoming stronger with time in the vegetative phase. In the reproductive phase, on the other hand, leaves start senescing, and the light environment, particularly of smaller individuals, will be improved.

Does leaf shedding increase the whole-plant carbon gain despite some nitrogen being lost with shedding?

When old leaves are shed, part of the nitrogen in the leaf is retranslocated to new leaves. This retranslocation will increase the whole-plant carbon gain when daily C gain : leaf N ratio (daily photosynthetic N-use efficiency, NUE) in the old leaf, expressed as a fraction of NUE in the new leaf, becomes lower than the fraction of leaf N that is resorbed before shedding (R(N)). We examined whether plants shed their leaves to increase the whole-plant C gain in accord with this criterion in a dense stand of an annual herb, Xanthium canadense, grown under high (HN) and low (LN) nitrogen availability.

Leaf lifespan and lifetime carbon balance of individual leaves in a stand of an annual herb, Xanthium canadense.

Leaf lifespan in response to resource availability has been documented in many studies, but it still remains uncertain what determines the timing of leaf shedding. Here, we evaluate the lifetime carbon (C) balance of a leaf in a canopy as influenced by nitrogen (N) availability. Stands of Xanthium canadense were established with high-nitrogen (HN) and low-nitrogen (LN) treatments and temporal changes of C gain of individual leaves were investigated with a canopy photosynthesis model.

Dynamics of leaf area and nitrogen in the canopy of an annual herb, Xanthium canadense.

We studied leaf area and nitrogen dynamics in the canopy of stands of an annual herb Xanthium canadense, grown at a high (HN)- and a low-nitorgen (LN) availability. Standing leaf area increased continuously through the vegetative growth period in the LN stand, or leveled off in the later stage in the HN stand. When scaled against standing leaf area, both production and loss rates of leaf area increased but with different patterns: the production rate was retarded, while the loss rate was accelerated, implying an upper limit of standing leaf area of the canopy.