Mass-based Nitrogen Content Research Articles

Estimating leaf nitrogen content by coupling a nitrogen allocation model with canopy reflectance

The area-based leaf nitrogen content (LNCA) has gained increasing attention recently in ecology and plant physiology, and the mass-based nitrogen content (LNCM) has been extensively used by agronomists for making fertilization recommendations. Remote sensing has been emerging as an important tool to quantify LNCA and LNCM across multiple observation scales, such as leaf and canopy. Most models for estimating LNCA and LNCM are based on their empirical relationships with chlorophyll-related vegetation indices (VIs), which cannot capture the dynamic allocation of nitrogen into different components throughout the growing season. This study proposed a simplified nitrogen allocation model by dividing the total nitrogen into photosynthetic nitrogen (PN) and non-photosynthetic nitrogen with the purpose of estimating LNCA and LNCM in rice and winter wheat. The nitrogen allocation model was calibrated with an independent leaf-scale dataset (R2 = 0.82) and then applied to the canopy scale without the need to adjust the model coefficients. The estimated fractions of PN were 71% and 78% for rice and wheat leaves, respectively, which were close to the reported value (∼75%) for common C3 plants. Overall, the nitrogen allocation-based models were applicable for estimating both LNCA and LNCM with relative root mean square error (RRMSE) values <15% for the jointing and booting stages. In addition, our novel estimation model was generic for rice and wheat, yielding the best estimations for LNCM (R2 = 0.63) across the entire growing season compared with traditional empirical models based on VIs. This study represents a first attempt to couple nitrogen allocation theory with remote sensing data to improve the spectroscopic estimation of LNCA and LNCM.

Functional relationships between leaf structure and photosynthetic traits as modulated by irradiance and nutrient availability in a sclerophyllous and a non-sclerophyllous mediterranean oak species

Plasticity of structural and physiological leaf traits elicited by irradiance and soil nutrients was investigated in two sympatric mediterranean oaks: a sclerophyllous (Quercus suber L.) and a non-sclerophyllous species (Q. canariensis Willd.). Seedlings were grown for 2 years in pots in a 2-way crossed factors design. Leaf mass-to-area ratio (LMA) and nitrogen were recorded, and photosynthetic capacity (i.e. the apparent maximal carboxylation rate by rubisco, V cmax) was derived from response curves of net CO2 assimilation (A) versus intercellular CO2 mol fraction (C i). Structural equation modelling was applied to the data for disentangling the complex correlation structure between variables. The two species differed significantly in photosynthetic nitrogen use efficiency (PNUE). They displayed the expected responses to irradiance, with large increases in LMA, V cmax and nitrogen per unit leaf area and decreases in mass-based nitrogen content. Nutrient availability modulated severely leaf N content (mass- and area-based) and mass-based maximal carboxylation rate, but not the plastic response of all these parameters to irradiance. Irradiance primarily modulated leaf structure (LMA), and secondarily nitrogen content, while nutrient availability modulated directly nitrogen content. Nitrogen content in turn had a severe impact on mass-based photosynthetic capacity. It is concluded that in young trees solely leaf structure displayed irradiance-elicited plasticity. This plasticity was not modulated by nutrient availability and was similar in a sclerophyllous and a non-sclerophyllous species.

Ontogenetic changes in water-use efficiency ( δ13C) and leaf traits differ among tree species growing in a semiarid region of the Loess Plateau, China

On the Loess Plateau, China, several planted tree species such as Populus hopeinsis and Robinia pseudoacacia suffer occasional diebacks in the top shoots, reducing growth rates after maturation. However, this does not usually occur in other species, e.g., Ulmus pumila and Zizyphus jujuba. We compared stable carbon isotope ratios ( δ 13C) as indicators of leaf water-use efficiency (WUE), leaf mass per unit area (LMA), and leaf area- and mass-based nitrogen content (N area and N mass) by tree height (1, 5, and 10 m) in P. hopeinsis, R. pseudoacacia, U. pumila, and Z. jujuba. In P. hopeinsis and R. pseudoacacia, leaf δ 13C and N area were significantly lower in 10-m trees than in 1-m saplings, indicating that leaf WUE and photosynthetic rates of both species decreased with tree height. In contrast, δ 13C in Z. jujuba varied little with tree height. The δ 13C of 10-m-tall U. pumila trees was significantly higher than that of 1-m plants, demonstrating an increase in WUE with tree height. Decreasing WUE, leaf N area, and N mass with height increases in P. hopeinsis and R. pseudoacacia may be related to water and nutrient limitations for these species in semiarid regions. In contrast, stable or increasing δ 13C with tree height in U. pumila and Z. jujuba may account (to some extent) for successful production of these species under identical environmental conditions. Diameter growth rate also decreased with maturity in P. hopeinsis and R. pseudoacacia, but increased or was stable for U. pumila and Z. jujuba. The differences in leaf WUE and LMA among species with tree maturity may be related to species’ growth patterns and susceptibility to drought stress, and are likely to be important new criteria for plantation species selection on the Loess Plateau.

Effect of soil moisture on leaf ecophysiology of Parasenecio yatabei, a summer-green herb in a cool–temperate forest understory in Japan

Leaf physiological and gas-exchange traits of a summer-green herbaceous perennial, Parasenecio yatabei, growing along a stream were examined in relation to leaf age. In its vegetative phase, the aerial part of this plant consists of only one leaf and provides an ideal system for the study of leaf longevity. Volumetric soil water content (SWC) decreased with increasing distance from the stream, whereas relative light intensity was nearly constant. The light-saturated net CO2 assimilation rate (Asat) and leaf stomatal conductance (gs) were approximately 1.5-fold and 1.4-fold higher, respectively, in the lower slope near the mountain stream than in the upper slope far from the mountain stream. The lifespan of aerial parts of vegetative plants significantly increased with decreasing SWC. The leaf mass-based nitrogen content of the leaves (N mass) was almost constant (ca. 2.2%); however, the maximum carboxylation rate by ribulose-1,5-biphosphate carboxylase/oxygenase (rubisco) (V cmax) and photosynthetic nitrogen use efficiency (PNUE, A sat/N area) decreased more slowly in the upper slope than in the lower slope. The higher leaf photosynthetic activity of P. yatabei plants growing lower on the slope leads to a decrease in V (cmax) and PNUE in the early growing season, and to a shorter leaf lifespan.

Plasticity in mesophyll volume fraction modulates light-acclimation in needle photosynthesis in two pines

Acclimation potential of needle photosynthetic capacity varies greatly among pine species, but the underlying chemical, anatomical and morphological controls are not entirely understood. We investigated the light-dependent variation in needle characteristics in individuals of Pinus patula Schlect. & Cham., which has 19-31-cm long pendulous needles, and individuals of P. radiata D. Don., which has shorter (8-17-cm-long) stiffer needles. Needle nitrogen and carbon contents, mesophyll and structural tissue volume fractions, needle dry mass per unit total area (M(A)) and its components, volume to total area ratio (V/A(T)) and needle density (D = M(A)/(V/A(T))), and maximum carboxylase activity of Rubisco (V(cmax)) and capacity of photosynthetic electron transport (J(max)) were investigated in relation to seasonal mean integrated irradiance (Q(int)). Increases in Q(int) from canopy bottom to top resulted in proportional increases in both needle thickness and width such that needle total to projected surface area ratio, characterizing the efficiency of light interception, was independent of Q(int). Increased light availability also led to larger M(A) and nitrogen content per unit area (N(A)). Light-dependent modifications in M(A) resulted from increases in both V/A(T) and D, whereas N(A) changed because of increases in both M(A) and mass-based nitrogen content (N(M)) (N(A) = N(M)M(A)). Overall, the volume fraction of mesophyll cells increased with increasing irradiance and V/A(T) as the fraction of hypodermis and epidermis decreased with increasing needle thickness. Increases in M(A) and N(A) resulted in enhanced J(max) and V(cmax) per unit area in both species, but mass-based photosynthetic capacity increased only in P. patula. In addition, J(max) and V(cmax) showed greater plasticity in response to light in P. patula. Species differences in mesophyll volume fraction explained most of the variation in mass-based needle photosynthetic capacity between species, demonstrating that differences in plastic adjustments in mass-based photosynthetic activities among these representative individuals were mainly associated with contrasting investments in mesophyll cells. Greater area-based photosynthetic plasticity in P. patula relative to P. radiata was associated with larger increases in M(A) and mesophyll volume fraction with increasing irradiance. These data collectively demonstrate that light-dependent increases in mass-based nitrogen contents and photosynthetic activities were associated with an increased mesophyll volume fraction in needles at higher irradiances. They also emphasize the importance of light-dependent anatomical modifications in determining needle photosynthetic capacity.

Improvement of growth conditions and gas exchange of Fagus sylvatica L. seedlings planted below a recently thinned Pinus sylvestris L. stand

Gas exchange and growth of beech seedlings planted in the understory of a recently thinned pinewood were recorded for 2 years. Relative irradiance was assessed by hemispherical photographs taken just after the thinning. Predawn water potential (Ψpd), daily gas exchange and chlorophyll fluorescence were measured several times during the two growing seasons. Maximum values of photosynthesis (A max) and stomatal conductance to water vapour (g wvmax) were established from daily data. Maximum quantum efficiency of PS II was recorded at dawn by taking the variable to maximum chlorophyll fluorescence ratio on dark adapted leaves (F v/F m). In the middle of each summer, leaf nitrogen content and leaf mass per area were evaluated, and height growth and basal area increment were recorded at the end of the season. The thinning treatment removed half the trees and generated around 10% more available relative irradiance (GLF). This was followed by an increase in net photosynthesis at saturating PPFD (A sat) and in maximum stomatal conductance to water vapour (g wvmax). Moreover, specific leaf mass (SLM) and mass based nitrogen content (Nm) showed higher values for seedlings in the thinned stand. In both years, a positive relationship was established between the area based nitrogen content (Na) and maximum net photosynthesis (A max). In 1998, a year with a dry summer, seedlings suffered a significant drop in daily A max irrespective of the thinning regime. This was a response to an increase in stomatal limitation to net photosynthesis, g wvmax reaching the lowest value on dates with the highest drought. A lack of decrease of Fv/Fm confirmed the absence of significant non-stomatal limitation to A as a consequence of photoinhibition after opening the pinewood. A higher maximum quantum efficiency of open PS II centres (Fv/Fm) was registered in seedlings in the thinned stand. The significance of the differences between the treatments was stronger in the second year after thinning. In 1999, a year with frequent summer storms, water availability increased for seedlings growing under the thinned pinewood. Overall, the reduced pine overstory had a positive effect on physiological responses of beech seedlings, which was translated into improved seedling growth.

Needle longevity of Scots pine in relation to foliar nitrogen content, specific leaf area, and shoot growth in different forest types

The aim of the study was to examine whether the variation in needle longevity of Scots pine (Pinus sylvestris L.) is of a community-specific nature. Altogether 300 trees were examined in Vaccinium, dry heath, and pine bog forests in Estonia. Mean number of needle age-classes was 4.1 for all forest types, while mean survivorship of needles averaged 70% in Vaccinium forests and 80% in the others (p &lt; 0.01). Mean mass-based nitrogen content (Nm) of the needles was the highest in Vaccinium forests (11.8 mg·g–1, p &lt; 0.05) and lower in dry heath (10.4 mg·g–1) and pine bog (9.8 mg·g–1) forests. Specific leaf area (SLA) did not differ between Vaccinium (6.3 mm2·mg–1) and dry heath (6.0 mm2·mg–1) forests but was lower in pine bog forests (5.5 mm2·mg–1, p &lt; 0.05). Shoot length increment was the smallest in pine bog forests (45.1 mm·year–1, p &lt; 0.05) and did not differ between Vaccinium (92.2 mm·year–1) and dry heath (95.2 mm·year–1) forests. Our findings confirm that the small-scale variation in needle longevity of Scots pine has a community-specific pattern and is in accordance with the trends in Nm and SLA.