Photosynthetic Phosphorus-use Efficiency Research Articles

Enhancing photosynthetic phosphorus-use efficiency through coordination of leaf phosphorus fractions, allocation and anatomy during soybean domestication.

Soybean domestication has significantly changed key agronomic traits, yet its impact on leaf photosynthetic phosphorus-use efficiency (PPUE) and its underlying traits remain poorly known. Further information on this would be important to increase soybean P-use efficiency. To address this gap, 48 soybean accessions (16 wild relatives, 16 landraces and 16 cultivars) were used to compare leaf anatomical traits, foliar chemical P fractions, P allocation and PPUE under two P levels. The results showed that the cultivars had higher area-based and mass-based photosynthesis rates, PPUE, metabolite P concentration, and its percentage of leaf total P, as well as a greater percentage of lipid P, nucleic acid P and residual P. Conversely, wild relatives tended to have higher leaf P concentration, palisade:spongy thickness ratio, and concentrations of inorganic P, nucleic acid P, lipid P and residual P. PPUE was negatively correlated with leaf inorganic P concentration and its percentage relative to leaf total P, while it was positively correlated with the concentration and percentage of metabolite P. We concluded that soybean domestication increased PPUE, as a result of both increased photosynthesis rate and decreased leaf P concentration; domestication reduced the palisade:spongy thickness ratio coupled with increased allocation of P to P-containing metabolites, thereby contributing to faster photosynthesis and higher PPUE. This study shed light on the significance of leaf P allocation and anatomical traits affecting PPUE during soybean domestication, offering a mechanistic understanding to further enhance soybean P-use efficiency.

Crop domestication increased photosynthetic phosphorus-use efficiency associated with changes in leaf phosphorus fractions under low soil phosphorus conditions

Crop domestication increased photosynthetic phosphorus-use efficiency associated with changes in leaf phosphorus fractions under low soil phosphorus conditions

Physiological and Structural Changes in Leaves of Platycrater arguta Seedlings Exposed to Increasing Light Intensities.

Understanding the light adaptation of plants is critical for conservation. Platycrater arguta, an endangered deciduous shrub endemic to East Asia, possesses high ornamental and phylogeographic value. However, the weak environmental adaptability of P. arguta species has limited its general growth and conservation. To obtain a deeper understanding of the P. arguta growth conditions, we examined the leaf morphology and physiology via anatomical and chloroplast ultrastructural analyses following exposure to different natural light intensities (full light, 40%, and 10%). The findings indicated that P. arguta seedings in the 10% light intensity had significantly improved leaf morphological characteristics and specific leaf area compared to those exposed to other intensities. The net photosynthetic rate, chlorophyll (Chl) content, photosynthetic nitrogen use efficiency (PNUE), and photosynthetic phosphorus use efficiency (PPUE) exhibited marked increases at a 10% light intensity compared to both 40% light and full light intensities, whereas the light compensation point and dark respiration levels reached their lowest values under the 10% light condition. With reduced light, leaf thickness, palisade tissue, spongy tissue, and stomatal density significantly decreased, whereas the stomatal length, stomatal width, and stomatal aperture were significantly elevated. When exposed to 10% light intensity, the ultrastructure of chloroplasts was well developed, chloroplasts and starch grain size, the number of grana, and thylakoids all increased significantly, while the number of plastoglobules was significantly reduced. Relative distance phenotypic plasticity index analysis exhibited that P. arguta adapts to varying light environments predominantly by adjusting PPUE, Chl b, PNUE, chloroplast area, and the activity of PSII reaction centers. We proposed that P. arguta efficiently utilizes low light to reconfigure its energy metabolism by regulating its leaf structure, photosynthetic capacity, nutrient use efficiency, and chloroplast development.

GWAS unravels acid phosphatase ACP2 as a photosynthesis regulator under phosphate starvation conditions through modulating serine metabolism in rice

Inorganic phosphorus (Pi) deficiency significantly impacts plant growth, development, and photosynthetic efficiency. This study evaluated 206 rice accessions from a MiniCore population under both Pi-sufficient (Pi+) and Pi-starvation (Pi−) conditions in the field to assess photosynthetic phosphorus use efficiency (PPUE), defined as the ratio of AsatPi− to AsatPi+. A genome-wide association study and differential gene expression analyses identified an acid phosphatase gene (ACP2) that responds strongly to phosphate availability. Overexpression and knockout of ACP2 led to a 67% increase and 32% decrease in PPUE, respectively, compared with wild type. Introduction of an elite allele A, by substituting the v5 SNP G with A, resulted in an 18% increase in PPUE in gene-edited ACP2 rice lines. The phosphate-responsive gene PHR2 was found to transcriptionally activate ACP2 in parallel with PHR2 overexpression, resulting in an 11% increase in PPUE. Biochemical assays indicated that ACP2 primarily catalyzes the hydrolysis of phosphoethanolamine and phospho-L-serine. In addition, serine levels increased significantly in the ACP2v8G-overexpression line, along with a concomitant decrease in the expression of all nine genes involved in the photorespiratory pathway. Application of serine enhanced PPUE and reduced photorespiration rates in ACP2 mutants under Pi-starvation conditions. We deduce that ACP2 plays a crucial role in promoting photosynthesis adaptation to Pi starvation by regulating serine metabolism in rice.

Application of the strip clear-cutting system in a running bamboo (Phyllostachys glauca McClure) forest: feasibility and sustainability assessments.

As a renewable forest resource, bamboo plays a role in sustainable forest development. However, traditional cutting systems, selection cutting (SeC) and clear-cutting (ClC), result in an unsustainable production of bamboo forests due to labor-consuming or bamboo degradation. Recently, a strip clear-cutting (StC) was theoretically proposed to promote the sustainability of bamboo production, while little is known about its application consequence. Based on a 6-year experiment, we applied the strip clear-cutting system in a typical running bamboo (Phyllostachys glauca McClure) forest to assess its feasibility and sustainability. Using SeC and ClC as controls, we set three treatments with different strip widths (5 m, 10 m, and 20 m) for strip clear-cutting, simplified as StC-5, StC-10, and StC-20, respectively. Then, we investigated leaf physiological traits, bamboo size and productivity, population features, and economic benefits for all treatments. The stands managed by StC had high eco-physiological activities, such as net photosynthetic rate (P n), photosynthetic nitrogen use efficiency (PNUE), and photosynthetic phosphorus use efficiency (PPUE), and thus grew well, achieved a large diameter at breast height (DBH), and were tall. The stand biomass of StC (8.78 t hm-2 year-1) was 1.19-fold and 1.49-fold greater than that of SeC and ClC, respectively, and StC-10 and StC-20 were significantly higher than SeC or ClC (p< 0.05). The income and profit increased with the increase in stand density and biomass, and StC-20 and StC-10 were significantly higher than SeC or ClC (p< 0.05). Using principal components analysis and subordinate function analysis, we constructed a composite index to indicate the sustainability of bamboo forests. For the sustainability assessment, StC-10 had the highest productive sustainability (0.59 ± 0.06) and the second highest economic sustainability (0.59 ± 0.11) in all cutting treatments. StC-10 had the maximum overall sustainability, with a value of 0.53 ± 0.02, which was significantly higher than that of ClC (p< 0.05). The results verified that StC for Phyllostachys glauca forests is feasible and sustainable as its sustainability index outweighs those of traditional cutting systems (SeC and ClC), and 10 m is the optimum distance for the strip width of StC. Our findings provide a new cutting system for managing other running bamboo forests sustainably.

More than colorful: phosphorus allocation to major chemical fractions shifts during leaf development in species exhibiting delayed greening

The colorful “delayed leaf greening” is a common but overlooked phenomenon in phosphorus (P)-limited environments in habitats in tropical, subtropical and temperate forests, but the physiological mechanism underpinning it remains unclear. It is important to understand how allocation of phosphorus to major leaf P fractions shifts during leaf development, as a strategy for utilizing P efficiently. We measured concentrations of leaf nitrogen and P and five chemical P fractions, and eight leaf chemical element concentrations (K, Ca, Mg, Mn, Fe, Cu, Zn and Se) in young and mature leaves of six woody plants exhibiting delayed greening in China. We also measured leaf mass per area, photosynthetic rate, photosynthetic phosphorus-use efficiency, and soil nutrient concentrations. The results indicate six species exhibiting delayed greening had different leaf P concentrations during leaf development, but the same nitrogen concentrations. We further show major leaf chemical P fractions like metabolite P, nucleic acid P and lipid P showed differences in young and mature leaves. The concentration of lipid P, nucleic acid P, Pi and residual P significantly decreased from young to mature leaves, while that of metabolite P was constant. There was a greater allocation of P to phospholipids and metabolite P in mature leaves. The concentration of Cu and K were significantly higher in young leaves. This study provides new insight to investigate the roles of different P fractions in young and mature leaves, and how the allocation shifts for plants to utilize phosphorus.

Long-term effects of 7-year warming experiment in the field on leaf hydraulic and economic traits of subtropical tree species.

Rising temperature associated with climate change may have substantial impacts on forest tree functions. We conducted a 7-year warming experiment in subtropical China by translocating important native forest tree species (Machilas breviflora, Syzygium rehderianum, Schima superba and Itea chinensis) from cooler high-elevation sites (600m) to 1-2°C warmer low-elevation sites (300 and 30m) to investigate warming effects on leaf hydraulic and economic traits. Here, we report data from the last 3years (Years 5-7) of the experiment. Warming increased leaf hydraulic conductance of S. superba to meet the higher evaporative demand. M. breviflora (300m), S. rehderianum, S. superba and I. chinensis (300 and 30m) exhibited higher area-based and mass-based maximum photosynthetic rates (Aa and Am , respectively) related to increasing stomatal conductance (gs ) and stomatal density in the wet season, which led to rapid growth; however, we observed decreased growth of M. breviflora at 30m due to lower stomatal density and decreased Aa in the wet season. Warming increased photosynthetic nitrogen-use efficiency and photosynthetic phosphorus-use efficiency, but reduced leaf dry mass per unit area due to lower leaf thickness, suggesting that these tree species allocated more resources into upregulating photosynthesis rather than into structural investment. Our findings highlight that there was trait variation in the capacity of trees to acclimate to warmer temperatures such that I. chinensis may benefit from warming, but S. superba may be negatively influenced by warming in future climates.

Relationship between photosynthetic phosphorus-use efficiency and foliar phosphorus fractions in tropical tree species.

How plants develop adaptive strategies to efficiently use nutrients on infertile soils is an important topic in plant ecology. It has been suggested that, with decreasing phosphorus (P) availability, plants increase photosynthetic P-use efficiency (PPUE) (i.e., the ratio of instantaneous photosynthetic carbon assimilation rate per unit foliar P). However, the mechanism to increase PPUE remains unclear. In this study, we tested whether high PPUE is explained by an optimized allocation of P in cells among P-containing biochemical compounds (i.e., foliar P fractions). We investigated the relationships among mass-based photosynthetic carbon assimilation rate (Amass), PPUE, total foliar P concentration, and foliar P fractions in 10 tree species in two tropical montane rain forests with differing soil P availability (five species on sedimentary soils and five species on P-poorer ultrabasic serpentine soils) on Mount Kinabalu, Borneo. We chemically fractionated foliar P into the following four fractions: metabolic P, lipid P, nucleic acid P, and residual P. Amass was positively correlated with the concentrations of total foliar P and of metabolic P across 10 tree species. Mean Amass and mean concentrations of total foliar P and of each foliar P fraction were lower on the P-poorer ultrabasic serpentine soils than on the sedimentary soils. There was a negative relationship between the proportion of metabolic P per total P and the proportion of lipid P per total P. PPUE was positively correlated with the ratio of metabolic P to lipid P. High PPUE is explained by the net effect of a relatively greater investment of P into P-containing metabolites and a relatively lesser investment into phospholipids in addition to generally reduced concentrations of all P fractions. We conclude that plants optimize the allocation of P among foliar P fractions for maintaining their productivity and growth and for reducing demand for P as their adaptation to P-poor soils.

Proteaceae from severely phosphorus‐impoverished soils extensively replace phospholipids with galactolipids and sulfolipids during leaf development to achieve a high photosynthetic phosphorus‐use‐efficiency

Proteaceae species in south-western Australia occur on severely phosphorus (P)-impoverished soils. They have very low leaf P concentrations, but relatively fast rates of photosynthesis, thus exhibiting extremely high photosynthetic phosphorus-use-efficiency (PPUE). Although the mechanisms underpinning their high PPUE remain unknown, one possibility is that these species may be able to replace phospholipids with nonphospholipids during leaf development, without compromising photosynthesis. For six Proteaceae species, we measured soil and leaf P concentrations and rates of photosynthesis of both young expanding and mature leaves. We also assessed the investment in galactolipids, sulfolipids and phospholipids in young and mature leaves, and compared these results with those on Arabidopsis thaliana, grown under both P-sufficient and P-deficient conditions. In all Proteaceae species, phospholipid levels strongly decreased during leaf development, whereas those of galactolipids and sulfolipids strongly increased. Photosynthetic rates increased from young to mature leaves. This shows that these species extensively replace phospholipids with nonphospholipids during leaf development, without compromising photosynthesis. A considerably less pronounced shift was observed in A. thaliana. Our results clearly show that a low investment in phospholipids, relative to nonphospholipids, offers a partial explanation for a high photosynthetic rate per unit leaf P in Proteaceae adapted to P-impoverished soils.

Does strategy of resource acquisition in tropical woody species vary with life form, leaf texture, and canopy gradient?

In order to test whether the strategy of resource acquisition varies with life form, leaf texture and canopy gradient, we measured light-saturated net photosynthetic capacity (A max-mass) and leaf nitrogen and phosphorus concentrations (N mass and P mass) for 127 woody species of understory (small shrubs and tree seedlings) and 47 woody species of canopy (large shrubs and tree adults) in a tropical montane rain forest of Hainan Island, South China. Photosynthetic nitrogen use efficiency (PNUE) and photosynthetic phosphorus use efficiency (PPUE) were studied by taking into account functional groups, which classified by either life form (FG1) or leaf texture (FG2). For FG1, there were significant (P < 0.05) differences between trees and shrubs in A mass, N mass and P mass, but not in PNUE and PPUE; whereas for FG2, there were significant (P < 0.05) differences between the papery-leaved species and those with leathery leaves in the measured leaf traits inclusive of PNUE and PPUE. Within the same classification systems, significant allometric scaling relationships were found in the leaf trait pairs of A mass-N mass and A mass-P mass. Considered separately, the slope and y-intercept of the linear regression between A mass and N mass did not differ among functional groups nor between understory and canopy, but those for the linear regression between A mass and P mass differed significantly (P = 0.001) between understory and canopy species regardless of functional groups. The results of phylogenetic comparative analyses were in accordance with the observed positive scaling relationships. The overall results indicate that there are no fundamentally different nitrogen capture strategies in tropical woody species regardless of their life form, leaf texture and canopy gradient. However, the strategies of phosphorus acquisition of tropical woody species differ with canopy layer increases. This variation may correspond to the special soil conditions in this ecosystem, as phosphorus is an element limiting plant growth in tropical areas.

Plant size effects on the relationships among specific leaf area, leaf nutrient content, and photosynthetic capacity in tropical woody species

To test whether leaf trait relationships vary with plant size, specific leaf area (SLA), area- and mass-based leaf nutrient contents ( N area and N mass, P area and P mass), and area- and mass-based leaf photosynthetic capacities ( A area and A mass) of 127 small individuals (woody plants shorter than 2 m) and 47 large trees (taller than 10 m) were measured in a tropical montane rain forest, China. A standardized major axis (SMA) method was used to scale the mass-based trait relationships. We found that A mass, P area, P mass, and SLA were higher in the small individuals than in the large trees, but the changes of A area, N area and N mass leveled off. Trait pairs of N mass − A mass, SLA − A mass and N mass − SLA were positively correlated with slopes in common, but the y-intercept of SLA − N mass was higher in the large trees than in the small individuals, indicating large trees had a higher N investment at a given SLA. In the pairs of N mass − A mass and SLA − A mass, small individuals were shifted upwards along a common slope than large trees, corresponding to their large A mass and SLA. At a given SLA, the upwards shift along a common slope of small individuals does not mean that they have higher photosynthetic nitrogen use efficiency (PNUE) than large trees, since a common slope and homogenous elevations of SLA-PNUE were found between them. Trait pairs of P mass − A mass and N mass − P mass were positively correlated and the slopes differed between small and large trees. The slope of P mass − A mass was steeper in the large than in the small individuals, suggesting large trees would have a disproportionally larger return with the same increase in P mass. However, the pattern of slope of N mass − P mass was the reverse of that observed for P mass − A mass, indicating a higher N/P ratio in the large than in the small individuals. At a given SLA, large trees had higher photosynthetic phosphorus use efficiency (PPUE) than small individuals, corresponding to their higher elevation of SLA-PPUE. In conclusion, leaf trait relationships can be modified by plant size but the positive correlations among SLA, N mass, P mass and A mass generally remain invariant.

Divergent patterns of photosynthetic phosphorus‐use efficiency versus nitrogen‐use efficiency of tree leaves along nutrient‐availability gradients

Summary 1. Nitrogen (N) and phosphorus (P) are essential nutrients for photosynthetic carbon assimilation and most frequently limit primary productivity in terrestrial ecosystems. Efficient use of those nutrients is important for plants growing in nutrient‐poor environments. 2. We investigated the pattern of photosynthetic phosphorus‐use efficiency (PPUE) in comparison with photosynthetic nitrogen‐use efficiency (PNUE) along gradients of P and N availability across biomes with 340 tree and shrub species. We used both total soil N and P concentration and foliar N/P ratios for indicating nutrient‐availability gradients. 3. Photosynthetic phosphorus‐use efficiency increased with greater leaf mass per area (LMA) toward decreasing P availability. By contrast, PNUE decreased with greater LMA towards decreasing N and P availability. 4. The increase in PPUE with decreasing P availability was caused by the net effects of a relatively greater reduction in foliar P concentration and a relatively constant photosynthetic carbon assimilation rate. The decrease in PNUE with decreasing N availability was caused by the effects of a reduction in photosynthetic carbon assimilation rate with greater LMA. 5. Synthesis. Our results suggest that higher PPUE may be an effective leaf‐level adaptation to P‐poor soils, especially in tropical tree species. Future research should focus on the difference between PPUE and PNUE in relation to leaf economics, physiology and strategy.

Novel mannose‐sequestration technique reveals variation in subcellular orthophosphate pools do not explain the effects of phosphorus nutrition on photosynthesis in Eucalyptus globulus seedlings

Although only a small proportion of plant phosphorus (P) is used for photosynthesis, the relationships between P and photosynthesis can be strong. It was hypothesized, in this study, that variation in the allocation of orthophosphate (Pi) between active (cytoplasmic) and nonactive (vacuolar) pools would underpin differences in rates of photosynthesis in 4-month-old Eucalyptus globulus seedlings grown with a varying P supply. Photosynthetic biochemistry was assessed by the response of net photosynthesis to increasing intercellular [CO2]. Cytoplasmic Pi was sequestered as mannose 6-phosphate. Total P and the proportion of P as Pi were positively related to P supply. The ratios of active : stored Pi (10-24%) varied little over the range of treatments. Active Pi was positively related to P supply, as was photosynthesis (7 micromol CO2 m(-2) s(-1) with 0 mM P vs. 16 micromol CO2 m(-2) s(-1) with 0.32 mM P). Positive relationships between P supply and photosynthesis were explained best by leaf P content, not by active pools of Pi. The distribution of Pi between the vacuole and the cytoplasm had little impact on the photosynthetic phosphorus-use efficiency (PPUE), and reductions in cytoplasmic Pi had little effect on photosynthesis. Hence, PPUE is an unsuitable guide for assessing plant responses to increasingly unavailable P in the environment.

Mycorrhizal benefit in two low arctic herbs increases with increasing temperature

Climate change may influence the relationship between arctic plants and their symbiotic mycorrhizal fungi. The benefit of the symbiosis for the host plant affects vegetation succession and may be a key parameter in predicting vegetation responses to warming. We investigated the mycorrhizal benefit in the low arctic perennial herbs Potentilla crantzii and Ranunculus acris in symbiosis with the arbuscular mycorrhizal fungus Glomus claroideum. Temperature response in the mycorrhiza-mediated acquisition of nitrogen (N) and phosphorus (P), growth, and photosynthetic nutrient-use efficiency were determined. Near the average natural soil temperature (12°C), mycorrhiza did not improve plant nutrient capture but significantly enhanced plant P capture at 17°C. Photosynthetic nitrogen-use efficiency was higher at 17°C than at 12°C and was further increased by mycorrhiza at 17°C. Photosynthetic phosphorus-use efficiency was not affected by temperature or mycorrhiza. Increasing the growing temperature by 5°C increased the relative shoot growth rate by 15%. Mycorrhizal symbiosis did not enhance plant growth rate, but the plants gained between 20% and 90% more mycorrhiza-mediated P when grown at higher temperature. The results suggest that these low arctic species have good potential to respond positively to increasing temperatures.

Effects of carbon dioxide concentration and nutrition on photosynthetic functions of white birch seedlings

To investigate the interactive effects of atmospheric carbon dioxide concentration ([CO(2)]) and nutrition on photosynthesis and its acclimation to elevated [CO(2)], a two-way factorial experiment was carried out with two nutritional regimes (high- and low-nitrogen (N), phosphorus (P) and potassium (K)) and two CO(2) concentrations (360 and 720 ppm) with white birch seedlings (Betula papyrifera Marsh.) grown for four months in environment-controlled greenhouses. Elevated [CO(2)] enhanced maximal carboxylation rate (V(cmax)), photosynthetically active radiation-saturated electron transport rate (J(max)), actual photochemical efficiency of photosystem II (PSII) in the light (DeltaF/F(m)') and photosynthetic linear electron transport to carboxylation (J(c)) after 2.5 months of treatment, and it increased net photosynthetic rate (A(n)), photosynthetic water-use efficiency (WUE), photosynthetic nitrogen-use efficiency (NUE) and photosynthetic phosphorus-use efficiency (PUE) after 2.5 and 3.5 months of treatment, but it reduced stomatal conductance (g(s)), transpiration rate (E) and the fraction of total photosynthetic linear electron transport partitioned to oxygenation (J(o)/J(T)) after 2.5 and 3.5 months of treatment. Low nutrient availability decreased A(n), WUE, V(cmax), J(max), triose phosphate utilization (TPU), (/F(m)' - F)//F(m)' and J(c), but increased J(o)/J(T) and NUE. Generally, V(cmax) was more sensitive to nutrient availability than J(max). There were significant interactive effects of [CO(2)] and nutrition over time, e.g., the positive effects of high nutrition on A(n), V(cmax), J(max), DeltaF/F(m)' and J(c) were significantly greater in elevated [CO(2)] than in ambient [CO(2)]. In contrast, the interactive effect of [CO(2)] and nutrition on NUE was significant after 2.5 months of treatment, but not after 3.5 months. High nutrient availability generally increased PUE after 3.5 months of treatment. There was evidence for photosynthetic up-regulation in response to elevated [CO(2)], particularly in seedlings receiving high nutrition. Photosynthetic depression in response to low nutrient availability was attributed to biochemical limitation (or increased mesophyll resistance) rather than stomatal limitation. Elevated [CO(2)] reduced leaf N concentration, particularly in seedlings receiving low nutrition, but had no significant effect on leaf P or K concentration. High nutrient availability generally increased area-based leaf N, P and K concentrations, but had negligible effects on K after 2.5 months of treatment.

Regulation of leaf life-span and nutrient-use efficiency of Metrosideros polymorpha trees at two extremes of a long chronosequence in Hawaii

Leaf traits related to life-span and nutrient-use efficiency were studied in the dominant Hawaiian tree species, Metrosideros polymorpha, at both ends of a natural fertility gradient, from young, nitrogen-poor soils to older, phosphorus-poor soils. The main objective of this study was to understand how nutrient limitations affect leaf-level attributes that ultimately play a mechanistic role in regulating whole-ecosystem function. Different types of adjustments to removal of nutrient limitation by long-term fertilization (9-15years) with nitrogen (N), phosphorus (P), and a combined treatment of N plus P were observed at each site. Nitrogen fertilization at the young, mostly N-limited site did not significantly affect net CO2 assimilation (A), foliar N content, or N resorption. The primary response to N fertilization was a decrease in average leaf life span to approximately 553days compared with 898days in the control plot. Significantly shorter average leaf life-span coupled with constant A and foliar N content resulted in reduced integrated photosynthetic nitrogen-use efficiency (PNUE: A summed over the life-span of a leaf divided by foliar N) in the fertilized plots. In contrast, removal of nutrient limitations at the old, mostly P-limited site resulted in increased A, and increased foliar P concentration which also resulted in reduced integrated photosynthetic phosphorus-use efficiency (PPUE). P resorption was also reduced at this site, yet leaf life-span remained constant. When results from both sites and all treatments were combined, statistically significant relationships between leaf life-span, and A, leaf mass per area (LMA), and the cost of leaf construction per unit carbon gain (cost of construction determined by combustion of leaf samples divided by A) were found. As leaf life-span increased, A decreased asymptotically, and LMA and the carbon cost per carbon gain increased linearly. It appears that the balance between leaf carbon cost and carbon uptake is a major determinant of leaf longevity in M. polymorpha despite contrasting responses to removal of N and P limitations by long-term fertilization. Removal of the main nutrient limitations at both sites also resulted in reduced integrated nutrient use efficiency. However, the regulatory mechanisms were different depending on the site limitations: a shorter leaf life-span in the young, N-limited site and substantially higher foliar P concentration in the P-fertilized plots at the old, P-limited site.

Seed size is closely related to phosphorus use efficiency and photosynthetic phosphorus use efficiency in common bean

Seed size might have a significant impact on the growth and phosphorus (P) efficiency of the common bean by 1) enhancing seed reserves so the young plant has higher growth rate and hence higher biomass produced by per unit P absorbed and/or 2) increasing cell size in leaf tissue so the plant has greater leaf expansion and thereby permitting higher photosynthesis rate per unit P. To verify this hypothesis, parameters related to plant growth, photosynthesis, and P use efficiency were evaluated for common bean genotypes from different geographic origins with contrasting seed size and tolerance of P deficiency. It was found that under hydroponic conditions, shoots responded more sensitively to P deficiency than roots, and inhibition of shoot growth by P limitation was mainly reflected by reduction in leaf area. Large‐seeded Andean genotypes were better than small‐seeded Mesoamerican genotypes in leaf growth and expansion hence the former had better shoot growth and higher P efficiency Ratio (PER), which was defined as the amount of biomass produced per unit P in the tissue. There was significant genotypic variation in CO2 exchange rate (CER) and photosynthetic phosphorus use efficiency (PPUE), defined as CER per unit P in the leaf tissue. The large‐seeded Andean genotypes in general had lower CER but higher PPUE, particularly in the primary leaves. We conclude that 1) seed size is closely related to P efficiency in common bean mainly by affecting leaf growth and expansion and 2) although CO2 exchange rate is not positively correlated with seed size, large‐seeded genotypes appear to have higher photosynthetic P use efficiency at early growth stage.