Nitrogen and phosphorus resorption in trees of a Mexican tropical dry forest

Resorption efficiency (RE) and proficiency, foliar nutrient concentrations, and relative soil nutrient availability were determined during 3 consecutive years in tree species growing under contrasting topographic positions (i.e., top vs. bottom and north vs. south aspect) in a tropical dry forest in Mexico. The sites differed in soil nutrient levels, soil water content, and potential radiation interception. Leaf mass per area (g m^–2) increased during the growing season in all species. Soil P availability and mean foliar P concentrations were generally higher at the bottom than at the top site during the 3 years of the study. Leaf N concentrations ranged from 45.4 to 31.4 mg g^–1. Leaf P varied from 2.3 to 1.8 mg g^–1. Mean N and P RE varied among species, occasionally between top and bottom sites, and were higher in the dry than in the wet years of study. Senesced-leaf nutrient concentrations (i.e., a measure of resorption proficiency) varied from 13.7 to 31.2 mg g^–1 (N) and 0.4 to 3.3 mg g^–1 (P) among the different species and were generally indicative of incomplete nutrient resorption. Phosphorus concentrations in senesced leaves were higher at the bottom than at the top site and decreased from the wettest to the the driest year. Soil N and P availability were significantly different in the north- and south-facing slopes, but neither nutrient concentrations of mature and senesced leaves nor RE differed between aspects. Our results suggest that water more than soil nutrient availability controls RE in the Chamela dry forest, while resorption proficiency may be interactively controlled by both nutrient and water availability.     

Altitudinal variation in leaf mass per unit area,leaf tissue density and foliar nitrogen and phosphorus content along an Amazon-Andes gradient in Peru

Background: Leaf traits are important in determining the capacity for a plant to acquire carbon, but few data are available for montane cloud forests in the Andes.

Aims: To investigate the changes in leaf traits along a large altitudinal transect (220–3600 m) from lowland to montane cloud forest in Peru.

Methods: We determined leaf mass per area (LMA, g m^?2), leaf tissue density (L _d, g cm^?3), and foliar nitrogen (N) and phosphorus (P) content, both on a mass (N _m and P _m, %) and area (N _a and P _a, g m^?2) basis for the most abundant species locally.

Results: LMA increased with altitude (62.8–169.4 g m^?2), though overall, LMA was lower than in comparable tropical elevation gradients. N _m declined significantly with altitude (2.39–1.25 %, P < 0.05), but N _m contents were higher than in comparable studies. The relatively high N _m and low LMA values are consistent with published global leaf trait datasets. No altitudinal trend for P _m was found; rather, our data highlighted the spatial variability in P _m (and P _a) within and among sites at different elevations. Foliar N:P ratios did not show a trend with altitude and did not indicate N limitation except at 3000 m altitude.

Conclusions: Though leaf traits showed altitudinal trends similar to other studies, contrary to the general hypothesis, our data suggest that the tropical montane forests presented here are not N limited.     

Leaf age and season influence the relationships between leaf nitrogen, leaf mass per area and photosynthesis in maple and oak trees

Abstract. Seasonal changes in photosynthesis, leaf nitrogen (N) contents and leaf mass per area (LMA) were observed over three growing seasons in open-grown sun-lit leaves of red maple ( Acer rubrum ), sugar maple ( A. sacchamm ) and northern pin oak ( Quereus ellipsoidalis ) trees in southern Wisconsin. Net photosynthesis and leaf N were highly linearly correlated on both mass and area bases within all species from late spring until leaf senescence in fall. Very early in the growing season leaves had high N concentrations, but low photosynthetic rates per unit leaf N, suggesting that leaves were not fully functionally developed at that time. Leaf N per unit area and LMA had nonparallel seasonal patterns, resulting in differing relationships between leaf N/area and LMA in the "early versus late growing season. As a result of differences in seasonal patterns between leaf N/area and LMA, net photosynthesis/area was higher for a given LMA in the spring than fall, and the overall relationships between these two parameters were poor.     

Impact of temperature on the relationship between respiration and nitrogen concentration in roots: an analysis of scaling relationships, Q10 values and thermal acclimation ratios

* The impact of nitrogen (N) supply on the temperature response of root respiratory O(2) uptake (R) was assessed in several herbaceous species grown in solution culture. Warm-grown (25 : 20 degrees C, day:night) plants differing in root N concentration were shifted to 13 : 8 degrees C for 7 d to cold-acclimate. * Log-log plots of root R vs root N concentration both showed that R increased with increasing tissue N concentration, irrespective of the growth temperature. Although the regression slopes of the log-log plots did not differ between the warm-grown and cold-acclimated plants, cold-acclimated plants did exhibit a higher y-axis intercept than their warm-grown counterparts. This suggests that cold acclimation of root R is not entirely dependent on cold-induced increases in tissue N concentration and that scaling relationships (i.e. regression equations fitted to the log-log plots) between root R and N concentration are not fixed. * No systematic differences were found in the short-term Q(10) (proportional change in R per 10 degrees C change in temperature), or degree of cold acclimation (as measured by the proportional difference between warm- and cold-acclimated roots) among roots differing in root N concentration. The temperature response of root R is therefore insensitive to tissue N concentration. * The insensitivity of Q(10) values and acclimation to tissue N concentration raises the possibility that root R and its temperature sensitivity can be predicted for a range of N supply scenarios.     

Aboveground nitrogen and phosphorus use by five plantation-grown trees with different leaf longevities

Aboveground nitrogen (N) and phosphorus (P) requirement, retranslocation and use efficiency were determined for 28-year-old red oak (Quercus rubra L.), European larch (Larix decidua Miller), white pine (Pinus strobes L.), red pine (Pinus resinosa Ait.) and Norway spruce (Picea abies (L) Karst.) plantations on a similar soil in southwestern Wisconsin. Annual aboveground N and P requirements (kg/ha/yr) totaled 126 and 13 for red oak, 86 and 9 for European larch, 80 and 9 for white pine, 38 and 6 for red pine, and 81 and 13 for Norway spruce, respectively. Nitrogen and P retranslocation from current foliage ranged from 81 and 72%, respectively, for European larch, whereas red pine retranslocated the smallest amount of N (13%) and Norway spruce retranslocated the smallest amount of P (18%). In three evergreen species, uptake accounted for 72 to 74% of annual N requirement whereas for two deciduous species retranslocation accounted for 76 to 77% of the annual N requirement. Nitrogen and P use (ANPP/uptake) was more efficient in deciduous species than evergreen species. The results from this common garden experiment demonstrate that differences in N and P cycling among species may result from intrinsic characteristics (e.g. leaf longevity) rather than environmental conditions.     

Changes in leaf nitrogen and carbohydrates underlie temperature and CO2 acclimation of dark respiration in five boreal tree species

We tested the hypothesis that acclimation of foliar dark respiration to CO₂ concentration and temperature is associated with adjustments in leaf structure and chemistry. Populus tremuloides Michx. , Betula papyrifera Marsh. , Larix laricina (Du Roi) K. Koch , Pinus banksiana Lamb., and Picea mariana (Mill.) B.S.P. were grown from seed in combined CO₂ (370 or 580 μ mol mol^–1) and temperature treatments (18/12, 24/18, or 30/24 °C). Temperature and CO₂ effects were predominately independent. Specific respiration rates partially acclimated to warmer thermal environments through downward adjustment in the intercept, but not Q ₁₀ of the temperature–response functions. Temperature acclimation of respiration was larger for conifers than broad-leaved species and was associated with pronounced reductions in leaf nitrogen concentrations in conifers at higher growth temperatures. Short-term increases in CO₂ concentration did not inhibit respiration. Growth in the elevated CO₂ concentration reduced leaf nitrogen and increased non-structural carbohydrate concentrations. However, for a given nitrogen concentration, respiration was higher in leaves grown in the elevated CO₂ concentration, as rates increased with increasing carbohydrates. Across species and treatments, respiration rates were a function of both leaf nitrogen and carbohydrate concentrations ( R ² = 0·71, P < 0·0001). Long-term acclimation of foliar dark respiration to temperature and CO₂ concentration is largely associated with changes in nitrogen and carbohydrate concentrations.     

Effect of nitrogen,phosphorus and potassium on spikelet sterility induced by low temperature at the reproductive stage of rice

Spikelet sterility induced by low temperature at the reproductive stage of rice increased further with the increase of nitrogen supply. Spikelet sterility in Fujisaka-5 did not increase due to low temperature when nitrogen supply was increased from 10 to 40 ppm and at 80 ppm nitrogen supply it was less affected than IR36. Total nitrogen content in the leaves increased with the increase of nitrogen supply and was forced to be associated with the spikelet sterility induced by low temperature. Based on auricle distance between the last two leaves, the most sensitive stage to low temperature damage differed in Fujisaka-5 and IR36. Spikelet sterility induced by low temperature for 10 days was very high in both the varieties and the effect of nitrogen was not clear.The effect of phosphorus on the spikelet sterility induced by low temperature at reproductive stage was not clear except that at the highest phosphorus (P) level (10 ppm) the spikelet sterility increased both in Fujisaka-5 and IR36.Spikelet sterility induced by low temperature at the reproductive stage of rice decreased with the increase of Potassium (K) supply in both Fujisaka-5 and IR36. With an increase of potassium supply, nitrogen (N) content decreased in the leaves and panicles and spikelet sterility induced by low temperature decreased with an increase of the K to N ratio in the leaves and panicles. The results suggest that potassium might play a major role to counteract the low temperature damage at the reproductive stage of rice.     

Leaf nitrogen distribution in relation to leaf age and photon flux density in dominant and subordinate plants in dense stands of a dicotyledonous herb

We studied the effects of photon flux density (PFD) and leaf position, a measure of developmental age, on the distribution of nitrogen content per unit leaf area (N _area) in plants of different heights, in dense stands grown at two nitrogen availabilities and in solitary plants of the erect dicotyledonous herb Xanthium canadense. Taller more dominant plants received higher PFD levels and experienced a larger difference in relative PFD between their youngest and oldest leaves than shorter subordinate plants in the stands. Differences in PFD between leaves of solitary plants were assumed to be minimal and differences in leaf traits, found for these plants, could thus be mainly attributed to an effect of leaf position. In the solitary plants, N _area decreased with leaf position while in the plants from the stands it decreased with decreasing relative PFD, indicating both factors to be important in determining the distribution of N _area. Due to the effect of leaf position on N _area, leaves of subordinate plants had a higher N _area than older leaves of dominant plants which were at the same height or slightly higher in the canopy. Consequently, the N _area distribution patterns of individual plants plotted as a function of relative PFD were steeper, and probably closer to the optimal distribution which maximizes photosynthesis, than the average distribution in the stand. Leaves of subordinate plants had a lower mass per unit area (LMA) than those of dominant plants. In the dominant plants, LMA decreased with decreasing relative PFD (and with leaf position) while in the subordinate plants it increased. This surprising result for the subordinate plants can be explained by the fact that, during the course of a growing season, these plants became increasingly shaded and newer leaves were thus formed at progressively lower light availability. This indicates that LMA was strongly determined by the relative PFD at leaf formation and to a lesser extent by the current PFD. Leaf N content per unit mass (N _mass) was strongly determined by leaf position independent of relative PFD. This indicates that N _mass is strongly ontogenetically related to the leaf-aging process while changes in N _area, in response to PFD, were regulated through changes in LMA. Received: 11 May 1997 / Accepted: 9 September 1997     

Responses to internal nitrogen and phosphorus concentrations of two Taraxacum microspecies of contrasting mineral ecology: critical N and P concentrations of whole plants

Of the two Taraxacum microspecies used. Taraxacum sellandii Dahlst. usually occurs in grasslands with a high nutrient level; Taraxacum nordstedtii Dahlst. is generally restricted to undisturbed and mineral-poor habitats. Growth response curves for internal N and P were established, based on relative yield of (whole) plant tissue water and (whole plant) internal mineral concentration on a tissue water basis. Critical nutrient concentrations of N and P were determined from the response curves derived. For both macroelements, T. nordstedtii showed lower critical nutrient concentrations. The difference in critical N concentrations coincided with differences in internal NO₃^-₃ concentrations between the microspecies. Finally, we discuss the use of tissue water as a (whole) plant growth parameter and internal mineral concentration on tissue water basis as a parameter describing the mineral status.     

Influence of temperature and soil nitrogen and phosphorus availabilities on fine-root productivity in tropical rainforests on Mount Kinabalu,Borneo

We investigated how temperature and nutrient availability regulate fine-root productivity in nine tropical rainforest ecosystems on two altitudinal gradients with contrasting soil phosphorus (P) availabilities on Mount Kinabalu, Borneo. We measured the productivity and the nutrient contents of fine roots, and analyzed the relationships between fine-root parameters and environmental factors. The fine-root net primary productivity (NPP), total NPP, and ratio of fine-root NPP to total NPP differed greatly among the sites, ranging from 72 to 228 (g m^?2 year^?1), 281–2240 (g m^?2 year^?1), and 0.06–0.30, respectively. A multiple-regression analysis suggested a positive effect of P availability on total NPP, whereas fine-root NPP was positively correlated with mean annual temperature and with P and negatively correlated with N. The biomass and longevity of fine roots increased in response to the impoverishment of soil P. The carbon (C) to P ratio (C/P) of fine roots was significantly and positively correlated with the P-use efficiency of above-ground litter production, indicating that tropical rainforest trees dilute P in fine roots to maintain the C allocation ratio to these roots. We highlighted the mechanisms regulating the fine-root productivity of tropical rainforest ecosystems in relation to the magnitude of nutrient deficiency. The trees showed C-conservation mechanisms rather than C investment as responses to decreasing soil P availability, which demonstrates that the below-ground systems at these sites are strongly limited by P, similar to the above-ground systems.     

新疆准噶尔荒漠植物叶片功能性状的进化和环境驱动机制初探

植物功能性状是由遗传因素和环境条件共同决定的。剖析各因素对植物性状变异的相对影响,对揭示植物对环境变化的响应和适应规律至关重要。作者以干旱区植物为研究对象,定量化分析了植物叶片功能性状变异及其与环境梯度的关系。研究区域位于中国新疆准噶尔盆地及其周边区域。在30个样地中,观测了110种植物的叶比重、叶片单位质量氮含量和单位面积氮含量以及叶片干物质含量,通过插值法获得每个样地的生物气候数据。结果表明:物种水平上叶片性状(性状值为每个物种的实际观测值)的变异在很大程度上由植物进化背景所决定,气候因子和功能群的作用次之;在群落尺度上(性状值为每个样地的权重和),叶比重与气候干旱程度呈正相关,单位质量氮含量在水热组合最优的区域出现最大值,而叶片干物质含量和单位面积氮含量与气候因子的相关性较小。叶比重是群落尺度上探讨叶片功能性状与环境梯度关系的一个合适的指标。此外,在研究植物性状-环境关系过程中,尽可能观测多个植物功能性状是必要的。但是,只有排除植物系统背景的影响,关于植物性状-环境关系的研究结论才可能接近真实情况。将来应该加强同一种内不同种群间的叶片性状的采样和分析工作。     

Leaf Mechanical Properties in Sclerophyll Woodland and Shrubland on Contrasting Soils

Sclerophylly is a common feature of vegetation on infertile soils, and its adaptive significance has been linked to nutrient-use efficiency by protection of leaves to maximise carbon gain. However, there has been little investigation of how the leaf mechanical properties that contribute to the phenomenon of sclerophylly vary along nutrient gradients. In this paper, we investigate how leaf mechanical properties vary among plants on three contrasting soil types (grey sand, laterite soil, and soil overlying dolerite) in a Mediterranean climate in southwestern Australia. Most species were sclerophyllous, but there was 5-fold variation in leaf mass per unit area (LMA) and 17- to 473-fold variation in mechanical properties among species. Species growing on laterite and/or sand (low-nutrient soils) had higher punch strength, work (a measure of toughness) to punch, specific (per unit leaf thickness) work to punch, work to shear, specific work to shear, and flexural stiffness (EI _W) than those on dolerite soils (higher in nutrients). There were few differences in mean values of leaf mechanical properties between the two low-nutrient soils, possibly because the lower concentration of nutrients in the sand is balanced by the greater soil volume than the laterite soil (higher concentration of nutrients, but shallower). There were also few differences in leaf properties between plants of the same species growing on contrasting soil types. There was some variation among sclerophyllous species in their mechanical characteristics, but overall, EI _W provided the strongest contribution to sclerophylly, explaining up to 81% of the variation in LMA. There was no evidence of differences among soil types in the relationships of mechanical properties with LMA, and therefore, no evidence of variation in the mechanical constitution of sclerophylly among soil types.     

Leaf nitrogen and phosphorus stoichiometry across 753 terrestrial plant species in China

Leaf nitrogen and phosphorus stoichiometry of Chinese terrestrial plants was studied based on a national data set including 753 species across the country. Geometric means were calculated for functional groups based on life form, phylogeny and photosynthetic pathway, as well as for all 753 species. The relationships between leaf N and P stoichiometric traits and latitude (and temperature) were analysed. The geometric means of leaf N, P, and N : P ratio for the 753 species were 18.6 and 1.21 mg g(-1) and 14.4, respectively. With increasing latitude (decreasing mean annual temperature, MAT), leaf N and P increased, but the N : P ratio did not show significant changes. Although patterns of leaf N, P and N : P ratios across the functional groups were generally consistent with those reported previously, the overall N : P ratio of China's flora was considerably higher than the global averages, probably caused by a greater shortage of soil P in China than elsewhere. The relationships between leaf N, P and N : P ratio and latitude (and MAT) also suggested the existence of broad biogeographical patterns of these leaf traits in Chinese flora.     

Effects of phosphorus and nitrogen enrichment on the phytoplankton in a tropical reservoir (Lobo Reservoir,Brazil)

The effects of enrichment with phosphate (0–500 µg. 1^–1) and forms of nitrogen (nitrate, nitrite, ammonia an and urea) (0–3500 µgg. ^–1) on the phytoplankton growth of Lobo Reservoir (Brazil) were studied in July, 1979. Suspended matter, chlorophyll a, cell concentrations and the carotenoid:cchlorophyll ratio were estimated following 14 days of in situ incubation. Phosphate alone caused no significant effects, but enrichment with nitrogen caused a substantial increase on the growth of phytoplankton. Comparison between the different forms of nitrogen showed insignificant effects after their additions with 350 µg. ^–1 and in combination with phosphate. However, when nitrogen was added in large quantities (3 500 µg. ^–1), significant differences between the nitrogeneous forms were found, with urea causing the strongest effect. In July, nitrogen is mhe main limiting nutrient to phytoplankton growth of Lobo Reservoir.Supported by CNPq and FAPESP.