Nitrogen-use efficiency in six perennial grasses from contrasting habitats

1. We studied the nitrogen-use efficiency (NUE) in six perennial grasses adapted to a wide range of nutrient availability. The glasshouse experiment was carried out in pots containing nutrient solution, with two fertility treatments. Nitrogen-use efficiency was considered as the product of nitrogen productivity and mean residence time of the nitrogen in the plant (calculated using ¹⁵N pulse labelling).
2. The species investigated are characteristic of habitats ranging from very nutrient rich to extremely nutrient poor, in the following order: Lolium perenne, Arrhenatherum elatius, Festuca rubra, Anthoxanthum odoratum, Festuca ovina and Molinia caerulea .
3. Lolium perenne (adapted to nutrient-rich habitats) had higher nitrogen productivity ( A ) than M. caerulea (species adapted to nutrient-poor habitats) but lower than that of F. rubra (from habitats with an intermediate availability of nutrients).
4. In the low fertility treatment, species with the lowest nitrogen-use efficiency had the lowest N productivity and the highest mean nitrogen residence time (MRT); however, although species with the highest nitrogen use efficiency had the highest N productivity they did not have the lowest MRT. In all species the nitrogen-use efficiency decreased with increasing N supply. The two components of the NUE ( A and MRT) are inversely correlated along gradients of nutrient availability, but not at very high levels of nutrient availability.
5. The nitrogen-use efficiency of species at constant levels of nutrient supply tends to increase with increasing nutrient availability in their preferred habitat, according to the Clausman nutrient index, up to a certain nutrient availability and then decreases. The results support the contention that species from nutrient-poor sites are not necessarily adapted by a high nitrogen-use efficiency, but by low nutrient loss rates (high mean residence time of N in the plant).     

Nutrient resorption from senescing leaves in two Stipa species native to central Argentina

Abstract Nutrient resorption from senescing leaves enables plants to conserve and reuse nutrients. As such, it could be expected that plant species adapted to infertile soils have a higher nutrient resorption efficiency (percentage reduction of nutrients between green and senesced leaves) and/or higher nutrient resorption proficiency (absolute reduction of nutrients in senesced leaves) than those adapted to fertile soils. Our objective was to compare nitrogen (N) and phosphorous (P) resorption of two congener grasses that successfully occupy uplands of relatively low fertility (Stipa gynerioides) or lowlands of relatively high fertility (Stipa brachychaeta) in natural grasslands of central Argentina. The two Stipa species did not differ in N and P resorption efficiency, but S. gynerioides had a higher N and P resorption proficiency than S. brachychaeta. As a consequence, leaf‐level N and P use efficiency were higher in the species adapted to low fertility conditions than in the species adapted to high fertility conditions. The higher nutrient resorption proficiency of S. gynerioides was also associated with relatively low leaf‐litter decomposition and nutrient release rates found in a previous study.     

广西猫儿山不同海拔常绿和落叶树种的营养再吸收模式

土壤养分供给性大小是否影响植物氮和磷再吸收效率仍存在争议。调查了广西猫儿山不同海拔常绿和落叶树种成熟和衰老叶片的氮和磷含量,探讨营养再吸收是否受到叶片习性和海拔的影响。所有树种氮和磷再吸收效率的平均值分别为56.5%和52.1%。常绿树种比落叶树种有显著较高的氮再吸收效率(P0.001)和磷再吸收效率(P0.01),这与前者有较低的衰老叶片氮和磷含量密切相关。随着海拔的上升,氮再吸收效率显著下降(P0.01),磷再吸收效率显著提高(P0.05)。氮再吸收效率与土壤氮:磷比(r=-0.41,P0.05)和成熟叶片氮:磷比(r=-0.37,P0.05)负相关,磷再吸收效率与土壤氮:磷比(r=0.44,P0.05)和成熟叶片氮:磷比(r=0.47,P0.01)正相关,表明了树种对低海拔氮限制的适应逐渐转变为对高海拔磷限制的适应。此外,氮再吸收效率与年均温正相关(r=0.43,P0.05)而磷再吸收效率与年均温负相关(r=-0.45,P0.01),这表明气温也是调节树木营养再吸收格局的重要影响因素。不同海拔树种氮和磷再吸收模式的差异可能是引起广西猫儿山常绿树种沿海拔形成双峰分布的原因之一。     

植被光能利用率:模型及其不确定性

光能利用率（Light use efficiency： LUE）指植物截获的光能转化为化学能的效率,表示为生产力和吸收光能之比。基于LUE概念的模型对模拟预测全球变化下碳循环、植被生产力及其潜力具有重要意义。全球变化和人类活动影响给植被生产力和碳循环的评估带来了巨大挑战。系统梳理了LUE模型的不确定性并分析其原因,以期提高生产力模拟预测的准确度。分析发现LUE模型准确度仅为62%-70%且模型间差异较大（32%）,误差随着植被类型、时间尺度和空间区域的不同存在显著差别。目前计算LUE的误差是模型不确定性的关键,原因主要在于LUE与影响因素尤其是水分的关系并不清楚。一方面不能准确区分水分胁迫指标对LUE的影响机制,另一方面无法准确模拟水分等影响因素与LUE关系的时空演变特征。未来该领域研究的重要方向是发展集成样地和区域尺度的叶绿素荧光、光化学指数等研究方法,厘定LUE与影响因素特别是的水分关系,并分析其时空演变特征。     

一次基施水稻控释肥技术的养分利用率及增产效果

通过盆栽试验、田间小区试验和生产大面积应用示范研究了一次基施水稻控释肥的养分利用率及其增产效果.结果表明,一次基施水稻控释肥技术与等养分量的专用肥处理比较,盆栽试验相对提高氮素利用率12.2%～22.7%,磷素利用率7.0%～35.0%;小区试验相对提高氮素利用率17.1%.综合广东不同水稻生态类型稻作区连续3年共167点(次)应用示范结果,表明一次基施水稻控释肥技术较常规分次施肥平均减少氮和磷养分用量分别为22.11%和21.81%,降低了施肥成本,获得8.2%的增产效果.     

Forest floor mass,litterfall and nutrient return in Central Himalayan high altitude forests

Dynamics of forest floor biomass, pattern of litter fall and nutrient return in three central Himalayan high elevation forests are described. Fresh and partially decomposed litter layer occur throughout the year. In maple and birch the highest leaf litter value was found in October and in low-rhododendron in August. The relative contribution of partially and more decomposed litter to the total forest floor remains greatest the year round. The total calculated input of litter was 627.7 g m^-2 yr^-1 for maple, 477.87 g m^-2 yr^-1 for birch and 345.9 g m^-2 yr^-1 for low-rhododendron forests. 49–61% of the forest floor was replaced per year with a subsequent turnover time of 1.6–2.0 yr. The annual nutrient return through litter fall amounted to (kg ha^-1 yr^-1) 25.5–56.1 N, 2.0–5.4 P and 9.9–23.3 K. The tree litter showed an annual replacement of 26–54% for different nutrients and it decreased towards higher elevation. The nutrient use efficiency in terms of litter produced per unit of nutrient was higher in present study compared to certain mid- and high-elevation forests of the central Himalaya.     

The effect of varying nitrogen and phosphorus availability on nutrient use by Larrea tridentata,a desert evergreen shrub

Summary In a phytotron study of the effects of nitrogen and phosphorus supply ratio on nutrient uptake and use by Larrea tridentata, seedlings responded to increases in N and P availability with increases in leaf size, total biomass, and leaf nutrient concentration, and with decreases in root: shoot ratio. N and P use efficiency decreased with increasing N and P availability, respectively, but increased with increasing availability of the other nutrient, suggesting that Larrea responds both to the absolute and to the relative availability of limiting nutrients. Absolute amounts of N and P resorption, as well as N and P resorption efficiencies did not demonstrate a significant trend with nutrient availability, and there was no evidence of significant interactions between the two nutrients. More studies of the effects of nutrient interactions in the cycling and use of nutrients by different plant species are needed before more general conclusions can be drawn.     

Nutrient availability and nutrient use efficiency in plants growing in the transition zone between land and water

The transition zone between terrestrial and freshwater habitats is highly dynamic, with large variability in environmental characteristics. Here, we investigate how these characteristics influence the nutritional status and performance of plant life forms inhabiting this zone. Specifically, we hypothesised that: (i) tissue nutrient content differs among submerged, amphibious and terrestrial species, with higher content in submerged species; and (ii) PNUE gradually increases from submerged over amphibious to terrestrial species, reflecting differences in the availability of N and P relative to inorganic C across the land–water ecotone. We found that tissue nutrient content was generally higher in submerged species and C:N and C:P ratios indicated that content was limiting for growth for ca. 20% of plant individuals, particularly those belonging to amphibious and terrestrial species groups. As predicted, the PNUE increased from submerged over amphibious to terrestrial species. We suggest that this pattern reflects that amphibious and terrestrial species allocate proportionally more nutrients into processes of importance for photosynthesis at saturating CO₂ availability, i.e. enzymes involved in substrate regeneration, compared to submerged species that are acclimated to lower availability of CO₂ in the aquatic environment. Our results indicate that enhanced nutrient loading may affect relative abundance of the three species groups in the land–water ecotone of stream ecosystems. Thus, species of amphibious and terrestrial species groups are likely to benefit more from enhanced nutrient availability in terms of faster growth compared to aquatic species, and that this can be detrimental to aquatic species growing in the land–water ecotone, e.g. Ranunculus and Callitriche.     

植物养分利用效率研究综述

养分利用效率的概念是理解生态系统功能的中心。本文从植物养分利用效率的概念出发,对养分利用效率的表示与计算方法、影响因素以及养分再吸收的生物化学基础等进行综述,分析目前研究中存在的问题,最后指出今后应加强研究的方面。     

藜个体在高密度种群中的氮素利用效率

 氮素利用效率（NUE）是植物养分策略研究中的一项重要内容。该文利用Berendse和Aerts提出的氮素利用效率概念和原理研究了高密度的藜(Chenopodium album)种群中不同植物个体在种内竞争条件下的氮素利用效率。结果表明,由于植株的氮素吸收速率与其个体大小成非线性关系,说明不同植株个体对氮素的竞争属于非对称竞争。个体较大的植株氮素输入较高,而个体较小的植株氮素输出较高,因而较大个体植株的氮素净增加也较高。植株的氮素损失随着个体大小的增加而增加,较大植株个体的氮素浓度随着生长而下降,而较小植株个体的氮素浓度随时间的变化不大,说明个体较小的植株的生长受光照的限制比受氮素的限制更大,而对较大的植株个体而言,它们的生长受氮素的限制更大。高密度藜种群中的不同植物个体具有不同的养分策略,氮素利用效率及其组成部分氮素生产力（NP）和氮素滞留时间（MRT）均不同。植株的NP和MRT与其个体大小正相关,较大的植物个体具有较高的NP和较长的MRT,因而氮素利用效率也高于个体较小的植株。在个体水平上,种内不同植株的NP与MRT不存在权衡关系（Trade-off）。因此,Berendse和Aerts提出的氮素利用效率概念不仅适用于研究种间的养分策略,对于研究种内不同植株的养分策略也同样适用。     

亚热带常绿人工针叶林冠层内光能利用率

以我国南方主要造林树种湿地松(Pinus elliottii)、马尾松(P.massoniana)、杉木(Cunninghamia lanceolata)为研究对象,采用Li-6400便携式CO2/H2O红外气体分析仪测定生长中期(7月)和后期(10月)树冠内部不同层次(上层和下层)、方位(阳面和阴面)和叶龄(当年生和1年生)光环境、净光合速率(Pn),计算了光能利用效率(LUE)。结果表明:光合有效辐射(PAR)在树冠不同层次和方位间存在显著差异(P<0.05);当年生叶所处环境PAR高于1年生叶所处环境PAR,即在一定光环境之下发育的叶片往往被后来形成的新叶所遮荫。两时期3树种上层针叶的Pn均高于下层针叶;生长中期下层针叶的LUE高于上层叶,而生长后期层次间LUE相近或下层针叶不及上层针叶。不同方位针叶Pn因树种不同而不同,湿地松和马尾松阳面叶Pn高于阴面叶,而杉木阴面叶Pn高于阳面叶;两时期3树种阴面叶LUE均高于阳面叶。总体而言,叶片Pn和LUE对森林树冠内部光环境做出较强的可塑性。由于当年生针叶生理机能和光环境均优于1年生针叶,两时期3树种当年生针叶Pn均高于1年生针叶;生长中期湿地松和马尾松当年生...     

Shifts in plant nutrient use strategies under secondary forest succession

In evergreen broad-leaved forests (EBLFs) in Tiantong National Forest Park, Eastern China, we studied the soil chemistry and plant leaf nutrient concentration along a chronosequence of secondary forest succession. Soil total N, P and leaf N, P concentration of the most abundant plant species increased with forest succession. We further examined leaf lifespan, leaf nutrient characteristics and root–shoot attributes of Pinus massoniana Lamb, the early-successional species, Schima superba Gardn. et Champ, the mid-successional species, and Castanopsis fargesii Franch, the late-successional species. These species showed both intraspecific and interspecific variability along succession. Leaf N concentration of the three dominant species increased while N resorption tended to decrease with succession; leaf P and P resorption didn’t show a consistent trend along forest succession. Compared with the other two species, C. fargesii had the shortest leaf lifespan, largest decay rate and the highest taproot diameter to shoot base diameter ratio while P. massoniana had the highest root–shoot biomass ratio and taproot length to shoot height ratio. Overall, P. massoniana used ‘conservative consumption’ nutrient use strategy in the infertile soil conditions while C. fargesii took up nutrients in the way of ‘resource spending’ when nutrient supply increased. The attributes of S. superba were intermediate between the other two species, which may contribute to its coexistence with other species in a wide range of soil conditions.     

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 (A_mass), 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. A_mass was positively correlated with the concentrations of total foliar P and of metabolic P across 10 tree species. Mean A_mass 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.     

The effect of water and nitrogen amendments on photosynthesis,leaf demography,and resource-use efficiency in Larrea tridentata,a desert evergreen shrub

Summary In the Chihuahuan Desert of southern New Mexico, both water and nitrogen limit the primary productivity of Larrea tridentata, a xerophytic evergreen shrub. Net photosynthesis was positively correlated to leaf N, but only in plants that received supplemental water. Nutrient-use efficiency, defined as photosynthetic carbon gain per unit N invested in leaf tissue, declined with increasing leaf N. However, water-use efficiency, defined as the ratio of photosynthesis to transpiration, increased with increasing leaf N, and thus these two measures of resource-use efficiency were inversely correlated. Resorption efficiency was not significantly altered over the nutrient gradient, nor was it affected by irrigation treatments. Leaf longevity decreased significantly with fertilization although the absolute magnitude of this decrease was fairly small, in part due to a large background of insect-induced mortality. Age-specific gas exchange measurements support the hypothesis that leaf aging represents a redistribution of resources, rather than actual deterioration or declining resource-use efficiency.     

Litterfall and nutrient dynamics in a montane moist evergreen broad-leaved forest in Ailao Mountains,SW China

Montane moist evergreen broad-leaved forest, dominated byLithocarpus and Castanopsis species,is the most extensive stand of subtropical mountain in Yunnan Province, SWChina. Litter production, standing crop of litter on forest floor and nutrientreturn patterns were studied over nine years (1991–1999) in a stand ofprimary evergreen broad-leaved forest in northern crest of the Ailao MountainRange. There were significant yearly variations in litter production, which ismainly related with the masting year of canopy species, and exceptionalphysicalevents (strong winds and snow) in the natural forest. The mean annual smalllitterfall is 7.12 t ha^–1 yr^–1ofwhich leaf litter account for 65% of the total litterfall. The seasonality ofsmall litterfall was bia-modal, with the main one in the late dry season(April–May) and a lesser one in early winter (October–November).Decomposition quotient value was relatively low with 0.58 for total smalllitterfall. Mean large-wood ( 2.5 cm in diameter) ranged from0.21 to 1.41 t ha^–1 yr^–1 with amean of 0.52 t ha^–1 yr^–1.Concentrations of most elements in leaf and twig were slightly greater in wetmonths than dry months, except for C and K. Woody litter had low N and Pconcentrations compared with the leaf and reproductive parts. Nutrient returntothe soil through small litterfall decrease in the orderC>N>Ca>K>Mg>Mn>Al>P>Fe, while nutrient reserve inlitteron the forest floor was in the declining sequenceC>N>Ca>K>Mg>P>Fe>Al>Mn.     

Photosynthesis or persistence: nitrogen allocation in leaves of evergreen and deciduous Quercus species

Photosynthetic nitrogen use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) is one of the most important factors for the interspecific variation in photosynthetic capacity. PNUE was analysed in two evergreen and two deciduous species of the genus Quercus. PNUE was lower in evergreen than in deciduous species, which was primarily ascribed to a smaller fraction of nitrogen allocated to the photosynthetic apparatus in evergreen species. Leaf nitrogen was further analysed into proteins in the water‐soluble, the detergent‐soluble, and the detergent‐insoluble fractions. It was assumed that the detergent‐insoluble protein represented the cell wall proteins. The fraction of nitrogen allocated to the detergent‐insoluble protein was greater in evergreen than in deciduous leaves. Thus the smaller allocation of nitrogen to the photosynthetic apparatus in evergreen species was associated with the greater allocation to cell walls. Across species, the fraction of nitrogen in detergent‐insoluble proteins was positively correlated with leaf mass per area, whereas that in the photosynthetic proteins was negatively correlated. There may be a trade‐off in nitrogen partitioning between components pertaining to productivity (photosynthetic proteins) and those pertaining to persistence (structural proteins). This trade‐off may result in the convergence of leaf traits, where species with a longer leaf life‐span have a greater leaf mass per area, lower photosynthetic capacity, and lower PNUE regardless of life form, phyllogeny, and biome.     

中国东部南北样带森林优势植物叶片的水分利用效率和氮素利用效率

通过测定中国东部南北样带主要森林生态系统中10种优势植物(兴安落叶松、蒙古栎、水曲柳、紫椴、色木槭、红松、杉木、木荷、马尾松、锥栗)叶片的碳氮含量(Cmass、Nmass)、同位素丰度(δ13C、δ15N)以及光合响应曲线,分析了不同优势植物叶片的水分利用效率和氮素利用效率之间的差异及其相互关系.结果表明： 不同生活型植物叶片的Nmass和δ15N差异显著,表现为阔叶植物>针叶植物,落叶植物>常绿植物;最大光合速率(Pn max)表现为针叶植物>阔叶植物,落叶植物>常绿植物;植物叶片的瞬时水分利用效率(WUEi)和长期水分利用效率(WUE)均表现为阔叶植物>针叶植物,常绿植物>落叶植物;植物叶片的瞬时氮素利用效率(NUEi)和长期氮素利用效率(NUE)则表现出相反的规律,且常绿植物和落叶植物叶片的NUE差异显著;WUEi和WUE之间相关性不显著,而NUEi和NUE之间呈显著正相关.植物叶片的水分利用效率与氮素利用效率显著负相关.两种资源利用效率均受植物生活型的影响,并且存在一定的制约关系.