Leaf life spans in wild perennial herbaceous plants: a survey and attempts at a functional interpretation

Summary Leaf longevity in 29 herbaceous plant species of Central Europe was studied by inspecting tagged leaves at weekly intervals. About half of the species are elements of the lowland meadow flora, the other half comprises a representative sample of species from the highest sites where vascular plants grow in the Alps. Shaded and water-stressed sites were avoided. Overall mean leaf longevity did not differ significantly between sites and amounted to 71±5 days at low and 68±4 days at high altitude. Leaf life spans ranged (with no clear altitudinal trend) from 41 to 95 days. Low-altitude forbs and grasses produced several leaf cohorts during their growth period, while most alpine species produced only one. Correlations were found between leaf duration and percent nitrogen content and carbon-cost/carbon-gain ratios, but not with leaf dry mass per unit leaf area and photosynthetic capacity alone. As leaf life spans increase, more C tends to be invested per unit CO₂ uptake and less N is invested per unit invested C. Thus, mass relationships rather than area relationships seem to be linked to leaf life span in these species, suggesting that leaf duration is associated with properties other than the efficiency of light utilization (e.g. mechanical strength, herbivory or pathogen resistance). It seems that the explanations of leaf duration that have been developed for evergreen/deciduous plants and for plants along steep light gradients do not apply to the variable life spans in leaves of perennial herbaceous plants of open habitats.     

Altitudinal variation in stomatal conductance,nitrogen content and leaf anatomy in different plant life forms in New Zealand

Summary This study is part of a series of investigations on the influence of altitude on structure and function of plant leaves. Unlike most other mountain areas, the Southern Alps of New Zealand provide localities where physiologically effective moisture stress occurs neither at high nor at low elevation, but the changes in temperature and radiation with elevation are similar or even steeper than in most other regions. In comparison with results from other mountains, where moisture may impair plant functioning at low elevation, this study allows an estimation of the relative role of water for the expression of various leaf features typically associated with alpine plants. Maximum leaf diffusive conductance (g), leaf nitrogen content (LN), stomatal density (n) and distribution, as well as area (A), thickness (d) and specific area (SLA) of leaves were studied. Three different plant life forms were investigated over their full altitudinal range (m): trees, represented by Nothofagus menziesii (1,200 m), ericaceous dwarf shrubs (1,700 m), and herbaceous plants of the genus Ranunculus (2,500 m). In all three life forms g, LN, and n increased, while SLA and A decreased with elevation. Recent investigations have found similar trends in other mountains from the temperate zone, but the changes are larger in New Zealand than elsewhere. Herbs show the greatest differences, followed by shrubs and then trees.It is concluded that g is dependent upon light climate rather than water supply, whereas SLA and related structural features appear to be controlled by the temperature regime, as they show similar altitudinal changes under different light and moisture gradients. The higher leaf nitrogen content found at high elevations in all three life forms, suggests that metabolic activity of mature leaves is not restricted by low nitrogen supply at high altitude. In general, the leaves of herbaceous plants show more pronounced structural and functional changes with altitude than the leaves of shrubs and trees.     

Resorption proficiency and efficiency of leaf nutrients in woody plants in eastern China

Aims (i) To explore variations in nutrient resorption of woody plants and their relationship with nutrient limitation and (ii) to identify the factors that control these variations in forests of eastern China.Methods We measured nitrogen (N) and phosphorus (P) concentrations in both green and senesced leaves of 172 woody species at 10 forest sites across eastern China. We compared the nutrient resorption proficiency (NuRP) and efficiency (NuRE) of N and P in plant leaves for different functional groups; we further investigated the latitudinal and altitudinal variations in NuRP and NuRE and the impacts of climate, soil and plant types on leaf nutrient resorptions.Important findings On average, the leaf N resorption proficiency (NRP) and P resorption proficiency (PRP) of woody plants in eastern China were 11.1mg g ? 1 and 0.65 mg g ? 1, respectively; and the corresponding N resorption efficiency (NRE) and P resorption efficiency (PRE) were 49.1% and 51.0%, respectively. Angiosperms have higher NRP (are less proficient) values and lower NRE and PRE values than gymnosperms, but there are no significant differences in NRP, PRP and PRE values between species with different leaf habits (evergreen vs. deciduous angiosperms). Trees have higher NRE and PRE than shrubs. Significant geographical patterns of plant nutrient resorption exist in forests of eastern China. In general, NRP and PRE decrease and PRP and NRE increase with increasing latitude/altitude for all woody species and for the different plant groups. Plant functional groups show more controls than environmental factors (climate and soil) on the N resorption traits (NRP and NRE), while site-related variables present more controls than plant types on PRP and PRE. NRP increases and PRP and NRE decrease significantly with increasing temperature and precipitation for the overall plants and for most groups, except that significant PRE–climate relationship holds for only evergreen angiosperms. Leaf nutrient resorption did not show consistent responses in relation to soil total N and P stoichiometry, probably because the resorption process is regulated by the relative costs of drawing nutrients from soil versus from senescing leaves. These results support our hypothesis that plants growing in P-limited habitats (low latitudes/altitudes or areas with high precipitation/temperature) should have lower PRP and higher PRE, compared with their counterparts in relatively N-limited places (high latitudes/altitudes or areas with low precipitation/temperature). Our findings can improve the understanding of variations in N and P resorption and their responses to global change, and thus facilitate to incorporate these nutrient resorption processes into future biogeochemical models.     

Carbon isotope discrimination by plants follows latitudinal and altitudinal trends

Summary In an earlier paper we provided evidence that carbon isotope discrimination during photosynthesis of terrestrial C3 plants decreases with altitude, and it was found that this was associated with greater carboxylation efficiency at high altitudes. Changing partial pressures of CO₂ and O₂ and changing temperature are possible explanations, since influences of moisture and light were reduced to a minimum by selective sampling. Here we analyse plants sampled using the same criteria, but from high and low altitudes along latitudinal gradients from the equator to the polar ends of plant distribution. These data should permit separation of the pressure and temperature components (Fig. 1). Only leaves of fully sunlit, non-water-stressed, herbaceous C3 plants are compared. The survey covers pressure differences of 400 mbar (ca. 5000 m) and 78 degrees of latitude (ca 25 K of mean temperature of growth period). When habitats of similar low temperature (i.e. high altitude at low latitude and low altitude at polar latitude) are compared, discrimination increases towards the pole (with decreasing altitude and thus increasing atmospheric pressure). Latitudinally decreasing temperature at almost constant atmospheric pressure (samples from low altitude) is associated with a decrease in discrimination. So, polar low-altitude plants have ¹³C values half way between humid tropical lowland and tropical alpine plants. It is unlikely that latitudinal changes of the light regime had an effect, since low and high altitude plants show contrasting latitudinal trends in ¹³C although local altitudinal differences in overall light consumption were small. These results suggest that both temperature and atmospheric pressure are responsible for the altitudinal trends in ¹³C discrimination. Temperature effects may partly be related to increased leaf thickness (within the same leaf type) in cold environments. Theoretical considerations and laboratory experiments suggest that it is the oxygen partial pressure that is responsible for the pressure related change in discrimination. The study also provided results of practical significance for the use of carbon isotope data. Within a community of C3 plants, discrimination in species of similar life form, exposed to similar light, water and ambient CO₂ conditions ranges over 4, with standard deviations for 10–30 species of ±0.6 to 1.2. This natural variation has to be taken into account by using a sufficient sample size and standardization of sampling in any attempt at ecological site characterization using carbon isotope data. Evidence of a pronounced genotypic component of this variation in ¹³C discrimination in wild C3 plant species is provided. Correlations with dry matter partitioning, mesophyll thickness and nitrogen content are also present.     

Altitudinal variation in ant–aphid mutualism in nitrogen transfer of oak (<Emphasis Type="Italic">Quercus liaotungensis</Emphasis>)

Ant–plant relationship is a model for the study of the ecology and evolution of interspecific interactions. In direct ant–plant mutualism (i.e., plants providing food or nesting places for ants, and ants protecting the plants in return) ants provide nutrients to plants. However, whether a similar mechanism exists in indirect ant–plant mutualism (i.e., an ant–aphid–plant system) remains unknown. In this work, we used the ¹⁵N stable isotope method to study altitudinal variations in the roles of ants in the nutrient transfer of oak (Quercus liaotungensis). Our work shows that ants deliver nitrogen in indirect ant–plant interactions, and that the effect of nutrient transfer differed significantly with altitude. Ants’ trophic level at high altitudes was significantly lower than that at low altitudes, indicating that the degree of ant–aphid mutualism was greater at high altitudes, which may be beneficial in nitrogen transfer. Our work suggests that ant–aphid mutualism might be context dependent, such that it affects nutrient transfer in the food web, and that this context dependency is an important factor that influences altitudinal variation in nutrient transfer.     

海拔对高山栎光合气体交换和叶性状的影响

理解影响植物分布的式样及过程是生态学研究的中心内容之一,但对许多物种而言,限制其分布的原因还不清楚。为了认识高山栎分布与生理生态特性的关系,我们在不同海拔的4个观测点研究了帽斗栎的光合气体交换、叶氮含量、叶绿素含量和比叶重。由于高的水气压亏缺和气温,帽斗栎的光合作用和蒸腾作用在午间表现出明显的降低现象。帽斗栎的饱和光合速率、水分利用效率、最大羧化速率、最大电子传递速率和氮利用效率在海拔中部比低海拔或高海拔处的为高。不同海拔的叶氮含量在5月份有差异,8月份则没有明显不同。叶片厚度随海拔增加,但叶绿素含量及光合最适温度随海拔升高而降低。帽斗栎光合作用的海拔变化与叶片的生化效率和氮含量有关,而与比叶重无关。研究结果说明,温度的海拔变化对高山栎的光合作用和叶性状有明显影响,最适宜帽斗栎光合碳获取及生长的海拔范围是3180～3610m。     

海拔对高山栎光合气体交换和叶性状的影响

理解影响植物分布的式样及过程是生态学研究的中心内容之一,但对许多物种而言,限制其分布的原因还不清楚。为了认识高山栎分布与生理生态特性的关系,我们在不同海拔的4个观测点研究了帽斗栎的光合气体交换、叶氮含量、叶绿素含量和比叶重。由于高的水气压亏缺和气温,帽斗栎的光合作用和蒸腾作用在午间表现出明显的降低现象。帽斗栎的饱和光合速率、水分利用效率、最大羧化速率、最大电子传递速率和氮利用效率在海拔中部比低海拔或高海拔处的为高。不同海拔的叶氮含量在5月份有差异,8月份则没有明显不同。叶片厚度随海拔增加,但叶绿素含量及光合最适温度随海拔升高而降低。帽斗栎光合作用的海拔变化与叶片的生化效率和氮含量有关,而与比叶重无关。研究结果说明,温度的海拔变化对高山栎的光合作用和叶性状有明显影响,最适宜帽斗栎光合碳获取及生长的海拔范围是3180~3610m。     

重庆石灰岩地区主要木本植物叶片性状及养分再吸收特征

以重庆石灰岩地区15种常绿木本植物和14种落叶木本植物为研究对象,对两种生活型植物叶片衰老前后叶干物质含量(LDMC)、比叶面积(SLA)和叶片厚度(LT)进行了比较,并采用不同的计算方法(单位质量叶片养分含量、单位面积叶片养分含量)分析了两类植物叶片衰老前后养分含量及再吸收特征,最后对养分再吸收效率与其他叶性状因子之间的关系进行了相关分析。结果表明:常绿植物成熟叶LDMC、LT及衰老叶LT显著低于落叶植物,落叶植物成熟叶和衰老叶SLA均显著高于常绿植物(P0.05);基于单位质量叶片计算的养分含量,常绿植物成熟和衰老叶N、P量均低于落叶植物,而基于单位面积叶片计算的N、P含量则表现出相反的趋势;基于不同方法计算的N、P再吸收效率差异不明显,其中常绿植物基于单位质量叶片养分含量计算的N、P平均再吸收效率为39.42%、43.79%,落叶植物的为24.08%、33.59%;常绿和落叶植物N、P再吸收效率与LDMC、SLA、LT和成熟叶N、P含量之间没有显著相关性,但与衰老叶养分含量存在显著负相关(P0.05)。研究发现,无论是常绿植物还是落叶植物,衰老叶N、P含量均较低,表明石灰岩地区植物具有较高的养分再吸收程度。     

红池坝草地常见物种叶片性状沿海拔梯度的响应特征

叶片性状是决定植物光合能力和羧化能力的关键因素,研究叶片性状在海拔梯度上的变化特征是解释植物对于环境变化的适应策略的重要手段。本文以分布于红池坝(10958′E, 3130′ N)草地的5个常见物种红三叶(Trifolium pratense)、老鹳草(Geranium wilfordii)、紫菀(Aster tataricus)、火绒草(Leontopodium leontopodioides)和绣线菊(Spiraea prunifolia)为研究对象,分析了所有物种(n=56)和不同物种的叶片比叶重(LMA)、叶氮含量(单位面积氮含量Narea、单位重量氮含量Nmass)以及叶片δ13C含量沿海拔梯度(815-2545m)的变化趋势及叶片性状之间的关系。研究结果表明：所有物种样品(n=56)的比叶重(LMA)、Narea和δ13C含量沿海拔梯度的增加呈显著增加趋势;Nmass沿海拔梯度的变化趋势不明显;δ13C含量与LMA、Narea呈现极显著正相关关系;不同物种的叶片性状沿着海拔梯度的响应特征有所不同,绣线菊(S. prunifolia)和老鹳草(G. wilfordii)的叶片性状沿海拔梯度的分布规律与所有物种(n=56)样品分布规律一致,红三叶(T. pratense)、紫菀(A. tataricus)、火绒草(L. leontopodioides)的各叶片性状沿海拔梯度的分布特征有所不同。     

Contrasting altitudinal patterns of leaf UV reflectance and absorbance in four herbaceous species on the Qinghai–Tibetan Plateau

Aims Alpine plants have to cope with intense ultraviolet (UV) radiation and its altitudinal changes. It has been argued that leaf UV reflectance and absorbance should play a central role in acclimation and adaptation to changes in UV radiation, but evidence is limited from high altitudinal ecosystems. In this study, we assessed whether leaf UV reflectance and leaf pigments jointly vary with altitude in alpine broadleaved herbaceous species. The primary hypothesis is that leaves with higher UV reflectance should have lower UV absorbance and/or lower contents of photosynthetic pigments.