Plant mineral nutrition in ancient landscapes: high plant species diversity on infertile soils is linked to functional diversity for nutritional strategies

Ancient landscapes, which have not been glaciated in recent times or disturbed by other major catastrophic events such as volcanic eruptions, are dominated by nutrient-impoverished soils. If these parts of the world have had a relatively stable climate, due to buffering by oceans, their floras tend to be very biodiverse. This review compares the functional ecophysiological plant traits that dominate in old, climatically buffered, infertile landscapes (OCBILS) with those commonly found in young, frequently disturbed, fertile landscapes (YODFELs). We show that, within the OCBILs of Western Australia, non-mycorrhizal species with specialised root clusters predominantly occur on the most phosphate-impoverished soils, where they co-occur with mycorrhizal species without such specialised root clusters. In global comparisons, we show that plants in OCBILs, especially in Western Australia, are characterised by very low leaf phosphorus (P) concentrations, very high N:P ratios, and very high LMA values (LMA = leaf mass per unit leaf area). In addition, we show that species in OCBILs are far more likely to show P-toxicity symptoms when exposed to slightly elevated soil P levels when compared with plants in YODFELs. In addition, some species in OCBILs exhibit a remarkable P-resorption proficiency, with some plants in Western Australia achieving leaf P concentrations in recently shed leaves that are lower than ever reported before. We discuss how this knowledge on functional traits can guide us towards sustainable management of ancient landscapes.     

OCBIL theory: towards an integrated understanding of the evolution, ecology and conservation of biodiversity on old, climatically buffered, infertile landscapes

OCBIL theory aims to develop an integrated series of hypotheses explaining the evolution and ecology of, and best conservation practices for, biota on very old, climatically buffered, infertile landscapes (OCBILs). Conventional theory for ecology and evolutionary and conservation biology has developed primarily from data on species and communities from young, often disturbed, fertile landscapes (YODFELs), mainly in the Northern Hemisphere. OCBILs are rare, but are prominent in the Southwest Australian Floristic Region, South Africa’s Greater Cape, and Venezuela’s Pantepui Highlands. They may have been more common globally before Pleistocene glaciations. Based on the premise that natural selection has favoured limited dispersability of sedentary organisms, OCBILs should have elevated persistence of lineages (Gondwanan Heritage Hypothesis) and long-lived individuals (Ultimate Self Hypothesis), high numbers of localised rare endemics and strongly differentiated population systems. To counter such natural fragmentation and inbreeding due to small population size, ecological, cytogenetic and genetic mechanisms selecting for the retention of heterozygosity should feature (the James Effect). The climatic stability of OCBILs should be paralleled by persistence of adjacent semi-arid areas, conducive to speciation (Semiarid Cradle Hypothesis). Special nutritional and other biological traits associated with coping with infertile lands should be evident, accentuated in plants, for example, through water-foraging strategies, symbioses, carnivory, pollination and parasitism. The uniquely flat landscapes of southwestern Australia have had prolonged presence of saline lakes along palaeoriver systems favouring evolution of accentuated tolerance to salinity. Lastly, unusual resiliences and vulnerabilities might be evident among OCBIL organisms, such as enhanced abilities to persist in small fragmented populations but great susceptibility to major soil disturbances. In those places where it is most pertinent, OCBIL theory hopefully lays a foundation for future research and for better informed conservation management.     

Root structure and functioning for efficient acquisition of phosphorus: Matching morphological and physiological traits

BACKGROUND: Global phosphorus (P) reserves are being depleted, with half-depletion predicted to occur between 2040 and 2060. Most of the P applied in fertilizers may be sorbed by soil, and not be available for plants lacking specific adaptations. On the severely P-impoverished soils of south-western Australia and the Cape region in South Africa, non-mycorrhizal species exhibit highly effective adaptations to acquire P. A wide range of these non-mycorrhizal species, belonging to two monocotyledonous and eight dicotyledonous families, produce root clusters. Non-mycorrhizal species with root clusters appear to be particularly effective at accessing P when its availability is extremely low. SCOPE: There is a need to develop crops that are highly effective at acquiring inorganic P (Pi) from P-sorbing soils. Traits such as those found in non-mycorrhizal root-cluster-bearing species in Australia, South Africa and other P-impoverished environments are highly desirable for future crops. Root clusters combine a specialized structure with a specialized metabolism. Native species with such traits could be domesticated or crossed with existing crop species. An alternative approach would be to develop future crops with root clusters based on knowledge of the genes involved in development and functioning of root clusters. CONCLUSIONS: Root clusters offer enormous potential for future research of both a fundamental and a strategic nature. New discoveries of the development and functioning of root clusters in both monocotyledonous and dicotyledonous families are essential to produce new crops with superior P-acquisition traits.     

黄土丘陵区植物叶片与细根功能性状关系及其变化

通过植物叶片功能性状(比叶面积、叶组织密度、叶氮含量)和细根功能性状(比根长、根组织密度、根氮含量)间的相互关系,分析植物对环境的适应途径;然后根据性状间的差异进行了层次聚类,将物种划分为3大功能型,并分析了不同功能型对环境的适应策略.结果表明:黄土丘陵区延河流域149种植物的叶氮含量与比叶面积和根氮含量正相关、与叶组织密度负相关,比根长与根组织密度负相关,除了根氮含量,其余根性状与叶性状不相关.此外,功能性状间关系变化和适应策略在不同功能型之间也存在差异.功能型1的植物具有最强的耐旱力和防御力;功能型3的植物具有最强的养分维持能力用以对抗营养贫瘠的环境;功能型2的植物居中,生长速率最高,具有较强的竞争力、分布最广;根据C-S-R理论,功能型1和3属于“胁迫忍耐型”策略(S策略),功能型2则属于“竞争型”(C)和“干扰型”(R)策略的综合.研究结果为黄土丘陵区植被恢复规划及物种配置等提供依据.     

Mechanisms for enhancing nutrient uptake in plants,with particular reference to mediterranean South Africa and Western Australia

The major constraints to nutrient uptake by vascular plants in mediterranean South Africa and Western Australia are: very infertile soils, relatively low temperatures when water availability is high, and hot, dry summers. These constraints are partly overcome through increased efficiency of uptake, tapping novel sources of nutrients, and prolonging water uptake. Absorptive area per unit “cost” may be enlarged directly through increased fineness of the root system and proliferation of long root hairs. This reaches its greatest development in the root clusters of the Proteaceae (proteoid roots), Restionaceae (“capillaroid” roots) and Cyperaceae (dauciform roots). Absorptive area is increased indirectly through fungal hyphae which extend from hairless rootlets into the soil. Two major groups can be recognised: general (VA mycorrhizas) and host-specific (ericoid, orchid and sheathing mycorrhizas). Mycorrhizas are the most widespread specialised modes of nutrition and are probably universal in such major taxa here asPodocarpus, Acacia, Fabaceae, Poaceae, Asteraceae, Rutaceae, terrestrial orchids, Ericales and Myrtaceae. General mycorrhizas are the least drought-adapted of mechanisms for maximising absorptive area. All have been implicated in enhancing P uptake through increasing access to inorganic P, solubilisation and shortening the diffusion path. However, selective uptake of other nutrients, especially N, by host-specific mycorrhizas may be equally important. Included under novel sources of nutrients are free N₂ (utilised by N₂-fixing nodules), small-animal prey (carnivorous leaves) and persistent leaf bases (aerial roots ofKingia australis). Both legume and non-legume N₂-fixing species are well-represented in these two regions, with stands of individual species in southwestern Australia estimated to contribute 2–19 kg N/ha/yr to the ecosystem. Free nitrogen fixation requires additional nutrients, especially Mo and Co, but is enhanced following fires and by supplementary uptake mechanisms, especially VA mycorrhizas. Southwestern Australia is particularly rich in carnivorous species. Nitrogen, P, K and S are important nutrients absorbed, with digestion aided by enzymes provided by bacteria and the glands. Parasitic plants both tap novel sources of nutrients and capitalise on any efficient water and nutrient uptake mechanisms of the hosts. Root parasites are better represented than stem parasites in mediterranean South Africa and Western Australia. Phosphorus and K in particular are absorbed preferentially by the haustoria, but much remains to be known about their modes of operation. Maximum activity of all uptake mechanisms, except those attached to some deep-rooted plants, is restricted to winter-spring. Most new seasons’s rootlets and specialised roots are confined to the uppermost 15 cm of soil, especially in or near the decomposing litter zone. Nutrient uptake is further enhanced by the tendency for the rootlets to cluster, trapping water by capillary action and prolonging nutrient release. As an early product of decomposition, N tends to be available as NH₄ (rather than NO₃) and it is absorbed preferentially by almost all specialised modes of nutrition. Microorganisms are required in the formation and/or functioning of all these structures, except haustoria. Uptake mechanisms which are optional to the plant reach their peak contribution to the root system at soil nutrient levels well below those required for greatest plant growth, when they may be absent altogether. It is only over the narrow range of nutrient availability, where shoot content of a nutrient is greater in the presence of the mechanism than in its absence (other factors remaining constant), that specialised modes can be termed nutrient-uptake “strategies.” For all specialised modes of nutrition, the component genera are better represented in these two regions than in the surrounding more fertile, arid to subtropical regions of much greater area. Endemism of species with each mode exceeds that for the two floras overall (75%). This is taken as preliminary evidence that specialised modes of nutrition are best represented in nutrient-poor soils. While they serve to limit nutrient loss from the ecosystem, their proliferation is therefore not necessarily a response to increasing “leaks” in the system. A hierarchical scheme of the functional/structural relationships between the various mechanisms is presented, starting with the rootless, VA-mycorrhizal plant as the most primitive condition. Taxa with many of the specialised modes of nutrition at present in southwestern South Africa and Western Australia have been evident in the pollen record since the early Tertiary Period. The absence of ectomycorrhizal forests in mediterranean South Africa, in marked contrast to Western Australia, can be traced to differences in their paleohistory. In both regions, the combination of fluctuating, but essentially diminishing, nutrient and water availability that began with the first mediterranean climate < 5 million years ago resulted in decimation of the less-tolerant rainforest ancestors on the one hand, and remarkable rates of speciation of the pre-adapted sclerophyll nucleus on the other.     

Shifts and plasticity of plant leaf mass per area and leaf size among slope aspects in a subalpine meadow

The composition of vegetation on a slope frequently changes substantially owing to the different micro‐environments of various slope aspects. To understand how the slope aspect affects the vegetation changes, we examined the variations in leaf mass per area (LMA) and leaf size (LS) within and among populations for 66 species from 14 plots with a variety of slope aspects in a subalpine meadow. LMA is a leaf economic trait that is tightly correlated with plant physiological traits, while the LS shows a tight correlation with leaf temperature, indicating the strategy of plants to self‐adjust in different thermal and hydraulic conditions. In this study, we compared the two leaf traits between slope aspects and between functional types and explored their correlation with soil variables and heat load. Our results showed that high‐LMA, small‐leaved species were favored in south‐facing slopes, while the reverse was true in north‐facing areas. In detail, small dense‐leaved graminoids dominated the south slopes, while large thin‐leaved forbs dominated the north slopes. Soil moisture and the availability of soil P were the two most important soil factors that related to both LMA and LS, and heat load also contributed substantially. Moreover, we disentangled the relative importance of intraspecific trait variation and species turnover in the trait variation among plots and found that the intraspecific variation contributed 98% and 56% to LMA and LS variation among communities, respectively, implying a large contribution of intraspecific trait plasticity. These results indicate that LMA and LS are two essential leaf traits that affect the adaptation or acclimation of plants underlying the vegetation composition changes in different slope aspects in the subalpine meadow.     

Are correlations among foliar traits in ferns consistent with those in the seed plants?

Broad-based studies of gymnosperms and angiosperms reveal consistent and functionally significant correlations among foliar traits such as leaf mass per area (LMA), maximum photosynthetic rate (A(area)), foliar nitrogen (N(area)), foliar chlorophyll (Chl) and leaf longevity. To assess the generality of these relationships, we studied 20 fern species growing in the understorey of a temperate deciduous forest. We found that foliar N(area) increases with LMA, and that foliar N(area) and A(area) are positively correlated with one another, as are foliar N(area) and Chl. The ferns in general have very low LMA compared with most seed plants; A(area), N(area) and Chl are below median values for seed plants but are not extreme. Species with overwintering fronds have significantly higher LMA than species with fronds that senesce at the end of the growing season, as well as a significantly higher C : N ratio in frond tissue and relatively high foliar N on an areal basis. Correlations among foliar traits associated with gas exchange in these forest understorey ferns are in accordance with patterns reported for seed plants, suggesting a high degree of functional constraint on the interrelationships among key elements in foliar design.     

The cost of carnivory for Darlingtonia californica (Sarraceniaceae): evidence from relationships among leaf traits

Scaling relationships among photosynthetic rate, foliar nutrient concentration, and leaf mass per unit area (LMA) have been observed for a broad range of plants. Leaf traits of the carnivorous pitcher plant Darlingtonia californica, endemic to southern Oregon and northern California, USA, differ substantially from the predictions of these general scaling relationships; net photosynthetic rates of Darlingtonia are much lower than predicted by general scaling relationships given observed foliar nitrogen (N) and phosphorus (P) concentrations and LMA. At five sites in the center of its range, leaf traits of Darlingtonia were strongly correlated with elevation and differed with soil calcium availability and bedrock type. The mean foliar N : P of 25.2 ± 15.4 of Darlingtonia suggested that these plants were P-limited, although N concentration in the substrate also was extremely low and prey capture was uncommon. Foliar N : P stoichiometry and the observed deviation of Darlingtonia leaf traits from predictions of general scaling relationships permit an initial assessment of the "cost of carnivory" in this species. Carnivory in plants is thought to have evolved in response to N limitation, but for Darlingtonia, carnivory is an evolutionary last resort when both N and P are severely limiting and photosynthesis is greatly reduced.     

Leaf trait variations associated with habitat affinity of tropical karst tree species

Karst hills, that is, jagged topography created by dissolution of limestone and other soluble rocks, are distributed extensively in tropical forest regions, including southern parts of China. They are characterized by a sharp mosaic of water and nutrient availability, from exposed hilltops with poor soil development to valleys with occasional flooding, to which trees show species‐specific distributions. Here we report the relationship of leaf functional traits to habitat preference of tropical karst trees. We described leaf traits of 19 tropical tree species in a seasonal karst rainforest in Guangxi Province, China, 12 species in situ and 13 ex situ in a non‐karst arboretum, which served as a common garden, with six species sampled in both. We examined how the measured leaf traits differed in relation to species’ habitat affinity and evaluated trait consistency between natural habitats vs. the arboretum. Leaf mass per area (LMA) and optical traits (light absorption and reflectance characteristics between 400 and 1,050 nm) showed significant associations with each other and habitats, with hilltop species showing high values of LMA and low values of photochemical reflectance index (PRI). For the six species sampled in both the karst forest and the arboretum, LMA, leaf dry matter content, stomatal density, and vein length per area showed inconsistent within‐species variations, whereas some traits (stomatal pore index and lamina thickness) were similar between the two sites. In conclusion, trees specialized in exposed karst hilltops with little soils are characterized by thick leaves with high tissue density indicative of conservative resources use, and this trait syndrome could potentially be sensed remotely with PRI.     

Relationships between leaf morphological traits, nutrient concentrations and isotopic signatures for Mediterranean woody plant species and communities

Background and aims

Soil factors are driving forces that influence spatial distribution and functional traits of plant species. We test whether two anchor morphological traits—leaf mass per area (LMA) and leaf dry matter content (LDMC)—are significantly related to a broad range of leaf nutrient concentrations in Mediterranean woody plant species. We also explore the main environmental filters (light availability, soil moisture and soil nutrients) that determine the patterns of these functional traits in a forest stand.

Methods

Four morphological and 19 chemical leaf traits (macronutrients and trace elements and δ¹³C and δ¹⁵N signatures) were analysed in 17 woody plant species. Community-weighted leaf traits were calculated for 57 plots within the forest. Links between LMA, LDMC and other leaf traits were analysed at the species and the community level using standardised major axis (SMA) regressions

Results

LMA and LDMC were significantly related to many leaf nutrient concentrations, but only when using abundance-weighted values at community level. Among-traits links were much weaker for the cross-species analysis. Nitrogen isotopic signatures were useful to understand different resource-use strategies. Community-weighted LMA and LDMC were negatively related to light availability, contrary to what was expected.

Conclusion

Community leaf traits have parallel shifts along the environmental factors that determine the community assembly, even though they are weakly related across individual taxa. Light availability is the main environmental factor determining this convergence of the community leaf traits.     

Are traits measured on pot grown plants representative of those in natural communities?

Question: The quantification of functional traits in natural communities can be difficult (e.g. root traits, RGR). Can functional traits measured on pot grown plants be reliably applied to natural communities? Alternatively, can below‐ground plant traits be predicted from above‐ground traits? Location: Southeastern Australia. Methods: We compared 17 shoot, root and whole‐plant morphological traits measured on 14 plant species in a native grassland community to those measured under two different pot conditions: unfertilised and fertilised. Results: The majority of trait values for pot grown plants differed to plants in the field, however, species ranking remained consistent for most leaf traits between the field and the two pot growing conditions. In contrast, species ranking was not consistent for most whole plant traits when comparing field plants to fertilised pot grown plants, providing a caution against the tendency to grow plants in controlled conditions at ‘optimal’ (high) resource levels. Moderate to strong correlations were found between below‐ground and above‐ground plant traits, including between root dry matter content and leaf dry matter content, and between specific root area and specific leaf area. Conclusions: The utility of pot grown plants to quantify traits for field plants is highly dependent on the selection of the growing conditions in the controlled environment. The consistency we observed between above‐ground and below‐ground trait strategies suggests that below‐ground traits may be predictable based on above‐ground traits, reducing the need to quantify root traits on cultured plants.     

Leaf functional traits vary with the adult height of plant species in forest communities

Aims Within-community variation accounts for a remarkable proportion of the variation in leaf functional traits. Plant height may be used to explain within-community variances of leaf traits because different microenvironments, especially light intensity, may occur at different heights. This study determines whether or not leaf nitrogen (N) and phosphorus (P) contents as well as leaf mass per area (LMA) are interspecifically correlated with the adult height of forest woody species. We also discuss these relationships with respect to community structure and functions of the ecosystem.Methods A total of 136 dicotyledonous woody species from 6 natural forests (3 evergreen and 3 deciduous ones) in East China (18°44′–45°25′N, 108°50′–128°05′E) were investigated. For each of the 157 species–site combinations, 6 traits were measured: plant adult height relative to the forest canopy (H R), leaf N and P contents per unit area (N area and P area), N and P contents per unit dry mass (N mass and P mass) and LMA. The total variances of each leaf trait across sites were partitioned in a hierarchical manner. The relationships between leaf traits and H R within forest communities were then analyzed using both standardized major axis regression and Felsenstein's phylogenetic independent contrasts. Relationships between evergreen and deciduous forests were compared by linear mixed models.Important findings H R is a robust predictor of leaf N area, P area and LMA, explaining 36.7, 39.4 and 12.0% of their total variations across forests, respectively. Leaf N area, P area and LMA increased with H R in all of the studied forests, with slopes that were steeper in evergreen forests than in deciduous ones. Leaf N mass and P mass showed no significant relationship with H R generally. The increase in leaf N area, P area and LMA with H R across species is assumed to maximize community photosynthesis and may favor species with larger H R .     

干旱和湿润生境中主要优势树种叶片功能性状的比较

以云南南部的沟谷雨林(湿润生境)和干热河谷萨瓦纳(savanna)稀树灌丛(干旱生境)中共31种主要优势木本植物为材料,研究了叶片主要功能性状单位面积叶干重(LMA)、单位干重氮含量(Nmass)和单位干重最大净光合速率(Amass)在2个生境中的差异及各性状间的关系。结果表明:在物种水平上,干旱和湿润生境中各树种的LMA值分别为46.88～178.63和45.35～93.16g·m-2;Amass值分别为48.12～176.65和71.38～265.76nmol·g-1·s-1;Nmass值分别为11.8～36.71和12.98～31.78mg·g-1;在群落水平上,干旱生境中LMA显著高于湿润生境,而Amass显著低于湿润生境,Nmass在2个生境中差异不显著;在群落尺度上,干旱生境中LMA与Nmass和Amass均呈显著负相关;在2生境中Nmass与Amass均呈显著正相关。同一生境下不同植物对环境的适应策略有差异,但各性状间的相关关系具有趋同性;从湿润到干旱生境,植物由快速生长转向以提高资源利用效率为主的适应策略。     

三峡水库消落带植物叶片光合与营养性状特征

自2007年三峡大坝试运行以来,其独特的人工水位调度节律给当地的水库消落带生态系统带来了巨大的负面影响。植物功能性状可以反映某一特殊生境植物的生理生态过程特殊性,是指示生态系统结构与功能的有效指标。因此,在三峡水库消落带形成2a后,于2009年调查了消落带的42种适生植物以及对照带33种植物的6个叶片功能性状:最大净光合速率(Amax)、叶片气孔导度(Gs)、比叶重(LMA)、叶片全氮含量(Nmass)、全磷含量(Pmass)和全钾含量(Kmass)。运用标准化主轴回归分析对消落带植物叶片各功能性状之间关系进行分析,并对照全球尺度叶片功能性状数据库,旨在说明反季节淹水对消落带植物叶片功能性状之间关系与全球尺度对比发生了哪些变化。同时,运用成对方差t检验的分析方法,对比了在消落带和对照带都存在的33个种的叶片光合与营养性状之间的差异,以阐明消落带植物对消落带特殊生境的生理响应。结果表明:(1)消落带植物叶片各性状关系呈现出与全球尺度基本一致的格局,表现出植物叶性状之间关系的趋同性;(2)消落带植物Amass、Nmass、Pmass和Kmass显著高于全球尺度,而LMA则显著低于全球尺度。处于驯化阶段的消落带植物各叶片性状处在全球叶片经济型谱"低投入-快速回收"的一端。(3)消落带植物叶片Amass与对照带相比,有显著提高。表明三峡水库消落带植物叶片光合能力得到显著提高,这可能是其适应消落带特殊生境的关键生理生态对策之一。     

Is N‐resorption efficiency related to secondary compounds and leaf longevity in coexisting plant species of the arid Patagonian Monte,Argentina?

Leaf longevity and nutrient resorption efficiency are important strategies to conserve plant nutrients. Theory suggests a negative relationship between them and also proposes that high concentration of phenolics in long‐lived leaves may reduce nutrient resorption. In order to provide new evidence on these relationships, we explored whether N‐resorption efficiency is related to leaf longevity, secondary compounds and other leaf traits in coexisting plant species of different life forms in the arid Patagonian Monte, Argentina. We assessed N‐resorption efficiency, green leaf traits (leaf mass per area (LMA), leaf longevity and lignin, total soluble phenolics and N concentrations) and N concentration in senescent leaves of 12 species of different life forms (evergreen shrubs, deciduous shrubs and perennial grasses) with contrasting leaf traits. We found that leaf longevity was positively correlated to LMA and lignin, and negatively correlated to N concentration in green leaves. N concentrations both in green and senescent leaves were positively related. N‐resorption efficiency was not associated with the concentration of secondary compounds (total soluble phenolics and lignin) but it was negatively related to LMA and leaf longevity and positively related to N concentration in green leaves. Furthermore, leaf traits overlapped among life forms highlighting that life forms are not a good indicator of the functional properties (at least in relation to nutrient conservation) of species. In conclusion, our findings indicated that differences in N‐resorption efficiency among coexisting species were more related to N concentration in green leaves, leaf lifespan and LMA than to the presence of secondary compounds at least those assessed in our study (soluble phenolics and lignin). Accordingly, N‐resorption efficiency seems to be modulated, at least in part, by the productivity–persistence trade‐off.     

Coordination between leaf and stem traits related to leaf carbon gain and hydraulics across 32 drought-tolerant angiosperms

We examined 15 traits in leaves and stems related to leaf C economy and water use for 32 co-existing angiosperms at ridge sites with shallow soil in the Bonin Islands. Across species, stem density was positively correlated to leaf mass per area (LMA), leaf lifespan (LLS), and total phenolics and condensed tannins per unit leaf N (N-based), and negatively correlated to leaf osmotic potential and saturated water content in leaves. LMA and LLS were negatively correlated to photosynthetic parameters, such as area-, mass-, and N-based assimilation rates. Although stem density and leaf osmotic potential were not associated with photosynthetic parameters, they were associated with some parameters of the leaf C economy, such as LMA and LLS. In the principal component (PCA) analysis, the first three axes accounted for 74.4% of total variation. Axis 1, which explained 41.8% of the total variation, was well associated with parameters for leaf C and N economy. Similarly, axis 2, which explained 22.3% of the total variation, was associated with parameters for water use. Axis 3, which explained 10.3% of the total variation, was associated with chemical defense within leaves. Axes 1 and 2 separated functional types relatively well, i.e., creeping trees, ruderal trees, other woody plants, C₃ shrubs and forbs, palms, and CAM plants, indicating that plant functional types were characterized by similar attributes of traits related to leaf C and N economy and water use. In addition, when the plot was extended by two unrelated traits, leaf mass-based assimilation rates and stem density, it also separated these functional types. These data indicate that differences in the functional types with contrasting plant strategies can be attributed to functional integration among leaf C economy, hydraulics, and leaf longevity, and that both leaf mass-based assimilation rates and stem density are key factors reflecting the different functions of plant species.     

The relationship between nuclear DNA content and leaf strategy in seed plants

BACKGROUND AND AIMS: Species' 2C-values (mass of DNA in G(1) phase 2n nuclei) vary by at least four orders of magnitude among seed plants. The 2C-value has been shown to be co-ordinated with a number of other species traits, and with environmental variables. A prediction that species 2C-values are negatively related to leaf life span (LL) and leaf mass per area (LMA) is tested. These leaf traits are components of a major dimension of ecological variation among plant species. METHODS: Flow cytometry was used to measure the 2C-values for 41 Australian seed plant species, 40 of which were new to the literature. Where possible, LL and LMA data from the global literature were combined with 2C-values from our data set and online C-value databases. KEY RESULTS: Across all species, weak positive relationships were found between 2C-values and both LL and LMA; however, these did not reflect the relationships within either angiosperms or gymnosperms. Across 59 angiosperm species, there were weak negative relationships between 2C-values and both LL (r2 = 0.13, P = 0.005) and LMA (r2 = 0.15, P = 0.002). These relationships were the result of shifts to longer LL and greater LMA in woody compared with herbaceous growth forms, with no relationships present within growth forms. It was not possible to explain a positive relationship between 2C-values and LMA (r2 = 0.30, P = 0.024) across 17 gymnosperm species. The 2C-value was not related to LL or LMA either across species within orders (except for LMA among Pinales), or as radiation divergences in a model phylogeny. CONCLUSIONS: Gymnosperms appear to vary along a spectrum different from angiosperms. Among angiosperms, weak negative cross-species relationships were associated with growth form differences, and traced to a few divergences deep in the model phylogeny. These results suggest that among angiosperms, nuclear DNA content and leaf strategy are unrelated.     

漓江水陆交错带植物叶性状对水淹胁迫的响应及经济谱分析

以漓江水陆交错带为研究区,分两个条带分别量测了适生植物的5个叶性状指标:最大净光合速率(A_(max))、比叶重(LMA)、单位质量叶片全氮含量(N_(mass))、单位质量叶片全磷含量(P_(mass))、单位质量叶片全钾含量(K_(mass))。研究重度淹没带与微度淹没带不同功能型植物叶性状间的差异,分析并讨论重度淹没带叶性状间的关系与全球尺度是否存在差异,探究重度淹没带植物对水淹生境的生理响应机制。结果如下:(1)重度淹没带植物叶片的A_(mass)、N_(mass)、P_(mass)显著高于微度淹没带。(2)乔木、灌木叶片的LMA均显著高于草本植物,而A_(mass)、PPUE均显著低于草本植物。(3)重度淹没带草本叶性状指标的N_(mass)、P_(mass)、PNUE均显著高于微度微度淹没带,而乔木、灌木的叶性状在两个条带的差异则不显著。(4)重度淹没带植物叶性状关系与全球尺度基本一致,其植物叶片具有低LMA,高A_(mass)、Nmas s、P_(mass)。分析可知,重度淹没带植物在出露期提高叶片光合效率及相关营养水平可能是其适应水淹胁迫特殊生境的关键策略之一;不同功能型植物对同一环境的适应能力存在一定的差异,草本对于水淹环境的响应更为积极,适应能力更好;重度淹没带也存在叶经济谱,其植物在经济谱中属于"快速投资-收益"型物种。     

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.     

Distribution and Function of Proteoid Roots and other Root Clusters

Proteoid roots are bottlebrush-like clusters of rootlets which form along lateral roots. They are characteristic of most species of the Proteaceae, which are mainly distributed in Australia and South Africa. Homologous root clusters are present in species of the Casuarinaceae, Mimosaceae, Fabaceae, Myricaceae and Moraceae. Many similarities exist between these species in relation to morphology and function of root clusters. Many are non-mycorrhizal and are highly efficient in phosphorus (P) acquisition. In these species, proteoid roots and proteoid-like root clusters are abundant when grown on infertile soils. Their formation is predominantly affected by the P status of the plants, being induced at low P levels and repressed at high P levels. Proteoid roots and proteoid-like root clusters play an important role in acquisition of P and other mineral nutrients. Although increase in root surface area may be a contributing factor, in many species these roots excrete large amounts of organic acids and phenolics. The excretion of these compounds in a small soil volume gives rise to extensive nutrient mobilization by acidification, reduction and chelation of sparingly soluble forms of P and micronutrients such as Fe and Mn.