Cuticle Micromorphology of Pinus krempfii Lecomte (Pinaceae) and Additional Species from Southeast Asia

Cuticle micromorphology of the unusual Vietnamese pine, Pinus krempfii Lecomte, and three additional endemic southeast Asian species of Pinus L. (Pinaceae) is characterized for the first time. Taxa studied include (1) P. krempfii, typically placed in its own subgenus Ducampopinus (Chevalier) Ferré ex Little & Critchfield; (2) the endemic Vietnamese species Pinus dalatensis Ferré and (3) the southeast Asian species Pinus kwantungensis Chun ex Tsiang, both of subgenus Strobus; and (4) the widespread Asian species Pinus kesiya Royle ex Gordon of subgenus Pinus. The current and previous studies demonstrate that the genus Pinus and its subgenera are delimited by unique combinations of cuticular characters, although some of these characters may occur individually in other conifers. Cuticular micromorphology supports taxonomic assignment of P. krempfii to subgenus Strobus rather than to its own subgenus, a result that is also indicated by other anatomical studies and recent molecular studies. Sectional affinities of P. krempfii are usually with Parrya, subsection Krempfianae. An alternative classification of P. krempfii with subsection Gerardianae can be supported by micromorphological characters including broad cuticular bridges between stomata, details of the intercellular flanges of the epidermal cells, and usually an amphistomatic stomatal distribution. Features of other Asian species studied are consistent with their taxonomic assignments. The study demonstrates the utility of cuticle micromorphology to taxonomic delimitation within the family Pinaceae.     

Leaf hydraulic capacity in ferns, conifers and angiosperms: impacts on photosynthetic maxima

* The hydraulic plumbing of vascular plant leaves varies considerably between major plant groups both in the spatial organization of veins, as well as their anatomical structure. * Five conifers, three ferns and 12 angiosperm trees were selected from tropical and temperate forests to investigate whether the profound differences in foliar morphology of these groups lead to correspondingly profound differences in leaf hydraulic efficiency. * We found that angiosperm leaves spanned a range of leaf hydraulic conductance from 3.9 to 36 mmol m2 s-1 MPa-1, whereas ferns (5.9-11.4 mmol m-2 s-1 MPa-1) and conifers (1.6-9.0 mmol m-2 s-1 MPa-1) were uniformly less conductive to liquid water. Leaf hydraulic conductance (Kleaf) correlated strongly with stomatal conductance indicating an internal leaf-level regulation of liquid and vapour conductances. Photosynthetic capacity also increased with Kleaf, however, it became saturated at values of Kleaf over 20 mmol m-2 s-1 MPa-1. * The data suggest that vessels in the leaves of the angiosperms studied provide them with the flexibility to produce highly conductive leaves with correspondingly high photosynthetic capacities relative to tracheid-bearing species.     

The photosynthetic drought physiology of a diverse group of southern hemisphere conifer species is correlated with minimum seasonal rainfall

1. The instantaneous and integrated leaf gas exchange of 13 species of southern hemisphere conifers grown under identical glasshouse conditions were examined to determine whether there was any correlation between the characteristics of water use at the leaf level and environmental water availability.
2. In the conifer species examined, the minimum ratio of internal to ambient CO₂ measured in leaves during artificially imposed drought [( c _i/ c _a)_min] was strongly correlated with the minimum rainfall observed within the natural range of each species. This suggests that the distributions of these species are constrained by the drought tolerance of their photosynthetic apparatus.
3. A good correlation was found between the ratio of internal to ambient CO₂ measured in leaves under optimal conditions ( c _i/ c _a)_max and leaf δ¹³C (and hence inferred ∫[ c _i/ c _a]). Neither of these, however, correlated with the environmental parameters considered most likely to be limiting species distribution, i.e. precipitation and altitude.
4. These data suggest that decreasing water availability may have been the major factor responsible for the restriction and extinction of conifers in the southern hemisphere.     

The Heterogeneity and Spatial Patterning of Structure and Physiology across the Leaf Surface in Giant Leaves of Alocasia macrorrhiza

Leaf physiology determines the carbon acquisition of the whole plant, but there can be considerable variation in physiology and carbon acquisition within individual leaves. Alocasia macrorrhiza (L.) Schott is an herbaceous species that can develop very large leaves of up to 1 m in length. However, little is known about the hydraulic and photosynthetic design of such giant leaves. Based on previous studies of smaller leaves, and on the greater surface area for trait variation in large leaves, we hypothesized that A. macrorrhiza leaves would exhibit significant heterogeneity in structure and function. We found evidence of reduced hydraulic supply and demand in the outer leaf regions; leaf mass per area, chlorophyll concentration, and guard cell length decreased, as did stomatal conductance, net photosynthetic rate and quantum efficiency of photosystem II. This heterogeneity in physiology was opposite to that expected from a thinner boundary layer at the leaf edge, which would have led to greater rates of gas exchange. Leaf temperature was 8.8°C higher in the outer than in the central region in the afternoon, consistent with reduced stomatal conductance and transpiration caused by a hydraulic limitation to the outer lamina. The reduced stomatal conductance in the outer regions would explain the observed homogeneous distribution of leaf water potential across the leaf surface. These findings indicate substantial heterogeneity in gas exchange across the leaf surface in large leaves, greater than that reported for smaller-leafed species, though the observed structural differences across the lamina were within the range reported for smaller-leafed species. Future work will determine whether the challenge of transporting water to the outer regions can limit leaf size for plants experiencing drought, and whether the heterogeneity of function across the leaf surface represents a particular disadvantage for large simple leaves that might explain their global rarity, even in resource-rich environments.     

Stem hydraulic supply is linked to leaf photosynthetic capacity: evidence from New Caledonian and Tasmanian rainforests

A strong relationship between hydraulic supply of water to leaves and maximum photosynthetic capacity was found in a group of seven conifers and 16 angiosperm species, including two vessel‐less taxa, from similar rainforest communities in New Caledonia and Tasmania (Australia). Stem hydraulic supply was expressed as the hydraulic conductivity of branches in terms of leaf area supplied (K_L) and leaf photosynthetic capacity was measured as the mean quantum yield of PSII (Ø_PSII) in leaves exposed to full sun, as determined by chlorophyll fluorescence analysis. A single, highly significant linear regression (r² = 0·74) described the relationship between hydraulic conductivity and quantum yield in all species. This suggests that the maximum photosynthetic rate of leaves is constrained by their vascular supply. In both rainforest locations, the K_L of conifer wood overlapped broadly with that of associated vessel‐bearing and vessel‐less angiosperms indicating a degree of hydraulic convergence in these forests.     

Stem water transport and freeze-thaw xylem embolism in conifers and angiosperms in a Tasmanian treeline heath

The effect of freezing on stem xylem hydraulic conductivity and leaf chlorophyll a fluorescence was measured in 12 tree and shrub species from a treeline heath in Tasmania, Australia. Reduction in stem hydraulic conductivity after a single freeze-thaw cycle was minimal in conifers and the vessel-less angiosperm species Tasmannia lanceolata (Winteraceae), whereas mean loss of conductivity in vessel-forming angiosperms fell in the range 17-83%. A positive linear relationship was observed between percentage loss of hydraulic conductivity by freeze-thaw and the average conduit diameter across all 12 species. This supports the hypothesis that large-diameter vascular conduits have a greater likelihood of freeze-thaw cavitation because larger bubbles are produced, which are more likely to expand under tension. Leaf frost tolerances, as measured by a 50% loss of maximum PSII quantum yield, varied from -6 to -13°C, indicating that these species were more frost-sensitive than plants from northern hemisphere temperate forest and treeline communities. There was no evidence of a relationship between frost tolerance of leaves and the resilience of stem water transport to freezing, suggesting that low temperature survival and the resistance of stem water transport to freezing are independently evolving traits. The results of this study bear on the ecological importance of stem freezing in the southern hemisphere treeline zones.     

Hydraulic and photosynthetic characteristics differ between co-generic tree and liana species: a case study of Millettia and Gnetum in tropical forest

木质藤本是热带森林的重要组成部分, 显著影响森林的结构和功能。已有研究发现木质藤本与乔木的水力结构存在显著差异: 木质藤本的缠绕或攀缘茎细小, 但其木质部具有粗大的长导管, 输水效率高, 抗栓塞能力低。为降低基因型差异对比较结果的影响, 该研究选取热带崖豆藤属(Millettia)和买麻藤属(Gnetum)的乔木和木质藤本, 比较同属内不同生长型植物的水力和光合性状的差异, 分析水分传导效率与抗栓塞能力之间以及水力与光合性状之间的相关关系。结果发现: (1)崖豆藤属植物水力性状的种间差异大, 与生活型和需光性有关。耐阴的木质藤本反而具有较低的水分传导效率和较高的抗栓塞能力。(2)买麻藤属植物是裸子植物较为进化的类群(具有导管和阔叶), 其乔木的水分传导效率很低, 但是其木质藤本的水分传导效率高于其他阳生性的被子植物。(3)不论乔木还是木质藤本, 水分传导的有效性与安全性在枝条和叶片水平上均没有显著的权衡关系。(4)与同属乔木相比, 木质藤本的叶片较枝条的抗栓塞能力更强, 在旱季具有更高的最大净光合速率和气孔导度, 支持了木质藤本的“旱季生长优势假说”。该研究揭示了热带木质藤本水力性状的多样性和重要性, 为阐明环境变化对这一重要植物类群的影响, 需要对它们的水力特征进行更广泛的研究。     

Small trees,big problems: Comparative leaf function under extreme edaphic stress

Premise of the Study

The pygmy forest, a plant community of severely stunted conifers and ericaceous angiosperms, occurs on patches of highly acidic, nutrient‐poor soils along the coast of Northern California, USA. This system is an excellent opportunity to study the effect of severe nutrient deficiency on leaf physiology in a naturally‐occurring ecosystem. In this study, we seek to understand the physiological mechanisms stunting the plants' growth and their implications for whole plant function.

Methods

We measured 14 traits pertaining to leaf photosynthetic function or physical structure on seven species. Samples were taken from the pygmy forest community and from conspecifics growing on higher‐nutrient soils, where trees may grow over 30 m tall.

Key Results

Pygmy plants of most species maintained similar area‐based photosynthetic and stomatal conductance rates to conspecific controls, but had lower specific leaf area (leaf area divided by dry weight), lower percent nitrogen, and less leaf area relative to xylem growth. Sequoia sempervirens, a species rare in the pygmy forest, had a categorically different response from the more common plants and had remarkably low photosynthetic rates.

Conclusions

Pygmy plants were not stunted by low photosynthetic rates on a leaf‐area basis; instead, several species had restricted whole‐plant photosynthesis due to low leaf area production. Pygmy plants of all species showed signs of greater carbon investment in their leaves and higher production of nonphotosynthetic leaf tissue, further contributing to slow growth rates.     

东北地区城市针叶树冬季滞尘效应研究

对不同种针叶树同一降尘条件及同种针叶树不同降尘条件的滞尘能力进行研究,结果表明,针叶树在东北的冬季有很强的滞尘作用,不同的针叶树滞尘能力排序为沙松冷杉>沙地云杉>红皮云杉>东北红豆杉>白皮松>华山松>油松,不同针叶树叶表面结构不同,滞尘量较小的白皮松、华山松和油松表面平滑,细胞与气孔排列整齐,而滞尘量较大的红皮云杉、沙松冷杉、东北红豆杉的针叶表皮平滑程度较差,细胞与气孔排列较前3种植物差,在红皮云杉叶表面上有大小不等的瘤状物,不同针叶树叶断面形状与滞尘量相关,白皮松和油松叶片的上表面呈弧形,不易附着灰尘;华山松叶片呈三棱形,上表面较窄,附着灰尘的量较小;两种云杉的叶片呈四棱形,上表面较3种松属植物的叶片要宽与平展,因此相对滞尘量要大;沙松冷杉和东北红豆杉的叶断面形状都较扁、平,这种断面正是构成其滞尘量大于3种松属和两种云杉属植物的主要因素。     

Xylem hydraulic and photosynthetic function of Gnetum (Gnetales) species from Papua New Guinea

Gnetum (Gnetales) species are suggested to be unique extant gymnosperms that have acquired high photosynthetic and transpiration capacities as well as greater xylem hydraulic capacity and efficiency compared with all other extant gymnosperms. This is because Gnetum is the only extant gymnosperm lineage that combines vessels, broad pinnate-veined leaves and an ecological distribution in wet, productive lowland tropical rainforest habitats. Yet, field-based observations on the group's ecophysiological performance are lacking. To test a hypothesis that Gnetum species are ecophysiologically analogous to light-demanding woody tropical angiosperms, stem xylem hydraulic performance, photosynthesis and stomatal conductance were investigated in Gnetum as compared with a diverse group of co-occurring woody plants in a lowland tropical rainforest. It was found that Gnetum species combined low photosynthetic capacity and low stomatal conductances with a low stem water transport ability. The physiological observations are consistent with the general occurrence of Gnetum species in shady, primary forest habitats. These results on Gnetum ecophysiology indicate that the coupling of vessels, broad pinnate-veined leaves and the liana habit do not signal the evolution of a highly opportunistic, light-demanding life history in gymnosperms.     

Responses of leaf structure and photosynthetic properties to intra-canopy light gradients: a common garden test with four broadleaf deciduous angiosperm and seven evergreen conifer tree species

Spectra of leaf traits in northern temperate forest canopies reflect major differences in leaf longevity between evergreen conifers and deciduous broadleaf angiosperms, as well as plastic modifications caused by within-crown shading. We investigated (1) whether long-lived conifer leaves exhibit similar intra-canopy plasticity as short-lived broadleaves, and (2) whether global interspecific relationships between photosynthesis, nitrogen, and leaf structure identified for sun leaves adequately describe leaves differentiated in response to light gradients. We studied structural and photosynthetic properties of intra-tree sun and shade foliage in adult trees of seven conifer and four broadleaf angiosperm species in a common garden in Poland. Shade leaves exhibited lower leaf mass-per-area (LMA) than sun leaves; however, the relative difference was smaller in conifers than in broadleaves. In broadleaves, LMA was correlated with lamina thickness and tissue density, while in conifers, it was correlated with thickness but not density. In broadleaves, but not in conifers, reduction of lamina thickness was correlated with a thinner palisade layer. The more conservative adjustment of conifer leaves could result from a combination of phylogenetic constraints, contrasting leaf anatomies and shoot geometries, but also from functional requirements of long-lived foliage. Mass-based nitrogen concentration (N(mass)) was similar between sun and shade leaves, and was lower in conifers than in deciduous broadleaved species. Given this, the smaller LMA in shade corresponded with a lower area-based N concentration (N(area)). In evergreen conifers, LMA and N(area) were less powerful predictors of area-based photosynthetic rate (A (max(area))) in comparison with deciduous broadleaved angiosperms. Multiple regression for sun and shade leaves showed that, in each group, A (max(mass)) was related to N(mass) but not to LMA, whereas LMA became a significant codeterminant of A (max(mass)) in analysis combining both groups. Thus, a fundamental mass-based relationship between photosynthesis, nitrogen, and leaf structure reported previously also exists in a dataset combining within-crown and across-functional type variation.     

Quantitative analyses of shade-shoot architecture of conifers native to New Zealand

Shoot architecture was quantified by measuring the "maximum silhouette area ratio" (R_max). R_max was calculated from the maximum silhouette area (or projected area) of the intact shoot, divided by the silhouette area of the leaves or phylloclades (leaf-like flattened stems) when they are removed from the shoot and laid out flat. Like conifers of the Northern Hemisphere (NH) with non-appressed foliage, the R_max of shade-adapted shoots ranged from 0.5 to 1.0 in New Zealand (NZ) conifers with non-appressed foliage. Defining a "leaf" to mean either a true leaf or a phylloclade, the following was found: leaf area/leaf dry weight, leaf area/shoot dry weight, and leaf dry weight/shoot dry weight, were all similar in the shade-shoots of NZ and NH conifers. None of these variables were significantly correlated with R_max in the NZ conifers, unless species with leaves averaging less than 4 mm² in size were excluded from the analyses. Foliage dry weight/shoot projected area was strongly correlated with R_max. NZ conifers had both smaller and larger mean leaf sizes in comparison to NH conifers. The mean projected area per shade-adapted leaf of NZ conifers varied from 2.7 to 436 mm². In NH conifers, the mean projected area per shade leaf varied from 12 to 83 mm². Except for the strikingly larger range in leaf size in NZ conifers, the data support a hypothesis of strong convergent evolution of shade-shoot architecture in NZ and NH conifers. The results are discussed in relation to photosynthesis, stand production, and the ecological distribution of conifers.     

Decline of photosynthetic capacity with leaf age and position in two tropical pioneer tree species

The effect of leaf age on photosynthetic capacity, a critical parameter in the theory of optimal leaf longevity, was studied for two tropical pioneer tree species, Cecropia longipes and Urera caracasana, in a seasonally dry forest in Panama. These species continuously produce short-lived leaves (74 and 93 d, respectively) during the rainy season (May-December) on orthotropic branches. However, they differ in leaf production rate, maximum number of leaves per branch, light environment experienced by the leaves, leaf mass per unit area, and nitrogen content. Light-saturated photosynthetic rates for marked leaves of known ages (±1 wk) were measured with two contrasting schemes (repeated measurements vs. chronosequence within branch), which overall produced similar results. In both species, photosynthetic rates and nitrogen use efficiency were negatively correlated with leaf age and positively correlated with light availability. Photosynthetic rates declined faster with leaf age in Cecropia than in Urera as predicted by the theory. The rate of decline was faster for leaves on branches with faster leaf turnover rates. Nitrogen per unit leaf area decreased with leaf age only for Urera. Leaf mass per unit area increased with leaf age, either partly (in Cecropia) or entirely (in Urera) due to ash accumulation.     

Anatomical changes with needle length are correlated with leaf structural and physiological traits across five Pinus species

The genus Pinus has wide geographical range and includes species that are the most economically valued among forest trees worldwide. Pine needle length varies greatly among species, but the effects of needle length on anatomy, function, and coordination and trade‐offs among traits are poorly understood. We examined variation in leaf morphological, anatomical, mechanical, chemical, and physiological characteristics among five southern pine species: Pinus echinata, Pinus elliottii, Pinus palustris, Pinus taeda, and Pinus virginiana. We found that increasing needle length contributed to a trade‐off between the relative fractions of support versus photosynthetic tissue (mesophyll) across species. From the shortest (7 cm) to the longest (36 cm) needles, mechanical tissue fraction increased by 50%, whereas needle dry density decreased by 21%, revealing multiple adjustments to a greater need for mechanical support in longer needles. We also found a fourfold increase in leaf hydraulic conductance over the range of needle length across species, associated with weaker upward trends in stomatal conductance and photosynthetic capacity. Our results suggest that the leaf size strongly influences their anatomical traits, which, in turn, are reflected in leaf mechanical support and physiological capacity.     

Photosynthesis and Photoprotection in Overwintering Plants

Abstract: Seasonal differences in the capacity of photosynthetic electron transport, leaf pigment composition, xanthophyll cycle characteristics and chlorophyll fluorescence emission were investigated in two biennial mesophytes ( Malva neglecta and Verbascum thapsus ) that grow in full sunlight, and in leaves/needles of sun and shade populations of several broad-leafed evergreens and conifers (Vinca minor, Euonymus kiautschovicus, Mahonia repens, Pseudotsuga menziesii [Douglas fir], and Pinus ponderosa). Both mesophytic species maintained or upregulated photosynthetic capacity in the winter and exhibited no upregulation of photoprotection. In contrast, photosynthetic capacity was downregulated in sun leaves/needles of V. minor, Douglas fir, and Ponderosa pine, and even in shade needles of Douglas fir. Interestingly, photosynthetic capacity was upregulated during the winter in shade leaves/needles of V. minor, Ponderosa pine and Euonymus kiautschovicus. Nocturnal retention of zeaxanthin and antheraxanthin, and their sustained engagement in a state primed for energy dissipation, were observed largely in the leaves/needles of sun-exposed evergreen species during winter. Factors that may contribute to these differing responses to winter stress, including chloroplast redox state, the relative levels of source and sink activity at the whole plant level, and apoplastic versus symplastic phloem loading, are discussed.     

Morphological and phenological characteristics of leaf development ofDurio zibethinus Murray (Bombacaceae)

The morphological and phenological characteristics of leaf development ofDurio zibethinus Murray were investigated at an experimental field of Universiti Pertanian Malaysia (UPM) in Selangor. Proportionality was observed in the relations of leaf length to leaf width and of leaf area to the product of leaf width and length. The proportionality was explained from the similarity of leaf shape. New leaves emerged continuously, but the number of new leaves fluctuated seasonally. The emergence of leaves was inhibited by the flower bud formation. In the survival curves of leaves, the relative fall rate was lower at the early stage of leaf development than at the late stage. Leaf longevity of 100 to 133 days was low and leaf expansion period of two weeks was short in comparison with the published data on tropical trees. From the ecophysiological viewpoint, the leaf survival strategy of the present species was discussed: the present species manages to set up a photosynthetic system in a short period by the rapid leaf growth; the lower leaf longevity is advantageous to reaching more frequently high photosynthetic production by newly emerged leaves.     

Photosynthetic responses to light in seedlings of selected Amazonian and Australian rainforest tree species

Summary Seedlings of the Caesalpinoids Hymenaea courbaril, H. parvifolia and Copaifera venezuelana, emergent trees of Amazonian rainforest canopies, and of the Araucarian conifers Agathis microstachya and A. robusta, important elements in tropical Australian rainforests, were grown at 6% (shade) and 100% full sunlight (sun) in glasshouses. All species produced more leaves in full sunlight than in shade and leaves of sun plants contained more nitrogen and less chlorophyll per unit leaf area, and had a higher specific leaf weight than leaves of shade plants. The photosynthetic response curves as a function of photon flux density for leaves of shade-grown seedlings showed lower compensation points, higher quantum yields and lower respiration rates per unit leaf area than those of sun-grown seedlings. However, except for A. robusta, photosynthetic acclimation between sun and shade was not observed; the light saturated rates of assimilation were not significantly different. Intercellular CO₂ partial pressure was similar in leaves of sun and shade-grown plants, and assimilation was limited more by intrinsic mesophyll factors than by stomata. Comparison of assimilation as a function of intercellular CO₂ partial pressure in sun- and shade-grown Agathis spp. showed a higher initial slope in leaves of sun plants, which was correlated with higher leaf nitrogen content. Assimilation was reduced at high transpiration rates and substantial photoinhibition was observed when seedlings were transferred from shade to sun. However, after transfer, newly formed leaves in A. robusta showed the same light responses as leaves of sun-grown seedlings. These observations on the limited potential for acclimation to high light in leaves of seedlings of rainforest trees are discussed in relation to regeneration following formation of gaps in the canopy.     

Evolutionary relationships among Pinus (Pinaceae) subsections inferred from multiple low-copy nuclear loci

Sequence data from nrITS and cpDNA have failed to fully resolve phylogenetic relationships among Pinus species. Four low-copy nuclear genes, developed from the screening of 73 mapped conifer anchor loci, were sequenced from 12 species representing all subsections. Individual loci do not uniformly support either the nrITS or cpDNA hypotheses and in some cases produce unique topologies. Combined analysis of low-copy nuclear loci produces a well-supported subsectional topology of two subgenera, each divided into two sections, congruent with prior hypotheses of deep divergence in Pinus. The placements of P. nelsonii, P. krempfii, and P. contorta have been of continued systematic interest. Results strongly support the placement of P. nelsonii as sister to the remaining members of sect. Parrya, suggest a moderately well-supported and consistent position of P. krempfii as sister to the remaining members of sect. Quinquefoliae, and are ambiguous about the placement of P. contorta. A successful phylogenetic strategy in Pinus will require many low-copy nuclear loci that include a high proportion of silent sites and derive from independent linkage groups. The locus screening and evaluation strategy presented here can be broadly applied to facilitate the development of phylogenetic markers from the increasing number of available genomic resources.     

Dynamics of leaf hydraulic conductance with water status: quantification and analysis of species differences under steady state

Leaf hydraulic conductance (K(leaf)) is a major determinant of photosynthetic rate in well-watered and drought-stressed plants. Previous work assessed the decline of K(leaf) with decreasing leaf water potential (Ψ(leaf)), most typically using rehydration kinetics methods, and found that species varied in the shape of their vulnerability curve, and that hydraulic vulnerability correlated with other leaf functional traits and with drought sensitivity. These findings were tested and extended, using a new steady-state evaporative flux method under high irradiance, and the function for the vulnerability curve of each species was determined individually using maximum likelihood for 10 species varying strongly in drought tolerance. Additionally, the ability of excised leaves to recover in K(leaf) with rehydration was assessed, and a new theoretical framework was developed to estimate how rehydration of measured leaves may affect estimation of hydraulic parameters. As hypothesized, species differed in their vulnerability function. Drought-tolerant species showed shallow linear declines and more negative Ψ(leaf) at 80% loss of K(leaf) (P(80)), whereas drought-sensitive species showed steeper, non-linear declines, and less negative P(80). Across species, the maximum K(leaf) was independent of hydraulic vulnerability. Recovery of K(leaf) after 1 h rehydration of leaves dehydrated below their turgor loss point occurred only for four of 10 species. Across species without recovery, a more negative P(80) correlated with the ability to maintain K(leaf) through both dehydration and rehydration. These findings indicate that resistance to K(leaf) decline is important not only in maintaining open stomata during the onset of drought, but also in enabling sustained function during drought recovery.     

Productive leaf functional traits of Chinese savanna species

The river valleys in Southwest China are characterized by a dry?Chot climate and relatively rich soils, and host valley-type savannas that are dominated by deciduous species. However, little is known about the ecological adaptations of Chinese savanna plants to the local environments. We hypothesize that Chinese savanna species mainly possess a drought-avoiding strategy by having a deciduous leaf habit and have productive leaf traits. To test this hypothesis, we measured 26 anatomical, morphological, physiological, and chemical traits for 33 woody species from a valley savanna in Southwest China and compared them with the literature data of other dry and wet tropical tree species and a global dataset. We found that Chinese savanna species showed drought avoidance adaptations and exhibited productive leaf traits, such as thin and dense leaves with high ratio of palisade to spongy mesophyll, leaf nutrient concentrations and photosynthetic capacity. Correlations of photosynthetic capacity with N, P, and stomatal conductance across Chinese savanna species were consistent with global patterns reported for seed plants. However, the Chinese savanna species had consistently greater carbon gain at a given specific leaf area, N, P, and stomatal conductance, suggesting higher nutrient- and intrinsic water use efficiencies. These results suggest that paradoxically, Chinese savanna species are adapted to the stressful dry?Chot valley habitat by having productive leaves.